In the past decade, considerable attention has been paid to examination of the impact of amblyopia, and strabismus, upon the lives of the individuals. Although an extensive amount of literature exists regarding amblyopia and its associated visual defects, little is known about the contribution of the amblyopic eye in the habitual viewing condition (i.e. both eyes viewing). The purpose of these studies was to determine whether amblyopes are disadvantaged in the performance of tasks under habitual viewing conditions, highlighting any functional differences which may exist as a consequence of amblyopia. Secondly, the work aimed to investigate whether the amblyopic eye contributes to the habitual performance of these tasks. A simple light detection task, in a dichoptic arrangement based upon blue/yellow stimuli viewed through yellow filters, was used to investigate the above two aims and investigate the degree of interocular suppression in amblyopic participants. Using a 3D motion analysis system performance was assessed for an obstacle crossing task (adaptive gait) and a task of reaching for and grasping of an isolated object and in a 'cluttered' environment. Fine motor skills were assessed in a threading a needle task. On the whole it was found that amblyopes are not disadvantaged under habitual viewing conditions, and in cases where differences were found to exist this appeared to be in tasks requiring speed and accuracy. Consistently across all studies it was found that the amblyopic eye contributed in a positive manner, thus, as in visual normals, two eyes are better than one.

This thesis investigates sensorimotor adaptive mechanisms that maintain the accuracy of goal-directed saccades in amblyopia, a developmental disorder characterized by impairment of spatiotemporal visual processing. Saccadic adaptation was induced by displacing the visual target toward initial fixation during the saccade. Eleven visually normal controls and seven patients with amblyopia were tested binocularly and monocularly with the amblyopic and fellow eye (non-dominant and dominant eye in controls) in three separate sessions. Patients with amblyopia exhibited reduced adaptation of saccadic gain compared to controls when viewing with the amblyopic eye and binocularly. Initiation of saccades was also delayed in patients when viewing with the amblyopic eye. It is proposed that the adaptive ability to modify the initial saccadic motor commands for maintaining short-term saccadic accuracy is impaired in amblyopia due to imprecise error signals. Moreover, this thesis reaffirms the notion that the error signals driving saccadic adaptation are visual in nature.

This thesis investigates sensorimotor adaptive mechanisms that maintain the accuracy of goal-directed saccades in amblyopia, a developmental disorder characterized by impairment of spatiotemporal visual processing. Saccadic adaptation was induced by displacing the visual target toward initial fixation during the saccade. Eleven visually normal controls and seven patients with amblyopia were tested binocularly and monocularly with the amblyopic and fellow eye (non-dominant and dominant eye in controls) in three separate sessions. Patients with amblyopia exhibited reduced adaptation of saccadic gain compared to controls when viewing with the amblyopic eye and binocularly. Initiation of saccades was also delayed in patients when viewing with the amblyopic eye. It is proposed that the adaptive ability to modify the initial saccadic motor commands for maintaining short-term saccadic accuracy is impaired in amblyopia due to imprecise error signals. Moreover, this thesis reaffirms the notion that the error signals driving saccadic adaptation are visual in nature.

In the past decade, considerable attention has been paid to examination of the impact of amblyopia, and strabismus, upon the lives of the individuals. Although an extensive amount of literature exists regarding amblyopia and its associated visual defects, little is known about the contribution of the amblyopic eye in the habitual viewing condition (i.e. both eyes viewing). The purpose of these studies was to determine whether amblyopes are disadvantaged in the performance of tasks under habitual viewing conditions, highlighting any functional differences which may exist as a consequence of amblyopia. Secondly, the work aimed to investigate whether the amblyopic eye contributes to the habitual performance of these tasks. A simple light detection task, in a dichoptic arrangement based upon blue/yellow stimuli viewed through yellow filters, was used to investigate the above two aims and investigate the degree of interocular suppression in amblyopic participants. Using a 3D motion analysis system performance was assessed for an obstacle crossing task (adaptive gait) and a task of reaching for and grasping of an isolated object and in a ¿cluttered¿ environment. Fine motor skills were assessed in a threading a needle task. On the whole it was found that amblyopes are not disadvantaged under habitual viewing conditions, and in cases where differences were found to exist this appeared to be in tasks requiring speed and accuracy. Consistently across all studies it was found that the amblyopic eye contributed in a positive manner, thus, as in visual normals, two eyes are better than one.

No description available.

No / PURPOSE. Amblyopia is a developmental disorder of spatial vision. There is evidence to suggest that some amblyopes misperceive spatial structure when viewing with the affected eye. However, there are few examples of these perceptual errors in the literature. This study was an investigation of the prevalence and nature of misperceptions in human amblyopia. METHODS. Thirty amblyopes with strabismus and/or anisometropia participated in the study. Subjects viewed sinusoidal gratings of various spatial frequencies, orientations, and contrasts. After interocular comparison, subjects sketched the subjective appearance of those stimuli that had nonveridical appearances. RESULTS. Nonveridical visual perception was revealed in 20 amblyopes (~67%). In some subjects, misperceptions were present despite the absence of a deficit in contrast sensitivity. The presence of distortions was not simply linked to the depth of amblyopia, and anisometropes were affected as well as those with strabismus. In most cases, these spatial distortions arose at spatial frequencies far below the contrast detection acuity cutoff. Errors in perception became more severe at higher spatial frequencies, with low spatial frequencies being mostly perceived veridically. The prevalence and severity of misperceptions were frequently found to depend on the orientation of the grating used in the test, with horizontal orientations typically less affected than other orientations. Contrast had a much smaller effect on misperceptions, although there were cases in which severity was greater at higher contrasts. CONCLUSIONS. Many types of misperceptions documented in the present study have appeared in previous investigations. This suggests that the wide range of distortions previously reported reflect genuine intersubject differences. It is proposed that nonveridical perception in human amblyopia has its origins in errors in the neural coding of orientation in primary visual cortex.

No / Amblyopia results in a severe loss of positional information and in the ability to accurately enumerate objects (V. Sharma, D. M. Levi, & S. A. Klein, 2000). In this study, we asked whether amblyopia also disrupts the ability to track a near-threshold change in the trajectory of a single target amongst multiple similar potential targets. In the first experiment, we examined the precision for detecting a deviation in the linear motion trajectory of a dot by measuring deviation thresholds as a function of the number of moving trajectories (T). As in normal observers, we found that in both eyes of amblyopes, threshold increases steeply as T increases from 1 to 4. Surprisingly, for T = 1-4, thresholds were essentially identical in both eyes of the amblyopes and were similar to those of normal observers. In a second experiment, we measured the precision for detecting a deviation in the orientation of a static, bilinear "trajectory" by again measuring deviation thresholds (i.e., angle discrimination) as a function of the number of oriented line "trajectories" (T). Relative to the nonamblyopic eye, amblyopes show a marked threshold elevation for a static target when T = 1. However, thresholds increased with T with approximately the same slope as in their preferred eye and in the eyes of the normal controls. We conclude that while amblyopia disrupts static angle discrimination, amblyopic dynamic deviation detection thresholds are normal or very nearly so.

Amblyopia is the leading cause of monocular visual impairment in children. Therapy for amblyopia is extremely beneficial in some children but ineffective in others. It is critical that the reasons for this discrepancy are understood. Emerging evidence indicates that current clinical protocols for the diagnosis of amblyopia may not be sufficiently sensitive in identifying individuals who, on more detailed examination, exhibit subtle structural defects of the eye. Presently, the magnitude of this problem is unknown. The aim of this study was to establish the prevalence of subtle retinal/optic nerve head defects in eyes diagnosed with amblyopia, to distinguish between possible explanations for the origin of such defects and to investigate the relationship between quantitative measures of retinal structure, retinal nerve fibre layer thickness and optic nerve head dimensions. Using the imaging technique of Optical Coherence Tomography (OCT) retinal structure has been investigated in detail, following the visual pathway across the retina from the fovea, via the paramacular bundle to the optic disc, where peripapillary retinal nerve fibre thickness has been imaged and subjected to detailed measures along with optic disc size and shape. The study formed two phases, the first imaging the eyes of visually normal adults and children, comparing them to amblyopes, both adults and children who had completed their treatment. The second phase, a longitudinal study, investigated retinal structure of amblyopic children undertaking occlusion therapy for the first time. By relating pre-therapy quantitative measures to the visual outcome the second phase of the study aimed to examine whether OCT imaging could identify children achieving a poor final outcome. The results show a clear picture of inter-ocular symmetry structure in all individuals, visually normal and amblyopic. Optic disc characteristics revealed no structural abnormalities in amblyopes, in any of the measured parameters, nor was there any association between the level of visual acuity and the measured structure. At the fovea differences were shown to occur in the presence of amblyopia, with thickening of the fovea and reduction of the foveal pit depth. The structural changes were found to be both bilateral and symmetrical with the fellow eye also affected. In the longitudinal phase of the study these changes were demonstrated to a greater extent in children who 'failed' to respond to treatment. This bilateral, symmetrical structural change found at the fovea, which has not been previously reported, cannot therefore be the primary cause of the visual loss which has been diagnosed as amblyopia.

Bakgrund: Amblyopi är en synnedsättning som uppkommer under de första levnadsåren och orsakas av bristande stimulans eller hämning av celler i synbarken. Följsamhet till behandlingen är viktig hos barn med amblyopi för att kunna utveckla en optimal synskärpa. En dålig följsamhet kan leda till bestående synnedsättning, ökat lidande och minskad livskvalitet. Följsamhet kan kopplas till de tre engelska termerna compliance, adherence och concordance, som definieras på olika sätt. 
 Syfte: Syftet med studien var att ur ortoptistens perspektiv belysa vad som är av betydelse för följsamhet vid behandling av barn med amblyopi.
 Metod: Data samlades in genom nio intervjuer med verksamma ortoptister. Databearbetning genomfördes med hjälp av kvalitativ innehållsanalys. 
 Resultat: I resultatet framträder fyra områden som påverkar följsamheten. Barnets förutsättningar, hur behandlingen hanteras, kommunikation och behandlingens utformning, resultat och påverkan i vardagen upplevs av ortoptisterna som faktorer som både främjar och försvårar följsamheten. Mycket av resultatet stämmer överens med tidigare forskning, men att ortoptisterna upplever att familjekonstellation och bemötande har betydelse för följsamhet är nytt.
 Slutsats: Vid amblyopibehandling hos barn är det nödvändigt att ortoptisten har kunskap om och förståelse för vad som har betydelse för följsamhet. Med denna kunskap kan ortoptisten på flera områden verka för ett bättre behandlingsresultat där barnet uppnår optimal synskärpa. Ortoptistens syn på följsamhet påverkar på vilket sätt som hen får ansvar för barnets följsamhet.

Introdução: Ambliopia é uma alteração neurológica cortical causada por experiência visual anormal durante o período crítico do desenvolvimento visual. Trabalhos recentes vêm demonstrando que além das conhecidas alterações visuais classicamente descritas na ambliopia, como a acuidade visual, inúmeras funções perceptuais da visão (locais e globais) estão afetadas. Objetivo: Analisar e comparar o impacto de diferentes tipos de ambliopia no processamento visual de cor e sensibilidade ao contraste (SC). Material e métodos: Foram estudados 42 indivíduos amblíopes de 7-40 anos (estrabismo n=16, anisometropia n=18 e de causa mista n=8) e 33 controles pareados por idade. Testou-se a visão de cores pela medida de limiar de cromaticidade para os eixos protan, deutan e tritan com o Cambridge Color Test (CCT-v.02), a sensibilidade ao contraste (SC) espacial de luminância de primeira ordem para as frequências espaciais 0,4; 1,6; 3,2; 6,4; 12,8 cpg, segunda ordem para as frequências 0,4; 1,6; 3,2; 6,4 cpg e contraste radial para as frequências espaciais 0,4; 1,6; 3,2; 6,4; 12,8 cpg com o sistema Psyknematix (v.1.4.3. Kybervision Consulting R&D). Resultados: Não houve alteração na discriminação de cores em amblíopes; mas redução de sensibilidade ao contraste para estímulo linear de primeira ordem para a frequência espacial 0,4 cpg (F= 3,24, p= 0,027) nos olhos dominantes dos amblíopes estrábicos e 12,8 cpg (F= 6,71, p= 0,002) nos olhos não dominantes de indivíduos amblíopes por anisometropia e de causa mista; redução da SC de segunda ordem para a frequência espacial 6,4 cpg (F =5,30, p= 0,002) nos olhos não dominantes dos amblíopes anisométropes e mista e redução de SC radial para a frequência espacial 1,6cpg (F= 3,79; p= 0,014), 3,2cpg (F= 2,84; p= 0,044), 6,4cpg (F= 5,19; p= 0,003) e 12,8 cpg (F= 9,80; p< 0,001) nos olhos não dominantes do grupo de ambliopia mista e para a frequência espacial 12,8cpg para todos os grupos de ambliopia em relação aos controles. Conclusão: Não há impacto na discriminação de cores para nenhum tipo de ambliopia. Existem diferentes impactos para a sensibilidade ao contraste de distintos níveis de complexidade entre diferentes tipos de ambliopia, e o tipo mista apresenta pior desempenho para todas as funções, desde as mais elementares às mais complexas / Introduction: Amblyopia is a cortical neural disfunction caused by abnormal visual experience during critical period of visual development. Recent work has shown that beyond deficits on visual acuity many other perceptual visual functions (local and global) are affected. Purpose: To analyze and compare the impact of different types of amblyopia on visual processing of color vision and contrast sensitivity. Methods: We studied 42 amblyopes aged 7-40 years (strabismus n=16, anisometropia n=18 and mixed n=8 ) and 33 age-matched controls. We tested color vision by chromaticity threshold measurement for protan, deutan and tritan axes with Cambridge Color Test (CCT-v.2.0) and spatial contrast sensitivity of luminance (SC) of first order for spatial frequencies (sf) 0.4; 1.6; 3.2; 6.4; 12.8 cpd; second order for frequencies 0.4; 1.6; 3.2; 6.4 cpd and radial contrast for frequencies 0.4; 1.6; 3.2; 6.4; 12.8 cpd with Psyknematix System (v.1.4.3. Kybervision Consulting R&D). Results: Our results demonstrate no alterations on colour discrimination in amblyopes. Decrease of contrast sensitivity for first order stimuli for frequency 0.4 cpd (F = 3.24, p = 0.027) in dominant eyes of strabismic amblyopia and for 12.8 cpd (F = 6.71, p = 0.002) in nondominant eyes of amblyopic individuals with anisometropia and mixed cause; decrease of CS for second order stimuli for 12,8 cpd (F = 5.30, p = 0.002) in nondominant eyes of anisomotropic and mixed amblyopia and decrease of radial SC for frequency 1.6cpd (F = 3.79 , p = 0.014), 3.2cpd (F = 2.84, p = 0.044), 6.4cpd (F = 5.19, p = 0.003) and 12.8 cpd (F = 9.80, p <0.001 ) in non-dominant eyes of mixed amblyopia and for frequency 12.8 cpd for all amblyopia groups compared to control. Conclusion: There is no impact in color discrimination of any group of amblyopia. There are different impacts between types of amblyopia on contrast sensitivity of different levels of complexity. Mixed type presents the worst performance for all functions from the most elementary to the most complex stimuli