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S. A. Haymes, D. A. Westwood, K. A. Kellner, R. P. LeBlanc, M. T. Nicolela, L. A. Chiasson, B. C. Chauhan, P. H. Artes; The Effect of Glaucoma on Visual Search Tasks. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2875. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of glaucoma on eye movements and performance of visual search tasks.
The sample comprised 13 glaucoma patients recruited from a hospital-based ophthalmology clinic, and 16 volunteer control subjects with normal vision, who were enrolled in an ongoing study of risk factors for falls and motor vehicle collisions in glaucoma. Participants performed two visual search tasks. In the first task (serial search), a 6 x 5 array of optotypes was presented, where the target was a single O, and distractors were Landolt Cs. In the second task (parallel search), targets and distractors were reversed. Target presence, location within the array, and gap position of Landolt Cs were randomized over 60 trials. Eye movements were monitored with the EyeLink II (SR Research Ltd, Osgoode, ON). Main performance measures were mean number of fixations, errors and search time. Visual field impairment was measured with standard automated perimetry (SITA 24-2 MD [dB]; binocular Esterman [% detected]).
Mean age was 68 years (SD, 7 years) and 67 years (SD, 6 years) for glaucoma patients and controls, respectively (P = 0.69). Visual field damage (MD) in the better eye of the glaucoma patients ranged from +1.1 dB to -6.9 dB (mean, -2.1 dB). In the serial search task with and without presence of a target, the search time of the glaucoma patients (median, 4.6s and 7.5s, respectively) was 25% and 28% longer than that of the controls (p<0.1, Mann-Whitney U [MWU]). In the serial tasks, glaucoma patients also tended to fixate longer (median duration of fixations, 192ms) compared to healthy controls (170ms, p<0.05, MWU) and make a larger number of saccades (9 and 6 vs 6 and 4 in target-absent vs target-present conditions, respectively, NS). In the parallel search tasks, the findings were broadly similar; glaucoma patients tended to search longer and make more saccades, particularly during trials in which no target was present. In the glaucoma patients, visual field damage (MD) of the better eye was weakly but significantly related to an increase in search time (by 6% and 8% per 1 dB reduction of MD in target-present and -absent conditions, respectively, r-square 0.07, p<0.05)
In this study, glaucoma patients made more fixations and took longer to perform a visual search task than persons with normal vision. Visual search performance decreased with increasing visual field damage. This challenges the assumption that early visual field losses in glaucoma do not impair real-world visual performance.
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