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A. F. Macedo, M. D. Crossland, G. S. Rubin; Maximising Reading Speed in Macular Disease. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3061.
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Fixation instability is increased in people with macular disease (MD) and appears to be linked to reduced reading speed. In this study we measured reading speed in people with MD whilst compensating for fixation instability.
Five patients with MD and dense central scotoma were recruited. Participants were asked to read whilst their eye position was monitored using an infrared eyetracker which controlled word position. Four-word sentences were presented using rapid serial visual presentation (RSVP). Reading speed was measured twice in each of four conditions: (i) baseline, normal RSVP; (ii) compensated for fixation instability whilst not allowing intra-word saccades (screen blanked during saccades); (iii) compensated for fixation instability whilst allowing for intra-word saccades (words were visible and static during saccades); (iv) overcompensated for fixation instability whilst allowing intra-word saccades. Compensation of fixation was achieved by moving the word with the same velocity as the eye and overcompensation by moving the word with 10x the velocity of the eye. Data were normalized using the baseline reading speed and analysed using linear mixed models
Participants’ visual acuity was between 0.7 and 1.0 logMAR, critical print size (used to scale the text) was between 1.2 and 1.7 logMAR. Reading speed improved, compared to baseline, for compensated fixation instability when allowing intra-word saccades (mean improvement = 39%, p = .034). For the other two conditions reading speed was not significantly different from baseline. When intra-word saccades were allowed, overcompensated fixation instability caused a reduction in reading speed compared with compensated fixation instability (mean reduction = 55%, p = .01).
Compensating for fixation instability improved reading speed. Intra-word saccades were necessary presumably to compensate for reduced visual span. We hypothesise that the benefits of compensating instability are due to a reduction in crowding and motion blur. These findings have implications for the design of training programs and assistive devices for this type of visual impairment.
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