Visual Abnormalities and Sensory Integration in Infantile Nystagmus

Introduction: Individuals with albinism and IIN demonstrate retinal structural abnormalities. However, there are no consistent functional retinal differences apparent using full-field flash electroretinography (ffERG). This thesis aims to investigate abnormalities in albinism and IIN at: (i) early stages of visual processing (i.e. retinal deficits) using ffERG; (ii) late stages of visual processing, where the brain integrates visual inputs with other sensory to control posture, using Computerized Dynamic Posturography (CDP). Methods: ffERG and OCT were used to measure functional and structural retinal deficits, respectively. Binocular pupil tracker was used to characterise nystagmus to investigate its effect on ffERG responses. CDP was used to evaluate sensory organization during postural control. Results: Patients with IIN had significant smaller a- and b-wave amplitudes under photopic condition compared to healthy controls. However, individuals with albinism were relatively normal. Test-retest showed that ffERG testing is mostly reliability despite nystagmus being present. Photopic a-wave amplitudes were correlated with combined photoreceptor layer thickness and scotopic S.F. b-wave amplitudes were correlated with the inner nuclear layer thickness. Patients with albinism and IIN have relative good overall postural control. However, both groups present lower visual score and higher somatosensory score than controls. The albinism group also had a higher vestibular sensory score. Conclusion: Reductions of photopic a- and b-wave amplitudes in IIN indicate a subclinical retinal deficit, which has not been previously detected. Interestingly, participants with albinism did not show abnormalities probably due to hypopigmentation shifting the baseline of ERG responses into normal ranges. Correlations between ffERGs and OCT measurements suggest ffERG may contain useful information in albinism and open up an interesting field for future study. Brain plasticity can rearrange the weighting of sensory inputs in both patient groups with the albinism group attaching a stronger weighting to vestibular cues than the other two groups.