Normal Binocular Function Research Articles

A typical case of miraculous relief from blindness

This article describes a case of hysterical amblyopia in a 10.5-year-old girl. She complained of decreased vision for 4 months. The decrease in vision was a result of infectious mononucleosis and conjunctivitis. During the initial examination, typical signs of hysterical amblyopia were observed: a bilateral decrease in visual acuity, loss of field to tubular, and a corresponding impaired orientation in the surrounding space. Reversible changes in visual evoked potentials (VEP) were noted, indicating functional changes in the visual system, impaired color perception. A complete ophthalmological examination was performed, including standard methods and electrophysiological studies. Upon repeated examination after 1 day, complete relief of signs of hysterical amblyopia was noted, namely, an increase in visual acuity to 1.2, expansion of the boundaries of the visual field to normal values, normal binocular and accommodation functions, and normal trichromasia. This case was unique because of the complete restoration of visual functions that occurred spontaneously within 1 day. For the first time, reversible changes in visual evoked potential that were not previously described in the literature were revealed, and an undifferentiated violation of color perception was described.

Impact of strabismus and binocular dysfunctions in the developmental eye movement test and test of visual perception skills: A multicentric and retrospective study

PurposeTo compare the performance in the Developmental Eye Movement test (DEM) and the Test of Visual Perceptual Skills (TVPS) between three groups: individuals with strabismus and amblyopia, patients with binocular and accommodative dysfunctions, and subjects with normal binocular and accommodative function. MethodsA multicentric, retrospective study including 110 children aged 6–14 years old was conducted to investigate the potential impact of strabismus, amblyopia, and different binocular conditions in DEM results (adjusted time in vertical and horizontal parts) and TVPS (percentiles in the seven sub-skills). ResultsNo significant differences were found in the different subtests of the vertical and horizontal DEM and all the sub-skills in the TVPS between the three groups of the study. We found high variability of performance in the DEM test between participants with strabismus and amblyopia compared with binocular and accommodative problems. ConclusionDEM and TVPS scores have not been found to be influenced by the presence of strabismus with or without amblyopia, nor by binocular and accommodative dysfunctions. A slightly correlation tendency with horizontal DEM and degree of exotropia deviation was observed.

A Study to Assess the Feasibility of Utilising Virtual Reality for the Treatment of Accommodative and Vergence Infacility

Background:To assess the feasibility, as well as viability, of utilising gaming using virtual reality (VR) to treat accommodative and vergence infacilities.Methods:Forty-two emmetropic and asymptomatic participants between the ages of 18 and 30, with normal binocular visual function, were selected for the study in 2018. Participants with binocular accommodative infacilities and/or vergence infacilities comprised the study population. The binocular accommodative facilities (BAF) were assessed using amplitude-scaled facilities (probe lens = 30% amplitude of accommodation; test distance = 45% amplitude of accommodation). All those with less than 10 cycles per minute (cpm) were regarded as failing. Vergence facilities were assessed using 12 pd base out and 3 pd base in prisms. All those with less than 15 cpm were regarded as failing. The participants were separated into age-matched experimental and control groups. The experimental group played a fast-paced game using Samsung Gear VR (SM-R323), whilst the control group watched a television film projected onto a two-dimensional screen at a distance of one metre. Pre-test and post-test binocular amplitude-scaled facilities and vergence facilities were measured for both groups after exposure for 25 minutes.Results:There was a significant, mean increase in binocular accommodative facilities of 4.67 ± 5.05 cpm (p = 0.008) for the experimental group (n = 12). There was a significant mean increase in vergence facilities of 3.72 ± 3.18 cpm (p < 0.001) for the experimental group (n = 32). A statistically significant mean difference of 4.07 cpm (95%CI: 0.97, 9.19; p = 0.03) between the respective control and experimental groups was found for binocular accommodative facilities and 2.45 cpm (95%CI: 0.68, 4.22; p = 0.008) for vergence facilities.Conclusion:Binocular accommodative facilities and vergence facilities increased after 25 minutes of VR gaming in asymptomatic emmetropic participants with accommodative infacilities and vergence infacilities. However, due to the small-scale, unmasked and unrandomised nature of the study more research is needed to confirm the results of this study.

Acute Acquired Comitant Esotropia: Etiology, Clinical Course, and Management.

PurposeTo identify the etiologies, clinical course and management of acute acquired comitant esotropia in Ramathibodi Hospital, Thailand.MethodsThirty patients who were diagnosed with acute acquired comitant esotropia at Ramathibodi Hospital from January 1 2017 to December 31 2019 were identified using electronic medical records, from which demographic, etiology, clinical course and management, laboratory, and neuroimaging data were collected.ResultsThe etiologies of acute acquired comitant esotropia were Swan (16.67%), Burian–Franceschetti (30.00%), Bielschowsky (36.67%), Arnold Chiari malformation (3.33%) and decompensated esophoria (13.33%). Mean age of onset was 19.8 ± 18.3 years. Mean angle of esodeviation was 28.4 ± 12.1 prism diopters for distance fixation and 29.3 ± 11.8 prism diopters for near fixation. Refraction differed between age groups: children under 10 years had mild hyperopia (median +0.63 diopters, first quartile +0.25 diopters, third quartile +0.75 diopters) and teenagers (10–18 years old) had emmetropia to mild myopia (median +0.25 diopters, first quartile −2.50 diopters, third quartile +0.75 diopters), whereas adults had mild to moderate myopia (median −0.75 diopters, first quartile −5.25 diopters, third quartile ±0.00 diopters). Twelve patients (40.00%) were prescribed spectacles and surgical intervention was performed in 26 patients (86.67%). All patients except one case of Arnold Chiari malformation (96.67%) maintained normal binocular function and alignment following strabismus surgery or spectacles correction.ConclusionBielschowsky was the most common etiology of acute acquired comitant esotropia in our study. We suggest that refraction should be performed in all patients with acute acquired comitant esotropia. Most etiologies were benign and might not require neuroimaging. However, neuroimaging is recommended in those with atypical presentations, such as nystagmus, headache, or cerebellar signs. Surgical intervention with a 0.5–1.0 mm increase in recession was effective for restoring ocular alignment and binocular function in our patients.

Changes in corneal astigmatism and near heterophoria after smartphone use while walking and sitting.

Smartphone use has become an indispensable part of our daily life. The handy design and powerful processor allow smartphone users to perform diversified tasks even when walking. This study aimed to investigate and compare the optical aftereffect and vergence adaptation of using a smartphone while walking and sitting. Twenty-nine young healthy adults (aged 19 to 24 years old) with normal binocular and accommodative functions were recruited. Participants were asked to watch a movie for 30 minutes using a smartphone while either walking on a treadmill or sitting on a chair. Corneal aberrations and near heterophoria were measured before and after smartphone use by a corneal topographer and modified Thorington heterophoria test, respectively. Using the smartphone while walking induced a change in corneal H/V astigmatism, becoming 0.11±0.03 μm less negative (two-way ANOVA repeated measures, Bonferroni post-hoc test, p = 0.001). This optical aftereffect was significantly higher than after smartphone use while sitting by 0.10±0.03 μm (paired t-test, p = 0.003). Although smartphone use did not result in a significant change in near heterophoria (Bonferroni post-hoc test, p > 0.15), the vergence adaptation showed relatively more eso- or less exo-deviation by 0.79±0.36Δ in the walking than the sitting condition (paired t-test, p = 0.037). Eyecare practitioners should be cautious of the potential optical after effect and vergence adaptation after prolonged smartphone usage.

Technical Report: Repeatability of Contrast Sensitivity Test in Children.

This study aimed to evaluate the repeatability and normal range of the contrast sensitivity function measured using the Topcon CC-100 instrument, in children aged between 4 and 9 years, for use as a diagnostic tool. Contrast sensitivity was measured in 25 children, 11 boys and 14 girls, with normal or corrected-to-normal visual acuity, normal binocular function, and stereopsis. Two measurements were performed, 3 months apart, with a Topcon CC-100 device using achromatic sinusoidal gratings of 1.5, 3, 6, 12, and 18 cycles per degree (cpd) with random orientation in a circular window with sharp edges. The normal range in the first visit is wider than in the second. Coefficients of variation are better for the middle-range spatial frequencies (6.6 and 7.8% at 3 and 6 cpd, respectively) and worst at 18 cpd (18.2%), with intermediate values at 1.5 cpd (11.3%) and 12 cpd (13.7%), and better for older than for younger children. No significant sex differences were found (P > .05, Mann-Whitney U test). Repeatability measured by the coefficient of variation is better for the middle frequency range (3 and 6 cpd) than for low (1.5 cpd) and high frequencies (12 and 18 cpd). The variability of the differences between the first and second measurements suggests that the participants were not able to maintain a stable response criterion. The test seems to be subject to a learning effect, and the standard normality range may not be adequate for children.

The effect of gaming on accommodative and vergence facilities after exposure to virtual reality head-mounted display

BackgroundTo investigate the change between accommodative and vergence facilities before and after exposure to gaming in a virtual reality (VR) device amongst participants with normal binocular visual function. Methods62 participants between the ages of 18–30 years with normal binocular visual function and inter-pupillary distances between 51 and 70 mm were selected for the study. Spectacle and contact lenses users were excluded. The experimental group (n = 42) was exposed to gaming using Samsung Gear VR(SM -R323) whilst the control group (n = 20) watched a television film projected on a two-dimensional screen at 1 m. Pre-test and post-test binocular amplitude-scaled facilities and vergence facilities were obtained for both groups after exposures of 25 min. ResultsBinocular accommodative facilities for the experimental group had a mean pre-test and post-test facility of 11.14 ± 3.67 cpm and 13.38 ± 3.63 cpm, respectively, after gaming using VR device. The vergence facilities for the experimental group had a mean pre-test and post-test facility of 11.41 ± 3.86 cpm and 15.28 ± 4.93 cpm, respectively, after gaming using a VR device. Binocular accommodative facilities for the control group had a mean pre-test and post-test facility of 11.70 ± 3.2 cpm and 11.95 ± 3.4 cpm, respectively. Vergence facilities for the control group had a mean pre-test and post-test facility of 11.55 ± 6.4 cpm and 11.70 ± 4.9 cpm, respectively. The mean change for binocular accommodative facilities was 2.24 ± 3.43 cpm and 0.25 ± 1.25 cpm for the experimental and control group, respectively. The mean change for vergence facilities was 3.81 ± 3.09 cpm and 0.15 ± 2.72 cpm for the experimental and control group, respectively. Binocular accommodative facilities and vergence facility showed a statistically significant mean increase greater than the control group after gaming using a VR device using an independent t-test (p < 0.05). ConclusionThe results showed that binocular accommodative facilities and vergence facilities increased after 25 min of VR gaming in emmetropic participants under 30 years of age with inter-pupillary distances between 51 mm and 70 mm.

Effect of Wearing Plus Lens on Reading Ability of College Students with Normal Binocular Function

Purpose : The purpose of this study was to investigate the effect of wearing plus lens on reading ability in college students with normal binocular function. Methods : Accommodative lag and reading ability were measured in 42 college students with normal binocular function, and no eye disease. For the control lag test the subjective cross cylinder method was applied, and for the reading ability the duration of fixation, number of regression, saccadic in return sweep and reading rate were measured using the Readalyzer. The subjects reading abilities were measured before and after with the plus lens corresponding to the amount of accommodative lag. Statistical analysis using SPSS version 21.0(SPSS Inc, Chicago, IL, USA) was used to analyze the change of the ability before and after wearing the plus lens through a paired t-test. Results : When the subjects wore the plus lens corresponding to the accommodative lag, the duration of fixation was slightly increased, the number of regression was significantly decreased, and the reading rate was significantly increased. Conclusion : It was considered that wearing plus lens with low refractive power may affect the time to look at words during reading. During reading with the lens, it may also have an effect changes such as reducing the number of regression and increasing the reading rate.

Nonstrabismic binocular dysfunctions and cervical complaints: The possibility of a cross-dysfunction.

The aim of this study is to establish a relationship between non-strabismic binocular dysfunction and neck pain. One hundred twelve participants underwent binocular vision assessment by evaluating horizontal heterophoria, horizontal and vertical fusional vergence ranges and vergence facility. The subjects were classified into two groups: binocular anomalies and normal binocular function. Neck complaints were measured with the Neck Disability Index, visual analogue scale, cervical range of motion, deep-flexor muscle activation score (AS) and performance index (PI). Our results showed that participants with low AS had significantly altered values of lateral phoria (near) (mean = -6.99 SD ± 6.96 PD) and PFV (near) blur (mean = 9.49 SD ± 5.45 PD) against those who presented normal AS (lateral phoria (near) mean = -3.64 SD ± 6.37 PD; PFV (near) blur mean = 12.84 SD ± 6.20 PD). In addition, participants with NFV (near) recovery outside the norm had a significantly lower right side-bending (mean = 35.63 SD ± 8.35 PD) than those within the standard (mean = 39.64 SD ± 9 PD). The subjects with binocular vision impairment showed a diminished response to the deep cervical musculature, with low AS and PI, as well as a tendency to suffer from cervicalgia of more than three months’ evolution and a lower range of motion.

The comparison of accommodative response and ocular movements in viewing 3D and 2D displays

Some people often appear asthenopia symptoms of eye fatigue, double vision, nausea, and dizziness while viewing 3D movies. By testing the changes of accommodation function and ocular movements during watching 3D and 2D movies, the factors in visual discomfort are confirmed in this study.20 subjects with normal visual acuity and binocular vision function view 3D and 2D movies with the same content for 30min, and the amplitude of accommodation, binocular vergence ability, stereo-acuity, and tear break-up time of the subjects before and after viewing the films are measured. Furthermore, an open-field auto-refractor is utilized for synchronously testing the change of accommodative response while viewing 3D and 2D films, and Skalar IRIS tracking system is applied to record ocular movements through infrared positioning.In comparison with viewing 2D movies, the accommodative response and ocular movements reveal obvious changes while viewing 3D movies. The accommodation ability and binocular vergence ability obviously drop after viewing 3D movies; moreover, the stability of stereo-acuity and tear film also gets worse. The changes of such physiological factors might be the major cause of asthenopia.

Fusional Amplitudes: Developing Testing Standards

ABSTRACTPurpose: The stability of binocular vision depends upon good fusional amplitudes, but the clinical assessment of fusional amplitudes varies around the world. The purpose of this study was to determine whether or not there is variation in the assessment of fusional amplitudes in normal subjects. The author looked at the testing distance, the order of testing, the role of examiner encouragement, and the subject’s level of alertness.Methods: In a prospective study using a modified crossover design, the author assessed fusional amplitudes in 99 subjects with normal eye exams. The measurements were done in two separate sessions on different days with each subject being randomized as to the order of fusional vergence testing. All subjects were assessed without and with encouragement in the first session. In the second session, all were assessed at different testing distances.Results: The author previously presented data on 50 subjects. In this expanded cohort, statistical significance was reached confirming the previous findings that convergence is significantly affected by encouragement, divergence is significantly reduced if assessed after convergence, and near amplitudes are significantly higher than distance amplitudes. Finally, there is a negative correlation between age and convergence break point.Conclusions: The results of this study demonstrate that divergence is significantly reduced if assessed after convergence in the subject with normal binocular function. Next, convergence is significantly affected by the use of encouragement. Measurements at near produced significantly higher results for all of the convergence and divergence tests. Finally, there is a significant negative correlation between age and convergence break point. We need to develop a standard of testing fusional amplitudes so there is consistency in the clinical assessment.

Short Term Effect of Monocular Wearable Device on Accommodation

Purpose: This study is to investigate various problems of wearing google glass, and to compare an accommodative response of short term usage of a computer, tablet PC, and google glass. Methods: We measured accommodative responses of thirty university students (8 males and 22 females) who presented normal binocular function (accommodation and vergence). To compare accommodative response, subjects viewed 10 min of computer, tablet PC, google glass in order respectively, after distance refractive error was measured. Accommodative response was measured by using open-view auto-refractometer (Nvision-K5001, shin-nippon, Japan). Results: When accommodative stimulation was different, each accommodative response was 1.13±0.33D on the right eye and 1.15±0.35D on the left eye, and there is no significant correlation between right and left. The average accommodative response with left eye was 0.77±0.54D (computer), 1.42±0.45D(tablet PC) a nd 0 .2 9±0.18D (google glass) respectively. There was no significant correlation between computer and tablet PC. However, there were significant correlations between computer and google glass and between tablet PC and google glass (p<0.05). Conclusions: When google glass was used, the amount of accommodative response was small in quantity. This accommodative response was not enough to make spasm of accommodation or diplopia. Thus, much researches about accommodation are needed. Although the image of google glass is virtual image, a certain degree of accommodative response was induced. Therefore, wearers of google glass with presbyopia or high degree of hypermetropia can have difficulty on seeing the clearer image.

Frequency thresholds for stereopsis in the case of alternative presenting the left and right images of stereopair in children with ophthalmopathology

In this paper, we report the results of estimating the minimum frequency of alternative left-right stereopair image presentation necessary to obtain stereopsis in children with ophthalmopathology including or not including binocular disorders. It was found that all subjects without binocular disorders had stereo-effect with linear as well as with random-dot images. However, for stereopsis with random-dot stereotests, all children needed higher frequency of alternation than for stereopsis with simple linear images. It appeared that about 90% of children with binocular disorders were capable to perceive depth when simple linear stereoscopic images were presented alternatively to the two eyes. However, these patients needed a higher frequency of alternation than children with normal binocular functions. Only a small part (about 30%) of children with binocular disorders was capable to stereopsis with complex random-dot images and they needed rather high frequency (more than 30 Hz) of alternation for success.

Clinically Normal Stereopsis Does Not Ensure a Performance Benefit from Stereoscopic 3D Depth Cues

To investigate the effect of manipulating disparity on task performance and viewing comfort, twelve participants were tested on a virtual object precision placement task while viewing a stereoscopic 3D (S3D) display. All participants had normal or corrected-to-normal visual acuity, passed the Titmus stereovision clinical test, and demonstrated normal binocular function, including phorias and binocular fusion ranges. Each participant completed six experimental sessions with different maximum binocular disparity limits. The results for ten of the twelve participants were generally as expected, demonstrating a large performance advantage when S3D cues were provided. The sessions with the larger disparity limits typically resulted in the best performance, and the sessions with no S3D cues the poorest performance. However, one participant demonstrated poorer performance in sessions with smaller disparity limits but improved performance in sessions with the larger disparity limits. Another participant's performance declined whenever any S3D cues were provided. Follow-up testing suggested that the phenomenon of pseudo-stereoanomaly may account for one viewer's atypical performance, while the phenomenon of stereoanomaly might account for the other. Overall, the results demonstrate that a subset of viewers with clinically normal binocular and stereoscopic vision may have difficulty performing depth-related tasks on S3D displays. The possibility of the vergence---accommodation conflict contributing to individual performance differences is also discussed.

Does Partial Occlusion Promote Normal Binocular Function?

There is growing evidence that abnormal binocular interactions play a key role in the amblyopia syndrome and represent a viable target for treatment interventions. In this context the use of partial occlusion using optical devices such as Bangerter filters as an alternative to complete occlusion is of particular interest. The aims of this study were to understand why Bangerter filters do not result in improved binocular outcomes compared to complete occlusion, and to compare the effects of Bangerter filters, optical blur and neutral density (ND) filters on normal binocular function. The effects of four strengths of Bangerter filters (0.8, 0.6, 0.4, 0.2) on letter and vernier acuity, contrast sensitivity, stereoacuity, and interocular suppression were measured in 21 observers with normal vision. In a subset of 14 observers, the partial occlusion effects of Bangerter filters, ND filters and plus lenses on stereopsis and interocular suppression were compared. Bangerter filters did not have graded effect on vision and induced significant disruption to binocular function. This disruption was greater than that of monocular defocus but weaker than that of ND filters. The effect of the Bangerter filters on stereopsis was more pronounced than their effect on monocular acuity, and the induced monocular acuity deficits did not predict the induced deficits in stereopsis. Bangerter filters appear to be particularly disruptive to binocular function. Other interventions, such as optical defocus and those employing computer generated dichoptic stimulus presentation, may be more appropriate than partial occlusion for targeting binocular function during amblyopia treatment.

Endoscopic and Trans-Fornix Removal of a Giant Orbital-Ethmoidal Osteoma

A 39-year old female was referred with a 2 year history of slowly progressive headache, exophthalmos, diplopia and restricted eye movements with exotropia of the right eye. Orthoptic examination revealed restricted elevation and mildly restricted adduction of the right eye. CT and MRI demonstrated a large (35 × 20 × 23 mm) calcified infraorbital lesion extending into the ethmoidal sinus. Because the visual field defects were progressive and the acuity OD dropped to 20/80 surgical intervention was necessary. The osteoma was succeffully removed using an inferior and medial orbitotomy with swinging eyelid combined with an endoscopic approach. In a second procedure the orbital floor was reconstructed with a porous polyethylene (Medpor) implant. A final procedure consisted of a 3 mm recession of the left superior rectus muscle and infundibulotomy by the sinus surgeon to open the blocked maxillary sinus. After 6 months visual acuity OD had returned to 20/20. Orthoptic examination showed normal binocular function.

Binocular visual function in congenital esotropia after bilateral medial rectus recession with loop suture

PURPOSE Our aim was to evaluate the binocular visual function in congenital esotropia after bimedial rectus recession with loop suture and to address the factors that could take part in the attainment of binocular function. SUBJECTS AND METHODS Forty children with congenital esotropia who were operated on between 12 and 48 months of age were included in the study group. Postoperative follow-up ranged from 2 to 10 years. In order to determine the factors affecting the sensory results in congenital esotropia, we classified our patients into two groups according to their fusion status. We compared the preoperative and postoperative characteristics of patients in these two groups. RESULTS Twenty-one of 40 patients (52.5%) fused the Worth four-dot at near (Group 1), 19 patients (47.5%) did not (Group 2) at the final examination. No patient showed evidence of stereopsis. We found significant differences between these two groups in respect to the final angle of vertical deviation, the age at surgery, the presence of postoperative inferior oblique overaction, dissociated vertical deviation and abnormal head position. Correlation analysis revealed that early alignment of the eyes and the absence of postoperative vertical deviation were associated with increased incidence of achieving some degree of binocular vision. CONCLUSION In congenital esotropia, not all infants may have the potential for normal binocular function owing to yet unknown constitutional factors. We determined that achieving some degree of binocular function may be related to early alignment of the eyes. Additionally, close follow-up and precise treatment of the accompanying vertical deviation, especially inferior oblique overaction and dissociated vertical deviation,in a timely manner may enhance the attainment of binocular sensory function.

Binocular Function of Intermittent Exotropia Before and After Surgery

Purpose: We examined the binocular function of intermittent exotropia before and after surgery, and studied the effect of the surgery and the factor that might be involved in its result. Materials and Methods: 402 intermittent exotropic patients, who underwent their first surgical correction for the strabismus at Teikyo University Hospital, were examined for retinal correspondence and stereo acuity before and after surgery. Results: 367 patients (91.3%) had already had good stereo acuity before surgery when their eyes were straight. Regarding retinal correspondence, though 192 patients (47.8%) were abnormal (dual) before surgery, 301 patients (74.9%) were normal after surgery. The eye deviation of 101 patients who could not get normal retinal correspondence after surgery was significantly larger than normal ( P < .001), and 77.2% of them had also vertical strabismus which was mainly composed of dissociated vertical deviation. Conclusion: Normal binocular function could be recovered by surgical treatment in most intermittent exotropic patients. When patients could not get normal retinal correspondence after surgery, we supposed that dissociated vertical deviation might exert an important effect upon their binocular function.

Vertical fixation disparity curve and the effects of vergence training in a normal young adult population.

The vertical forced vergence fixation disparity (VFD) curve represents the amount of vertical fixation disparity, the steady-state vertical bifixation error of the eyes, at various levels of vertical vergence demand. The main aim of the present study was to examine the effects of vertical vergence training on the slope of the VFD curve in a normal, young adult population. Forty-five subjects with normal vision and binocular function underwent vertical vergence training for 1 week. The training was done using a vertical prism bar, and the vertical fixation disparity was measured using the Disparometer. The mean slope of the VFD curve in a normal, young adult population was 1.103 min arc/delta. The slope of the VFD curve decreased significantly after the training and remained flattened for at least 3 months. There was no evidence to support the idea that the decrease in the VFD slope was related to the increase of vertical fusional amplitude. Vertical prism bar training provided a long-term effect, both increasing the vertical fusional amplitude and flattening the slope of the VFD curve. The decrease in the slope of the VFD curve was thought to be independent of the increase of vertical fusional amplitude.

Early refractive development in humans

Over recent years much interest has been directed toward understanding the process by which refractive errors develop, how this is controlled and the effect of refractive errors on subsequent visual status. There are obvious difficulties in studying such mechanisms in human subjects and for this reason many studies have employed animal models. The present paper compiles the evidence available from human subjects, examining the significance of different aspects of refractive status, normal and abnormal patterns of development and their significance in the development of normal binocular function.