Functional burden of strabismus: decreased binocular summation and binocular inhibition

Characteristics and type of strabismus associated to macular diplopia. Treatment outcomes

OBJECTIVE

To study the clinical characteristics of macular diplopia, treatment, and outcome.

METHODS

Retrospective descriptive study of cases referred to the ocular motility section of a tertiary hospital with diplopia, diagnosed with macular diplopia between 2022-23. The etiology of the macular pathology and the type of associated strabismus were recorded. The result was considered good if the diplopia improved or was eliminated with the medical or surgical treatment. Follow-up time from the onset of diplopia until data collection was recorded.

RESULTS

a total of 19 cases comprised the sample (63.2% women), mean age: 67.16 years. Amblyopia (21.1%), high myopia (47.4%), epirretinal membrane (ERM) (36.8%), neovascular membrane (26.3%), macular hole (10.5%), and lamellar (15.8%), and age macular degeneration (5.3%) were registered. The 47.4% had vertical diplopia, horizontal: 5.3 and 47.4% mixed. The mean horizontal deviation was: 7.3 PD (prism diopters) and vertical: 6.22 PD. Ocular extorsion was observed in 26.3%, and intorsion: 5.3%. Torticollis was present in 15.8%. The treatment consisted of strabismus surgery + Botox (15.8%), strabismus surgery (47.4%), medical treatment with Fresnel prims or Scotch cellophane (36.8%). A 68.4% presented a good result at the end of the study. The mean follow-up was 55.58 months.

CONCLUSIONS

Misregistration of macular photoreceptors is the most common cause of binocular diplopia in patients with ERM or other macular pathologies. Most complains of vertical or mixed diplopia. Sensorimotor evaluation of these patients should be thorough. Early diagnosis prevents unnecessary prescription of prism glasses. Surgical and/or medical treatment achieves good results in most cases.

The effects of refractive status on the outcomes of strabismus surgery in patients with esotropia

BACKGROUND

The success of the strabismus surgery can hinge on several factors. One of these factors is refractive condition like hyperopia or myopia. Our study seeks to evaluate the surgical outcomes in patients with esotropia and myopia.

METHODS

This case-control study encompassed all surgical cases of esotropia at Torfe and Negah Hospital between 2016 and 2021, which satisfied our specified inclusion criteria. The initial variables from electronic medical records were collected, including demographic, clinical, and surgery-related factors. At the final follow-up appointment, the level of eye deviation, both at distance and near, was recorded. We considered the operation a "success" for patients with a post-surgery distance eye deviation of 10(Pd) or less. Patients with greater deviation were classified as surgery failure. Statistical analyses were executed using SPSS software (version 16.0), and a P-value less than 0.05 was considered significant.

RESULTS

Of the 194 patients evaluated, 112 were incorporated into the study. Surgical failure was observed in 14.29% of myopic patients, 29.79% of hyperopic patients, and 31.82% of emmetropic patients. The myopia group displayed a 0.19 odd ratio for surgical failure compared to the combined hyperopia and emmetropia groups, not statistically significant (OR: 0.19, CI 95%: 0.03-1.02). Additionally, patients diagnosed with Lateral Rectus Under-action were found to be 6.85 times more likely to experience surgery failure(OR: 6.85, CI 95%: 1.52-30.94). An elevated risk of surgical failure was also identified in patients who underwent Inferior Oblique Weakening procedure, indicated by a 3.77-fold increase in the odds ratio for failure(OR: 3.77, CI 95%: 1.08-13.17).

CONCLUSION

In our study, despite numerical disparities, there was no statistical difference among the success rates of all esotropia patients with different refractive errors. The patients with LRUA or IOOA showed lower success rates. Myopic patients had higher post-op overcorrection with lower reoperation rates compared to hyperopic or emmetropic patients.

Scotopic and Photopic Conventional Visual Acuity and Hyperacuity - Binocular Summation

Purpose

The purpose of this study was to determine and compare binocular summation (BiS) of conventional visual acuity (cVA) versus hyperacuity (hVA) for photopic and scotopic luminance conditions as a potential biomarker to assess the outcome of interventions on binocular function.

Methods

Sixteen young adults (age range [years] = 21-31; 8 women; cVA logMAR < 0.0) participated in this study. The Freiburg Visual Acuity Test (FrACT) was used for VA testing and retested on another day. Both cVA and hVA were determined for dark grey optotypes on light grey background. Participants underwent 40 minutes of dark adaptation prior to scotopic VA testing. Binocular and monocular VA testing was performed. The eye with better VA over the 2 days of testing was selected, the BiS was quantified (binocular VA - better monocular VA) and repeated measures ANOVAs were performed.

Results

Binocular VA exceeded monocular VA for all luminance conditions, VA-types, and sessions. We report BiS estimates for photopic and scotopic cVA and hVA, (logMAR BiS ± SEM [decimal BiS]): photopic = -0.01 ± 0.01 [1.03] and -0.06 ± 0.03 [1.15]; and scotopic = -0.05 ± 0.01 [1.12] and -0.11 ± 0.04 [1.28], respectively). Improvement for binocular vision estimates ranged from 0.01 to 0.11 logMAR. A repeated-measures ANOVA (RM ANOVA) did not reveal significant effects of LUMINANCE or VA TYPE on BiS, albeit a trend for strongest BiS for scotopic hVA (15% vs. 28%, photopic versus scotopic, respectively) and weakest for photopic cVA (3% vs. 12%, photopic versus scotopic conditions, respectively).

Conclusions

Our results indicate that BiS of VA is relevant to scotopic and photopic hVA and cVA. It appears therefore a plausible candidate biomarker to assess the outcome of retinal therapies restoring rod or cone function on binocular vision.

Translational Relevance

Binocular summation of visual acuity might serve as a clinical biomarker to monitor therapy outcome on binocular rod and cone-mediated vision.

Binocular Summation With Quantitative Contrast Sensitivity Function: A Novel Parameter to Evaluate Binocular Function in Intermittent Exotropia

Purpose

Intermittent exotropia (IXT) is the most common form of strabismus. Surgery can potentially improve binocular function in patients with IXT. We aimed to evaluate binocular function using a novel parameter-binocular summation ratio (BSR), measured using quantitative contrast sensitivity function (CSF) in patients with IXT before and after surgery.

Methods

Prospective study of 63 patients with IXT and 41 healthy controls were consecutively enrolled and underwent quantitative CSF testing binocularly and monocularly. BSR was calculated by dividing the CSF of the binocular value by the better monocular value. Forty-eight patients with IXT underwent strabismus surgery. BSR, stereoacuity, fusion ability, and strabismus questionnaires were assessed pre-operatively and 2 months postoperatively.

Results

Sixty-three patients with IXT (median age = 9 years) compared with 41 healthy controls showed a worse mean BSR based on all CSF metrics at baseline (the area under the log CSF [AULCSF], spatial frequency [SF] cutoff, and contrast sensitivity at 1.0-18.0 cpd SF). All 48 patients with IXT showed successful alignment after surgery, and there were significant improvements in BSR based on the AULCSF, SF cutoff, and contrast sensitivity at 6.0, 12.0, and 18.0 cpd SF, respectively. The distance stereoacuity and fusion ability also improved after surgery, and a better BSR was associated with better stereoacuity and fusion. For strabismus questionnaires, the psychosocial subscale scores improved postoperatively, whereas the functional subscale scores did not change.

Conclusions

BSR based on quantitative CSF can characterize binocular function across a range of spatial frequencies and can be used as a supplemental measurement for monitoring binocularity in patients with IXT in clinical settings.

Contrast sensitivity, optotype acuity and fixation eye movement abnormalities in amblyopia under binocular viewing

INTRODUCTION

Visual function deficits are seen in amblyopic subjects during fellow and binocular viewing. The purpose of the study was to examine the relationship between Fixation Eye Movement (FEM) abnormalities and binocular contrast sensitivity and optotype acuity deficits in amblyopia.

METHODS

We recruited 10 controls and 25 amblyopic subjects [Anisometropic = 6, Strabismic = 10, Mixed = 9]. We measured binocular contrast sensitivity at spatial frequencies 1,2, 4, 8, 12 and 16 and binocular and monocular optotype acuity using a staircase procedure. We recorded FEMs using high-resolution video-oculography and classified subjects as having no nystagmus(None = 9) or nystagmus without FMN(n = 7) and with Fusion Maldevelopment Nystagmus (FMN)(n = 9). We computed the fixation instability, amplitude and velocity of the fast and slow FEMs.

RESULTS

Amblyopic subjects with and without nystagmus had worse binocular contrast sensitivity at spatial frequencies 12 and 16 and binocular optotype acuity than controls. The abnormalities were most pronounced in amblyopic subjects with FMN. Fixation instability of the Fellow Eye and Amblyopic Eye and vergence instability, amplitude of fast FEMs and velocity of slow FEMs were increased with reduced binocular contrast sensitivity and reduced optotype acuity in amblyopic subjects.

CONCLUSIONS

Fixation instability of Fellow Eye and Amblyopic Eye, optotype acuity and contrast sensitivity deficits are seen under binocular viewing in amblyopic subjects with and without nystagmus but are most pronounced in those with FMN. FEMs abnormalities correlate with both lower order (contrast sensitivity) and higher order (optotype acuity) visual function impairment in amblyopia.

Binocular summation in high and low contrast letter acuities

Binocular summation, a well-known phenomenon in letter acuity measurement, refers to the improvement in visual performance when viewing with both eyes compared to one eye alone. The present study aims to assess the relationship in binocular summation between high and low contrast letter acuities, and examine whether baseline measure (binocular summation at either high or low contrast) is predictive of the change in binocular summation between contrast conditions. Corrected high and low contrast letter acuities were assessed monocularly and binocularly in 358 normal vision observers aged 18-37 years using Bailey-Lovie charts. All observers had high contrast acuities (both monocular and binocular) of 0.1 LogMAR or better and no known eye disease. Binocular summation was calculated as the difference in LogMAR between the better eye acuity and binocular acuity. We found that binocular summation was present at both contrast levels (0.044 ± 0.002 LogMAR for high and 0.069 ± 0.002 LogMAR for low contrast) with higher magnitude of summation at low contrast, and declined with increasing interocular difference. There was a correlation in binocular summation between high and low contrast. The difference in binocular summation between the two contrast levels was found to be correlated with the baseline measurement. Using common commercially available letter acuity charts, we replicated the findings on binocular acuity summation in normally sighted young adults for both high and low contrast letters. Our study revealed a positive relationship in binocular acuity summation between high and low contrast, and an association between a baseline measure and the change in binocular summation between contrast levels. These findings may serve as a reference in clinical practice and research when high and low contrast binocular summations are measured in assessing binocular functional vision.

Binocular summation of visual acuity and contrast sensitivity in children with intermittent exotropia

PURPOSE

To investigate the binocular summation (BiS) of visual acuity (VA) and contrast sensitivity (CS) in children with intermittent exotropia (IXT) before and after surgery and to probe the relationship between the two BiS phenomena and corresponding influencing factors.

METHODS

This prospective study included 21 IXT children (11 males and 10 females; aged 6-13 years) who underwent strabismus surgery in Tianjin Eye Hospital from January to April 2022. The visual function was assessed preoperatively and 2.95 ± 0.14 months postoperatively, including monocular/ binocular visual acuity (MVA/BVA) at 100% contrast and 2.5% contrast as well as monocular/binocular contrast sensitivity (MCS/BCS), deviation, near and distant stereopsis, and fusion.

RESULTS

All patients had postoperative deviation ranging from 0 to -4 PD. Either preoperative or postoperative BVA at 2.5% contrast was superior to the MVA. The postoperative BiS at 2.5% contrast was significantly superior to the preoperative BiS for 2.5% contrast and postoperative BiS for 100% contrast (P < 0.05). Except for 3 c/d, the MCS and BCS at 6 c/d, 12 c/d and 18 c/d spatial frequencies were all notably improved postoperatively. The postoperative binocular summation ratio of CS (BSR) was highest while interocular difference ratio of CS (IOR) was the lowest at 6 c/d among 4 spatial frequencies. The deviation, distant and near stereopsis, and fusion performance were all remarkably improved after surgery (p = 0.001; p = 0.041; p = 0.000), all of which were not related to BVA at 2.5% contrast, BiS, BSC and BSR. The BCS at middle and high frequencies (6 c/ds, 12 c/ds, and 18 c/ds) was significantly negatively correlated with the BVA at 2.5% contrast, and BSR was irrelevant to the corresponding IOR across different spatial frequencies.

CONCLUSION

BVA at low contrast and BCS examinations were not equivalent to stereopsis and fusion status, which contributed to the evaluation of binocular function in the real environment and in the different aspects. BVA in 2.5% contrast is related with BCS in moderate and high spacial frequencies (especially 18c/d) but BCS in 6c/d presents more binocular summation of contrast sensitivity. MCS, BCS and the BSR persist inhibition at 3c/d after surgery. The improvement of BCS is better than that of BSR to evaluate the binouclar function in IXT. Those two methods showed different sensitivities to impairment and rehabilitation of binocular summation and inhibition.

Quantitative Evaluation of Binocular Visual Perception in Patients With Strabismus: An Observational Study

PURPOSE

To quantitatively evaluate and compare binocular visual perception between normal individuals and patients with different types of strabismus using a binocular phase combination paradigm.

METHODS

A total of 117 participants were included in the study and were divided into the normal control group, exophoria group, comitant exotropia group, comitant esotropia group, and special strabismus group according to the type of strabismus. The effective contrast ratio (ECR) was measured to quantitatively evaluate binocular visual perception. Binocular fusion was evaluated using the Worth 4-dots flashlight. Stereoacuity was detected by the Titmus stereo test.

RESULTS

The mean ECRs in the normal control group, exophoria group, comitant exotropia group, comitant esotropia group, and special strabismus group were 0.896 ± 0.214, 0.824 ± 0.234, 0.520 ± 0.279, 0.261 ± 0.139, and 0.461 ± 0.243, respectively. Within-group differences in the ECR were statistically significant. In addition, there was no statistically significant difference between the normal control group and exophoria group, and the concomitant exotropia group and special strabismus group and the other groups were statistically significant in pairwise comparison. The binocular visual perception was basically balanced in the exotropia group and most imbalanced in the comitant esotropia group, followed by the comitant exotropia group and the special strabismus group. The results also indicated that the decreased ECR was related to poor stereopsis and ECR had a significant positive correlation with binocular fusion function.

CONCLUSIONS

Different types of strabismus have different degrees of visual perception imbalance. The binocular phase combination paradigm applied in this study can quickly and accurately quantify the degree of binocular visual perception imbalance in patients with strabismus by measuring ECR. [J Pediatr Ophthalmol Strabismus. 2023;60(2):120-130.].

Binocular Summation of Visual Acuity at High and Low Contrast in Early Glaucoma

PRCIS

This study examined the integrity of binocular summation function in patients with mild glaucoma. We found that binocular summation of visual acuity is preserved in these patients, despite their reduced monocular inputs.

PURPOSE

Binocular summation represents superiority of binocular to monocular performance. In this study we examined the integrity of binocular summation function in patients with early glaucoma who had structural glaucomatous changes but otherwise had no significant interocular acuity asymmetry or other functional deficit detected with standard clinical measures.

MATERIALS AND METHODS

Participants included 48 patients with early glaucoma according to Hodapp, Anderson, and Parrish 2 (HAP2) criteria (age 65±12 y) and 42 healthy controls (age 60±12 y), matched for stereoacuity. Visual acuity was assessed binocularly and monocularly at high (95%) and low (25%) contrast using the Early Treatment Diabetic Retinopathy Study (ETDRS) charts at 6 m. Binocular acuity summation was evaluated utilizing a binocular ratio (BR).

RESULTS

Overall, binocular and monocular visual acuity of the control group was better than that of the glaucoma group for both contrast levels, P =0.001. For the glaucoma group, there was a significant difference between BRs at high and low contrast, 0.01±0.05 and 0.04±0.06 ( P =0.003), respectively. For the control group, the difference between BR at high and low contrast was not statistically significant, 0.00±0.07 and 0.02±0.06 ( P =0.25), respectively.

CONCLUSION

For patients with early glaucoma, binocular summation function for visual acuity was preserved at both contrast levels. This suggests an adaptation of the visual system in early stages of glaucoma that allows for normal binocular summation in the presence of reduced monocular visual input.

Artificial Intelligence Segmentation Algorithm-Based Optical Coherence Tomography Image in Evaluation of Binocular Retinopathy

On account of optical coherence tomography (OCT) images with intelligent segmentation algorithm, this article investigated the clinical efficacy and safety of docetaxel combined with fluorouracil. In this study, 60 patients with retinopathy treated in hospital were selected as the research objects. There were 30 cases in each group, the control group was treated with conventional images, and the observation group was treated with algorithm-based OCT images. Intelligent segmentation boundary detection algorithm, boundary tracking, and contour localization were proposed and applied to the OCT images of patients to analyze features and measure corneal thickness in OCT images with high signal-to-noise ratio and noise and artifacts. Objects in the control group were treated with semiconductor laser, and those in the observation group were treated with OCT images with algorithm in addition to the treatment of the control group. The results showed that the number of images with relative error of 2 was more, and the number of images with relative error of -2 was the least. The average thickness of high-quality images was 562.7 μm, and the average thickness of images with noise and artifacts was 573.8 μm. The total effective rate of the observation group was 96.67%, which was significantly higher than that of the control group (80%), and the curative effect and physical improvement rate of the observation group were significantly better than that of the control group (P < 0.05). All in all, the feature extraction of OCT images and corneal measurement proposed in this study had a good measurement effect, and the method had the advantages of strong anti-interference ability and high measurement accuracy.

Strabismus Surgery Decreases the Risk of Injuries in Pediatric Patients in the OptumLabs Data Warehouse

PURPOSE

Previous studies have shown an association between injury risk and strabismus in aged Medicare beneficiaries and children. The injury prevalence in strabismic children was 30% in a study of >10 million patients in the OptumLabs Data Warehouse. The purpose of this study was to determine whether strabismus surgery decreases the risk of injury.

DESIGN

Retrospective cohort study.

METHODS

The OptumLabs Data Warehouse is a deidentified, longitudinal health database that was queried for strabismic patients aged <19 years. The patients who underwent strabismus surgery were compared with those strabismic patients who did not undergo surgery for injury. Injury risk (fractures, musculoskeletal injuries, and head injuries) during their insurance enrollment was calculated in the nonsurgical patients after their first strabismus claim and compared with the risk in surgical patients postoperatively.

RESULTS

There were 344,794 patients with strabismus. Surgery was performed in 26,459 (7.7%). Esotropia was the most common diagnosis (n = 181,195, 52.6%) followed by exotropia (n = 161,712, 46.9%) and hypertropia (n = 43,831, 12.7%). Within these groups, patients with hypertropia were significantly more likely to undergo surgery (24.2%) compared with patients with esotropia and exotropia (10.2% and 9.6%, respectively). Injuries were diagnosed after the first strabismus claim in 94,960 (29.8%) nonsurgical patients vs 5790 (21.9%) postsurgical patients (P < .001) with a mean follow-up of 4.3 ± 3.1 vs 3.8 ± 3.1 years, respectively. The adjusted hazard ratio for injuries was 0.85 (95% confidence interval [CI]: 0.83-0.87) for the risk of any injury after strabismus surgery. The hazard ratio was significantly decreased after surgery for each type of strabismus: esotropia (0.91, 95% CI: 0.88-0.94), exotropia (0.82, 95% CI: 0.80-0.85), and hypertropia (0.89, 95% CI: 0.85-0.93).

DISCUSSION

Strabismus surgery was associated with a 15% decrease in the risk of physical injury over approximately 4 years of follow-up. Surgery may be a factor in decreasing injury risk in strabismic patients, particularly in exotropia. Given the large number of children with strabismus in the United States, further assessment of strategies such as strabismus surgery to reduce injuries in children with strabismus is needed.

Factors Determining Improvement in Stereopsis and Binocularity After Good Postoperative Alignment in Patients With Childhood-Onset Strabismus

Introduction: The purpose of the present study was to determine the factors that affect the outcome of strabismus surgery in terms of improvement in stereopsis and binocularity.

Methods: Data were collected prospectively from patients with childhood-onset, concomitant, constant strabismus greater than 30 prism diopters (PD) with postoperative alignment within 10 PD. Pre- and postoperative stereopsis and binocularity testing were performed using the Titmus fly test, random dot test, Bagolini striated glass test, and Worth four dot test at one, four, and 12 weeks postoperatively.

Results: A total of 73 patients (55% males and 45% females) who underwent surgery at our center were studied. The mean age at the time of surgery was 16 ± 7.7 years (range: 5-35 years). We found that factors such as age of strabismus onset, type of deviation, and amblyopia had a statistically significant influence on the postoperative surgical outcome. A statistically insignificant relationship was noted with gender, refractive error, and duration of strabismus. Patients who had strabismus after six months of age noticed a significant improvement in stereopsis (p-value = 0.000) than those who had strabismus before six months of age (p-value = 0.660). Further, there was a statistically significant improvement in patients having exotropia (p-value = 0.018) or combined horizontal and vertical deviations (p-value = 0.000), but there was no significant improvement in patients with esotropia (p-value = 0.180). Moreover, non-amblyopes had a significantly better postoperative stereopsis than amblyopes (p-value = 0.006). Although there was no association between preoperative deviation and improvement in stereopsis (p-value = 0.081), patients having preoperative deviation in the range of 31-45 PD had a statistically significant improvement in stereopsis (p-value = 0.000). There was no significant difference between postoperative residual deviation and final stereopsis (p-value > 0.05). All the results were the same for both the Titmus test and the random dot test. Binocular fusion was observed in 34 subjects, and uniocular suppression was noted in 38 subjects preoperatively. It was observed that only one patient gained binocular single vision postoperatively.

Conclusion: The presence of amblyopia, esotropia, early onset of strabismus (within six months of age), and a larger preoperative deviation (>45 PD) were associated with poorer stereopsis. In patients with horizontal strabismus, the coexistence of vertical deviation had a positive impact on the postoperative stereopsis. Gender, refractive error, and duration of strabismus did not influence the final stereopsis in our study.

Binocular summation in comitant exotropia: Change after surgery

Purpose:

To assess the change in binocular summation (BiS) in comitant exotropia (XT) after strabismus surgery.

Methods:

This is a prospective study on 20 patients who underwent surgery for comitant XT over a one year period. Patients with sensory exotropia and nystagmus were excluded. Best-corrected visual acuity (VA) and contrast sensitivity (CS) of both eyes separately and together (binocularly) were recorded. BiS score was calculated as binocular score minus better eye score. BiS score at the end of 3 months was compared with the preoperative data.

Results:

The mean ± SD of BiS score increased from 2.95 ± 0.88 to 4.55 ± 0.68 (P-value < 0.0001) for VA (on ETDRS letters) and from 2.75 ± 0.44 to 4.5 ± 0.76 (P-value < 0.001 for CS (on Pelli–Robson chart) after surgery.

Conclusion:

There is significant improvement in BiS in XT after strabismus surgery. Authors recommend its inclusion in evaluation of functional outcome of XT surgery.

Binocular Summation Is Intact in Intermittent Exotropia After Surgery

Purpose: To determine binocular summation of surgically treated intermittent exotropia (IXT) patients by measuring the contrast threshold.

Methods: We recruited 38 surgically treated IXT patients aged 8–24 years and 20 age-matched healthy controls. All participants had normal or corrected-to-normal visual acuity (Snellen ≥ 20/20) in both eyes. The IXT patients had undergone the surgery at least a year prior to the study. Twenty-one of them obtained good alignment and 17 experienced a recurrence of exotropia. We measured the observers' monocular and binocular contrast sensitivities (CS) at six spatial frequencies (1.5, 3, 6, 12, 18, 24 cycles/degree) as an index of visual information processing at the threshold level. Binocular summation was evaluated against a baseline model of simple probability summation based on the CS at each spatial frequency and the area under the log contrast sensitivity function (AULCSF).

Results: The exo-deviation of IXTs with good alignment was −6.38 ± 3.61 prism diopters (pd) at 33 cm and −5.14 ± 4.07 pd at 5 m. For the patients with recurrence, it was −23.47 ± 5.53 pd and −21.12 ± 4.28 pd, respectively. There was no significant difference in the binocular summation ratio (BSR) between the surgically treated IXT patients, including those with good alignment and recurrence, and normal controls at each spatial frequency [F_(2,55) = 0.416, P = 0.662] and AULCSF [F_(2,55) = 0.469, P = 0.628]. In addition, the BSR was not associated with stereopsis (r = −0.151, P = 0.365).

Conclusion: Our findings of normal contrast sensitivity binocular summation ratio in IXT after surgical treatment suggest that the ability of the visual cortex in processing binocular information is intact at the contrast threshold level.

Binocular visual function and fixational control in patients with macular disease: A review

For normally sighted observers, the centre of the macula—the fovea—provides the sharpest vision and serves as the reference point for the oculomotor system. Typically, healthy observers have precise oculomotor control and binocular visual performance that is superior to monocular performance. These functions are disturbed in patients with macular disease who lose foveal vision. An adaptation to central vision loss is the development of a preferred retinal locus (PRL) in the functional eccentric retina, which is determined with a fixation task during monocular viewing. Macular disease often affects the two eyes unequally, but its impact on binocular function and fixational control is poorly understood. Given that patients’ natural viewing condition is binocular, the aim of this article was to review current research on binocular visual function and fixational oculomotor control in macular disease. Our findings reveal that there is no overall binocular gain across a range of visual functions, although clear evidence exists for subgroups of patients who exhibit binocular summation or binocular inhibition, depending on the clinical characteristics of their two eyes. The monocular PRL of the better eye has different characteristics from that of the worse eye, but during binocular viewing the PRL of the better eye drives fixational control and may serve as the new reference position for the oculomotor system. We conclude that evaluating binocular function in patients with macular disease reveals important clinical aspects that otherwise cannot be determined solely from examining monocular functions, and can lead to better disease management and interventions.

Risk of physical injuries in children and teens with ophthalmic diagnoses in the OptumLabs Data Warehouse

BACKGROUND

To evaluate how eye diseases affect the risk of injuries (fractures, musculoskeletal, head and eye injuries) in children and teens.

METHODS

Claims from the OptumLabs Data Warehouse, a longitudinal deidentified commercial insurance claims database, were analyzed. Eligible subjects were aged <19 years at the time of their eye disease diagnosis, enrolled in the health plan between 2007 and 2018, and had >1 visit for >1 significant eye disease (strabismus, amblyopia, nystagmus, structural diseases), based on ICD9/10 codes. Controls were children in the same database who had no eye disease codes reported. Demographics and injury claims (fractures, musculoskeletal injuries, head injuries and eye injuries) were compared.

RESULTS

The overall incidence of any subsequent physical injury (even into adulthood) was 29% in eye disease patients and 23% in controls (P < 0.001). After accounting for covariates, the hazard ratio for injury with any type of eye disease was 1.14 (95% CI, 1.13-1.15), 1.17 (95% CI, 1.16-1.18), 0.97 (95% CI, 0.96-0.98), and 1.63 (95% CI, 1.60-1.66) for musculoskeletal injuries, fractures, head injuries, and eye injuries, respectively. The eye disease with the highest adjusted injury risk was nystagmus (HR = 1.26; 95% CI, 1.23-1.28), followed by optic neuritis and pseudotumor cerebri (HR = 1.25). The eye diseases with the lowest risk included amblyopia, esotropia, and glaucoma (HR ≤ 1.06).

CONCLUSIONS

There was an increased long-term risk of physical injury among children and teens with eye disease. The clinical significance of these small differences is unclear.

Improvement of binocular summation in intermittent exotropia following successful postoperative alignment

To investigate the improvement of binocular summation (BiS) at high contrast (100%) and different low contrasts (10, 5 and 2.5%) in patients with intermittent exotropia (IXT) after successfully postoperative alignment. A total of 76 patients (aged 9–40 years) with IXT and poor control at distance before surgery were enrolled in this study. The postoperative deviations ranged between 4 PD esophoria to 10 PD exotropia in the primary position (at near and at distance) in all the enrolled patients. The follow-up visits were 2–3 months after the surgery. We analyzed preoperative and postoperative BiS and the proportions of patients with different BiS for the high contrast and the low contrasts. Binocular summation (BiS) was classified into three situations: binocular summation, equal and inbibition. The results of the distant random dots stereograph (RDS) were grouped into A, unable to recognize; B, moderate, 200″ ≤ RDS ≤ 400″ and C, good, RDS < 200″. Following the successful postoperative alignment, the proportion of patients with BiS were increased from 9.2 to 40.8%, 17.1 to 53.9%, 21.1 to 76.1% and 21.1 to 72.4% at 100%, 10%, 5% and 2.5% contrasts respectively. At 2.5% contrast, (1) more patients presented binocular summation in the groups B and C; (2) postoperative improvements of binocular visual acuity (BVA) in groups B (1.5 ± 1.03 lines) and C (1.57 ± 1.26 lines) were significantly different from the BVA in the group A (0.74 ± 1.00 line); and (3) in the group with central fusion, more patients presented BiS after surgery and the postoperative BVA improved by 1.43 ± 1.16 lines. Binocular summation for high contrast and different low contrasts can be improved in patients with IXT after successful surgical treatment. The improvement of BiS was associated with obtaining central fusion, recovering distant stereopsis and good alignment after the surgeries. The most significant improvement was shown at 2.5% contrast and was associated with good stereopsis and central fusion. The improvement of BiS, particularly at low contrast, has benefits for the daily activities in the real environment. BiS improvement could be used as a supplementary assessment of binocular function in patients with IXT before and after treatment.

Binocular Interference vs Diplopia in Patients With Epiretinal Membrane

Importance

Patients with epiretinal membrane (ERM) sometimes close 1 eye for improved vision, but associations have not been rigorously studied.

Objective

To evaluate associations with monocular eye closure in patients with ERM, and to report binocular interference (closing 1 eye to improve visual quality).

Design, Setting, and Participants

Retrospective medical record review of an adult strabismus clinic at a tertiary referral center. Patients with ERM referred from retina clinicians between June 2010 and October 2019 who completed the Adult Strabismus (AS)-20 questionnaire, including the question: "I cover or close one eye to see things better." Two groups were identified: (1) patients reporting eye closure sometimes or more, and (2) patients reporting no eye closure (as control patients).

Main Outcomes and Measures

Frequencies of (1) central-peripheral rivalry (CPR)-type diplopia (dragged fovea diplopia); (2) binocular interference (monocular eye closure but no diplopia or strabismus); and (3) other, associated with monocular eye closure. Visual acuity, metamorphopsia, aniseikonia, and AS-20 quality of life domain scores (self-perception, interactions, reading function, and general function) compared between binocular interference, CPR-type diplopia, and control patients.

Results

A total of 124 patients with ERM (58 of 124 were women [47%]; mean [SD] age, 70 [9] years) reported monocular eye closure. Associations were binocular interference in 36 (29%; 95% CI, 21%-38%), CPR-type diplopia in 34 (27%; 95% CI, 20%-36%), and other (primarily strabismus) in 54 (44%). Compared with control patients with ERM (n = 11), patients with ERM and binocular interference had worse quality of life on AS-20 reading function (95 vs 62; mean difference, 22 points; 95% CI, 7-27 points; P = .007) and general function (89 vs 68; mean difference, 23 points; 95% CI, 13-34 points; P = .01) domains. Compared with CPR-type diplopia, patients with binocular interference had poorer worst-eye visual acuity (median 0.50 vs 0.30 logMAR [20/63 vs 20/40]; mean difference, 0.13 logMAR; 95% CI, 0.00-0.25 logMAR [20/20 to 20/35]; P = .03), and a larger interocular difference (0.46 vs 0.19 logMAR [20/58 vs 20/30]; mean difference, 0.15 logMAR; 95% CI, 0.03-0.28 logMAR [20/21 to 20/38]; P = .004).

Conclusions and Relevance

Study findings suggest that binocular interference, manifesting as monocular eye closure (without diplopia or strabismus), is a distinct entity affecting quality of life in patients with epiretinal membrane.

Grey Filter Contact Lens as Therapeutic Option for Acquired Reduced Binocular Visual Performance

Disturbing binocular problems can be too complex to be treated in such a way that comfortable binocular single vision is restored. The grey filter contact lens could offer a safe and clinically useful way to help these patients.

Predictive factors of stereopsis outcomes following strabismus surgery

Purpose:

To determine the predictive factors of post-operative stereopsis in patients with strabismus.

Method:

In this retrospective study, records of patients who received surgical treatment for strabismus were reviewed. All types of strabismus were included. Pre- and post-treatment stereoacuity were measured using the Titmus Stereo Fly test, and predictive factors of stereopsis were evaluated.

Results:

A total of 194 patients (132 females and 62 males) with a mean age of 14.8 ± 8.4 years were included. There was a statistically significant improvement in stereopsis following surgery (p value < 0.001). Patients with a higher amount of deviation at baseline had poorer stereopsis on the final examination (p value < 0.001). Stereopsis improvement was more prominent in the pure horizontal strabismus group, compared to combined horizontal and vertical deviations. Baseline and the final stereopsis were higher in the “exotropia” group as compared to the “esotropia” group (p value = 0.003 and 0.0155, respectively); however, the within group change of stereopsis was not significantly different between these two groups (p value = 0.144). Post surgical residual deviation was associated with a poorer stereopsis (p value = 0.002, r = 0.251). A longer duration of strabismus before surgery was associated with poorer final stereopsis levels (p value = 0.026). The presence of amblyopia before surgery was associated with poorer stereopsis on last examination (p value < 0.001 for both correlations).

Conclusion:

Based on the result of this study, final stereopsis after strabismus surgery could be affected by the type, duration, and the amount of deviation before surgery, amblyopia, and post operative ocular deviation.

Block-building performance test using a virtual reality head-mounted display in children with intermittent exotropia

PURPOSE

To determine whether childhood intermittent exotropia (IXT) affects distance divergence and performance in block-building tasks within a virtual reality (VR) environment.

METHODS

Thirty-nine children with IXT, aged 6-12 years, who underwent muscle surgery and 37 normal controls were enrolled. Children were instructed to watch the target moving away and perform a block-building task while fitted with a VR head-mounted display equipped with eye- and hand-movement tracking systems. The change in inter-ocular distance with binocular distance viewing, time to stack five cube blocks of different sizes in order, and distance disparities between the largest and farthest cubes were assessed. All children were evaluated at baseline and 3-month time points.

RESULTS

The patients with IXT exhibited a larger distance divergence than did controls (p = 0.024), which was associated with greater distance angle of deviation and poorer distance control (r = 0.350, p = 0.001 and r = 0.349, p = 0.004). At baseline, the patients with IXT showed larger distance disparities in the block-building task than did controls in terms of the horizontal, vertical, and 3-dimensional (3-D) measurements (all ps < 0.050). Larger horizontal disparity was associated with greater distance angle of deviation (r = 0.383, p = 0.037). Three months after surgery, the horizontal and 3-D disparities in the patients with IXT improved significantly and were not comparably different compared with controls.

CONCLUSIONS

These preliminary findings suggest that VR-based block-building task may be useful in testing possible deficits in visuo-motor skills associated with childhood IXT.

Binocular Summation and Suppression of Contrast Sensitivity in Strabismus, Fusion and Amblyopia

Purpose: Amblyopia and strabismus affect 2%–5% of the population and cause a broad range of visual deficits. The response to treatment is generally assessed using visual acuity, which is an insensitive measure of visual function and may, therefore, underestimate binocular vision gains in these patients. On the other hand, the contrast sensitivity function (CSF) generally takes longer to assess than visual acuity, but it is better correlated with improvement in a range of visual tasks and, notably, with improvements in binocular vision. The present study aims to assess monocular and binocular CSFs in amblyopia and strabismus patients.

Methods: Both monocular CSFs and the binocular CSF were assessed for subjects with amblyopia (n = 11), strabismus without amblyopia (n = 20), and normally sighted controls (n = 24) using a tablet-based implementation of the quick CSF, which can assess a full CSF in <3 min. Binocular summation was evaluated against a baseline model of simple probability summation.

Results: The CSF of amblyopic eyes was impaired at mid-to-high spatial frequencies compared to fellow eyes, strabismic eyes without amblyopia, and control eyes. Binocular contrast summation exceeded probability summation in controls, but not in subjects with amblyopia (with or without strabismus) or strabismus without amblyopia who were able to fuse at the test distance. Binocular summation was less than probability summation in strabismic subjects who were unable to fuse.

Conclusions: We conclude that monocular and binocular contrast sensitivity deficits define important characteristics of amblyopia and strabismus that are not captured by visual acuity alone and can be measured efficiently using the quick CSF.

Threshold Values of Myopic Anisometropia Causing Loss of Stereopsis

Purpose

The aim of the study was to determine the threshold values of myopic anisometropia that lead to the loss of stereoacuity in most of patients.

Materials and Methods

Forty healthy subjects were included in the study. The inclusion criteria were as follows: lack of any functional or morphological ophthalmological disorders, or detectable damage to the visual system, anisometropia equal or less than 0.25 D in a spherical equivalent, and full stereoscopic vision for near and for distance. Myopic anisometropia was evoked by placing different focusing lenses in front of the right eye of the subject in the trial frame. Stereoscopic vision was assessed with the use of the Titmus test (dots) (Stereo Fly Test Stereo Optical Co. Inc.) for near and the Randot test for distance (Distance Randot Stereotest Stereo Optical Co. Inc.).

Results

The threshold values for different types of myopic anisometropia for the loss of stereopsis in more than 50% of patients were determined. For near, this value was 3 D for sphere and “against the rule astigmatism” and 4 D for “with the rule astigmatism”. For distance, the values were 2 D for sphere and “against the rule astigmatism” and 3 D for “with the rule astigmatism.” Conclusions. Myopic anisometropia of more than 2 D can cause a significant impairment of binocular vision. Stereoacuity at distance is more sensitive to myopic anisometropia than stereoacuity at near. Myopic anisometropia involving “against the rule” astigmatism potentially affects binocularity more than anisometropia with regular astigmatism. A prompt correction of anisometropia of more than 2 D is needed in children to prevent the development of amblyopia.

Binocular Summation for Reflexive Eye Movements: A Potential Diagnostic Tool for Stereodeficiencies

Purpose

Stereoscopic vision, by detecting interocular correlations, enhances depth perception. Stereodeficiencies often emerge during the first months of life, and left untreated can lead to severe loss of visual acuity in one eye and/or strabismus. Early treatment results in much better outcomes, yet diagnostic tests for infants are cumbersome and not widely available. We asked whether reflexive eye movements, which in principle can be recorded even in infants, can be used to identify stereodeficiencies.

Methods

Reflexive ocular following eye movements induced by fast drifting noise stimuli were recorded in 10 adult human participants (5 with normal stereoacuity, 5 stereodeficient). To manipulate interocular correlation, the stimuli shown to the two eyes were either identical, different, or had opposite contrast. Monocular presentations were also interleaved. The participants were asked to passively fixate the screen.

Results

In the participants with normal stereoacuity, the responses to binocular identical stimuli were significantly larger than those induced by binocular opposite stimuli. In the stereodeficient participants the responses were indistinguishable. Despite the small size of ocular following responses, 40 trials, corresponding to less than 2 minutes of testing, were sufficient to reliably differentiate normal from stereodeficient participants.

Conclusions

Ocular-following eye movements, because of their reliance on cortical neurons sensitive to interocular correlations, are affected by stereodeficiencies. Because these eye movements can be recorded noninvasively and with minimal participant cooperation, they can potentially be measured even in infants and might thus provide an useful screening tool for this currently underserved population.

Subnormal Binocular Contrast Sensitivity Summation in Patients with Intermittent Exotropia

BACKGROUND

To evaluate binocular summation ratio using contrast sensitivity (CS) testing and correlation between binocular summation and stereoacuity, and control scale in intermittent exotropia (IXT).

METHODS

We conducted a prospective case-control study. Thirty-seven IXT and 41 controls were evaluated with both monocular and binocular CS testing. We compared the binocular summation ratio of IXT to that of controls. Near and distance stereoacuity was assessed and office-based control scale was evaluated. We investigated correlation between binocular CS summation ratio and stereoacuity, and control scale in IXT, respectively.

RESULTS

IXT had lower binocular CS summation ratio than controls at 1.5 and 3.0 cycles/degree (1.01 ± 1.02 vs. 1.62 ± 1.88 and 1.17 ± 0.96 vs. 1.86 ± 1.75, Both P < 0.05). We found significant correlation between binocular CS summation ratio at 3.0 cycles/degree and both near and distance stereoacuity (r = -0.411, P = 0.012 and r = -0.624, P = 0.005), and ratio at 1.5 cycles/degree also correlated significantly with distance stereoacuity (r = -0.397, P = 0.034) in the IXT. Binocular CS summation ratio was correlated to control scale at 1.5 and 3.0 cycles/degree (r = -0.327, P = 0.041 and r = -0.418, P = 0.028), and the ratio significantly differed in control scale groupings analysis at the same frequencies (Both P < 0.05).

CONCLUSION

Our findings of subnormal binocular CS summation ratio in IXT had correlation with stereoacuity and control scale suggest that binocular CS testing may be a useful method in assessing binocular visual function in IXT.

The Functional Benefits of Strabismus Surgery

When performed prior to visual maturity, strabismus surgery can result in the development or recovery of binocularity. When strabismus surgery is performed after visual maturity, the functional benefits of the surgery should be dichotomized according to whether the onset of the strabismus was before or after visual maturity. If the onset was after visual maturity, patients typically are diplopic. Specific success rates for eliminating diplopia vary according to the nature of the strabismus; however, overall the success rate is quite high. There is a common misperception that surgery in adults for strabismus that began prior to visual maturity is merely cosmetic. Numerous studies contradict this misconception. Even if the strabismus has been longstanding, most adults will experience some improvement in binocular function after strabismus surgery. In esotropic patients, this improvement typically takes the form of an expansion of binocular visual fields; however, some patients may also regain stereopsis. There are many psychosocial benefits to adult strabismus surgery. This is reflected in the finding that the majority of adults surveyed with strabismus would trade a portion of their life expectancy to be rid of their strabismus.

The pursuit of stereopsis

BACKGROUND

Pediatric ophthalmologists are increasingly expected to promote, preserve, and restore binocular vision.

METHODS

Clinical studies on restoring alignment and stereopsis in the management of amblyopia, esotropia, exotropia, and complex strabismus are reviewed from the perspective of the author's published work and personal experiences.

RESULTS

Treatment of amblyopia by means of optical rehabilitation, occlusion, or penalization has been reinforced by medical treatment and perceptual training with monocular or binocular video games. Studies indicate that early management of esotropia and alignment within 8^Δ is required for regaining stereopsis. In the surgical management of intermittent exotropia, distance stereopsis by Frisby Davis Distance stereotest can predict better stereopsis, with patients having preoperative distance stereopsis of <70 arcsec less likely to improve after surgery. The surgeon's armamentarium for correcting alignment and restoring binocular vision include procedures such as adjustable, partial vertical rectus muscle transposition in cases of exotropic Duane syndrome and lateral rectus palsy, periosteal fixation of the globe or of the lateral rectus muscle, and medial transposition of the split lateral rectus muscle.

CONCLUSIONS

The goal for present-day strabismologists is not merely to correct strabismus but also to achieve alignment of eyes in time to ensure normal development of stereopsis in children and to restore alignment and stereopsis in adults.

Binocular Summation and Control of Intermittent Exotropia

BACKGROUND

Binocular summation (BiS), or improvement in binocular vision exceeding the better eye alone, is affected by strabismus. Being easily measured, BiS may be a useful indicator for subjective outcomes like stereopsis in strabismus. This study aims to investigate the relationship between BiS and measures of control of intermittent exotropia (IXT).

METHODS

Patients with IXT were recruited before undergoing strabismus surgery and underwent tests of binocular and monocular high- and low-contrast visual acuity, stereopsis at distance and near, and Newcastle Control Score (NCS), a score developed by incorporating home control and clinic control criteria into a control rating scale. BiS was calculated using high-contrast Early Treatment of Diabetic Retinopathy Study (ETDRS) and Sloan low-contrast acuity charts (LCA) at 2.5% and 1.25% contrast as the difference between the binocular score and that of the better eye. The relationship between BiS and measures of IXT control (NCS and distance near stereoacuity disparity) was evaluated using a correlation analysis by Spearman correlation coefficients and the Kruskal-Wallis test.

RESULTS

Thirty-four patients were included (mean [± standard deviation (SD)] age 19±16 years) having a mean (±SD) of 26±16Δ IXT at distance and 20±16Δ at near. Mean (±SD) BiS for ETDRS and Sloan LCA at 2.5% and 1.25% was 0.8±3.6, 1.9±6.0, and -2.3±7.2, respectively. The Spearman correlation coefficient of BiS and NCS was -0.53 (95% CI -0.85 to -0.25) for 2.5% LCA and -0.43 (95% CI -0.77 to -0.13) for 1.25% LCA. BiS at 2.5% LCA (P=0.006) and at 1.25% LCA (P=0.029) significantly differed between the groups based on NCS score groupings (1-3, 4-6, and 7-9), with patients who had better control scores having higher levels of BiS. BiS did not differ significantly between patients grouped according to the difference between stereoacuity measured at near versus distance.

CONCLUSION

Significantly lower low-contrast BiS in patients with higher NCS may suggest that decreased BiS is associated with less control in IXT. This finding suggests that BiS may reflect control in IXT across a population of patients with IXT.

Decreased Binocular Summation in Strabismic Amblyopes and Effect of Strabismus Surgery

PURPOSE

Binocular summation (BiS) occurs when binocular visual function surpasses that of the better eye alone. We sought to evaluate whether strabismic amblyopia reduces BiS more than strabismus alone, and determine whether BiS improves in strabismic amblyopes after strabismus surgery.

METHODS

We prospectively recruited 15 patients with strabismic amblyopia who then underwent strabismus surgery. Thirty age-matched normal subjects and 30 non-amblyopic strabismic patients served as controls. Subjects underwent binocular and monocular visual acuity testing on high-contrast Early Treatment Diabetic Retinopathy Study (ETDRS) as well as 2.5% and 1.25% Sloan low contrast acuity (LCA) charts. BiS was calculated as the difference between better eye and binocular scores.

RESULTS

Strabismic amblyopes and strabismic controls did not significantly differ in preoperative BiS, but both had subnormal BiS preoperatively on LCA charts. Among 11 strabismic amblyopes with preoperative and postoperative BiS measurements, average postoperative BiS was not significantly different from preoperative. Improved LCA BiS postoperatively occurred in some patients and was associated with measurable preoperative stereoacuity (P=0.02), older age at strabismus onset (P=0.02), and larger preoperative angle of strabismus (P=0.0043).

CONCLUSIONS

In this preliminary study, strabismic amblyopes experienced subnormal BiS, but amblyopia generally did not further impair BiS beyond that due to strabismus alone. Some strabismic amblyopes experienced improved low-contrast BiS after strabismus surgery. This suggests that further investigation in larger groups of patients should be undertaken to analyze a previously unrecognized functional benefit of strabismus surgery in strabismic amblyopes.

Binocular visual acuity interaction in children: summation and inhibition

OBJECTIVE

To compare binocular visual acuity with the monocular visual acuity of the better eye and investigate the factors contributing to binocular interaction.

DESIGN

Retrospective observational study.

PARTICIPANTS

We enrolled 332 children. They were divided into 3 groups according to binocular interaction: group A (binocular equivalency), group B (binocular summation), and group C (binocular inhibition).

METHODS

Monocular visual acuity, binocular visual acuity, and stereoacuity were evaluated. The main outcome measures were the prevalence rates of binocular interaction and factors associated with binocular interaction, including monocular visual acuity of the better eye, interocular difference of monocular visual acuity, and stereopsis.

RESULTS

Of 332 children, binocular summation and equivalency were noted in 218 (65.7%) and 95 (28.6%), respectively, and binocular inhibition in 19 (5.7%). The binocular visual acuity and monocular visual acuity of the better eye in group B were better than those in groups A and C, respectively (p = 0.000). There was a significant correlation between monocular visual acuity of the better eye and binocular visual acuity in groups B and C (r = 0.884, p = 0.000; r = 0.797, p = 0.000, respectively). The interocular difference of monocular visual acuity in group B (0.05 ± 0.07) was smaller than that in group C (0.13 ± 0.06) (p = 0.000). The proportion of children with good stereopsis was 74.3% in group B but only 31.6% in group C (p = 0.001).

CONCLUSIONS

About 66% of 332 patients had better binocular visual acuity than monocular visual acuity of the better eye. Our results suggest that the monocular visual acuity of the better eye, interocular difference of monocular visual acuity, and stereopsis affect binocular interaction.

Bilateral symmetry in vision and influence of ocular surgical procedures on binocular vision: A topical review

We analyze the role of bilateral symmetry in enhancing binocular visual ability in human eyes, and further explore how efficiently bilateral symmetry is preserved in different ocular surgical procedures. The inclusion criterion for this review was strict relevance to the clinical questions under research. Enantiomorphism has been reported in lower order aberrations, higher order aberrations and cone directionality. When contrast differs in the two eyes, binocular acuity is better than monocular acuity of the eye that receives higher contrast. Anisometropia has an uncommon occurrence in large populations. Anisometropia seen in infancy and childhood is transitory and of little consequence for the visual acuity. Binocular summation of contrast signals declines with age, independent of inter-ocular differences. The symmetric associations between the right and left eye could be explained by the symmetry in pupil offset and visual axis which is always nasal in both eyes. Binocular summation mitigates poor visual performance under low luminance conditions and strong inter-ocular disparity detrimentally affects binocular summation. Considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK and LASIK, however the method to determine whether or not symmetry is maintained consist of comparing individual terms in a variety of ad hoc ways both before and after the refractive surgery, ignoring the fact that retinal image quality for any individual is based on the sum of all terms. The analysis of bilateral symmetry should be related to the patients' binocular vision status. The role of aberrations in monocular and binocular vision needs further investigation.

Relationship Between Binocular Summation and Stereoacuity After Strabismus Surgery

PURPOSE

To describe the relationship between binocular summation and stereoacuity after strabismus surgery.

DESIGN

Prospective case series.

METHODS

setting: Stein Eye Institute, University of California Los Angeles.

PATIENT POPULATION

Pediatric strabismic patients who underwent strabismus surgery between 2010 and 2015.

OBSERVATION PROCEDURES

Early Treatment Diabetic Retinopathy Study visual acuity, Sloan low-contrast acuity (LCA, 2.5% and 1.25%), and Randot stereoacuity 2 months following surgical correction of strabismus.

MAIN OUTCOME MEASURES

The relationship between binocular summation (BiS), calculated as the difference between the binocular visual acuity score and that of the better eye, and stereoacuity.

RESULTS

A total of 130 postoperative strabismic patients were studied. The relationship between binocular summation and stereoacuity was studied by Spearman correlation. There were significant correlations between BiS for 2.5% LCA with near and distance stereoacuity (P = .006 and P = .009). BiS for 1.25% LCA was also significantly correlated with near stereoacuity (P = .04). Near stereoacuity and BiS for 2.5% and 1.25% LCA were significantly dependent (Pearson χ(2), P = .006 and P = .026). Patients with stereoacuity demonstrated significantly more BiS in 2.5% LCA of 2.7 (P = .022) and 3.1 (P = .014) letters than did those without near or distance stereoacuity, respectively.

CONCLUSIONS

These findings demonstrate that stereopsis and binocular summation are significantly correlated in patients who have undergone surgical correction of strabismus.

Improvement in binocular summation after strabismus surgery

IMPORTANCE

Binocular summation (BiS), or improvement in visual acuity using binocular vision compared with the better eye alone, is diminished in patients with strabismus. However, it is still not known how strabismus surgery affects BiS.

OBJECTIVE

To determine whether BiS improves after strabismus surgery.

DESIGN, SETTING, AND PARTICIPANTS

Prospective study of 97 patients undergoing strabismus surgery between September 1, 2011, and January 31, 2014, comparing preoperative and postoperative measures of BiS. Patients were recruited within 1 month before undergoing strabismus surgery. The study took place at an academic pediatric ophthalmology and strabismus practice.

INTERVENTION

Strabismus surgery.

MAIN OUTCOMES AND MEASURES

All patients underwent high- and low-contrast visual acuity testing binocularly and monocularly at preoperative and 2-month postoperative visits. Binocular summation was calculated for high-contrast Early Treatment of Diabetic Retinopathy Study charts and Sloan low-contrast acuity charts at 2.5% and 1.25% contrast as the difference between the binocular score and that of the better eye. Preoperative and postoperative values were compared.

RESULTS

There was an improvement in BiS at the 2 low-contrast levels for all patients and for all contrast levels in the 75 patients in whom surgery successfully restored binocular alignment. For low-contrast acuity, the proportion of patients with a BiS score of at least 5 letters postoperatively was almost twice that of preoperatively (21% to 30% and 13% to 26% for 2.5% contrast and 1.25% contrast, respectively). Similarly, the proportion of patients with binocular inhibition (BiS score worse by at least 5 letters than the better eye score) was decreased postoperatively at all contrast levels (from 22% to 14% for 1.25% contrast). Thirty-one percent of patients experienced improvement in BiS scores postoperatively at the lowest contrast level.

CONCLUSIONS AND RELEVANCE

Binocular summation scores improved postoperatively in most patients undergoing strabismus surgery. This occurred most frequently at the lowest contrast level. These findings suggest that improved BiS could represent a newly recognized functional benefit from the surgical correction of strabismus. Further studies evaluating the correlation of BiS with stereopsis, visual field expansion, and quality of life will be necessary to fully evaluate the role that improved BiS has in improving binocularity postoperatively.

Quality of life in adults with strabismus

PURPOSE

To assess relative quality of life in patients with strabismus.

DESIGN

Retrospective cohort study.

METHODS

The 25-item National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25) was performed in 42 strabismic adults over the age of 50 years at a single institution. Subscale scores were compared with those of patients with other ocular diseases, including diabetic retinopathy, age-related macular degeneration (AMD), glaucoma, cataract, cytomegalovirus (CMV) retinitis, and low vision.

RESULTS

Median visual acuity was 20/20 (range 20/12.5-20/50), and 34 patients (81%) reported diplopia. Strabismic patients performed the same or worse on nearly all vision-related subscales than did patients with diabetic retinopathy, age-related macular degeneration, glaucoma, cataract, and CMV retinitis. Additionally, strabismic patients reported significantly worse ocular pain than all comparison groups before any surgery was performed.

CONCLUSIONS

Strabismus impacts quality of life through both functional and psychosocial factors. Physicians treating strabismic patients should recognize these quality-of-life issues and address them accordingly.

Normative reference ranges for binocular summation as a function of age for low contrast letter charts

PURPOSE

Binocular summation (BiS), defined as the superiority of binocular over monocular viewing on visual threshold tasks, is most often studied in laboratory settings. Few studies have evaluated BiS with readily available clinical tools. Low contrast acuity (LCA) charts are increasingly popular in clinical research, yet their utility in detecting BiS has not been evaluated.

METHODS

129 normal subjects aged 3 to 85 years were prospectively enrolled and underwent monocular and binocular testing using 2.5% and 1.25% Sloan LCA charts and Pelli-Robson (PR) contrast sensitivity (CS) charts at an academic institution. Subjects also underwent similar testing with Early Treatment Diabetic Retinopathy Study (ETDRS) VA charts. BiS was calculated as the difference between the better eye and binocular scores.

RESULTS

Monocular and binocular scores decreased with increasing age for all metrics. The mean (±SD) BiS scores for 2.5% and 1.25% Sloan LCA were 6±4.5 and 3±5 letters, respectively. BiS score was 4.5±7 letters for PR charts and 2±3 letters for ETDRS VA. There was a significant effect of age on BiS for the low contrast metrics (P≤0.001 for all), but not for high-contrast ETDRS VA. Linear regression revealed significant associations between increased interocular difference (IOD) in acuity and decreased BiS for all tests, and associations between increasing age and decreased BiS for the LCA tests.

CONCLUSION

Of the clinical tests evaluated, 2.5% and 1.25% Sloan LCA charts most readily demonstrated BiS in young normal subjects. BiS declined with increasing age and increased IOD. Median values presented in this study may be useful for future clinical studies utilizing LCA.

Binocular inhibition in strabismic patients is associated with diminished quality of life

PURPOSE

To characterize the relationship between binocular summation (BiS) and binocular inhibition (BI) on the quality of life of adults and children with strabismus.

METHODS

Strabismus patients at a single center from 2010 to 2012 were prospectively enrolled. A BiS score was measured using ETDRS and Sloan low-contrast visual acuity (LCA) protocols at 2.5% and 1.25% contrast. Patients were categorized as having BiS (binocular better than better-eye visual acuity by ≥5 letters), BI (binocular worse than better-eye visual acuity by ≥5 letters), or otherwise indeterminate visual acuity (a difference between binocular visual acuity and monocular visual acuity of the better eye of <5 letters). Quality of life was evaluated by the National Eye Institute Visual Functioning Questionnaire 25 (VFQ-25), 20-item Adult Strabismus Questionnaire (AS-20), and the Amblyopia and Strabismus Questionnaire.

RESULTS

A total of 108 patients were included. There was no significant BiS or BI for high-contrast ETDRS or 2.5% LCA tests; however, a mean BiS score of -2.14 ± 7.0 letters for 1.25% LCA demonstrated significant binocular inhibition (P = 0.004) for this contrast level. The mean composite VFQ-25 score was significantly lower in subjects with BI on ETDRS (80 ± 19 vs 57 ± 7 for subjects with BiS and BI, resp. [P = 0.03]), 2.5% LCA (81 ± 14 vs 66 ± 16 for subjects with BiS and BI, resp. [P = 0.01]), and 1.25% LCA tests (91 ± 9 vs 72 ± 14 for subjects with BiS and BI, resp. [P = 0.005]). After accounting for potential covariates, significant association persisted for BI, demonstrated by 1.25% LCA (P = 0.01). With BI demonstrable at 2.5%, AS-20 scores were also significantly lower (P = 0.04).

CONCLUSIONS

Strabismic patients with BI had significantly lower quality-of -life scores than those who did not, even after accounting for potential covariates and the absence of diplopia.

Squinting and photophobia in intermittent exotropia

PURPOSE

To report factors associated with preoperative squinting, defined as transient eye closure in bright light, and photophobia and the factors affecting improvement of these symptoms postoperatively in intermittent exotropia.

METHODS

In this retrospective study, patients (N = 99) were divided into groups according to the presence (n = 54) or absence (n = 45) of preoperative squinting and the presence (n = 64) or absence (n = 35) of photophobia. Clinical characteristics, including overaction or underaction of the oblique muscle and fundus intorsion and extorsion, were compared between the two groups. The squinting and photophobia groups were further categorized into two subgroups each according to postoperative improvement. The extended list of characteristics, including the duration from onset to surgery, postoperative angle of deviation, and fusion, was compared between the two subgroups.

RESULTS

Preoperatively, 54 (54.5%) and 64 (64.6%) patients had squinting and photophobia, respectively. The coincidence of squinting and photophobia was marginally significant (p = 0.05). Postoperatively, squinting and photophobia disappeared in 64.8 and 59.4% of the patients, respectively. The photophobia group had a younger onset age of strabismus than the nonphotophobia group (39.3 vs. 56.4 months; p = 0.03). Good fusional status at the near range was more common in the nonsquinting group than in the squinting group (74.3 vs. 47.6%; p = 0.02). Superior oblique overaction was significantly more common in the squinting group than in the nonsquinting group (11.1 vs. 0%; p = 0.03). Early surgical correction and successful outcomes were associated with squinting improvement (p = 0.001 and p = 0.02, respectively).

CONCLUSIONS

More than 50% of patients with intermittent exotropia had squinting or photophobia, and approximately 60% of symptomatic patients experienced improvement postoperatively. The onset of strabismus, near fusion, superior oblique overaction, and fundus intorsion were related to these symptoms. Early surgery and successful eye position realignment were beneficial for improving squinting postoperatively.

Global processing in amblyopia: a review

Amblyopia is a neurodevelopmental disorder of the visual system that is associated with disrupted binocular vision during early childhood. There is evidence that the effects of amblyopia extend beyond the primary visual cortex to regions of the dorsal and ventral extra-striate visual cortex involved in visual integration. Here, we review the current literature on global processing deficits in observers with either strabismic, anisometropic, or deprivation amblyopia. A range of global processing tasks have been used to investigate the extent of the cortical deficit in amblyopia including: global motion perception, global form perception, face perception, and biological motion. These tasks appear to be differentially affected by amblyopia. In general, observers with unilateral amblyopia appear to show deficits for local spatial processing and global tasks that require the segregation of signal from noise. In bilateral cases, the global processing deficits are exaggerated, and appear to extend to specialized perceptual systems such as those involved in face processing.

Effects of visual noise on binocular summation in patients with strabismus without amblyopia

PURPOSE

Patients with strabismus often complain of difficulty navigating through visually stimulating environments without clear explanation for this symptom. Binocular summation (BiS), defined as the superiority of binocular over monocular viewing on visual threshold tasks, is decreased in conditions that cause large interocular differences in visual acuity, but is not well studied in strabismic populations without amblyopia. The authors hypothesized that strabismus may lead to decreased BiS for tasks related to discrimination within increased background complexity. The goal of this study was to test the extent of BiS in patients with strabismus during discrimination of a luminance target disk embedded in visual noise.

METHODS

Participants included 10 exotropic, 10 esotropic, and 13 age-matched control patients. Performance of a task detecting a luminance-target was measured at 0, 10, and 20 μdeg(2) of visual noise for binocular and monocular conditions. BiS was calculated as the ratio of binocular contrast sensitivity to monocular contrast sensitivity for the target embedded in noise.

RESULTS

Patients with strabismus had lower BiS values than controls, with a significant decrease on linear regression in patients with strabismus at 20 μdeg(2) of noise (P = .05), with a trend toward significance at 10 μdeg(2) of noise (P = .07). Patients with strabismus showed a mean binocular inhibition (summation ratio < 1) at both noise levels.

CONCLUSIONS

These findings support the hypothesis that strabismus can lead to decreased BiS and even binocular inhibition. Despite literature showing enhanced BiS in visually demanding situations such as high levels of visual noise or low contrast, BiS was not significantly affected by visual noise in either group.