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Esther G. Gonzalez, Luminita Tarita-Nistor, Linda Lillakas, Martin Steinbach; Eccentric Fixation with Simulated Scotomas in People with Normal Vision. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5734.
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To examine eccentric fixation in people with normal vision using simulated scotomas of various sizes and to compare the measurements obtained with those from patients with age-related macular degeneration (AMD).
Participants were 24 people with normal vision and 37 patients with AMD. For the normal vision group, a gaze-contingent paradigm with a high speed eyetracker was used to simulate central scotomas of 1.5, 3, 6, and 20 deg. They were informed that the target (a 3 deg cross) would be invisible with foveal vision and were instructed to press a button when, after scanning the computer screen, they could see the target in its entirety using peripheral vision. After the button press, they were required to maintain fixation as steady as possible for 15 seconds. The eccentric fixation of patients was tested with the MP-1 microperimeter.The measures obtained were 1) fixation stability (measured with a bivariate contour ellipse area, or BCEA), 2) locus of eccentric fixation, 3) fixation distance to the centre of the target, and 4) time required for participants to place the visual target in a suitable eccentric fixation locus.
Fixation stability (BCEA) was not related to the size of the simulated scotomas and showed no practice effects. Its magnitude was comparable to the worse fixation stability of the patients with AMD. In contrast to these, most controls moved their eyes so that the target would appear to the right of the simulated scotoma in the visual field. The distance from the centroid of eccentric fixation to the centre of the target was not significantly different for the three smaller simulated scotomas. The time elapsed before the button press was a function of the simulated scotoma size and showed a practice effect.
We measured the ability of normal subjects to fixate extra foveal targets directly and found differences between them and people with central vision loss. These findings may reflect differences in the retinal reference location of the two ocular motor systems as well as eccentric viewing practice effects.
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