Teixeira Macedo, A.F.; (2011) The effects of oculomotor instability on visual performance of people with macular disease. Doctoral thesis , UCL (University College London).

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Abstract

Background: People with macular disease often face difficulties using their preferred retinal locus (PRL) during visual tasks. These difficulties are due to impaired oculomotor control, amongst other causes. The aim of this work was to investigate whether stabilizing the visual target at the PRL is beneficial for visual acuity and reading. Methods: Control of retinal image instability at the PRL was achieved using an eyetracker that moved the target according to the eye movements. Crowded and uncrowded visual acuity was measured at the PRL in people with macular disease and in healthy peripheral retina of control subjects. RSVP reading speed was also measured using the same method of stabilization at the PRL and healthy peripheral retina. Results: Results of a series of experiments showed that stabilizing the visual target can improve visual performance in most cases. In healthy peripheral retina crowded visual acuity improved when the image was stabilized and reduced when fixation instability was over-compensated. At the PRL, in patients, no improvement in visual acuity was obtained under stabilized conditions and again visual acuity reduced for over-compensated fixation instability. However, reading speed improved under stabilized conditions, by 20% in healthy peripheral retina of control subjects, and by up to 40% at the PRL of people with macular disease. Discussion: Good oculomotor control is critical for complex crowded tasks like reading. The improvement in reading speed found whilst compensating for oculomotor instability at the PRL is encouraging. These results indicate that training programs which aim to improve fixation control are likely to bring benefits for visual tasks. The observed increase in reading speed might be clinically relevant but the technique used to control instability needs simplification to be implemented outside the laboratory.

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