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Effects of Anisometropia on Binocularity

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Abstract

To investigate the effects of anisometropia on binocular function and the relationship between stereopsis and fusion in anisometropia. Twenty-five patients with anisometropia were studied. The manifest refraction and best-corrected Snellen visual acuity of each patient was recorded. Patients, corrected with spectacles, were evaluated using Bagolini glasses, the 4-diopter (D) prism test, Worth four-dot test, and TNO stereotest. All patients indicated fusion by the Bagolini glasses. Although the 4-D prism test was positive in the anisometropic eye of all 25 patients, it was slower than the response of the other eye in 19 patients with reduced stereoacuity. On the distant Worth four-dot test, fusion response was positive in 15 patients. On theTNO test, stereoacuity levels were reduced or absent in 19 patients. The depth of amblyopia is more effective than the amount of anisometropia in causing a deterioration in binocularity. Even if fusion is weak, almost all patients with anisometropia have bifoveal fusion. Fusion becomes weak and stereoacuity decreases in proportion to the anisometropic amblyopia. Stereoacuity is related to the strength of fusion, and the TNO stereotest effectively detects those patients with significant anisometropic amblyopia.
... Binocular vision is the ability of two eyes to see two similar images simultaneously and blend them into one with depth perception. 1 It needs a good and near equal visual acuity in both eyes. High anisometropia leads to amblyopia and reduction in binocular single vision. ...
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Purpose: To assessthe impact ofinduced anisometropia on binocular visual function. Study Design: Quasi experimental study. Place and Duration of Study: Optometry clinicsof Qassim University, from January 2024 to June 2024. Methods: The study included 60 subjects of 16-26 years. Anisometropic myopia was induced by plus lenses (+1DS, +2DS, +3DS) and anisometropic hypermetropia was induced by minus lenses (-1DS, -2DS, -3DS) keeping them emmetrope with normal binocularity. Subjects with squint, suppression and amblyopia were excluded. Clinical assessment included;assessment of vision,refraction and near phoriawith Maddox wing. Assessment of bifovealfusion, suppression and diplopiawas done using Worthfour dot test and stereoscopic vision with Titmus fly test. Data was analyzed by using SPSS- v.25. Results: There were 66.7% males and 33.3% females. Mean agewas 22.37±2.81 years. A significant difference in stereoacuity was found in 1D (41.75±130.26 sec arc), 2D (233.77±172.09 sec arc) and 3D (399.267±181.31 sec arc) anisometropic myopia (p˂0.001) as well asanisometropic hypermetropia(p˂0.001).There was no significant difference in stereoacuity between males and females (p ˃ 0.05). However, diplopia was higher in 3D of anisometropic hyperopia (73.3%) than anisometropic myopia (66.7%). Monocular suppression was present in 6.7% and 3.3% of 3D anisometropic hyperopia and anisometropic myopia respectively. Alternate suppression was present in 1.7% of eyes with 2D anisometropic hyperopia only. Conclusion: Small degree of anisometropia significantlyimpact binocular vision. It affects bi-foveal fusion, leads to diplopia, suppression and reduction in stereopsis.
... The studies by Ying et al. [38] reported that a greater amount of anisometropia was associated with worse stereoacuity in a clear dose-response manner in children, supporting our observations. The mechanism by which anisometropia impairs children's stereoacuity is mainly through interrupting normal binocular fusion [39,40] . ...
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Purpose To investigate the distribution of stereoacuity and its ocular-associated factors in children aged 3–7 years in Guangxi, Southern China. Methods This cross-sectional study recruited 4,090 children aged 3–7 years (mean: 5.12 ± 0.95 years) from 12 randomly selected kindergartens using cluster sampling in Nanning, Guangxi Autonomous Region, Southern China. Comprehensive assessments included visual acuity assessment, noncycloplegic autorefraction, anterior segment examination, cover/uncover and alternating cover tests, fundus examination, and the Titmus stereo test. Univariate and multivariate logistic regression models were used to determine the factors associated with subnormal stereoacuity (> 40 arcsec). Results The prevalence rates of anisometropia, astigmatism, and strabismus were 18.24%, 26.11%, and 0.20%, respectively. The mean stereoacuity was 1.88 ± 0.34 log units (median: 60.25 arcsec), with the majority (65.18%) having subnormal stereoacuity. The mean log units of stereoacuity decreased with age (F = 144.7, P < 0.001). Compared with girls, boys had a significantly greater mean log unit stereoacuity (1.90 ± 0.35 vs 1.87 ± 0.34, t = 2.589, P = 0.010). In the multivariate logistic regression, older age (odds ratio [OR]: 0.040–0.461 for years 4–7, 95% confidence interval [CI]: 0.018–0.613 for years 4–7, all P < 0.001) and female sex (OR = 0.672, 95% CI: 0.584–0.772, P < 0.001) were protective factors, whereas interocular acuity difference [IAD] (OR = 6.906, 95% CI: 3.133–16.01, P < 0.001), mean LogMAR acuity (OR = 11.491, 95% CI: 6.065–22.153, P < 0.001), mean cylindrical error [CYLmean] (OR = 1.201, 95% CI: 1.055–1.365, P = 0.005), and anisometropia (OR = 1.452, 95% CI: 1.202–1.760, P < 0.001) were risk factors for subnormal stereopsis. Conclusion Ocular factors, including higher IAD, worse acuity, greater astigmatism, and greater anisometropia, were identified as risk factors for subnormal stereoacuity, highlighting the importance and urgency of early screening for stereoacuity and ocular risk factors in children aged 3–7 years in Guangxi.
... Several other studies showed similar results, which are in keeping with our results. [6][7][8][9][10][11] In the current study, we used 3 stereotests to measure stereoacuity. There were statistically significant differences in the stereoacuity measured by different tests. ...
... When foveal fusion fails to correct aniseikonia, patients suffer from altered binocular vision and decreased stereoacuity. [6][7][8][9][10][11][12] The defocused image from the amblyopic eye is usually suppressed, 6,13,14 and the severity of amblyopia directly correlates with the magnitude of anisometropia. 6 Anisometropic amblyopia is frequently associated with sensory strabismus and diplopia that increase the depth of amblyopia and further interfere with education, sports, self-esteem, and future career choice. ...
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Purpose: To evaluate long-term safety, effectiveness, and stability of unilateral LASIK in pediatric myopic anisometropic amblyopia. Methods: This retrospective study included children who received unilateral LASIK for myopic anisometropia of >6 D, after mandatory 6-month occlusion/penalization therapy. They were evaluated at 6 months, 1 year, 2 years and biannually until 10 years. Outcome measures included visual acuity, refraction, ocular alignment, stereopsis, corneal clarity, and corneal topography. Results: 32 patients (16 girls) with mean age of 8.6 ± 2.3 years completed 10 years of follow up after unilateral LASIK. Mean preoperative spherical equivalent refraction (SER) was -10.3D ±2.0D in the affected eye, with anisometropic difference of -9.5D ±1.7D. Mean post-LASIK SER was -1.3D±0.8D (p<0.001). Anisometropia significantly decreased to 0.3D±0.8D, 0.4D±1.0D, and 1.0±2.5D at 6 months, 1 year and 10 years respectively (p<0.001). 11 patients (34%) who had preoperative intermittent exotropia (< 15°) regained orthophoria in all gazes, while 5 of 10 who had constant exotropia with large angle (>30°) required strabismus surgery for ocular alignment. BCVA improved from 0.04±0.6 Decimal at baseline to 0.6 ±0.2 after LASIK and occlusion therapy (p< 0.001). Despite insignificant refractive regression in both eyes, patients have maintained orthophoria, improved stereopsis, clear cornea, and the topography showed no evidence of post-LASIK ectasia. Conclusion: LASIK appears safe, effective, and stable for correcting refractory pediatric myopic anisometropia, in which conventional measures fail or endanger normal visual development. Eliminating anisometropic aniseikonia consequently restores binocular vision and stereopsis which, along with amblyopia therapy, would reverse amblyopia and prevent recurrence.
... For example, patients with anisometropic amblyopia are more likely to have measurable stereopsis when compared to strabismic amblyopia [51,71]. It is important to note that patients with no measurable stereopsis may still have some degree of sensory fusion, which can be assessed using the Worth 4 Dot test [72,73]. Complete sensory suppression of the amblyopic eye is more likely in individuals with strabismus of large magnitude, which prevents motor fusion, and thus, sensory fusion is precluded. ...
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Vision provides a key sensory input for the performance of fine motor skills, which are fundamentally important to daily life activities, as well as skilled occupational and recreational performance. Binocular visual function is a crucial aspect of vision that requires the ability to combine inputs from both eyes into a unified percept. Summation and fusion are two aspects of binocular processing associated with performance advantages, including more efficient visuomotor control of upper limb movements. This paper uses the multiple processes model of limb control to explore how binocular viewing could facilitate the planning and execution of prehension movements in adults and typically developing children. Insight into the contribution of binocularity to visuomotor control also comes from examining motor performance in individuals with amblyopia, a condition characterized by reduced visual acuity and poor binocular function. Overall, research in this field has advanced our understanding of the role of binocular vision in the development and performance of visuomotor skills, the first step towards developing assessment tools and targeted rehabilitation for children with neurodevelopment disorders at risk of poor visuomotor outcomes. This article is part of a discussion meeting issue ‘New approaches to 3D vision’.
Article
Degradation and instability of depth perception that occurs when the retinal image mismatch of left and right eyes, including size difference and vertical disparity, can be improved by coordinating depths specified by motion parallax and binocular stereopsis. Even if the depths specified by motion parallax and binocular disparity do not completely match, the degradation and instability of depth perception can be improved by matching the directions of the depths by motion parallax and binocular disparity up to a certain difference. This finding contributes to improved depth perception in 3D display applications that use binocular disparity.
Chapter
Amblyopia is a leading cause of visual loss both in children and adults. Early recognition and timely appropriate management are the key issues both for prevention and treatment. Those who practice anterior or posterior segment surgery in pediatric age group should be familiar with the effect of amblyopia both pre and post operatively. The basics of management are first to eliminate the amblyogenic factor and then to enforce the use of the amblyopic eye. The current treatment methods as well as the promising new treatment options are discussed throughout this chapter.KeywordsAmblyopiaRefractive amblyopiaDeprivational amblyopiaOrganic amblyopiaStrabismic amblyopiaDynamic retinoscopyOcclusionPenalizationDichoptic treatmentLiquid crystal glasses
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Objective To investigate anisometropia's prevalence and associated factors in school-aged children. Methods A cross-sectional school-based study was conducted in Shandong Province, China, including children aged 4 to 17 from 9 schools. Anisometropia was defined as the differences between the two eyes in spherical equivalent (SE) or cylinder degree of 1.00 diopter (D) or more [SE or cylindrical (CYL) difference ≥ 1.00 D] after cycloplegic autorefraction. The Generalized Linear Model (GLM) was used to analyze the effects of ocular parameters [the differences between eyes in axial length (AL), habitual visual acuity (HVA), and corneal astigmatism (CA)] and lifestyle parameters (time spent indoor near work and outdoor activities) on anisometropia. Results Total 4,198 (93.4%) of the 4,494 children were included in the statistical analysis. The mean difference in inter-eye SE was 0.42 ± 0.61 D. The prevalence of anisometropia was 13.2% (95%CI: 12.1 to 14.2%) (SE anisometropia's prevalence:10.3%; CYL anisometropia's prevalence: 4.1%), increased with older age (OR = 1.10, P = 0.002), the worse myopic eye (myopia vs. premyopia, OR = 1.87, P = 0.002), the worse hyperopic eye (hyperopia vs. premyopia, OR = 1.77, P = 0.013), larger difference in inter-eye AL (0.1–0.3 vs. ≤ 0.1, OR = 1.67, P = 0.008; >0.3 vs. ≤ 0.1, OR = 28.61, P < 0.001), HVA (>0.2 vs. ≤ 0.2, OR = 3.01, P < 0.001), CA (OR = 6.24, P < 0.001), the worse stereoacuity (>100 vs. ≤ 100, OR = 1.59, P = 0.001), longer indoor near work time per day on weekends (4–8 vs. <4, OR = 1.41, P = 0.038; ≥8 vs. <4, OR = 1.40, P = 0.131), and shorter outdoor activity time per day on weekdays (≥1 vs. <1, OR = 0.75, P = 0.046) in multivariable analysis. In the SE anisometropia group, the difference in inter-eye AL (>0.3 vs. ≤ 0.1, β: 0.556, 95%CI: 0.050 to 1.063), HVA (>0.2 vs. ≤ 0.2, β: 0.511, 95%CI: 0.312 to 0.710), and CA (β: 0.488, 95%CI: 0.289 to 0.688), stereoacuity (>100 vs. ≤ 100, β: 0.299, 95%CI: 0.110 to 0.488) had a positive impact on the difference in inter-eye SE. Conclusions Ocular parameters and lifestyle parameters are associated with the occurrence of anisometropia in children aged 4 to 17 years, including the difference in inter-eye AL, HVA, CA, stereoacuity, indoor near work time, and outdoor activity time. Preventing myopia and early treating anisometropic amblyopia may be effective ways to reduce the prevalence of anisometropia.
Article
Preschool vision screening programs using visual acuity criteria as the basis for referral are hampered by untestability, overreferral and probable underreferral. Contour-type stereograms have failed as alternatives to visual acuity testing. Random dot stereograms have shown more promise as alternatives or supplements to visual acuity testing. The stereoacuity threshold at which a random dot stereogram achieves an acceptable level of testability among preschool children and yet reliably detects amblyopiogenic conditions such as anisometropic amblyopia is a key issue. For the Random Dot E stereotest, we have found that testability rates for children from 2 to 6 years old drop off sharply at 126 seconds of arc as compared to 168 seconds of arc. A threshold of 168 seconds of arc has an acceptable rate of testability but has not yet been shown to be a reliable level for amblyopia detection. We are currently conducting a randomized clinical trial to determine whether stereoacuity testing at this threshold is a valuable supplement to visual acuity testing in improving testability and referral accuracy.
Article
Some concepts regarding suppression, anomalous correspondence and amblyopia are revised according to the sensorial findings obtainable from esotropic patients directly in casual seeing (with the aid of the striated glasses test) and by grading a sensorial dissociating effect (with the aid of a bar of optical filters). The following points are emphasized: 1. Suppression appears to be minimal in small angle strabismus where diplopia seems mainly to be avoided by an anomalous correspondence mechanism. On the contrary, suppression is the prevalent mechanism in large angle strabismus. 2. The anomalous correspondence mechanism may lead to a weak type of anomalous binocular vision which is easily interrupted by light optical filters or by dissociating tests. 3. The subjective space of patients with anomalous binocular vision resembles that of normal binocular vision in some aspects. 4. The development of amblyopia is interpreted in the light of these new concepts on suppression and anomalous binocular vision. 5. Postoperatively, anomalous correspondence rapidly re-adapts to the smaller angle deviation and may normalize if the deviation is completely eliminated. This is evident only in casual seeing; for a certain time, dissociating tests reveal the preoperative correspondence status. This behaviour of correspondence in casual seeing has led to attempts at normalizing anomalous correspondence by prism therapy. Newly observed sensorio-motorial obstacles, however, have been found to frequently hamper treatment in casual seeing.
Article
+2-00 to +2-75 dioptres of spherical hypermetropia in the more emmetropic of a pair of eyes is significantly associated with esotropia (P less than 0-001) and the presence of amblyopia (P less than 0-01). Anisometropia is not significantly associated with esotropia (P = 0-31) unless there is spherical hypermetropia of +2-00 dioptres or more in the more emmetropic eye (P less than 0-001). Hypermetropic anisometropia of +1-00 DS or +1-00 D.Cyl. is associated with the presence of amblyopia (P less than 0-001). In the absence of esotropia there is also a significant association between the amount of anisometropia and the initial depth of amblyopia (P less than 0-01). The additional presence of esotropia increases the depth of amblyopia further (P less than 0-05) but not the incidence of amblyopia (P greater than 0-30). The level of significance of the association of refractive errors with squint/amblyopia was itself significantly higher (P less than 0-01) than that between a family history of squint or "lazy eye" on the one hand and squint and/or amblyopia on the other hand. 72 +/- 3% of all cases of esotropia and/or amblyopia in this sample of children had a refractive error of +2-00 DS or more spherical hypermetropia in the more emmetropic eye, or +1-00 D. or more spherical or cylindrical anisometropia. Since there is a close association between the refraction and how, when, and whether a child presents with squint and/or amblyopia, it would seem reasonable to reconsider refraction as a basis for screening young children for visual defects.
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A stereoscopic test was developed for the visual screening of preschool children. The TNO test for stereoscopic vision utilized the same principle as the Julesz random-dot stereogram, and provided a simple and unequivocal test criterion understood even by young children. The results of a comprative evaluation of the TNO and Titmus stereoscopic tests proved the TNO test to be the more reliable of the two, particularly in the 2- to 4-year-old age range. Failure to pass this test at the 240 seconds of arc disparity level yielded an excellent screening criterion, as attested by the results of a validation experiment employing 81 patients (2 to 7 years old) with known visual health records. Furthermore, the screening results obtained from 129 preschool children (2 to 5 years old) tested in the classroom by a nonprofessional examiner, suggest that, under these more realistic conditions, the TNO test yields at least 60% less overreferrals than the Titmus test.
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One hundred twenty-four patients with anisometropia of 1 diopter or greater and amblyopia were reviewed as to the type and amount of anisometropia, whether or not they had consulted with an ophthalmologist, visual acuity before and after treatment, and type of treatment. The patient population was divided into five groups according to the type of anisometropia. Eighty-two percent of all patients reached a visual acuity of 20/40 or better. Eighteen percent of all patients reached a visual acuity of 20/20. The best visual acuity obtained was not found to be related to the degree of anisometropia or the age at which treatment was begun. Patients with myopic and compound myopic astigmatism/mixed astigmatism anisometropia had poorer visual outcomes. There was a strong positive correlation between the initial visual acuity and the best visual acuity obtained (P = 0.0001).
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For orthoptists and ophthalmologists, anomalous retinal correspondence (ARC) is a reality and an important finding. But since it has not been found in animals, ARC seems to be unknown to neurophysiologists. Comparing results of different stereotests, e.g., random-dot stereograms and the two-pencil test, provides some insight into different levels of cortical binocular interaction. Patients with orthotropia and normal retinal correspondence (NRC) and even those with anisometropic amblyopia usually pass random-dot stereograms, whereas strabismic patients with ARC, even with microtropia, usually fail. Microtropic patients, however, may pass contour stereograms, and, in large esotropic angles, useful, daily-life binocular stereopsis can be found with the two-pencil test. Random-dot stereopsis suggests that normal binocular interaction must take place in or near area 17, where data processing for small dots occurs before form recognition. Anomalous correspondence most probably has its seat where the retinal topology is not exact, i.e., where the binocular receptive fields are very large and encompass the corpus callosum, such as in area 20 or 21. This new hypothesis may explain the different forms of ARC according to the clinical entities.
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In a hospital population of 1356 children 64 (4.7%) cases of anisometropia (at least 2 diopters in spherical or cylindrical power) were found. After the exclusion of all children with ocular lesions 53 remained. Twenty-seven (42%) of them had strabismus, which seemed to be related to accommodation effort rather than amount of anisometropia. Amblyopia was present in 17 (53%) of the patients with orthotropic anisometropia. Amblyopia increased with the amount of anisometropia. Therapy in the form of spectacle correction and part-time occlusion was successful in 47%. The success rate was related to the age of presentation.
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Appropriate use of base-out prisms may be useful objective test for detecting persistence of normal binocular vision (4-dioptre prism test). By prolonged observation of prismatic correction of an esotropic patient one may infer the presence of an anomalous sensorial status. This can be done when the prismatic correction is compensated for by an increase of the angle of esotropia (prism adaptation test). The increase in the angle of esotropia induced by base-out prisms, here called anomalous movements, is probably related to a type of anomalous movement fusional in nature. When anomalous movements are present, it is important to realise how powerfully they have developed. This may be inferred by determining what amount of prism overcorrection of the esotropic angle the patient is capable of compensating for (progressive prism compensation test). This has important implications for surgery. It has been statistically demonstrated that esotropia with strong anomalous movements tends to respond less effectively to surgery than esotropia without or with weak anomalous movements.
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Traditional screening measures for amblyopia, including visual acuity, the cover test (to detect the frequently associated strabismus), and the 4 diopter prism test have shortcomings when used with 3 to 4 yr old children who are the most important candidates for visual screening. In the present study, a widely used set of stereotests (Titmus Stereo Fly, Circle, and Animal Tests) were administered to 70 patients with known visual dysfunctions to determine if stereopsis testing, in the form of these tests, constituted a feasible alternative as a screening measure. The results indicated that, with the exception of the relatively fine thresholds of the No. 5 (100 arc sec) to No. 9 (40 arc sec) Circle tests these stereotests are not only unreliable in discriminating patients with amblyopia from normals, but may indicate an artifactual stereoscopic capability. Since a previous screening study reported that children in the 3 to 4 yr old range were unable to pass the No. 5 and above Circles targets, it appears that while stereopsis itself may be a pertinent amblyopia screening measure, this particular set of tests is not.