Understanding the Neural Basis of Amblyopia

Ability to Process Multisensory Information Is Impaired in Open Angle Glaucoma

PRCIS

Patients with glaucoma demonstrated deficiencies in their ability to process multisensory information when compared with controls, with those deficiencies being related to glaucoma severity. Impaired multisensory integration (MSI) may affect the quality of life in individuals with glaucoma and may contribute to the increased prevalence of falls and driving safety concerns. Therapeutic possibilities to influence cognition in glaucoma should be explored.

PURPOSE

Glaucoma is a neurodegenerative disease of the optic nerve that has also been linked to cognitive health decline. This study explored MSI as a function of glaucoma status and severity.

METHODS

MSI was assessed in 37 participants with open angle glaucoma relative to 18 age-matched healthy controls. The sound-induced flash illusion was used to assess MSI efficiency. Participants were presented with various combinations of simultaneous visual and/or auditory stimuli and were required to indicate the number of visual stimuli observed for each of the 96 total presentations. Central retinal sensitivity was assessed as an indicator of glaucoma severity (MAIA; CenterVue).

RESULTS

Participants with glaucoma performed with equivalent capacity to healthy controls on unisensory trials ( F1,53 =2.222, P =0.142). Both groups performed equivalently on congruent multisensory trials involving equal numbers of auditory and visual stimuli F1,53 =1.032, P =0.314). For incongruent presentations, that is, 2 beeps and 1 flash stimulus, individuals with glaucoma demonstrated a greater influence of the incongruent beeps when judging the number of flashes, indicating less efficient MSI relative to age-matched controls ( F1,53 =11.45, P <0.002). In addition, MSI performance was positively correlated with retinal sensitivity ( F3,49 =4.042, P <0.025), adjusted R ²=0.15).

CONCLUSIONS

Individuals with open angle glaucoma exhibited MSI deficiencies that relate to disease severity. The type of deficiencies observed were similar to those observed among older individuals with cognitive impairment and balance issues. Impaired MSI may, therefore, be relevant to the increased prevalence of falls observed among individuals with glaucoma, a concept that merits further investigation.

Assessment of amblyopic children undergoing occlusion therapy by pattern visual evoked potentials and contrast sensitivity tests

Background: Amblyopia is a case where one or less commonly, both eyes have impaired visual performance, even with the best optical correction and no visible disease of the visual system. Objectives: To assess contrast sensitivity tests (CST) and pattern visual evoked potentials (PVEP) results in amblyopic children who have already started occlusion therapy for durations ranging from 6 to 12 months. Methods: This cross-sectional study was conducted on 200 eyes of 50 patients with monocular amblyopia and 50 age and sex matched controls. Both patients and controls underwent ophthalmological assessment, PVEP, and CST. Results: There was no statistically significant difference in the results of P100 latencies of qualitative PVEP in amblyopic eyes compared to non-amblyopic eyes and control eyes, while the qualitative CST showed a highly statistically significant difference, being affected in 98% of amblyopic eyes compared to unaffected eyes (4%) and control eyes (4%). The maximum contrast level and minimal contrast level of quantitative CST were significantly lower in amblyopic eyes compared to non-amblyopic and control eyes. The cutoff value of maximal contrast level at mean frequencies of 2.5 ± 0.9 Hz, and a range of (1.1-4.1) for amblyopic eyes is ≤21 dB, while the cutoff value of minimal contrast level at mean frequencies of 13.4 ± 2.6 Hz, and a range of (6.7-18) for amblyopic eyes is ≤12 dB. Conclusion: Detection of amblyopia by CST is a noninvasive and easy procedure, which represents a promising tool to support the diagnosis of amblyopia.

Parents' Awareness, Knowledge, and Perception of Amblyopia in Children: A Study in Jazan Region, Saudi Arabia

Background Amblyopia is a vision disorder that results from a development problem in the brain rather than a neurological disease in the eye. The condition causes reduced visual acuity in one or both eyes due to the brain's inability to process inputs, rather than a structural abnormality. This study aims to assess parents' awareness, knowledge, and perception of amblyopia in their children in the Jazan region, Saudi Arabia. Methods This is a cross-sectional study that used an electronic questionnaire consisting of five main sections to assess the level of awareness of amblyopia among parents in the Jazan region. The Statistical Package for Social Sciences (SPSS v.25, IBM Corp., Armonk, NY, USA) was utilized to input the data. The degree to which participants' level of awareness was related to variables such as age, gender, and educational level was assessed through the chi-square test (χ2), and any values that scored p-values under 0.05 were deemed statistically significant. Results The analysis included 572 participants, 395 mothers (69.0%) and 177 fathers (31.0%). The age groups of the participants were divided into 36-45 years (38.0%), 26-35 years (36.0%), and above 46 years (17.0%). Out of the total, 36 participants (6.0%) had a history of amblyopia, and 73 (13.0%) had a child who suffered from amblyopia. The findings showed that only 18 participants (3.1%) had a good awareness of amblyopia, while 242 (42.3%) had a fair level of awareness. Most participants, 312 (54.5%), were classified as having a poor awareness level of amblyopia. Parents with postgraduate degrees, those with prior awareness, and parents whose children had eye diseases demonstrated higher levels of good awareness. However, gender, age, and residency did not have significant associations with awareness levels. Conclusion While parents must be involved in managing amblyopia, our research found that more than half of the parents surveyed had a limited understanding of various aspects of the disease, which can cause permanent damage to their child's vision. Therefore, we recommend implementing health education programs to increase awareness and knowledge about amblyopia in Jazan.

Combined therapy of bilateral transcranial direct current stimulation and ocular occlusion improves visual function in adults with amblyopia, a randomized pilot study

Background

Amblyopia is the interocular visual acuity difference of two lines or more with the best correction in both eyes. It is treated with ocular occlusion therapy, but its success depends on neuroplasticity, and thus is effective in children but not adults. Transcranial Direct Current Stimulation (tDCS) is suggested to increase neuroplasticity.

Objective

To determine if combined intervention of bilateral tDCS and ocular occlusion improves visual function in adults with amblyopia.

Methods

A double-blind randomized, controlled pilot trial was conducted in 10 volunteers with amblyopia. While applying ocular occlusion and performing a reading task, participants received bilateral tDCS (n = 5) or sham stimulation (n = 5), with the anodal tDCS electrode in the contralateral visual cortex and the cathodal in the ipsilateral visual cortex in relation to the amblyopic eye. Visual function (through visual acuity, stereopsis, and contrast sensitivity tests) and visual evoked potential (with checkerboard pattern stimuli presentation) were evaluated immediately after.

Results

A total of 30 min after treatment with bilateral tDCS, visual acuity improved by 0.16 (± 0.025) LogMAR in the treatment group compared with no improvement (-0.02 ± 0.02) in five controls (p = 0.0079), along with a significant increase in the amplitude of visual evoked potentials of the amblyopic eye response (p = 0.0286). No significant changes were observed in stereopsis and contrast sensitivity. No volunteer reported any harm derived from the intervention.

Conclusion

Our study is the first to combine anodal and cathodal tDCS for the treatment of amblyopia, showing transient improved visual acuity in amblyopic adults.

Long-Term Efficacy of the Combination of Active Vision Therapy and Occlusion in Children with Strabismic and Anisometropic Amblyopia

This retrospective study was conducted to evaluate the efficacy of the combined treatment of occlusion and active vision therapy in a total of 27 amblyopic children, including 14 strabismic and 13 anisometropic cases. For such purpose, changes in distance and near visual acuity as well as in the binocular function was evaluated during a two-year follow-up. In both amblyopia groups, significant improvements were found in distance and near visual acuity in the non-dominant eye (p < 0.001). In the strabismic amblyopia group, the percentage of patients with binocular function score (BF) > 3.3 decreased significantly from a baseline value of 64.3% to a two-year follow-up value of 7.1% (p < 0.001). In the anisometropic amblyopia group, this percentage also decreased significantly from a baseline value of 15.4% to a two-year follow-up value of 0.0% (p < 0.001). No recurrences were observed in the anisometropic amblyopia group, whereas recurrence occurred in two cases of the strabismic amblyopia group after finishing the vision rehabilitation process. In conclusion, the combined approach of the treatment evaluated is efficacious for providing an improvement in visual acuity and binocular function in both anisometropic and strabismic amblyopia, which was maintained over time.

Enhancement of visual perception by combining transcranial electrical stimulation and visual perceptual training

The visual system remains highly malleable even after its maturity or impairment. Our visual function can be enhanced through many ways, such as transcranial electrical stimulation (tES) and visual perceptual learning (VPL). TES can change visual function rapidly, but its modulation effect is short-lived and unstable. By contrast, VPL can lead to a substantial and long-lasting improvement in visual function, but extensive training is typically required. Theoretically, visual function could be further improved in a shorter time frame by combining tES and VPL than by solely using tES or VPL. Vision enhancement by combining these two methods concurrently is both theoretically and practically significant. In this review, we firstly introduced the basic concept and possible mechanisms of VPL and tES; then we reviewed the current research progress of visual enhancement using the combination of two methods in both general and clinical population; finally, we discussed the limitations and future directions in this field. Our review provides a guide for future research and application of vision enhancement and restoration by combining VPL and tES.

Increased Risk of Refractive Errors and Amblyopia among Children with Ptosis: A Nationwide Population-Based Study

Background: This study aimed to investigate the risk of refractive errors (astigmatism, myopia, and hyperopia) and amblyopia in children with ptosis and association between age at diagnosis of ptosis and subsequent risks of vision problems. Methods: Retrospective claims data from the Taiwan National Health Insurance Research Database (NHIRD) were analyzed. We identified 1799 children aged 0−18 years who were newly diagnosed with ptosis between 2000 and 2012 and 7187 individuals without the disease. Both cohorts were followed up until 2013 to estimate the incidence of refractive errors and amblyopia. Results: Children with ptosis had 5.93-fold, 3.46-fold, 7.60-fold, and 13.45-fold increases in the risk of developing astigmatism, myopia, hyperopia, and amblyopia, respectively, compared with the control cohort (astigmatism: adjusted hazard ratio, aHR = 5.93, 95% confidence interval, CI = 5.16−6.82; myopia: aHR = 3.46, 95% CI = 3.13−3.83; hyperopia: aHR = 7.60, 95% CI = 5.99−9.63; amblyopia: aHR = 13.45, 95% CI = 10.60−17.05). Children diagnosed with ptosis at an age older than 3 years old had a higher risk of myopia than patients diagnosed with ptosis before age 3. There was no significant difference of the risk of astigmatism, amblyopia, and hyperopia between age groups. Conclusions: Children with ptosis may exhibit a higher risk of astigmatism, myopia, hyperopia, and amblyopia than children without ptosis. The risk of myopia is higher in children with ptosis diagnosed at >3 years than those diagnosed at ≤3 years.

Binocular versus standard occlusion or blurring treatment for unilateral amblyopia in children aged three to eight years

BACKGROUND

Current treatments for amblyopia, typically patching or pharmacological blurring, have limited success. Less than two-thirds of children achieve good acuity of 0.20 logMAR in the amblyopic eye, with limited improvement of stereopsis, and poor adherence to treatment. A new approach, based on presentation of movies or computer games separately to each eye, may yield better results and improve adherence. These treatments aim to balance the input of visual information from each eye to the brain.  OBJECTIVES: To determine whether binocular treatments in children, aged three to eight years, with unilateral amblyopia result in better visual outcomes than conventional patching or pharmacological blurring treatment.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register), MEDLINE, Embase, ISRCTN, ClinicalTrials.gov, and the WHO ICTRP to 19 November 2020, with no language restrictions.

SELECTION CRITERIA

Two review authors independently screened the results of the search for relevant studies. We included randomised controlled trials (RCTs) that enrolled children between the ages of three and eight years old with unilateral amblyopia. Amblyopia was classed as present when the best-corrected visual acuity (BCVA) was worse than 0.200 logMAR in the amblyopic eye, with BCVA 0.200 logMAR or better in the fellow eye, in the presence of an amblyogenic risk factor, such as anisometropia, strabismus, or both. To be eligible, children needed to have undergone cycloplegic refraction and  ophthalmic examination, including fundal examination and optical treatment, if indicated, with stable BCVA in the amblyopic eye despite good adherence with wearing glasses. We included any type of binocular viewing intervention, on any device (e.g. computer monitors viewed with liquid-crystal display shutter glasses; hand-held screens, including mobile phones with lenticular prism overlay; or virtual reality displays). Control groups received standard amblyopia treatment, which could include patching or pharmacological blurring of the better-seeing eye. We included full-time (all waking hours) and part-time (between 1 and 12 hours a day) patching regimens. We excluded children who had received any treatment other than optical treatment; and studies with less than 8-week follow-up.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. The primary outcome of the review was the change from baseline of distance BCVA in the amblyopic eye after 16 (± 2) weeks of treatment, measured in logMAR units on an age-appropriate acuity test.

MAIN RESULTS

We identified one eligible RCT of conventional patching treatment versus novel binocular treatment, and analysed a subset of 68 children who fulfilled the age criterion of this review. We obtained data for the mean change in amblyopic eye visual acuity, adverse events (diplopia), and adherence to prescribed treatment at 8- and 16-week follow-up intervals, though no data were available for change in BCVA after 52 weeks. Risk of bias for the included study was considered to be low. The certainty of evidence for the visual acuity outcomes at 8 and 16 weeks of treatment and adherence to the study intervention was rated moderate using the GRADE criteria, downgrading by one level due to imprecision. The certainty of evidence was downgraded by two levels and rated low for the proportion of participants reporting adverse events due to the sample size.  Acuity improved in the amblyopic eye in both the binocular and patching groups following 16 weeks of treatment (improvement of -0.21 logMAR in the binocular group and -0.24 logMAR in the patching group, mean difference (MD) 0.03 logMAR (95% confidence interval (CI) -0.10 to 0.04; 63 children). This difference was non-significant and the improvements in both the binocular and patching groups are also considered clinically similar. Following 8 weeks of treatment, acuity improved in both the binocular and patching groups (improvement of -0.18 logMAR in the patching group compared to -0.16 logMAR improvement in the binocular-treatment group) (MD 0.02, 95% CI -0.04 to 0.08). Again this difference was statistically non-significant, and the differences observed between the patching and binocular groups are also clinically non-significant. No adverse event of permanent diplopia was reported. Adherence was higher in the patching group (47% of participants in the iPad group achieved over 75% compliance compared with 90% of the patching group).  Data were not available for changes in stereopsis nor for contrast sensitivity following treatment.

AUTHORS' CONCLUSIONS

Currently, there is only one RCT that offers evidence of the safety and effectiveness of binocular treatment. The authors are moderately confident that after 16 weeks of treatment, the gain in amblyopic eye acuity with binocular treatment is likely comparable to that of conventional patching treatment. However, due to the limited sample size and lack of long term (52 week) follow-up data, it is not yet possible to draw robust conclusions regarding the overall safety and sustained effectiveness of binocular treatment. Further research, using acknowledged methods of visual acuity and stereoacuity assessment with known reproducibility, is required to inform decisions about the implementation of binocular treatments for amblyopia in clinical practice, and should incorporate longer term follow-up to establish the effectiveness of binocular treatment. Randomised controlled trials should also include outcomes reported by users, adherence to prescribed treatment, and recurrence of amblyopia after cessation of treatment.

Socio-demographic disparities in amblyopia prevalence among 1.5 million adolescents

BACKGROUND

Amblyopia, when not diagnosed at appropriate age, leads to uncorrectable visual impairment with considerable social and financial implications. The aim of this study was to assess socio-demographic disparities in amblyopia prevalence among Israeli adolescents, in order to identify susceptible groups in the population.

METHODS

A nationwide, population-based, cross-sectional study of Israeli adolescents examined between 1993 and 2017. All study participants underwent visual acuity examination with socio-demographic data and previous medical history documented. Associations were analyzed using univariable and multivariable logistic regression models.

RESULTS

Among 1 334 650 Israeli-born candidates aged 17.15±0.26 years, amblyopia was diagnosed in 1.07%. The overall prevalence of amblyopia has declined from 1.59% in 1993 to 0.87% in 2017. Being in the lowest socioeconomic status and below average cognitive function scores increased the odds of amblyopia in both males [odds ratio (OR) 1.64, 95% confidence interval (CI) 1.45-1.87; OR 1.27, 95% CI 1.19-1.35, respectively] and females (OR 1.61, 95% CI 1.30-1.98; OR 1.27, 95% CI 1.18-1.36, respectively). Among males, Orthodox and ultra-Orthodox educational systems were associated with increased odds of amblyopia (OR 1.16, 95% CI 1.09-1.25; OR 1.90, 95% CI 1.73-2.09). A significantly higher prevalence of amblyopia was recorded among 219 983 immigrants (1.51%, P<0.001).

CONCLUSIONS

Although the overall prevalence of amblyopia has decreased during the observed years, we found substantial evidence of socio-demographic disparities in amblyopia prevalence among adolescents, suggesting disparities in the prevention of the disease and its treatment. Demonstration of inequities at a national level could aid future guidance of health policy and augment current vision screening programs.

Eye movements elevate crowding in idiopathic infantile nystagmus syndrome

Idiopathic infantile nystagmus syndrome is a disorder characterised by involuntary eye movements, which leads to decreased acuity and visual function. One such function is visual crowding – a process whereby objects that are easily recognised in isolation become impaired by nearby flankers. Crowding typically occurs in the peripheral visual field, although elevations in foveal vision have been reported in congenital nystagmus, similar to those found with amblyopia. Here, we examine whether elevated foveal crowding with nystagmus is driven by similar mechanisms to those of amblyopia – long-term neural changes associated with a sensory deficit – or by the momentary displacement of the stimulus through nystagmus eye movements. A Landolt-C orientation identification task was used to measure threshold gap sizes with and without either horizontally or vertically placed Landolt-C flankers. We assume that a sensory deficit should give equivalent crowding in these two dimensions, whereas an origin in eye movements should give stronger crowding with horizontal flankers given the predominantly horizontal eye movements of nystagmus. We observe elevations in nystagmic crowding that are above crowding in typical vision but below that of amblyopia. Consistent with an origin in eye movements, elevations were stronger with horizontal than vertical flankers in nystagmus, but not in typical or amblyopic vision. We further demonstrate the same horizontal elongation in typical vision with stimulus movement that simulates nystagmus. Consequently, we propose that the origin of nystagmic crowding lies in the eye movements, either through image smear of the target and flanker elements or through relocation of the stimulus into the peripheral retina.

Amblyopia and Routine Eye Exam in Children: Parent's Perspective

Amblyopia is a reduced best-corrected visual acuity of one or both eyes that cannot be attributed to a structural abnormality; it is a functional reduction in the vision of an eye caused by disuse during a critical period of visual development. It is considered the leading cause of visual defects in children. With early diagnosis and treatment, children with amblyopia can significantly improve their vision. However, if it is neglected and not treated during childhood, unfortunately, it permanently decreases vision. Therefore, prevention, detection, and treatment largely depend on parents. This article explores parents' perspectives on amblyopia and routine examination of their children's eyes. A cross-sectional study used an electronic questionnaire consisting of five main sections to assess the level of awareness of amblyopia among parents. As a result, a total of 325 participants were included in our analysis. 209 (64.3%) were mothers, and 116 (35/7%) were fathers. The age groups were 35-50 years of age (61.5%), 20-34 years (23.4%), and older than 50 years (15%). Participants with a history of amblyopia numbered 23 (7.1%), and 39 had an amblyopic child (12%). A good awareness level of amblyopia among parents was found in only 10 (3%) participants, a fair awareness level in 202 (62%), and 113 (35%) participants were classified as having a poor awareness level of amblyopia. Only 13.8% of the parents took their children for yearly routine eye exams, while the majority (72%) took their children only if they had a complaint, and 14.2% took them for eye checkups only before school entry. In conclusion, parents' awareness of amblyopia in Tabuk City, KSA, was low. In addition, a limited proportion of parents reported consistently taking their children for routine eye exams. Therefore, raising awareness should be considered in public education regarding the disease.

Binocular treatment for amblyopia: A meta-analysis of randomized clinical trials

Background

To date, there is still no consensus regarding the effect of binocular treatment for amblyopia. The purpose of this systematic review and meta-analysis was to summarize the available evidence to determine whether binocular treatment is more effective than patching in children with amblyopia.

Methods

Four electronic databases (PubMed, Scopus, Web of Science, and Cochrane Central Register of Controlled Trials) were searched for studies that compared binocular treatment and patching in children with amblyopia. The outcome measures were visual acuity and stereopsis. Pooled effects sizes were calculated with a random-effect model. The standardized difference in means (SDM) with 95% confidence intervals (CI) was calculated. Sensitivity analysis and assessment of publication bias were performed.

Results

Five randomized clinical trials were included. No significant difference in visual acuity between patients treated with binocular treatment and patching was observed (SDM = -0.12; 95% CI: -0.45–0.20; P = 0.464). No significant difference in stereopsis between patients treated with binocular treatment and patching was observed (SDM = -0.07; 95% CI: -0.61–0.48; P = 0.809). For both variables, the between-study heterogeneity was high (respectively, I² = 61% and I² = 57%).

Conclusions

This meta-analysis found no convincing evidence supporting the efficacy of binocular treatment as an alternative to conventional patching. Therefore, the binocular treatment cannot fully replace traditional treatment but, to date, it can be considered a valid complementary therapy in peculiar cases. Further studies are required to determine whether more engaging therapies and new treatment protocols are more effective.

Attentional eye selection modulates sensory eye dominance

Brief periods of monocular deprivation significantly modify binocular visual processing. For example, patching one eye for a few hours alters the inter-ocular balance, with the previously patched eye becoming dominant once the patch is removed. However, the contribution of higher-level visual processing to this phenomenon is still unclear. Here, we compared changes in sensory eye dominance produced by three types of monocular manipulations in adult participants with normal binocular vision. One eye was covered for 150 min using either an opaque patch, a diffusing lens, or a prism that inverted the image. All three manipulations altered dominance duration and predominance during binocular rivalry (BR) in favour of the treated eye and the time courses of the changes were similar. These results indicate that modifications of luminance or contrast are not strictly necessary to drive shifts in eye dominance, as both were unaltered in the prism condition. Next, we found that shifts in eye dominance were dependent on attentional demands during the monocular treatment period, providing support for the role of attentional eye selection in modulating eye dominance. Finally, we found relatively rapid build-up of the ocular dominance shift after the onset of monocular treatment. Taken together, our results suggest that modifications to monocular input alter inter-ocular balance via selective attentional mechanisms that bias output towards the deprived eye. Eye-based attention may play an important role in conditions where normal input to one eye is disrupted, such as childhood amblyopia.

Fixation stability after surgical treatment of strabismus and biofeedback fixation training in amblyopic eyes

Background

Visual fixation may be affected in amblyopic patients and, moreover, its stability may be associated with the effects of amblyopic treatments on visual performance in patients with strabismus. Therefore, fixation stability is a relevant biomarker that might predict the recurrence of amblyopia after a therapeutic intervention. Microperimetric biofeedback fixation training (BFT) can stabilize visual fixation in adult patients with central vision loss. It was the purpose of the present study to evaluate the effects of BFT on fixation stability in adult amblyopic patients after surgical intervention to treat strabismus.

Methods

Participants were 12 patients with strabismus (mean age = 29.6 ± 8.5 years; 6 females) and 12 healthy volunteers (mean age = 23.8 ± 1.5 years; 9 females). The protocol included ophthalmological and microperimetric follow-ups to measure fixation stability and macular sensitivity. BFT was applied monocularly to four amblyopic eyes either on the spontaneous preferential retinal locus or to a fixation area closer to the anatomical fovea after surgical treatment of strabismus.

Results

Baseline measurements showed significantly altered microperimetric average threshold in amblyopic eyes compared to fellow eyes (p = 0.024) and compared to control eyes (p < 0.001). Fixation was unstable in amblyopic eyes compared to control eyes (p < 0.001). Fixation stability did not significantly change after surgical alignment of strabismus (p = 0.805). BFT applied to operated eyes resulted in a more stable fixation with improvements of about 50% after three months of training.

Conclusions

Fixation stability improvements following BFT highlight its potential use in adult amblyopic eyes after the surgical alignment of the strabismus. Future investigations may also consider applying this method in combination with standard treatments to improve vision in amblyopic patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02020-3.

Virtual Reality Game Playing in Amblyopia Therapy: A Randomized Clinical Trial

PURPOSE

To compare the visual outcome of occlusion therapy with virtual reality game playing as a new therapy for children with amblyopia.

METHODS

This randomized clinical trial was performed on 50 children between 4 and 10 years old who had unilateral amblyopia. They were randomly divided into virtual reality and patching groups (n = 25 in each). The virtual reality group was trained binocularly using the virtual reality games through a head set for 1 hour per day 5 days a week for 4 weeks. Patients in the patching group occluded their non-amblyopic eyes 2, 4, and 6 hours for mild (best corrected visual acuity [BCVA] 0.2 to 0.3 logarithm of the minimum angle of resolution [logMAR]), moderate (0.3 to 0.6 logMAR), and severe (worse than 0.6 logMAR) amblyopia, respectively.

RESULTS

The mean BCVA based on logMAR units improved significantly in both groups (P < .0001), but the difference between the two groups was not significant (P = .59). BCVA based on the responded letters improved in both groups (virtual reality: P = .0001, patching: P = .001), and change in BCVA in the virtual reality group was higher than in the patching group (P = .002).

CONCLUSIONS

Virtual reality game playing was equal or superior to patching in an analysis of linear and letter BCVA, respectively. Therefore, applying this new amblyopia therapy is recommended. [J Pediatr Ophthalmol Strabismus. 2021;58(3):154-160.].

Dichotic listening performance with cochlear-implant simulations of ear asymmetry is consistent with difficulty ignoring clearer speech

There are an increasing number of bilateral and single-sided-deafness cochlear-implant (CI) users who hope to achieve improved spatial-hearing abilities through access to sound in both ears. It is, however, unclear how speech is processed when inputs are functionally asymmetrical, which may have an impact on spatial-hearing abilities. Therefore, functionally asymmetrical hearing was controlled and parametrically manipulated using a channel vocoder as a CI simulation. In Experiment 1, normal-hearing (NH) listeners performed a dichotic listening task (i.e., selective attention to one ear, ignoring the other) using asymmetrical signal degradation. Spectral resolution varied independently in each ear (4, 8, 16 channels, and unprocessed control). Performance decreased with decreasing resolution in the target ear and increasing resolution in the interferer ear. In Experiment 2, these results were replicated using a divided attention task (attend to both ears, report one after sentence completion) in both NH and bilateral CI listeners, although overall performance was lower than in Experiment 1. In Experiment 3, frequency-to-place mismatch simulated shallow CI insertion depths (0, 3, 6-mm shifts, and unprocessed control). Performance mostly decreased with increasing shift in the target ear and decreasing shift in the interferer ear; however, performance nonmonotonicities occurred. The worst performance occurred when the shift matched across ears, suggesting that pitch similarity increases difficulty. The results show that it is more difficult to attend an ear that is relatively degraded or distorted, which may set spatial-hearing limitations for CI users when trying to attend to a target in complex auditory scenes.

Efficacy of Perceptual Learning-Based Vision Training as an Adjuvant to Occlusion Therapy in the Management of Amblyopia: A Pilot Study

A retrospective study was conducted to evaluate preliminarily the efficacy of perceptual learning (PL) visual training in medium-term follow-up with a specific software (Amblyopia iNET, Home Therapy Systems Inc., Gold Canyon, AZ, USA) for visual acuity (VA) and contrast sensitivity (CS) recovering in a sample of 14 moderate to severe amblyopic subjects with a previously unsuccessful outcome or failure with patching (PL Group). This efficacy was compared with that achieved in a patching control group (13 subjects, Patching 2). At one-month follow-up, a significant VA improvement in the amblyopic eye (AE) was observed in both groups, with no significant differences between them. Additionally, CS was measured in PL Group and exhibited a significant improvement in the AE one month after the beginning of treatment for 3, 6, 12, and 18 cycles/º (p = 0.003). Both groups showed long-lasting retention of visual improvements. A combined therapy of PL-based visual training and patching seems to be effective for improving VA in children with amblyopia who did not recover vision with patching alone or had a poor patching compliance. This preliminary outcome should be confirmed in future clinical trials.

Stimuli Characteristics and Psychophysical Requirements for Visual Training in Amblyopia: A Narrative Review

Active vision therapy using perceptual learning and/or dichoptic or binocular environments has shown its potential effectiveness in amblyopia, but some doubts remain about the type of stimuli and the mode and sequence of presentation that should be used. A search was performed in PubMed, obtaining 143 articles with information related to the stimuli used in amblyopia rehabilitation, as well as to the neural mechanisms implied in such therapeutic process. Visual deficits in amblyopia and their neural mechanisms associated are revised, including visual acuity loss, contrast sensitivity reduction and stereopsis impairment. Likewise, the most appropriate stimuli according to the literature that should be used for an efficient rehabilitation of the amblyopic eye are described in detail, including optotypes, Gabor’s patches, random-dot stimuli and Vernier’s stimuli. Finally, the properties of these stimuli that can be modified during the visual training are discussed, as well as the psychophysical method of their presentation and the type of environment used (perceptual learning, dichoptic stimulation or virtual reality). Vision therapy using all these revised concepts can be an effective option for treating amblyopia or accelerating the treatment period when combining with patching. It is essential to adapt the stimuli to the patient’s individual features in both monocular and binocular training.

Characterising the orientation-specific pattern-onset visual evoked potentials in children with bilateral refractive amblyopia and non-amblyopic controls

PURPOSE

An orientation-specific visual evoked potential (osVEP) protocol was developed to probe meridional anisotropies in children with refractive amblyopia. The aim was to characterise the osVEP response in children with bilateral refractive amblyopia, evaluate the intra-session repeatability of the main osVEP components (C1, C2 and C3), coefficient of repeatability (CoR) of the response to gratings in different meridians and determine if refractive amblyopes have poorer repeatability as compared with non-amblyopic controls.

METHODS

Children aged 4-7 years with newly diagnosed and untreated bilateral refractive amblyopia and non-amblyopic controls were recruited. Orientation-specific pattern-onset VEPs were recorded in response to an achromatic sinewave grating stimulus of 4 cycles per degree under monocular and binocular stimulation. The grating lines used for monocular stimulation were parallel with the subjects' most positive and negative astigmatic meridians when considered in sphero-minus cylinder form (Meridians 1 and 2, respectively). In subjects without astigmatism, meridians 1 and 2 were designated horizontal and vertical gratings, respectively. Binocular stimuli were presented with grating lines parallel to meridians 45, 90, 135 and 180°. The repeatability of latencies of the main osVEP components (C1, C2 and C3) were investigated using two successive osVEPs recordings for each stimulus meridian and the CoR for each component's latencies were assessed.

RESULTS

Seven amblyopic children (Visual acuity (VA) ranging from 0.08 to 0.40 LogMAR in the less amblyopic eye and 0.26-0.52 LogMAR in the more amblyopic eye) and 7 non-amblyopic controls (VA ranging from 0.00 to 0.02 LogMAR in either eye), with a median age of 4.6 and 7.0 years, respectively, completed the study. C1 had the highest CoR for most conditions assessed. Ratio of CoRs C1:C2 was > 2 for all binocular meridians in controls and the 90 and 180 meridians in the amblyopes; C1:C3 was > 2 for the binocularly assessed 45, 90 and 135 meridians in the controls and the 90 and 180 meridians in the amblyopes; C2:C3 were all < 2 for all meridians assessed in both groups.

CONCLUSIONS

The osVEP waveforms are reliable and useful for future investigations into the meridional anisotropies in children with refractive amblyopia, particularly the C3 component. Component C1 had the poorest repeatability, which consequentially affected C2 amplitude estimation. Only C3 amplitude and latency could be consistently estimated as C2 and C3 latencies were similarly repeatable. Coefficients of repeatability of osVEP latencies did not appear to systematically differ between non-amblyopic and amblyopic children.

Dichoptic Spatial Contrast Sensitivity Reflects Binocular Balance in Normal and Stereoanomalous Subjects

Purpose

To study binocular balance by comparing dichoptic and standard monocular contrast sensitivity function (CSF) in stereonormal and stereoanomalous/stereoblind amblyopic subjects.

Methods

Sixteen amblyopes and 17 controls participated. Using the capability of the passive three-dimensional display, we measured their CSF both monocularly and dichoptically at spatial frequencies 0.5, 1, 2, 4, and 8 cpds using achromatic Gabor patches on a luminance noise background. During monocular stimulation, the untested eye was covered, while for the dichoptic stimulation the untested eye viewed background noise. Dichoptic CSF of both eyes was acquired within one block.

Results

In patients with central fixation, dichoptic viewing had a large negative impact on the CSF of the amblyopic eye, although it hardly affected that of the dominant eye. In contrast, dichoptic viewing had a small but significant effect on both eyes for controls. In addition, all participants lay along a continuum in terms of how much their two eyes were affected by dichoptic stimulation: by using two predefined contrast sensitivity ratios, namely, amblyopic sensitivity decrement and dichoptic sensitivity decrement, not only did we find a significant correlation between these variables among all participants, but also the two groups were identified with minimum error using a cluster analysis.

Conclusions

Dichoptic CSF may be considered to measure visual performance in patients with altered binocular vision, because it better reflects the visual capacity of the amblyopic eye than the standard monocular examinations. It may also be a more reliable parameter to assess the efficacy of modern approaches to treat amblyopia.

Active Vision Therapy for Anisometropic Amblyopia in Children: A Systematic Review

Purpose

The aim of the study was evaluation of the scientific evidence about the efficacy of vision therapy in children and teenagers with anisometropic amblyopia by performing a systematic literature review.

Methods

A search was performed using 3 searching strategies in 4 different databases (PubMed, Web of Science, Scopus, and PruQuest). The quality of the included articles was evaluated using two tools for the risk of bias assessment, ROBINS-I for nonrandomized studies of intervention (NRSI), and ROB 2.0 for randomized clinical trials.

Results

The search showed 1274 references, but only 8 of them passed the inclusion criteria after the complete text review. The articles that were finally included comprised 2 randomized control trials and 6 nonrandomized studies of intervention. These articles provided evidence supporting the efficacy of vision therapy for the treatment of anisometropic amblyopia in children and teenagers. Assessment of the risk of bias showed an appropriate risk of bias for the randomized control trials, but a high risk of bias for nonrandomized studies of intervention (NRSI). A main source of risk of bias for NRSI was the domain related to the measurements of the outcomes, due to a lack of double-blind studies.

Conclusion

Vision therapy is a promising option for the treatment of anisometropic amblyopia in children and teenagers. However, the level of scientific evidence provided by the studies revised is still limited, and further randomized clinical trials are necessary to confirm the results provided to date and to optimize the vision therapy techniques by knowing the specific neural mechanisms involved.

Evaluation of Metabolite Changes in the Occipital Cortex of Patients with Idiopathic Infantile Nystagmus or Bilateral Ametropic Amblyopia by Magnetic Resonance Spectroscopy

Purpose

To evaluate the effects of idiopathic infantile nystagmus (IN) and bilateral ametropic amblyopia on metabolites in the occipital cortex by magnetic resonance spectroscopy.

Methods

The children included in this prospective study were divided into three groups. Group 1 consisted of 11 patients with idiopathic IN, group 2 consisted of 10 patients with bilateral ametropic amblyopia and group 3 consisted of nine normal children. A single-voxel magnetic resonance spectroscopy examination was performed by placing a region of interest on the occipital cortex of each participant. N-acetyl aspartate (NAA), creatine (Cr) and choline (Cho) concentrations were measured in the occipital cortex. This was followed by calculating and comparing the NAA/Cr and Cho/Cr ratios between the three groups. The Kruskal-Wallis test, Mann-Whitney U-test, and chi-square test were used for statistical analysis.

Results

There was no statistically significant difference in NAA/Cr ratios between patients with idiopathic IN and normal children, but there was a statistically significant difference between these groups when Cho/Cr ratios were compared; the ratio was higher in the idiopathic IN group. There were no statistically significant differences in NAA/Cr or Cho/Cr ratios between patients with bilateral ametropic amblyopia and normal children.

Conclusions

Our findings suggest that the neurochemical profile of the occipital cortex is partially affected by idiopathic IN, but not by bilateral ametropic amblyopia.

Selective serotonin reuptake inhibitors may lead to improved cataract surgery outcomes in patients with amblyopia

Purpose

To evaluate the effects of selective serotonin reuptake inhibitor (SSRI)/serotonin norepinephrine reuptake inhibitor (SNRI) medications in combination with cataract surgery in treating amblyopia in adult patients.

Patients and methods

A retrospective chart review study was conducted on patients who had undergone cataract surgery at the Johns Hopkins Hospital Wilmer Eye Institute. Six inclusion criteria were used to assess patient eligibility: 1) >18 years of age, 2) diagnosis of amblyopia, 3) diagnosis of cataract and treatment with surgery, 4) electronic medical record contains pre-surgery and post-surgery visual acuity (VA) measurements, 5) electronic medical record contains information on whether the patient was ever prescribed a SSRI/SNRI and the treatment duration, and 6) interocular VA difference of two lines or more on Snellen chart prior to cataract surgery. From each record, preoperative VA, postoperative VA, date of surgery, date at which postoperative VA was measured, and age at surgery were collected.

Results

A total of 237 patients were included, with 38 of them being on SSRI/SNRI. The mean improvement in VA after surgery was not significantly greater in patients on SSRI/SNRI (SSRI/SNRI: −0.276 logMAR, control: −0.192 logMAR, p=0.15). Multivariable regression was subsequently performed and while holding all other variables constant, demonstrated a statistically significant improvement in VA in patients on SSRI/SNRI (95% CI: −0.194, −0.0116, p=0.03). The regression analysis further demonstrated that advanced age has an adverse effect on the change in post-op VA (CI: 3.34×10⁻³ logMAR, 9.77×10⁻³ logMAR, p<0.005). Worse baseline VA is associated with a greater improvement in post-op VA (95% CI: −0.659 logMAR, −0.463 logMAR, p<0.005) but adverse effect on the absolute post-op VA (95% CI: 0.341 logMAR, 0.544 logMAR, p<0.005).

Conclusion

This study suggests that patients with amblyopia undergoing cataract surgery may potentially have a greater visual improvement when treated with SSRI/SNRIs.

The Role of Binocularity in Anisometropic Amblyopia

Anisometropic amblyopia is unilateral by definition and current treatment recommendations reflect that characteristic. However, recent research suggests a binocular component that deserves consideration. The aim of this review is to consider the levels of anisometropia deemed amblyogenic, and the cortical changes that occur in the presence of anisometropic amblyopia. Particular attention is given to cortical changes that impact the binocularity of these individuals. Knowledge of binocular deficits in anisometropic amblyopia has implications for current, accepted treatment regimens which are monocular in nature. Therefore, the integrity of binocular function in anisometropic amblyopia and its impact on the visual outcome will be evaluated. Given the rise in binocular treatments under clinical trial for amblyopia, this review also aims to evaluate the evidence of potentially enhanced benefits to anisometropic amblyopes from proposed new binocular therapies.

Individual variation in inter-ocular suppression and sensory eye dominance

The competitive and inhibitory interactions between the two eyes' images are a pervasive aspect of binocular vision. Over the last decade, our understanding of the neural processes underpinning binocular rivalry (BR) and continuous flash suppression (CFS) has increased substantially, but we still have little understanding of the relationship between these two effects and their variation in the general population. Studies that pool data across individuals and eyes risk masking substantial variations in binocular vision that exist in the general population. To investigate this issue we compared the depth of inter-ocular suppression evoked by BR with that elicited by CFS, in a group (N = 25) of visually normal individuals. A noise pattern (either static for BR or dynamic for CFS) was presented to one eye and its suppressive influence on a probe grating presented simultaneously to the other eye was measured. We found substantial individual differences in the magnitude of suppression (a 10-fold variation in probe detection threshold) evoked by each task, but performance on BR was a significant predictor of performance on the CFS task. However many individuals showed marked asymmetries between the two eyes' ability to detect a suppressed target, that were not necessarily the same for the two tasks. There was a tendency for the magnitude of the asymmetry to increase as the refresh rate of the dynamic noise increased. The results suggest a common underlying mechanism is likely to be responsible, at least in part, for driving inter-ocular suppression under BR and CFS. The marked asymmetries in inter-ocular suppression at higher noise refresh rates, may be indicative of a difference in temporal processing between the eyes.

The awareness of amblyopia among parents in Saudi Arabia

Purpose

Amblyopia is the most common cause of unilateral visual impairment. This study investigated parents' awareness of amblyopia in different regions of Saudi Arabia.

Methods

This was a cross-sectional population study. The survey consisted of two main sections; the first section contained 13 general background questions, and the second section (10 questions) focused on awareness of amblyopia, routine vision checks and how to raise awareness of amblyopia in the community. The survey was distributed to respondents using email and social media.

Results

The responses of 1649 families were received. Respondents' age range was from 22-62 years (mean ± standard deviation = 33.6 ± 8.7 years). Most respondents had no previous knowledge of amblyopia (1155 participants, 70%), and 313 participants (19%) had no idea if their children had amblyopia. In total, 990 participants (60%) did not visit the eye clinic with their children for a routine eye exam. A total of 495 parents (30%), who were aware of amblyopia, knew of it mainly from eye clinic visits and from Internet websites. A total of 140 respondents reported that their children had amblyopia; 58.3% of those children underwent routine eye examinations once a year, and the rest underwent routine eye examinations twice a year.

Conclusion

The results clearly showed a lack of amblyopia awareness among the Saudi community. This lack of awareness can lead to visual impairment among children. More efficient efforts are urgently needed from health professionals, education centres, the media and social organizations to promote awareness of amblyopia.

Visuomotor Behaviour in Amblyopia: Deficits and Compensatory Adaptations

Amblyopia is a neurodevelopmental visual disorder arising from decorrelated binocular experience during the critical periods of development. The hallmark of amblyopia is reduced visual acuity and impairment in binocular vision. The consequences of amblyopia on various sensory and perceptual functions have been studied extensively over the past 50 years. Historically, relatively fewer studies examined the impact of amblyopia on visuomotor behaviours; however, research in this area has flourished over the past 10 years. Therefore, the aim of this review paper is to provide a comprehensive review of current knowledge about the effects of amblyopia on eye movements, upper limb reaching and grasping movements, as well as balance and gait. Accumulating evidence indicates that amblyopia is associated with considerable deficits in visuomotor behaviour during amblyopic eye viewing, as well as adaptations in behaviour during binocular and fellow eye viewing in adults and children. Importantly, due to amblyopia heterogeneity, visuomotor development in children and motor skill performance in adults may be significantly influenced by the etiology and clinical features, such as visual acuity and stereoacuity. Studies with larger cohorts of children and adults are needed to disentangle the unique contribution of these clinical characteristics to the development and performance of visuomotor behaviours.

From Basic Visual Science to Neurodevelopmental Disorders: The Voyage of Environmental Enrichment-Like Stimulation

Genes and environmental stimuli cooperate in the regulation of brain development and formation of the adult neuronal architecture. Genetic alterations or exposure to perturbing environmental conditions, therefore, can lead to altered neural processes associated with neurodevelopmental disorders and brain disabilities. In this context, environmental enrichment emerged as a promising and noninvasive experimental treatment for favoring recovery of cognitive and sensory functions in different neurodevelopmental disorders. The aim of this review is to depict, mainly through the much explicative examples of amblyopia, Down syndrome, and Rett syndrome, the increasing interest in the potentialities and applications of enriched environment-like protocols in the field of neurodevelopmental disorders and the understanding of the molecular mechanisms underlying the beneficial effects of these protocols, which might lead to development of pharmacological interventions.

Impaired Spatial Hearing in Amblyopia: Evidence for Calibration of Auditory Maps by Retinocollicular Input in Humans

Purpose

Evidence from animals and blind humans suggests that early visual experience influences the developmental calibration of auditory localization. Hypothesizing that unilateral amblyopia may involve cross-modal deficits in spatial hearing, we measured the precision and accuracy of sound localization in humans with amblyopia.

Methods

All participants passed a standard hearing test. Experiment 1 measured sound localization precision for click stimuli in 10 adults with amblyopia and 10 controls using a minimum audible angle (MAA) task. Experiment 2 measured sound localization error (i.e., accuracy) for click train stimuli in 14 adults with amblyopia and 16 controls using an absolute sound localization task.

Results

In Experiment 1, the MAA (mean ± SEM) was significantly greater in the amblyopia group compared with controls (2.75 ± 0.30° vs. 1.69 ± 0.09°, P = 0.006). In Experiment 2, the overall sound localization error was significantly greater in the amblyopia group compared with controls (P = 0.047). The amblyopia group also showed significantly greater sound localization error in the auditory hemispace ipsilateral to the amblyopic eye (P = 0.036). At a location within this auditory hemispace, the magnitude of sound localization error correlated significantly with deficits in stereo acuity (P = 0.036).

Conclusions

The precision and accuracy of sound localization are impaired in unilateral amblyopia. The asymmetric pattern of sound localization error suggests that amblyopic vision may interfere with the development of spatial hearing via the retinocollicular pathway.

Treating amblyopia in adults with prosthetic occluding contact lenses

PURPOSE

To investigate the feasibility, effectiveness and acceptability of using prosthetic occluding contact lenses (OCLs) to treat moderate amblyopia in adults and of the role of the multifocal visual evoked potential (mfVEP) as a predictor of postamblyopic therapy.

METHODS

A comparative, prospective, interventional, case series pilot study with amblyopic adults (mean age: 40 years, range 20-50 years) allocated into two intervention groups: eye patching and OCL. The primary outcome variable was logarithm of the minimum angle of resolution (logMAR) best-corrected visual acuity (BCVA), and secondary outcomes were mfVEP amplitude and latency and patients' health-related quality of life National Eye Institute Visual Function Questionnaire (NEI VFQ-25).

RESULTS

Significant improvements in pre- to postamblyopic therapy BCVA were seen at 1.5 months in the OCL group [0.29 logMAR, 95% confidence interval (CI): 0.10-0.47 versus 0.11 logMAR, 95% CI: 0.02-0.19; p < 0.001] and eye patching group (0.29 logMAR, 95% CI: 0.17-0.40 versus 0.18 logMAR, 95% CI: 0.12-0.23; p < 0.01). Post-treatment BCVA was inversely related to age (R: 0.009, 95% CI: -0.02 to -0.001; p = 0.04) and the presence of strabismus (R: -0.3, 95% CI: -0.434 to -0.17; p = 0.001). No significant changes in the number and size of the abnormal mfVEP amplitude and latency defects were observed after occlusion. The NEI VFQ-25 composite score showed significant improvement in the OCL users at 12 months compared to eye patching.

CONCLUSION

Significant vision improvement can be achieved, making occlusion with OCLs an effective and more acceptable therapy for adults with amblyopia.

The neural basis of spatial vision losses in the dysfunctional visual system

Human vision relies on correct information processing from the eye to various visual areas. Disturbances in the visual perception of simple features are believed to come from low-level network (e.g., V1) disruptions. In the present study, we modelled monocular losses in spatial vision through plausible multiple network modifications in early visual coding. We investigated perceptual deficits in anisometropic amblyopia and used the monocular tilt illusion as a probe of primary visual cortex orientation coding and inhibitory interactions. The psychophysical results showed that orientation misperception was higher in amblyopic eyes (AE) than in the fellow and neurotypical eyes and was correlated with the subject’s AE peak contrast sensitivity. The model fitted to the experimental results allowed to split these observations between different network characteristics by showing that these observations were explained by broader orientation tuning widths in AEs and stronger lateral inhibition in abnormal amblyopic system that had strong contrast sensitivity losses. Through psychophysics measures and computational modelling of V1, our study links multiple perceptual changes with localized modifications in the primary visual cortex.

Comparative electrophysiological responses in anisometropic and strabismic amblyopic children

Purpose

To compare anisometropic hypermetropic amblyopic and strabismic amblyopic responses to pattern electroretinogram (PERG) and pattern visual evocated potential (PVEP).

Materials and methods

Fifty-six patients – 18 hypermetropic anisometropic amblyopic children (mean age 9.70±2.5 years), 19 strabismic amblyopic children (mean age 10.30±2.6 years) and 19 normal emetropic subjects (mean age 10.10±2.2 years) – were enrolled in this study. After routine ophthalmic examination, PERG and PVEP were recorded in response to checks reversed at the rate of two reversals/second stimulating macular area.

Results

The difference between hypermetropic anisometropic amblyopia and strabismus amblyopia with respect to P100/P50/N95 wave latencies (P=0.055/0.855/0.132) and P100/P50/N95 amplitudes (P=0.980/0.095/0.045) was not statistically significant. However, there was a significant statistical difference between strabismic amblyopia group and controls for P100/P50/N95 latencies (P=0.000/0.006/0.004).

Conclusion

Our findings indicated that despite clinical differences between anisometropic amblyopic and strabismic amblyopic patients, no differences were found in the responses of PVEP and PERG. The abnormal components of the PVEP and PERG in amblyopic subjects could reflect a retinal dysfunction in the visual pathway.

Amblyopia in Children: Analysis Among Preschool and School Children in the City of Tuzla, Bosnia and Herzegovina

Aim:

This study measured the prevalence of amblyopia in preschool and school children between 4 and 15 years of age in Tuzla, Bosnia and Herzegovina and as well and to examine its relations with anisometropia and strabismus.

Methods:

Children from eight daycare centers and twenty four elementary schools were screened for amblyopia by volunteer personnel (medical students), any child who failed to pass the screening examination, was referred to the ophthalmologist for complete examination at University Clinic Center Tuzla. The examination included VA, stereopsis, cover testing, refractive retinoscopy, and examination of the red reflex and posterior pole.

Results:

Total of 7415 children, which included 3790 males and 3625 females, in the age range of 3 to 15 years from 24 schools and 8 preschool were screened. Fifty night children (1.9%) were diagnosed with amblyopia, unilateral in 28 and bilateral in 31.

Conclusion:

Prevalence of significant refractive errors is high enough to justify a school eye screening program solely for this purpose. preschool and school screening program in children in critical period of development of amblyopia must be conducted to find out the ametropias and amblyopia in time; and treat them earlier.

Childhood amblyopia: current management and new trends

INTRODUCTION OR BACKGROUND

With a prevalence of 2-5%, amblyopia is the most common vision deficit in children in the UK and the second most common cause of functional low vision in children in low-income countries.

SOURCES OF DATA

Pubmed, Cochrane library and clinical trial registries (clinicaltrials.gov, ISRCTN, UKCRN portfolio database).

AREAS OF AGREEMENT

Screening and treatment at the age of 4-5 years are cost efficient and clinically effective. Optical treatment (glasses) alone can improve visual acuity, with residual amblyopia treated by part-time occlusion or pharmacological blurring of the better-seeing eye. Treatment after the end of the conventional 'critical period' can improve vision, but in strabismic amblyopia carries a low risk of double vision.

AREAS OF CONTROVERSY

It is not clear whether earlier vision screening would be cost efficient and associated with better outcomes. Optimization of treatment by individualized patching regimes or early start of occlusion, and novel binocular treatment approaches may enhance adherence to treatment, provide better outcomes and shorten treatment duration.

GROWING POINTS

Binocular treatments for amblyopia.

AREAS TIMELY FOR DEVELOPING RESEARCH

Impact of amblyopia on education and quality of life; optimal screening timing and tests; optimal administration of conventional treatments; development of child-friendly, effective and safe binocular treatments.

Is the Cortical Deficit in Amblyopia Due to Reduced Cortical Magnification, Loss of Neural Resolution, or Neural Disorganization?

The neural basis of amblyopia is a matter of debate. The following possibilities have been suggested: loss of foveal cells, reduced cortical magnification, loss of spatial resolution of foveal cells, and topographical disarray in the cellular map. To resolve this we undertook a population receptive field (pRF) functional magnetic resonance imaging analysis in the central field in humans with moderate-to-severe amblyopia. We measured the relationship between averaged pRF size and retinal eccentricity in retinotopic visual areas. Results showed that cortical magnification is normal in the foveal field of strabismic amblyopes. However, the pRF sizes are enlarged for the amblyopic eye. We speculate that the pRF enlargement reflects loss of cellular resolution or an increased cellular positional disarray within the representation of the amblyopic eye.

SIGNIFICANCE STATEMENT

The neural basis of amblyopia, a visual deficit affecting 3% of the human population, remains a matter of debate. We undertook the first population receptive field functional magnetic resonance imaging analysis in participants with amblyopia and compared the projections from the amblyopic and fellow normal eye in the visual cortex. The projection from the amblyopic eye was found to have a normal cortical magnification factor, enlarged population receptive field sizes, and topographic disorganization in all early visual areas. This is consistent with an explanation of amblyopia as an immature system with a normal complement of cells whose spatial resolution is reduced and whose topographical map is disordered. This bears upon a number of competing theories for the psychophysical defect and affects future treatment therapies.

Perceptual learning improves neural processing in myopic vision

Visual performance is jointly determined by the quality of optical transmission of the eye and neural processing in the visual system. An open question is: Can effects of optical defects be compensated by perceptual learning in neural processing? To address this question, we conducted a perceptual learning study on 23 observers with myopic vision, targeting high frequency deficits by training them in a monocular grating detection task in the non-dominant eye near their individual cutoff spatial frequencies. The contrast sensitivity function and visual acuity in both eyes (without optical correction) were assessed for all the observers in the training group before and after training, and for all the observers in the control group twice with a 10-day interval between the tests. In addition, the threshold versus external noise contrast function was measured for five observers in the training group before and after training. We found that (a) training significantly improved contrast sensitivity at the trained spatial frequency, visual acuity, and contrast sensitivity over a wide range of spatial frequencies in both eyes; (b) training did not lead to any significant refractive changes; (c) the mechanism of improvements was a combination of internal additive noise reduction and external noise exclusion; and (d) the improvements in visual acuity and contrast sensitivity were almost fully retained for at least four months in the three observers tested. These results suggest that perceptual learning may provide a potential noninvasive procedure to compensate for optical defects in mild to modest myopia.

Amblyaudia: Review of Pathophysiology, Clinical Presentation, and Treatment of a New Diagnosis

OBJECTIVE

Similar to amblyopia in the visual system, "amblyaudia" is a term used to describe persistent hearing difficulty experienced by individuals with a history of asymmetric hearing loss (AHL) during a critical window of brain development. Few clinical reports have described this phenomenon and its consequent effects on central auditory processing. We aim to (1) define the concept of amblyaudia and (2) review contemporary research on its pathophysiology and emerging clinical relevance.

DATA SOURCES

PubMed, Embase, and Cochrane databases.

REVIEW METHODS

A systematic literature search was performed with combinations of search terms: "amblyaudia," "conductive hearing loss," "sensorineural hearing loss," "asymmetric," "pediatric," "auditory deprivation," and "auditory development." Relevant articles were considered for inclusion, including basic and clinical studies, case series, and major reviews.

CONCLUSIONS

During critical periods of infant brain development, imbalanced auditory input associated with AHL may lead to abnormalities in binaural processing. Patients with amblyaudia can demonstrate long-term deficits in auditory perception even with correction or resolution of AHL. The greatest impact is in sound localization and hearing in noisy environments, both of which rely on bilateral auditory cues. Diagnosis and quantification of amblyaudia remain controversial and poorly defined. Prevention of amblyaudia may be possible through early identification and timely management of reversible causes of AHL.

IMPLICATIONS FOR PRACTICE

Otolaryngologists, audiologists, and pediatricians should be aware of emerging data supporting amblyaudia as a diagnostic entity and be cognizant of the potential for lasting consequences of AHL. Prevention of long-term auditory deficits may be possible through rapid identification and correction.

Active training for amblyopia in adult rodents

Amblyopia is the most diffused form of visual function impairment affecting one eye, with a prevalence of 1–5% in the total world population. Amblyopia is usually caused by an early functional imbalance between the two eyes, deriving from anisometropia, strabismus, or congenital cataract, leading to severe deficits in visual acuity, contrast sensitivity and stereopsis. While amblyopia can be efficiently treated in children, it becomes irreversible in adults, as a result of a dramatic decline in visual cortex plasticity which occurs at the end of the critical period (CP) in the primary visual cortex. Notwithstanding this widely accepted dogma, recent evidence in animal models and in human patients have started to challenge this view, revealing a previously unsuspected possibility to enhance plasticity in the adult visual system and to achieve substantial visual function recovery. Among the new proposed intervention strategies, non invasive procedures based on environmental enrichment, physical exercise or visual perceptual learning (vPL) appear particularly promising in terms of future applicability in the clinical setting. In this survey, we will review recent literature concerning the application of these behavioral intervention strategies to the treatment of amblyopia, with a focus on possible underlying molecular and cellular mechanisms.

Binocular versus standard occlusion or blurring treatment for unilateral amblyopia in children aged three to eight years

BACKGROUND

Current treatments for amblyopia in children, occlusion and pharmacological blurring, have had limited success, with less than two-thirds of children achieving good visual acuity of at least 0.20 logMAR in the amblyopic eye, limited improvement of stereopsis, and poor compliance. A new treatment approach, based on the dichoptic presentation of movies or computer games (images presented separately to each eye), may yield better results, as it aims to balance the input of visual information from each eye to the brain. Compliance may also improve with these more child-friendly treatment procedures.

OBJECTIVES

To determine whether binocular treatments in children aged three to eight years with unilateral amblyopia result in better visual outcomes than conventional occlusion or pharmacological blurring treatment.

SEARCH METHODS

We searched the Cochrane Eyes and Vision Group Trials Register (last date of searches: 14 April 2015), the Cochrane Central Register of Controlled Trials (CENTRAL; 2015, Issue 3), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to April 2015), EMBASE (January 1980 to April 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov), and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials.

SELECTION CRITERIA

Two review authors independently screened the results of the search in order to identify studies that met the inclusion criteria of the review: randomised controlled trials (RCTs) that enrolled participants between the ages of three and eight years old with unilateral amblyopia, defined as best-corrected visual acuity (BCVA) worse than 0.200 logMAR in the amblyopic eye, and BCVA 0.200 logMAR or better in the fellow eye, in the presence of an amblyogenic risk factor such as anisometropia, strabismus, or both. Prior to enrolment, participants were to have undergone a cycloplegic refraction and comprehensive ophthalmic examination including fundal examination. In addition, participants had to have completed a period of optical treatment, if indicated, and BCVA in the amblyopic eye had to remain unchanged on two consecutive assessments despite reportedly good compliance with glasses wearing. Participants were not to have received any treatment other than optical treatment prior to enrolment. We planned to include any type of binocular viewing intervention; these could be delivered on different devices including computer monitors viewed with LCD shutter glasses or hand-held screens including mobile phone screens with lenticular prism overlay. Control groups were to have received standard amblyopia treatment; this could include occlusion or pharmacological blurring of the better-seeing eye. We planned to include full-time (all waking hours) and part-time (between 1 and 12 hours a day) occlusion regimens.

DATA COLLECTION AND ANALYSIS

We planned to use standard methodological procedures expected by The Cochrane Collaboration. We had planned to meta-analyse the primary outcome, that is mean distance BCVA in the amblyopic eye at 12 months after the cessation of treatment.

MAIN RESULTS

We could identify no RCTs in this subject area.

AUTHORS' CONCLUSIONS

Further research is required to allow decisions about implementation of binocular treatments for amblyopia in clinical practice. Currently there are no clinical trials offering standardised evidence of the safety and effectiveness of binocular treatments, but results from non-controlled cohort studies are encouraging. Future research should be conducted in the form of RCTs, using acknowledged methods of visual acuity and stereoacuity assessment with known reproducibility. Other important outcome measures include outcomes reported by users, compliance with treatment, and recurrence of amblyopia after cessation of treatment.

The Structural Properties of Major White Matter Tracts in Strabismic Amblyopia

PURPOSE

In order to better understand whether white matter structural deficits are present in strabismic amblyopia, we performed a survey of the tissue properties of 28 major white matter tracts using diffusion and quantitative magnetic resonance imaging approaches.

METHODS

We used diffusion-based tensor modeling and a new quantitative T1 protocol to measure fractional anisotropy (FA), mean diffusivity (MD), and myelin-sensitive T1 values. We surveyed tracts in the occipital lobe, including the vertical occipital fasciculus (VOF)-a newly rediscovered tract that bridges dorsal and ventral areas of the occipital lobe, as well as tracts across the rest of the brain.

RESULTS

Adults with long-standing strabismic amblyopia show tract-specific elevations in MD. We rank-ordered the tracts on the basis of their MD effect-size. The four most affected tracts were the anterior frontal corpus callosum (ACC), the right VOF, the left inferior longitudinal fasciculus (ILF) and the left optic radiation.

CONCLUSIONS

The results suggest that most white matter tissue properties are relatively robust to the early visual insult caused by strabismus. However, strabismic amblyopia does affect MD, not only in occipital tracts, such as the VOF and optic radiation, but also in long range association tracts connecting visual cortex to the frontal and temporal lobes (ILF) and connecting the two hemispheres (ACC).

The challenges of developing a contrast-based video game for treatment of amblyopia

Perceptual learning of visual tasks is emerging as a promising treatment for amblyopia, a developmental disorder of vision characterized by poor monocular visual acuity. The tasks tested thus far span the gamut from basic psychophysical discriminations to visually complex video games. One end of the spectrum offers precise control over stimulus parameters, whilst the other delivers the benefits of motivation and reward that sustain practice over long periods. Here, we combined the advantages of both approaches by developing a video game that trains contrast sensitivity, which in psychophysical experiments, is associated with significant improvements in visual acuity in amblyopia. Target contrast was varied adaptively in the game to derive a contrast threshold for each session. We tested the game on 20 amblyopic subjects (10 children and 10 adults), who played at home using their amblyopic eye for an average of 37 sessions (approximately 11 h). Contrast thresholds from the game improved reliably for adults but not for children. However, logMAR acuity improved for both groups (mean = 1.3 lines; range = 0–3.6 lines). We present the rationale leading to the development of the game and describe the challenges of incorporating psychophysical methods into game-like settings.

The amblyopic eye in subjects with anisometropia show increased saccadic latency in the delayed saccade task

The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination. Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood. Several studies have shown prolongation of saccadic latency time in amblyopic eye. In our opinion, study of saccadic latency in the context of central vision deficits assessment, should be based on central retina stimulation. For this reason, we proposed saccade delayed task. It requires inhibitory processing for maintaining fixation on the central target until it disappears—what constitutes the GO signal for saccade. The experiment consisted of 100 trials for each eye and was performed under two viewing conditions: monocular amblyopic/non-dominant eye and monocular dominant eye. We examined saccadic latency in 16 subjects (mean age 30 ± 11 years) with anisometropic amblyopia (two subjects had also microtropia) and in 17 control subjects (mean age 28 ± 8 years). Participants were instructed to look at central (fixation) target and when it disappears, to make the saccade toward the periphery (10°) as fast as possible, either left or the right target. The study results have proved the significant difference in saccadic latency between the amblyopic (mean 262 ± 48 ms) and dominant (mean 237 ± 45 ms) eye, in anisometropic group. In the control group, the saccadic latency for dominant (mean 226 ± 32 ms) and non-dominant (mean 230 ± 29 ms) eye was not significantly different. By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.

Origins of strabismus and loss of binocular vision

Strabismus is a frequent ocular disorder that develops early in life in humans. As a general rule, it is characterized by a misalignment of the visual axes which most often appears during the critical period of visual development. However other characteristics of strabismus may vary greatly among subjects, for example, being convergent or divergent, horizontal or vertical, with variable angles of deviation. Binocular vision may also vary greatly. Our main goal here is to develop the idea that such “polymorphy” reflects a wide variety in the possible origins of strabismus. We propose that strabismus must be considered as possibly resulting from abnormal genetic and/or acquired factors, anatomical and/or functional abnormalities, in the sensory and/or the motor systems, both peripherally and/or in the brain itself. We shall particularly develop the possible “central” origins of strabismus. Indeed, we are convinced that it is time now to open this “black box” in order to move forward. All of this will be developed on the basis of both presently available data in literature (including most recent data) and our own experience. Both data in biology and medicine will be referred to. Our conclusions will hopefully help ophthalmologists to better understand strabismus and to develop new therapeutic strategies in the future. Presently, physicians eliminate or limit the negative effects of such pathology both on the development of the visual system and visual perception through the use of optical correction and, in some cases, extraocular muscle surgery. To better circumscribe the problem of the origins of strabismus, including at a cerebral level, may improve its management, in particular with respect to binocular vision, through innovating tools by treating the pathology at the source.

Treatment of amblyopia in the adult: insights from a new rodent model of visual perceptual learning

Amblyopia is the most common form of impairment of visual function affecting one eye, with a prevalence of about 1–5% of the total world population. Amblyopia usually derives from conditions of early functional imbalance between the two eyes, owing to anisometropia, strabismus, or congenital cataract, and results in a pronounced reduction of visual acuity and severe deficits in contrast sensitivity and stereopsis. It is widely accepted that, due to a lack of sufficient plasticity in the adult brain, amblyopia becomes untreatable after the closure of the critical period in the primary visual cortex. However, recent results obtained both in animal models and in clinical trials have challenged this view, unmasking a previously unsuspected potential for promoting recovery even in adulthood. In this context, non invasive procedures based on visual perceptual learning, i.e., the improvement in visual performance on a variety of simple visual tasks following practice, emerge as particularly promising to rescue discrimination abilities in adult amblyopic subjects. This review will survey recent work regarding the impact of visual perceptual learning on amblyopia, with a special focus on a new experimental model of perceptual learning in the amblyopic rat.

Acuity-independent effects of visual deprivation on human visual cortex

Visual development depends on sensory input during an early developmental critical period. Deviation of the pointing direction of the two eyes (strabismus) or chronic optical blur (anisometropia) separately and together can disrupt the formation of normal binocular interactions and the development of spatial processing, leading to a loss of stereopsis and visual acuity known as amblyopia. To shed new light on how these two different forms of visual deprivation affect the development of visual cortex, we used event-related potentials (ERPs) to study the temporal evolution of visual responses in patients who had experienced either strabismus or anisometropia early in life. To make a specific statement about the locus of deprivation effects, we took advantage of a stimulation paradigm in which we could measure deprivation effects that arise either before or after a configuration-specific response to illusory contours (ICs). Extraction of ICs is known to first occur in extrastriate visual areas. Our ERP measurements indicate that deprivation via strabismus affects both the early part of the evoked response that occurs before ICs are formed as well as the later IC-selective response. Importantly, these effects are found in the normal-acuity nonamblyopic eyes of strabismic amblyopes and in both eyes of strabismic patients without amblyopia. The nonamblyopic eyes of anisometropic amblyopes, by contrast, are normal. Our results indicate that beyond the well-known effects of strabismus on the development of normal binocularity, it also affects the early stages of monocular feature processing in an acuity-independent fashion.

Unaffected smooth pursuit but impaired motion perception in monocularly enucleated observers

The objective of this paper was to study the characteristics of closed-loop smooth pursuit eye movements of 15 unilaterally eye enucleated individuals and 18 age-matched controls and to compare them to their performance in two tests of motion perception: relative motion and motion coherence. The relative motion test used a brief (150 ms) small stimulus with a continuously present fixation target to preclude pursuit eye movements. The duration of the motion coherence trials was 1s, which allowed a brief pursuit of the stimuli. Smooth pursuit data were obtained with a step-ramp procedure. Controls were tested both monocularly and binocularly. The data showed worse performance by the enucleated observers in the relative motion task but no statistically significant differences in motion coherence between the two groups. On the other hand, the smooth pursuit gain of the enucleated participants was as good as that of controls for whom we found no binocular advantage. The data show that enucleated observers do not exhibit deficits in the afferent or sensory pathways or in the efferent or motor pathways of the steady-state smooth pursuit system even though their visual processing of motion is impaired.

The expression of vasoactive intestinal polypeptide in visual cortex-17 in normal visual development and formation of anisometropic amblyopia

AIMS

To document the expression of vasoactive intestinal polypeptide (VIP) in the visual cortex-17 of kittens with anisometropic amblyopia, and to investigate the relationship between VIP and the development of the visual system.

METHODS

Sixteen normal kittens (4-wk of age) were randomly divided into two groups: control and amblyopic. Amblyopia was produced by atropinization of one eye in eight kittens. Four (2 normal and 2 amblyopia) kittens were sacrificed at weeks 3, 6, 9, or 12 post-treatment respectively. Expression of VIP-mRNA in the visual cortex-17 was detected through in-situ hybridization. Neurons in the visual cortex were visualized by transmission electron microscopy (TEM). The number of neurons was analyzed via light microscopy (LM).

RESULTS

VIP-mRNA expression was increased with age in control kittens but remained nearly static in age-matched anisometropic amblyopic kittens (p < 0.05). The number of VIP-positive cells of amblyopic kittens decreased dramatically when compared to normal age-matched kittens (p < 0.05). The total comparison between different positive ranks suggested a significant difference. The degree of expression between these two groups was significantly different. Ultrastructurally, in the control group, the nuclear membrane of most neurons was discernable and chromatin was evenly distributed within the nucleus. Abundant cytoplasm and tubular-shaped mitochondria were observed. These cells were also rich in Golgi bodies, ribosomes, and endoplasmic reticulum. In amblyopic kittens, nuclei of most neurons were aggregated, the number of ribosomes and Golgi bodies was reduced, mitochondria were swollen, and mitochondrial cristae were shortened or even absent. The endoplasmic reticulum was distended and reduced in magnitude.

CONCLUSIONS

VIP appears to play an important role in visual development, and its mRNA expression is affected by visual experiences. Visual dysfunction may down-regulate the expression of VIP-mRNA by impairing the structure and function of the neurons in the visual cortex, finally leading to amblyopia.

The relationship between anisometropia and amblyopia

This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.