No description available.

No description available.

No description available.

No description available.

Accommodation and vergence, the two important oculomotor systems, exhibit the property of adapation which maintains the response for comfortable prolonged viewing. Several mathematical models have been developed to describe the basic underlying mechanism of accommodation and vergence. Currently used models contradict with each other in the placement of critical elements in the model. This thesis addressed this controversy and empirically verified these models. The effect of vergence adaptation and its influence on certain critical oculomotor parameters have been evaluated in two studies. The specific aims, methods, results and conclusions of each chapter are as follows: Chapter 3 Aim To evaluate the effect of vergence adaptation on convergence accommodation (CA) response and the effect of CA stimulation on accommodative adaptation to determine the model that best fits human accommodation and vergence interaction. Methods This study investigated the effect of vergence adaptation on the convergence accommodation (CA) response as a function of vergence stimulus magnitude and duration in 10 emmetropes. Convergence was induced using no prism, 6, and 12 prism dioptres as stimuli at 0.4m, viewed for 5, 10 & 15 minutes of duration in randomized separate sessions. Phoria measures and CA responses were recorded at the baseline, immediately following prism insertion and following specific durations of viewing through the prism (post-task). Also the effect of CA cross-link on the tonic accommodation (TA) adaptation was investigated where TA response was measured before and after the convergence task. Results & conclusions Repeated measures of ANOVA showed no significant (p > 0.05) phoria adaptation or CA response change with no prism as the stimulus. For 6 and 12 prism dioptres, there were significant reductions (p< 0.01) in CA with phoria adaptation. No significant (p>0.05) phoria adaptation or reduction in the CA response between 5, 10 and 15 minutes of viewing showing no effect of duration. No significant difference (p = 0.85) between the pre and post task TA response while vergence was adapted. The results of the study show that vergence adaptation reduces CA response supporting models which predict the CA crosslink to reduce its output as tonic vergence adaptation progresses. However the convergence accommodation does not appear to lead to increased output of tonic accommodation. Chapter 4 Aim The purpose of this study was to evaluate certain critical parameters of vergence and accommodation under vergence adaptation (induced with a BO Δ), before and after positive fusional vergence training. Methods Eleven emmetropes with normal binocular vision participated in the study. Distance & near phoria, AC/A & CA/C ratios, & positive fusional amplitude at near were evaluated before and after two weeks of positive fusional vergence training. Phoria adaptation and CA responses were monitored every 3 minutes for 15 minutes while the subjects viewed through 12Δ BO under open-looped accommodation at 0.4m before and after training. On a separate vergence adaptation session (before training), phoria adaptation was induced under dual closed-loop condition using 12Δ BO at 0.4m. Cross-link ratios, BO fusional amplitude at 0.4m and near phoria were measured following 15 minutes of prism adaptation. Subjects underwent 2 weeks of positive fusional vergence training using variable tranaglyphs and aperture rule at 0.4m. Phoria adaptation and CA responses monitored over time were exponentially fit and were compared before and after training. AC/A & CA/ C ratios and BO to blur value at 0.4m taken before training, under the vergence adapted state and after training were analyzed using repeated measures ANOVA. Results & conclusions No significant difference (p > 0.05) in the cross-link ratios were found before and after training. However, there was a significant (p < 0.01) increase and decrease in the AC/A and CA/C ratios respectively under the vergence adapted state. BO to blur value at 0.4m was significantly increased (p < 0.01) from the pre training value under both vergence adapted condition and following training. Rate constants and magnitudes of phoria adaptation and CA response reduction were significantly (p < 0.01) different following training demonstrating robust and greater magnitude of vergence adaptation in the BO direction reducing the CA response faster. However, this improved vergence adaptability is not reflected in the static measures of AC/A and CA/C ratios. The increased BO to blur value following training is caused by the increased speed of prism adaptation reducing the CA response during BO fusional amplitude testing.

Accommodation and vergence, the two important oculomotor systems, exhibit the property of adapation which maintains the response for comfortable prolonged viewing. Several mathematical models have been developed to describe the basic underlying mechanism of accommodation and vergence. Currently used models contradict with each other in the placement of critical elements in the model. This thesis addressed this controversy and empirically verified these models. The effect of vergence adaptation and its influence on certain critical oculomotor parameters have been evaluated in two studies. The specific aims, methods, results and conclusions of each chapter are as follows: Chapter 3 Aim To evaluate the effect of vergence adaptation on convergence accommodation (CA) response and the effect of CA stimulation on accommodative adaptation to determine the model that best fits human accommodation and vergence interaction. Methods This study investigated the effect of vergence adaptation on the convergence accommodation (CA) response as a function of vergence stimulus magnitude and duration in 10 emmetropes. Convergence was induced using no prism, 6, and 12 prism dioptres as stimuli at 0.4m, viewed for 5, 10 & 15 minutes of duration in randomized separate sessions. Phoria measures and CA responses were recorded at the baseline, immediately following prism insertion and following specific durations of viewing through the prism (post-task). Also the effect of CA cross-link on the tonic accommodation (TA) adaptation was investigated where TA response was measured before and after the convergence task. Results & conclusions Repeated measures of ANOVA showed no significant (p > 0.05) phoria adaptation or CA response change with no prism as the stimulus. For 6 and 12 prism dioptres, there were significant reductions (p< 0.01) in CA with phoria adaptation. No significant (p>0.05) phoria adaptation or reduction in the CA response between 5, 10 and 15 minutes of viewing showing no effect of duration. No significant difference (p = 0.85) between the pre and post task TA response while vergence was adapted. The results of the study show that vergence adaptation reduces CA response supporting models which predict the CA crosslink to reduce its output as tonic vergence adaptation progresses. However the convergence accommodation does not appear to lead to increased output of tonic accommodation. Chapter 4 Aim The purpose of this study was to evaluate certain critical parameters of vergence and accommodation under vergence adaptation (induced with a BO Δ), before and after positive fusional vergence training. Methods Eleven emmetropes with normal binocular vision participated in the study. Distance & near phoria, AC/A & CA/C ratios, & positive fusional amplitude at near were evaluated before and after two weeks of positive fusional vergence training. Phoria adaptation and CA responses were monitored every 3 minutes for 15 minutes while the subjects viewed through 12Δ BO under open-looped accommodation at 0.4m before and after training. On a separate vergence adaptation session (before training), phoria adaptation was induced under dual closed-loop condition using 12Δ BO at 0.4m. Cross-link ratios, BO fusional amplitude at 0.4m and near phoria were measured following 15 minutes of prism adaptation. Subjects underwent 2 weeks of positive fusional vergence training using variable tranaglyphs and aperture rule at 0.4m. Phoria adaptation and CA responses monitored over time were exponentially fit and were compared before and after training. AC/A & CA/ C ratios and BO to blur value at 0.4m taken before training, under the vergence adapted state and after training were analyzed using repeated measures ANOVA. Results & conclusions No significant difference (p > 0.05) in the cross-link ratios were found before and after training. However, there was a significant (p < 0.01) increase and decrease in the AC/A and CA/C ratios respectively under the vergence adapted state. BO to blur value at 0.4m was significantly increased (p < 0.01) from the pre training value under both vergence adapted condition and following training. Rate constants and magnitudes of phoria adaptation and CA response reduction were significantly (p < 0.01) different following training demonstrating robust and greater magnitude of vergence adaptation in the BO direction reducing the CA response faster. However, this improved vergence adaptability is not reflected in the static measures of AC/A and CA/C ratios. The increased BO to blur value following training is caused by the increased speed of prism adaptation reducing the CA response during BO fusional amplitude testing.

No description available.

No description available.

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Accommodation and vergence are two interacting ocular motor systems that function to maintain clear and single vision across a wide range of distances. Sustained fixation results in the adaptation of these ocular motor systems and has been widely investigated in adults but not in children. Moreover, limited reports have measured adaptation to disparities induced by ophthalmic lenses. This thesis used near addition lenses as a means to investigate binocular adaptation in children. The specific aims of this thesis were three-fold. First, the thesis aimed to gain insight into the mechanism of changes to accommodation and vergence during binocular adaptation in children. The second objective was to determine the role of vergence-bias category (eso/exo/normals) on adaptation. Lastly, this thesis evaluated the influence of myopia on binocular adaptation. Thirty- eight myopic and 38 emmetropic children between 7-14 years of age were examined for the purpose of this thesis. A series of studies were performed to evaluate adaptation using varying demands for accommodation and vergence, stimulated by binocular fixation at near (33 cm), through the addition of +2D and -2D over corrective lenses (closed loop accommodation) and using 10 base-out prisms (open-loop accommodation at 4M). In each closed-loop condition, measures of binocular and monocular accommodation (PowerRefractor, Multichannel systems) and near phoria (modified Thorington technique) were recorded at frequent intervals when children binocularly fixated a high contrast near target (33 cm) for 20 min. For the open-loop condition (obtained using 0.5 mm pinhole pupils), binocular accommodation and tonic vergence (distance heterophoria through pinhole pupils) were determined at frequent intervals when binocular fixation was sustained at 4M for 20 min. For all conditions, tonic accommodation was measured before and after the near task to measure accommodative adaptation. The results of this thesis make three major contributions to the literature. First, it outlines that the addition of +2D and -2D lenses alters both accommodation and near phoria during sustained binocular fixation, which can be explained based on the models of accommodation and vergence. Second, it shows that the direction of phoria influences the pattern of binocular vs. monocular accommodation in closed-loop conditions and alters the degree of vergence adaptation in both closed and open-loop accommodation. These changes have been primarily attributed to the varying demands on fusional vergence. Lastly, this thesis demonstrates that myopic children show reduced vergence adaptation when fusional convergence was initiated through plus adds or base-out prisms but not when fusional divergence was initiated through minus addition lenses. Further, myopic children also showed variations in other ocular motor parameters such as higher accommodative lags, greater variability of accommodative response, larger accommodative after-effects, and higher AV/A ratios compared to emmetropes. Consistent with the models of accommodation and vergence, the thesis highlights that it is necessary to measure changes to both accommodation and vergence when evaluating the response of the ocular motor system. The direction of phoria and type of refractive error play a significant role in determining binocular adaptation in children. Future studies should differentiate these parameters when evaluating adaptation of the ocular motor system.