Optometry and Vision Sciences - Theses
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ItemVisual search and visual performance in infantile nystagmus syndrome( 2020)Abstract Infantile nystagmus syndrome (INS) is an involuntary ocular motor oscillation, which presents at or near birth and persists throughout life. The nystagmus intensity and visual acuity in INS may vary with gaze angle. The gaze with minimal nystagmus intensity and better visual performance is known as the null position. Nearly all the research on INS focused on visual acuity and the time needed to get the eyes onto the desired target (i.e., target acquisition time). In daily routines, we are constantly presented with search tasks that require us to find a target among distracters or tracking tasks where we need to identify moving objects and to estimate their speed of motion. These real-life visual activities entail complex visual functions, such as visual search and motion perception. However, research on INS and these visual functions is limited. Thus, this study aims to investigate how individuals with INS perform, compared with controls, when carrying out visual search tasks and motion perception tasks. Particularly, the study also aims to assess how the null position affects their visual performance. For visual search, two search conditions were presented: conjunction search and feature search. Search time and accuracy were used to assess visual search performance. For motion perception, three tasks were performed: coherent motion, velocity discrimination, and biological motion. Motion coherence thresholds, discrimination thresholds, and accuracy were measured for the three tasks, respectively. In visual search tasks, INS subjects showed poorer search performance, with longer search times compared to controls in both conjunction and feature search. No difference in accuracy between INS and control subjects was found. The null position did not affect the visual search performance in INS. In coherent motion and velocity discrimination tasks, INS subjects showed poorer performance, with elevated motion coherence and discrimination thresholds compared with controls. A positive null position effect was found only in velocity discrimination. In the biological motion task, no difference in accuracy between INS subjects and controls was found. In summary, visual search, coherent motion, and velocity discrimination were impaired in INS subjects, with the null position having a positive effect in velocity discrimination. However, biological motion perception was not affected by INS. Findings from this study could assist us in understanding of how INS actually affects the daily activities of patients, and aid us in developing new clinical visual function assessment for INS.