Factors influencing severity of and recovery from anisometropic amblyopia

Ocular and visual perceptive factors associated with treatment outcomes in patients with anisometropic amblyopia

BACKGROUND

The aim of this observational study was to identify ocular and visual perceptive risk factors related to treatment results following refractive correction and patching in children with anisometropic amblyopia, who were between the ages of 4 to 14 years old.

METHODS

One-hundred and two children with newly diagnosed anisometropic amblyopia were recruited. Successful treatment of amblyopia was defined as the final best corrected visual acuity (BCVA) better than or equal to 0.1 logMAR and amblyopic eye BCVA within 1 line of the sound eye BCVA by the end of the treatment period. BCVA, cycloplegic refraction, stereoacuity, perceptual eye position (PEP) and interocular suppression were measured.

RESULTS

Of these patients, 45.10% achieved successful treatment of amblyopia after refractive correction and patching for 10.5 months. The mean age was not significantly different between patients who were successfully and unsuccessfully treated (5.50 ± 1.59 years vs 6.14 ± 2.19 years, respectively). Patients who failed treatment had significantly larger interocular difference of BCVA at the time of initial treatment (successful group: 0.33 ± 0.29 logMAR, unsuccessful group: 0.65 ± 0.35 logMAR) and after refractive adaptation (successful group: 0.15 ± 0.13 logMAR, unsuccessful group: 0.42 ± 0.35 logMAR). They also had higher spherical equivalent (SE) of amblyopic eyes (successful group: 3.08 ± 3.61 D, unsuccessful group: 5.27 ± 3.38 D), bigger interocular difference of SE (successful group: 0.94 ± 2.71 D, unsuccessful group: 3.09 ± 3.05 D), worse stereoacuity (successful group: 2.32 ± 0.37 log seconds of arc, unsuccessful group: 2.75 ± 0.32 log seconds of arc), larger vertical PEP deviation (successful group: 6.41 ± 6.08 pixel, unsuccessful group: 19.07 ± 24.96 pixel) and deeper interocular suppression (successful group: 21.7 ± 19.7%, unsuccessful group: 37.8 ± 27.1%) than those of successfully treated patients. The most influential treatment failure risk factors were larger vertical PEP deviation [adjusted odds ratio (OR) (95% confidence interval) 1.12 (1.02-1.22)] and worse stereoacuity [adjusted odds ratio (OR) (95% confidence interval) 7.72 (1.50-39.85)] in multiple logistic regression analysis.

CONCLUSIONS

Larger vertical PEP deviation and worse stereoacuity were the most influential treatment failure risk factors in children with anisometropic amblyopia. The vertical PEP deviation and stereoacuity, which can reflect interocular interaction, may be useful in predicting the response to therapy.

Binocular treatment for individual with amblyopia: A systematic review and meta-analysis

OBJECTIVE

To assess the efficacy of binocular treatment for individual with amblyopia.

METHODS

In this meta-analysis, a comprehensive search of literatures was performed from PubMed, Embase, Cochrane Library and Web of Science databases up to December 21, 2020. Sensitivity analysis was performed for all outcomes. The Begg's test was used to assess the publication bias. Heterogeneity test was conducted for each effect indicator. Indicators were analyzed by random-effects model when the heterogeneity statistic I2 ≥ 50%, on the contrary, indicators were analyzed by fixed-effect model. Standard mean difference (SMD) or weighted mean difference (WMD) was adopted as effect indicators, and the effect amount was expressed as 95% confidence intervals (CIs).

RESULTS

A total of 13 literatures including 1146 participants were finally enrolled, with 595 in the intervention group and 551 in the control group. The results indicated that the improvement of amblyopic eye visual acuity [SMD: 0.882, 95%CI: (0.152, 1.613), P = 0.018] in binocular treatment group was better than that in control group. And binocular treatment could improve stereo acuity in individual with amblyopia [WMD: 0.138, 95%CI: (0.068, 0.208), P < 0.001].

CONCLUSION

Binocular treatment may be beneficial to visual acuity, stereo acuity and binocular function improvement for individual with amblyopia. In clinical practice, binocular treatment can be used as one of the treatments for individual with amblyopia.

Examination of Macular Retina and Choroidal Thickness in High Myopic Amblyopia Using Spectral-Domain Optical Coherence Tomography

Purpose

The aim of this study was to investigate changes in the retinal and choroidal thickness between high myopic amblyopia (HMA), low myopia (LM), moderate myopia (MM), high myopia (HM), and normal group (NG) using a spectral-domain optical coherence tomography (SD-OCT).

Materials and Methods

A total of 75 Chinese children (128 eyes; mean age 10.5 years) were recruited. Retinal thickness (RT) and choroidal thickness (CT) were measured at different locations including subfoveal (SF), and at 0.5 mm/1.0 mm/1.5 mm/2.0 mm/2.5 mm/3.0 mm to the fovea in superior, nasal, inferior, and temporal sectors using enhanced depth imaging (EDI) system of SD-OCT. Axial length (AL), best-corrected visual acuity (BCVA), and refraction errors were also collected.

Results

No significant differences were found in subfoveal retinal thickness (SFRT). Moreover, a significantly thinner subfoveal choroidal thickness (SFCT) was found in HMA compared to NG, LM, and MM, but not compared to HM. RT at 0.5 mm to fovea, HMA was significantly thinner compared to LM and MM in the three sectors (superior, inferior, and temporal). Nevertheless, no significant differences were found compared to NG and HM. CT at 0.5 mm to fovea, HMA was the significantly thinnest in all four sectors compared to NG, LM, and MM. RT at 1.0 mm/1.5 mm/2.0 mm/2.5 mm/3.0 mm to fovea, HMA was thinner compared to NG, LM, and MM. CT at 1.0 mm/1.5 mm/2.0 mm/2.5 mm/3.0 mm to fovea, HMA was thinner compared to NG, LM, and MM. At the superior and inferior sectors, HMA showed to be statistically thinner compared with HM. Moreover, SFCT in the HMA, HM, and NG were negatively correlated with AL.

Conclusions

Thinner retina and choroidal tissue appear to be related to HMA, and thus can be used as useful parameters for discovering the underlying mechanisms of the disease.

Validity and repeatability of contour-based visotec distance stereoacuity test

CLINICAL RELEVANCE

The clinical assessment of distance stereoacuity is important in some ocular conditions. Given the different neurophysiological mechanism for crossed and uncrossed stereoacuities, evaluation of both may provide additional insight into binocular vision disorders.

BACKGROUND

Clinical devices measuring distance crossed and uncrossed stereopsis are not readily available. Visotec Distance Stereo Test (VDST) is a contour-based device designed to measure both forms of distance stereoacuity. This study assesses the validity and test-retest reliability of the device in comparison to the random dot-based Randot Distance Stereo Test (RDST).

METHOD

VDST and RDST were administered to a total of 107 children, that included 51 'normal' and 56 'abnormal' (37 intermittent exotropia and 19 amblyopia) between the ages of 5 and 15 years. Two examiners retested stereoacuities in a sub-set of 62 randomly selected subjects. Stereoacuity was transformed to log scale. 95% limits of agreement were calculated for test-retest reliability. The Bland-Altman plot was used to demonstrate the agreement between the tests and the examiners.

RESULTS

The mean ± SD crossed distance stereoacuities using VDST in normal, intermittent exotropia and amblyopic children were 93.1 ± 43.8, 161.9 ± 89.8 and 236.3 ± 122.4 arcseconds, respectively. For uncrossed stereoacuity, these were 104.7 ± 54.0, 187.6 ± 89.6 and 265.5 ± 144.0 arcseconds, respectively. Crossed stereoacuity was significantly better than uncrossed stereoacuity. 95% limits of test-retest agreement for crossed and uncrossed stereoacuities using the VDST were 0.27 and 0.30, respectively. An exact test-retest match using VDST was 84% in normals and 77% in abnormals for crossed and 83% in normal and 74% in abnormal for uncrossed stereoacuities.

CONCLUSION

VDST is a reliable, valid and easy-to-administer distance crossed and uncrossed stereoacuity measuring device. Further studies are required to establish the clinical importance of assessing these two forms stereoacuities in relation to various binocular vision disorders.

Clinical Aniseikonia in Anisometropia and Amblyopia

Purpose:

Clinically, aniseikonia (a perceived difference in shape and image size between the eyes) is often neglected in anisometropic amblyopia due to assumed measurement difficulties. Therefore, we currently lack evidence on whether correction of aniseikonia is beneficial. This study aimed to determine whether subjective aniseikonia is measurable in anisometropia with or without amblyopia.

Methods:

Participants (15–52 years) with Anisometropic Amblyopia (n = 7), Anisometropia without amblyopia (n = 6) and Isometropic Controls (n = 6) were recruited. Subjective aniseikonia was measured using three clinical techniques: Robertson Technique (RT) (penlight and Maddox rod), Aniseikonia Inspector Version 3 (AI3), and the New Aniseikonia Test booklet (NAT), and a psychophysical adaptive method, the Contrast-balanced Aniseikonia Test (CAT), where dichoptic contrast adjustments compensate for any suppression.

Results:

Eighteen participants completed all tests, one Anisometropic Amblyopia participant could only complete the CAT and NAT due to fusion loss. The Anisometropic Amblyopia group exhibited the most aniseikonia (range –1.50–+10.50%) followed by Anisometropic Controls (range –3.30–+4.50%) and Isometropic Controls (range –1.50–+3.28%). There was a significant trend of more subjective aniseikonia with increasing amounts of anisometropia across all four tests (AI3 r = 0.630, p = 0.005; NAT r = 0.542, p = 0.017; RT r = 0.499, p = 0.035; CAT r = 0.440, p = 0.059. Bland Altman analysis demonstrated clinically significant levels of variability between the tests.

Conclusions:

Subjective aniseikonia can be reliably measured in patients with anisometropia and suppression. Subjective aniseikonia measurement is recommended as four of the most commonly used clinical tests did not support the 1% per dioptre rule of thumb.

Does anisometropia affect the ciliary muscle thickness? An ultrasound biomicroscopy study

PURPOSE

To compare the ciliary muscle thickness (CMT) of the normal fellow eye to that of the amblyopic eye using ultrasound biomicroscopy (UBM) in patients with unilateral anisometropic amblyopia.

METHODS

Thirty patients with unilateral anisometropic amblyopia were involved. The patients were divided into two groups: 19 hyperopic and 11 myopic. Axial length (AL) was measured with optic biometry and anterior chamber depth (ACD), iris area, and CMT were measured with UBM.

RESULTS

The mean age was 34.10 ± 6.61 years. The mean spherical difference between two eyes was 2.59 diopter (D) in hyperopic patients and 3.77D in myopic patients. In the hyperopic patients, nasal CMT1(nCMT), temporal CMT1(tCMT), tCMT2, and tCMT3 values were statistically thinner in amblyopic eyes than healthy eyes (p = 0.036, p = 0.003, p = 0.023, p = 0.005, respectively). ACD values were statistically lower in amblyopic eyes (2.78 ± 0.26 mm) than healthy eyes (2.90 ± 0.21 mm) (p < 0.001). In the myopic patients, nCMT1, nCMT2, nCMT3, tCMT1, tCMT2, and tCMT3 values were statistically thicker in amblyopic eyes than healthy eyes (p = 0.003, p = 0.003, p = 0.005, p = 0.003, p = 0.003, p = 0.019, respectively). ACD values were statistically higher in amblyopic eyes (3.20 ± 0.30 mm) than healthy eyes (3.06 ± 0.29 mm) (p = 0.004). Also, there was no significant difference in the iris area between the amblyopic and normal eyes of the myopic and hyperopic patients (p > 0.05).

CONCLUSIONS

Amblyopic eyes in patients with unilateral myopic anisometropia have thicker CMT and deeper ACD than healthy eyes. Conversely, amblyopic eyes in patients with unilateral hyperopic anisometropia have thinner CMT and shorter ACD than healthy eyes. There is a positive correlation between AL and CMT.

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.

Anisometropia and refractive status in children with unilateral congenital nasolacrimal duct obstruction

OBJECTIVE:

The objective of the study was to evaluate the refractive status and thereby assess anisometropia in children with unilateral congenital nasolacrimal duct obstruction (CNLDO).

STUDY DESIGN:

This study design was a descriptive cross-sectional study.

PLACE AND DURATION:

this study was conducted at the Department of Pediatric Ophthalmology and Strabismology, Al-Shifa Trust Eye Hospital, Rawalpindi; from August 2013 to July 2014.

METHODOLOGY:

This study assessed consecutive children with unilateral CNLDO. Cycloplegic refraction on all children with CNLDO was performed followed by appropriate intervention. Refractive errors of the affected and normal eyes were compared.

RESULTS:

One hundred and twenty-four children with a mean age of 29.69 ± 21.12 months (range, 2 months to 8 years) were studied. Based on spherical equivalent (SE), hypermetropia was more common in the affected eyes (P < 0.001). Anisometropia of >1.5 diopters (D) was present in n = 17 (13.7%). Interocular difference was significant for spherical error and SE (P < 0.001) but not cylindrical errors.

CONCLUSION:

Unilateral CNLDO is associated with statistically significant anisometropia, especially anisohypermetropia which has amblyogenic potential. It is vital to perform cycloplegic refraction routinely and counsel parents regarding prognosis and regular follow-ups.

Distant stereoacuity in children with anisometropic amblyopia

PURPOSE

To characterize changes in distant stereoacuity using Frisby-Davis Distance test (FD2) and Distant Randot test (DR) during treatment for anisometropic amblyopia, to determine factors that influence posttreatment stereoacuity and to compare the two distant stereotests.

METHODS

Fifty-eight anisometropic amblyopic patients with an interocular difference of ≥1.00 diopter who achieved the visual acuity 20/20 following amblyopia treatment were retrospectively included. Stereoacuity using FD2 and DR for distant and Titmus test for near measurement were assessed and compared at the initial, intermediate, and final visit. Multivariate regression models were used to identify factors associated with initial and final stereoacuity.

RESULTS

The two distant stereotests revealed a significant improvement in distant stereoacuity after successful amblyopia treatment. Distant stereoacuity using FD2 showed the greatest improvement during the follow up period. The number of nil scores was higher in DR than FD2 at each period. In multivariate analysis, better final stereoacuity was associated with better initial amblyopic eye acuity in both distant stereotests, but not in the Titmus test. Comparing the two distant stereotests, final stereoacuity using FD2 was associated with initial stereoacuity and was moderately related with the Titmus test at each period, but final stereoacuity using DR was not.

CONCLUSIONS

Distant stereoacuity measured with both FD2 and DR showed significant improvement when the visual acuity of the amblyopic eye achieved 20/20. Changes in distant stereoacuity by FD2 and DR during the amblyopia treatment were somewhat different.

Risk factors for treatment failure and recurrence of anisometropic amblyopia

PURPOSE

The aim of this study was to identify factors associated with failed vision improvement and recurrence following occlusion therapy for anisometropic amblyopia in children aged 7-9 years.

METHODS

We retrospectively reviewed the medical records of 64 children aged 7-9 years who had been diagnosed as having anisometropic amblyopia and were treated with patching. Functional treatment failure was defined as final visual acuity in the amblyopic eye of worse than 20/32. Improvement of fewer than two logMAR lines was considered relative treatment failure. Recurrence was defined as the reduction of at least two logMAR levels of visual acuity after decreased or discontinued patching.

RESULTS

Functional and relative success rates were 51.6 and 62.5 %, respectively. The most important factor for functional treatment failure [adjusted odds ratio (OR) (95 % confidence interval, CI) 11.57 (1.4-95.74)] and the only risk factor for recurrence [adjusted OR (95 % CI) 3.04 (1.13-8.12)] were the same: high spherical equivalent (SE) of the amblyopic eye. A large interocular difference in the best-corrected visual acuity was found to be a risk factor for both functional and relative failure.

CONCLUSION

High SE of the amblyopic eye was the most influential risk factor for treatment failure and recurrence in compliant children aged 7-9 years.

Quantitative measurement of interocular suppression in anisometropic amblyopia: a case-control study

OBJECTIVE

The aims of this study were to assess (1) the relationship between interocular suppression and visual function in patients with anisometropic amblyopia, (2) whether suppression can be simulated in matched controls using monocular defocus or neutral density filters, (3) the effects of spectacle or rigid gas-permeable contact lens correction on suppression in patients with anisometropic amblyopia, and (4) the relationship between interocular suppression and outcomes of occlusion therapy.

DESIGN

Case-control study (aims 1-3) and cohort study (aim 4).

PARTICIPANTS

Forty-five participants with anisometropic amblyopia and 45 matched controls (mean age, 8.8 years for both groups).

METHODS

Interocular suppression was assessed using Bagolini striated lenses, neutral density filters, and an objective psychophysical technique that measures the amount of contrast imbalance between the 2 eyes that is required to overcome suppression (dichoptic motion coherence thresholds). Visual acuity was assessed using a logarithm minimum angle of resolution tumbling E chart and stereopsis using the Randot preschool test.

MAIN OUTCOME MEASURES

Interocular suppression assessed using dichoptic motion coherence thresholds.

RESULTS

Patients exhibited significantly stronger suppression than controls, and stronger suppression was correlated significantly with poorer visual acuity in amblyopic eyes. Reducing monocular acuity in controls to match that of cases using neutral density filters (luminance reduction) resulted in levels of interocular suppression comparable with that in patients. This was not the case for monocular defocus (optical blur). Rigid gas-permeable contact lens correction resulted in less suppression than spectacle correction, and stronger suppression was associated with poorer outcomes after occlusion therapy.

CONCLUSIONS

Interocular suppression plays a key role in the visual deficits associated with anisometropic amblyopia and can be simulated in controls by inducing a luminance difference between the eyes. Accurate quantification of suppression using the dichoptic motion coherence threshold technique may provide useful information for the management and treatment of anisometropic amblyopia.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Changes in binocular function in anisometropic nonstrabismic children with optical correction and occlusion therapy

PURPOSE

To identify factors that influence binocular function in anisometropic, nonstrabismic children before and after optical correction and amblyopia therapy.

METHODS

This was a prospective observational study of consecutive patients with nonstrabismic anisometropia. Visual acuity and responses to the 4(Δ) base-out prism test, the Worth 4-dot test, and the TNO test were recorded after spectacle correction and every 3 months for 1 year. Factors affecting visual acuity and binocular function were analyzed using univariate and multiple stepwise regression analysis.

RESULTS

A total of 118 subjects were enrolled. At the end of the first year, the mean improvement in visual acuity was 2.6 ± 2.3 lines. The percentage of patients showing a positive response to the 4(Δ) base-out prism test increased from 47% to 79%; fusion in the Worth 4-dot test, from 37% to 66%; and measurable stereopsis on TNO testing, from 59% to 80%. Better initial visual acuity and better final visual acuity were associated with better binocular function. Interocular refractive error difference was a predictor of poor binocular function in multiple regression analysis if the difference in spherical error exceeded 4 D. Patients with amblyopia showed significantly worse binocular function compared to those with no amblyopia.

CONCLUSIONS

Binocular function of anisometropic children can be improved with refractive correction and amblyopia therapy.

Stereoacuity in children with anisometropic amblyopia

PURPOSE

To determine factors associated with pretreatment and posttreatment stereoacuity in subjects with moderate anisometropic amblyopia.

METHODS

Data for subjects enrolled in seven studies conducted by the Pediatric Eye Disease Investigator Group were pooled. The sample included 633 subjects aged 3 to <18 years with anisometropic amblyopia, no heterotropia observed by cover test, and baseline amblyopic eye acuity of 20/100 or better. A subset included 248 subjects who were treated with patching or Bangerter filters and had stereoacuity testing at both the baseline and outcome examinations. Multivariate regression models identified factors associated with baseline stereoacuity and with outcome stereoacuity as measured by the Randot Preschool Stereoacuity test.

RESULTS

Better baseline stereoacuity was associated with better baseline amblyopic eye acuity (P < 0.001), less anisometropia (P = 0.03), and anisometropia due to astigmatism alone (P < 0.001). Better outcome stereoacuity was associated with better baseline stereoacuity (P < 0.001) and better amblyopic eye acuity at outcome (P < 0.001). Among 48 subjects whose amblyopic eye visual acuity at outcome was 20/25 or better and within one line of the fellow eye, stereoacuity was worse than that of children with normal vision of the same age.

CONCLUSIONS

In children with anisometropic amblyopia of 20/40 to 20/100 inclusive, better posttreatment stereoacuity is associated with better baseline stereoacuity and better posttreatment amblyopic eye acuity. Even if their visual acuity deficit resolves, many children with anisometropic amblyopia have stereoacuity worse than that of nonamblyopic children of the same age.

Risk factors for decreased visual acuity in preschool children: the multi-ethnic pediatric eye disease and Baltimore pediatric eye disease studies

OBJECTIVE

To investigate risk factors associated with unilateral or bilateral decreased visual acuity (VA) in preschool children.

DESIGN

Population-based, cross-sectional prevalence study.

PARTICIPANTS

Population-based samples of 6504 children ages 30 to 72 months from California and Maryland.

METHODS

Participants were preschool African-American, Hispanic, and non-Hispanic white children from Los Angeles, California, and Baltimore, Maryland. Data were obtained by a parental interview and a detailed ocular examination. Logistic regression models were used to evaluate the independent associations between demographic, behavioral, and clinical risk factors with unilateral and bilateral decreased VA.

MAIN OUTCOME MEASURES

Odds ratios (ORs) for various risk factors associated with interocular difference (IOD) in VA of ≥2 lines with ≤20/32 in the worse eye, or bilateral decreased VA <20/40 or <20/50 if <48 months of age.

RESULTS

In multivariate logistic regression analysis, 2-line IOD with a VA of ≤20/32 was independently associated with Hispanic ethnicity (OR, 2.05), esotropia (OR, 8.98), spherical equivalent (SE) anisometropia (ORs ranging between 1.5 and 39.7 for SE anisometropia ranging between 0.50 to <1.00 diopters [D] and ≥2.00 D), and aniso-astigmatism in J0 or J45 (ORs ranging between 1.4 and ≥5.3 for J0 or J45 differences ranging between 0.25 to <0.50 D and ≥1.00 D). Bilateral decreased VA was independently associated with lack of health insurance (OR, 2.9), lower primary caregiver education (OR, 1.7), astigmatism (OR, 2.3 and 17.6 for astigmatism 1.00 to <2.00 D and ≥2.00 D), and SE hyperopia ≥4.00 D (OR, 10.8).

CONCLUSIONS

Anisometropia and esotropia are risk factors for IOD in VA. Astigmatism and high hyperopia are risk factors for bilateral decreased VA. Guidelines for the screening and management of decreased VA in preschool children should be considered in light of these risk associations.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Effects of anisometropic amblyopia on visuomotor behavior, part 2: visually guided reaching

PURPOSE

The effects of impaired spatiotemporal vision in amblyopia on visuomotor skills have rarely been explored in detail. The goal of this study was to examine the influences of amblyopia on visually guided reaching.

METHODS

Fourteen patients with anisometropic amblyopia and 14 control subjects were recruited. Participants executed reach-to-touch movements toward targets presented randomly 5° or 10° to the left or right of central fixation in three viewing conditions: binocular, monocular amblyopic eye, and monocular fellow eye viewing (left and right monocular viewing for control subjects). Visual feedback of the target was removed on 50% of the trials at the initiation of reaching.

RESULTS

Reaching accuracy was comparable between patients and control subjects during all three viewing conditions. Patients' reaching responses were slightly less precise during amblyopic eye viewing, but their precision was normal during binocular or fellow eye viewing. Reaching reaction time was not affected by amblyopia. The duration of the acceleration phase was longer in patients than in control subjects under all viewing conditions, whereas the duration of the deceleration phase was unaffected. Peak acceleration and peak velocity were also reduced in patients.

CONCLUSIONS

Amblyopia affects both the programming and the execution of visually guided reaching. The increased duration of the acceleration phase, as well as the reduced peak acceleration and peak velocity, might reflect a strategy or adaptation of feedforward/feedback control of the visuomotor system to compensate for degraded spatiotemporal vision in amblyopia, allowing patients to optimize their reaching performance.

Effects of anisometropic amblyopia on visuomotor behavior, I: saccadic eye movements

PURPOSE

Impairment of spatiotemporal visual processing is the hallmark of amblyopia, but its effects on eye movements during visuomotor tasks have rarely been studied. Here the authors investigate how visual deficits in anisometropic amblyopia affect saccadic eye movements.

METHODS

Thirteen patients with anisometropic amblyopia and 13 control subjects participated. Participants executed saccades and manual reaching movements to a target presented randomly 5° or 10° to the left or right of fixation in three viewing conditions: binocular, amblyopic, and fellow eye viewing. Latency, amplitude, and peak velocity of primary and corrective saccades were measured.

RESULTS

Initiation of primary saccades was delayed and more variable when patients viewed monocularly with their amblyopic eye. During binocular viewing, saccadic latency exhibited increased variability and no binocular advantage in patients (i.e., mean latency was similar to that during fellow eye viewing). Mean amplitude and peak velocity of primary saccades were comparable between patients and control subjects; however, patients exhibited greater variability in saccade amplitude. The frequency of corrective saccades was greater when patients viewed with their fellow eye than it was with binocular or amblyopic eye viewing. Latency, amplitude, and peak velocity of corrective saccades in patients were normal in all viewing conditions.

CONCLUSIONS

Saccades had longer latency and decreased precision in amblyopia. Once saccades were initiated, however, the dynamics of saccades were not altered. These findings suggest that amblyopia is associated with slower visual processing in the afferent (sensory) pathway rather than a deficit in the efferent (motor) pathway of the saccadic system.

Associations between anisometropia, amblyopia, and reduced stereoacuity in a school-aged population with a high prevalence of astigmatism

PURPOSE

To describe the relation between magnitude of anisometropia and interocular acuity difference (IAD), stereoacuity (SA), and the presence of amblyopia in school-aged members of a Native American tribe with a high prevalence of astigmatism.

METHODS

Refractive error (cycloplegic autorefraction confirmed by retinoscopy), best corrected monocular visual acuity (VA; Early Treatment Diabetic Retinopathy Study logMAR charts), and best corrected SA (Randot Preschool Stereoacuity Test) were measured in 4- to 13-year-old Tohono O'odham children (N = 972). Anisometropia was calculated in clinical notation (spherical equivalent and cylinder) and in two forms of vector notation that take into account interocular differences in both axis and cylinder magnitude.

RESULTS

Astigmatism >or= 1.00 D was present in one or both eyes of 415 children (42.7%). Significant increases in IAD and presence of amblyopia (IAD >or= 2 logMAR lines) occurred, with >or=1 D of hyperopic anisometropia and >or=2 to 3 D of cylinder anisometropia. Significant decreases in SA occurred with >or=0.5 D of hyperopic, myopic, or cylinder anisometropia. Results for vector notation depended on the analysis used, but also showed disruption of SA at lower values of anisometropia than were associated with increases in IAD and presence of amblyopia.

CONCLUSIONS

Best corrected IAD and presence of amblyopia are related to amount and type of refractive error difference (hyperopic, myopic, or cylindrical) between eyes. Disruption of best corrected random dot SA occurs with smaller interocular differences than those producing an increase in IAD, suggesting that the development of SA is particularly dependent on similarity of the refractive error between eyes.