Fixation Stability and Viewing Distance in Patients with AMD.
People with normal vision perform activities of daily living binocularly, while changing viewing distance frequently and effortlessly. Typically, in patients with age-related macular degeneration (AMD), fixation stability is recorded with monocular instruments at a fixed viewing distance (i.e. optical infinity) to determine the location and precision of the preferred retinal loci (PRLs)-the part of the functional retina that fulfills the role of a pseudo-fovea. Fixation stability recorded with these instruments has been related to performance on visual tasks at shorter viewing distances, although it is not known how viewing distance affects the precision of ocular motor control in these patients. This study examined whether viewing distance affects fixation stability during binocular and monocular viewing. Thirty patients with bilateral AMD, 10 older controls, and 10 younger controls participated. Each patient's better eye (BE) and worse eye (WE) were identified based on their visual acuity. Fixation stability was recorded with a binocular eye-tracker at three viewing distances (40 cm, 1 m, 6 m) in binocular and monocular (with BE and with WE) viewing conditions. Fixation stability was evaluated with a bivariate contour ellipse area. For the AMD group, there was no effect of viewing distance on fixation stability, regardless of viewing condition (i.e. binocular, monocular with the BE or with the WE). The same pattern of results was found for the two control groups. Viewing distance does not affect fixation stability in patients with AMD. Fixation stability data recorded with an instrument at a fixed viewing distance can be related to performance on visual tasks at other viewing distances.