Purpose: To examine the relationship between visual acuity (VA) and radial deformation acuity (RDA) in children 6 to 12 years of age with amblyopia. Methods: RDA was measured in 35 participants with the Manchester RDA charts. VA was measured with the Early Treatment Diabetic Retinopathy Research Study (ETDRS) chart. Results: Median VA in non-amblyopic and amblyopic eyes was 0.04 logMAR (IQF -0.06 – 0.12) and 0.24 (IQF 0.12 – 0.04), respectively (Wilcoxon Signed Ranks test, z = -5.07, p < 0.001). Median RDA in non-amblyopic and amblyopic eyes was 2.73 log (IQF 2.53 – 2.87) and 2.63 log (IQF 2.53 – 2.77), respectively (Wilcoxon, z = -2.56, p < 0.05). Spearman correlation suggested that the amblyopic deficits in VA and RDA were related, r = -0.42, p < 0.05. Conclusion: A deficit in RDA was present in most children with amblyopia. A moderate relationship was noted between the amblyopic deficits found in VA and RDA.

Purpose: To test the hypothesis that the fixational stability (FS) of the amblyopic eye (AME) in strabismics will improve when binocular integration is enhanced through ocular alignment and inter-ocular suppression is attenuated by reducing the contrast to the fellow eye (FFE). Methods: 7 strabismic amblyopes (age: 30.8±9.7 yrs) (5 esotropes and 2 exotrope) (VA: AME=0.50±0.30; FFE=-0.12±0.04) showing clinical characteristics of central suppression were recruited. Suppression was then attenuated by a balance point procedure where the contrast to the FFE was reduced in order to maximize binocular integration during a global motion task (GMT) (Baker, 2007). In one case the balance point could not be determined, and the participant was excluded. Ocular alignment was established with a haploscope. Participants dichoptically viewed similar targets [a cross (2.3°) surrounded by a square (11.3°) visual angle] set at 40cm. Target contrasts presented to each eye were either equal (EQ) or attenuated in the FFE (UNEQ) by an amount defined by the GMT. FS was measured over a 5 min period (Viewpoint® Eye Tracker, Arrington Research) and quantified using bivariate contour ellipse areas (BCEA) in four different binocular conditions; unaligned/EQ, unaligned/UNEQ, aligned/EQ and aligned/UNEQ. FS was also measured in 6 control subjects (Age: 25.3±4 yrs; VA: -0.1±0.08). Results: Alignment of the AME was transient and lasting between 30 to 80 seconds. Accordingly, FS was analyzed over the first 30 seconds using repeated measures ANOVA. Post hoc analysis revealed that for the amblyopic subjects, the FS of the AME was significantly improved in aligned/EQ (p=0.015) and aligned/UNEQ (p=0.001). FS of FFE was not different statistically across conditions. BCEA(FFE) & BCEA(AME) were then averaged for each amblyope in the 4 conditions and compared with normals. This averaged BCEA (reduced FS) was significantly greater (p=0.0205) in amblyopes compared to controls except in the case of alignment coupled with reduced suppression (aligned/UNEQ) (p=0.1232). Conclusion: Fixation stability in the amblyopic eye of strabismics appears to improve directly with the degree of binocular integration. The hypothesis is therefore retained.

Diss. Linköping : Univ.

No / Amblyopia is the condition in which reduced visual function exists despite full optical correction and an absence of observable ocular pathology. Investigation of the underlying neurology of this condition began in earnest around 40 years ago with the pioneering studies conducted by Hubel and Wiesel. Their early work on the impact of monocular deprivation and strabismus initiated what is now a rapidly developing field of cortical plasticity research. Although the monocular deprivation paradigm originated by Hubel and Wiesel remains a key experimental manipulation in studies of cortical plasticity, somewhat ironically, the neurology underlying the human conditions of strabismus and amblyopia that motivated this early work remains elusive. In this review, the authors combine contemporary research on plasticity and development with data from human and animal investigations of amblyopic populations to assess what is known and to reexamine some of the key assumptions about human amblyopia.

Yes / Purpose: To compare full-time occlusion (FTO) and part-time occlusion (PTO) therapy in the treatment of amblyopia, with the secondary aim of evaluating the minimum number of hours of part-time patching required for maximal effect from occlusion. Methods: A literature search was performed in PubMed, Scopus, Science Direct, Ovid, Web of Science and Cochrane library. Methodological quality of the literature was evaluated according to the Oxford Center for Evidence Based Medicine and modified Newcastle-Ottawa scale. Statistical analyses were performed using Comprehensive Meta-Analysis (version 2, Biostat Inc., USA). Results: The present meta-analysis included six studies (three randomized controlled trials [RCTs] and three non-RCTs). Pooled standardized difference in the mean changes in the visual acuity was 0.337 [lower and upper limits: 0.009, 0.683] higher in the FTO as compared to the PTO group; however, this difference was not statistically significant (P ¼ 0.056, Cochrane Q value ¼ 20.4 (P ¼ 0.001), I2 ¼ 75.49%). Egger's regression intercept was 5.46 (P ¼ 0.04). The pooled standardized difference in means of visual acuity changes was 1.097 [lower and upper limits: 0.68, 1.513] higher in the FTO arm (P < 0.001), and 0.7 [lower and upper limits: 0.315, 1.085] higher in the PTO arm (P < 0.001) compared to PTO less than two hours. Conclusions: This meta-analysis shows no statistically significant difference between PTO and FTO in treatment of amblyopia. However, our results suggest that the minimum effective PTO duration, to observe maximal improvement in visual acuity is six hours per day.

Yes / Although their eyes are pointing in different directions, people with long-standing strabismic amblyopia typically do not experience double-vision or indeed any visual symptoms arising from their condition. It is generally believed that the phenomenon of suppression plays a major role in dealing with the consequences of amblyopia and strabismus, by preventing images from the weaker/deviating eye from reaching conscious awareness. Suppression is thus a highly sophisticated coping mechanism. Although suppression has been studied for over 100 years the literature is equivocal in relation to the extent of the retina that is suppressed, though the method used to investigate suppression is crucial to the outcome. There is growing evidence that some measurement methods lead to artefactual claims that suppression exists when it does not. Methodology/Results: Here we present the results of an experiment conducted with a new method to examine the prevalence, depth and extent of suppression in ten individuals with strabismic amblyopia. Seven subjects (70%) showed no evidence whatsoever for suppression and in the three individuals who did (30%), the depth and extent of suppression was small. Conclusions: Suppression may play a much smaller role in dealing with the negative consequences of strabismic amblyopia than previously thought. Whereas recent claims of this nature have been made only in those with micro-strabismus our results show extremely limited evidence for suppression across the central visual field in strabismic amblyopes more generally. Instead of suppressing the image from the weaker/deviating eye, we suggest the visual system of individuals with strabismic amblyopia may act to maximise the possibilities for binocular co-operation. This is consistent with recent evidence from strabismic and amblyopic individuals that their binocular mechanisms are intact, and that, just as in visual normals, performance with two eyes is better than with the better eye alone in these individuals.

Yes / Reduced binocularity is a prominent feature of amblyopia and binocular cues are thought to be important for prehension. We examine prehension in individuals with amblyopia when the target-object was flanked, thus mimicking everyday prehension. Methods: amblyopes (n=20, 36.4±11.7 years; 6 anisometropic, 3 strabismic, 11 mixed) and visually-normal controls (n=20, 27.5±6.3 years) reached forward, grasped and lifted a cylindrical target-object that was flanked with objects on either (lateral) side of the target, or in front and behind it in depth. Only 6 amblyopes (30%) had measurable stereoacuity. Trials were completed in binocular and monocular viewing, using the better eye in amblyopic participants. Results: Compared to visual normals, amblyopes displayed a longer overall movement time (p=0.031), lower average reach velocity (p=0.021), smaller maximum aperture (p=0.007) and longer durations between object contact and lift (p=0.003). Differences between groups were more apparent when the flankers were in front and behind, compared to either side, as evidenced by significant group-by-flanker configuration interactions for reach duration (p<0.001), size and timing of maximum aperture (p≤0.009), end-of-reach to object-contact (p<0.001), and between object contact and lift (p=0.044), suggesting that deficits are greatest when binocular cues are richest. Both groups demonstrated a significant binocular advantage, in that in both groups performance was worse for monocular compared to binocular viewing, but interestingly, amblyopic deficits in binocular viewing largely persisted during monocular viewing with the better eye. Conclusions: These results suggest that amblyopes either display considerable residual binocularity or that they have adapted to make good use of their abnormal binocularity.

Diss. (sammanfattning) Linköping : Univ., 2004. / Härtill 4 uppsatser.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vii, 94 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-94).

No / This review aims to disentangle cause and effect in the relationship between anisometropia and amblyopia. Specifically, we examine the literature for evidence to support different possible developmental sequences that could ultimately lead to the presentation of both conditions. The prevalence of anisometropia is around 20% for an inter-ocular difference of 0.5D or greater in spherical equivalent refraction, falling to 2-3%, for an inter-ocular difference of 3D or above. Anisometropia prevalence is relatively high in the weeks following birth, in the teenage years coinciding with the onset of myopia and, most notably, in older adults starting after the onset of presbyopia. It has about one-third the prevalence of bilateral refractive errors of the same magnitude. Importantly, the prevalence of anisometropia is higher in highly ametropic groups, suggesting that emmetropization failures underlying ametropia and anisometropia may be similar. Amblyopia is present in 1-3% of humans and around one-half to two-thirds of amblyopes have anisometropia either alone or in combination with strabismus. The frequent co-existence of amblyopia and anisometropia at a child's first clinical examination promotes the belief that the anisometropia has caused the amblyopia, as has been demonstrated in animal models of the condition. In reviewing the human and monkey literature however it is clear that there are additional paths beyond this classic hypothesis to the co-occurrence of anisometropia and amblyopia. For example, after the emergence of amblyopia secondary to either deprivation or strabismus, anisometropia often follows. In cases of anisometropia with no apparent deprivation or strabismus, questions remain about the failure of the emmetropization mechanism that routinely eliminates infantile anisometropia. Also, the chronology of amblyopia development is poorly documented in cases of 'pure' anisometropic amblyopia. Although indirect, the therapeutic impact of refractive correction on anisometropic amblyopia provides strong support for the hypothesis that the anisometropia caused the amblyopia. Direct evidence for the aetiology of anisometropic amblyopia will require longitudinal tracking of at-risk infants, which poses numerous methodological and ethical challenges. However, if we are to prevent this condition, we must understand the factors that cause it to develop.