The role of optical defocus in regulating refractive development in infant monkeys.
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Early in life, the two eyes of infant primates normally grow in a coordinated manner toward the ideal refractive state. We investigated the extent to which lens-induced changes in the effective focus of the eye affected refractive development in infant rhesus monkeys. The main finding was that spectacle lenses could predictably alter the growth of one or both eyes resulting in appropriate compensating refractive changes in both the hyperopic and myopic directions. Although the effective operating range of the emmetropization process in young monkeys is somewhat limited, the results demonstrate that emmetropization in this higher primate, as in a number of other species, is an active process that is regulated by optical defocus associated with the eye's effective refractive state. (+info)
The therapy of amblyopia: an analysis of the results of amblyopia therapy utilizing the pooled data of published studies.
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CONTEXT: Although the treatment of amblyopia with occlusion has changed little over the past 3 centuries, there is little agreement about which regimes are most effective and for what reasons. OBJECTIVE: To determine the outcome of occlusion therapy in patients with anisometropic, strabismic, and strabismic-anisometropic amblyopia employing the raw data from 961 patients reported in 23 studies published between 1965 and 1994. DESIGN: Analysis of the published literature on amblyopia therapy results during the above interval, utilizing primary data obtained from the authors of these articles or tables published in the articles detailing individual patient outcomes. PARTICIPANTS: 961 amblyopic patients, participants in 23 studies, undergoing patching therapy for amblyopia from 1965 to 1994 with anisometropia, strabismus, or anisometropia-strabismus. MAIN OUTCOMES: In the pooled data set, success of occlusion therapy was defined as visual acuity of 20/40 at the end of treatment. RESULTS: Success by the 20/40 criteria was achieved in 512 of 689 (74.3%) patients. By category, 312 of 402 (77.6%) were successful in strabismic amblyopia, 44 of 75 (58.7%) in strabismic-anisometropic amblyopia, and 72 of 108 (66.7%) in anisometropic amblyopia. Success was not related to the duration of occlusion therapy, type of occlusion used, accompanying refractive error, patient's sex, or eye. Univariate analyses showed that success was related to the age at which therapy was initiated; the type of amblyopia; the depth of visual loss before treatment for the anisometropic patients and the strabismic patients, but not for the anisometropic-strabismic patients; and the difference in spherical equivalents between eyes, for the anisometropic patients. Logistic/linear regression revealed that 3 were independent predictors of a successful outcome of amblyopia therapy. CONCLUSIONS: Factors that appear most closely related to a successful outcome are age, type of amblyopia, and depth of visual loss before treatment. These may be related to factors, as yet undetermined in the pathogenesis of amblyopia. With present emphasis on the value of screening and prevention and the development of new screening tools, such a look at the results of amblyopia therapy in a large population seems indicated. (+info)
Amblyopia and visual acuity in children with Down's syndrome.
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BACKGROUND/AIMS: Amblyopia in people with Down's syndrome has not been well investigated. This study was designed to determine the prevalence and associated conditions of amblyopia in a group of home reared children with Down's syndrome. METHODS: All children in the study group underwent an evaluation of visual acuity. In addition, previous ophthalmological records were reviewed, and a subgroup of children was examined. For the purposes of this study, amblyopia was defined quantitatively as a difference of two Snellen acuity lines between eyes or if unilateral central steady maintained (CSM) vision and a clear fixation preference was observed. A high refractive error was defined as a spherical equivalent more than 3 dioptres and astigmatism more than 1.75 dioptres. Anisometropia was defined as a difference of at least 1.5 dioptres of sphere and/or 1.0 dioptre of cylinder between eyes. 68 children with Down's syndrome between the ages of 5 and 19 years were enrolled in the final study group. RESULTS: Amblyopia was observed in 15 (22%) of 68 patients. An additional 16 (24%) patients had bilateral vision less than 20/50. Strabismus, high refractive errors, and anisometropia were the conditions most commonly associated with decreased vision and amblyopia CONCLUSION: This study suggests that the prevalence of amblyopia is higher than previously reported. Fully 46% of these children with Down's syndrome had evidence of substantial visual deficits. These patients may be at higher risk for visual impairment and should be carefully examined for ophthalmological problems. (+info)
The association between anisometropia, amblyopia, and binocularity in the absence of strabismus.
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PURPOSE: First, to determine if thresholds exist for the development of amblyopia and subnormal binocularity with various types of anisometropia and to confirm or refute existing guidelines for its treatment or observation. Second, to delineate any association between the degree or type of anisometropia and the depth of amblyopia and severity of binocular sensory abnormalities. METHODS: Four hundred eleven (411) patients with various levels of anisometropia, no previous therapy, and no other ocular pathology were evaluated. The effect of anisometropia (both corrected and uncorrected) on monocular acuity and binocular function was examined. RESULTS: Spherical myopic anisometropia (SMA) of > 2 diopters (D) or spherical hypermetropic anisometropia (SHA) of > 1 D results in a statistically significant increase in the incidence of amblyopia and decrease in binocular function when compared to non anisometropic patients. Increasing levels of SMA and SHA beyond these thresholds were also associated with increasing depth (and in the case of SHA, incidence as well) of amblyopia. Cylindrical myopic anisometropia (CMA) or cylindrical hyperopic anisometropia (CHA) of > 1.5 D results in a statistically significant increase in amblyopia and decrease in binocular function. A clinically significant increase in amblyopia occurs with > 1 D of CMA or CHA. Increasing levels of CMA and CHA beyond > 1 D were also associated with an increased incidence (and in the case of SMA, depth as well) of amblyopia. CONCLUSIONS: This study provides guidelines for the treatment or observation of anisometropia and confirms and characterizes the association between the type and degree of anisometropia and the incidence and severity of amblyopia and subnormal binocularity. (+info)
Factors limiting contrast sensitivity in experimentally amblyopic macaque monkeys.
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Contrast detection is impaired in amblyopes. To understand the contrast processing deficit in amblyopia, we studied the effects of masking noise on contrast threshold in amblyopic macaque monkeys. Amblyopia developed as a result of either experimentally induced strabismus or anisometropia. We used random spatiotemporal broadband noise of varying contrast power to mask the detection of sinusoidal grating patches. We compared masking in the amblyopic and non-amblyopic eyes. From the masking functions, we calculated equivalent noise contrast (the noise power at which detection threshold was elevated by square root of 2) and signal-to-noise ratio (the ratio of threshold contrast to noise contrast at high noise power). The relation between contrast threshold and masking noise level was similar for amblyopic and non-amblyopic eyes. Although in most cases there was some elevation in equivalent noise for amblyopic compared to fellow eyes, signal-to-noise ratio showed greater variation with the extent of amblyopia. These results support the idea that the contrast detection deficit in amblyopia is a cortical deficit. (+info)
Outcome in refractive accommodative esotropia.
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AIM: To examine outcome among children with refractive accommodative esotropia. METHODS: Children with accommodative esotropia associated with hyperopia were included in the study. The features studied were ocular alignment, amblyopia, and the response to treatment, binocular single vision, requirement for surgery, and the change in refraction with age. RESULTS: 103 children with refractive accommodative esotropia were identified. Mean follow up was 4.5 years (range 2-9.5 years). 41 children (39.8%) were fully accommodative (no manifest deviation with full hyperopic correction). The remaining 62 children (60.2%) were partially accommodative. At presentation 61.2% of children were amblyopic in one eye decreasing to 15.5% at the most recent examination. Stereopsis was demonstrated in 89.3% of children at the most recent examination. Mean cycloplegic refraction (dioptres, spherical equivalent) remained stable throughout the follow up period. The mean change in refraction per year was 0.005 dioptres (D) in right eyes (95% CL -0. 0098 to 0.02) and 0.001 D in left eyes (95% CL -0.018 to 0.021). No patients were able to discard their glasses and maintain alignment. CONCLUSIONS: Most children with refractive accommodative esotropia have an excellent outcome in terms of visual acuity and binocular single vision. Current management strategies for this condition result in a marked reduction in the prevalence of amblyopia compared with the prevalence at presentation. The degree of hyperopia, however, remains unchanged with poor prospects for discontinuing glasses wear. The possibility that long term full time glasses wear impedes emmetropisation must be considered. It is also conceivable, however, that these children may behave differently with normal and be predestined to remain hyperopic. (+info)
The role of anisometropia in the development of accommodative esotropia.
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PURPOSE: To determine if anisometropia increases the risk for the development of accommodative esotropia in hypermetropia. METHODS: Records of all new patients with a refractive error of > or = +2.00 (mean spherical equivalent [SE] of both eyes) over a 42-month period were reviewed. Three hundred forty-five (345) patients were thus analyzed to determine the effect of anisometropia (> or = 1 diopter [D]) on the relative risk of developing esodeviation and of requiring surgical correction once esodeviation was present (uncontrolled deviation). RESULTS: Anisometropia (> or = 1 D) increased the relative risk of developing accommodative esodeviation to 1.68 (P < .05). Anisometropia (> or = 1 D) increased the relative risk for esodeviation to 7.8 (P < .05) in patients with a mean SE of < 3 D and to 1.49 (P < .05) in patients with SE of > or = 3 D. This difference was significant (P = .016). In patients with esotropia and anisometropia (> or = 1 D), the relative risk for an uncontrolled deviation was 1.72 (P < .05) compared with nonanisometropic esotropic patients. Uncontrolled esodeviation was present in 33% of anisometropic patients versus 0% of nonanisometropic patients with a mean hypermetropic SE of < 3 D (P = .003); however, anisometropia did not increase the relative risk of uncontrolled esotropia in patients with SE of > or = 3 D. Although amblyopia and anisometropia were closely associated, anisometropia increased the relative risk of esodeviation to 2.14 (P < .05) even in the absence of amblyopia. CONCLUSIONS: Anisometropia (> 1 D) is a significant risk factor for the development of accommodative esodeviation, especially in patients with lower overall hypermetropia (< 3 D). Anisometropia also increases the risk that an accommodative esodeviation will not be fully eliminated with hypermetropic correction. (+info)
Contour integration deficits in anisometropic amblyopia.
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PURPOSE: Previous retrospective studies have found that integration of orientation information along contours defined by Gabor patches is abnormal in strabismic, but not in anisometropic, amblyopia. This study was conducted to reexamine the question of whether anisometropic amblyopes have contour integration deficits prospectively in an untreated sample, to isolate the effects of the disease from the effects of prior treatment-factors that may have confounded the results in previous retrospective studies. METHODS: Contour detection thresholds, optotype acuity, and stereoacuity were measured in a group of 19 newly diagnosed anisometropic amblyopes before initiation of occlusion therapy. Contour detection thresholds were measured using a card-based procedure. RESULTS: Significant interocular differences in contour detection thresholds were present in 14 of the 19 patients with anisometropic amblyopia. CONCLUSIONS: Contour integration deficits are a common, but not universal, finding in untreated anisometropic amblyopia. Differences in the prevalence of contour integration deficits between the present study and that of another study may lie in differences in treatment history and/or in the sensitivity of the two different contour integration tasks. (+info)