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Lei Liu, Alex Keith, Mark Bolding; How Patients Keep A Moving Target Out Of Their Central Scotoma While Tracking It?. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5176. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Our previous study of central vision loss (CVL) patients showed a moderate impairment of the smooth gain when visually tracking a moving target. The presence of a central scotoma dictates that the patient has to make an effort to prevent the moving target from falling into the scotoma and becoming invisible. We hypothesize that different strategies are used depending on the location of the preferred retinal locus (PRL) and the direction of target motion.
Seven subjects with long standing CVL were asked to visually follow a 0.87 deg yellow circular target moving across a computer monitor on a horizontal or a vertical trajectory. The velocity profile of the target was a sine-wave with a 10-deg amplitude and a frequency of either 0.15 or 0.4 Hz. A 250 Hz eye tracker was used to monitor the tracking eye movement. A microperimeter was used to map the central scotomata and PRLs of the subjects. To analyze scotoma evasion, the field map of each subject was thresholded at 2dB (maximum 20) to make a binary scotoma map. The map was pinned to the PRL used in eye tracker calibration to analyze the relative position between the scotoma and the target.
Our sample of CVL subjects did an excellent job in keeping the target out of the central scotoma. The average percentages of target out of scotoma were 91.9±4.8 and 85.0±12.1 for horizontal and vertical tracking respectively. The better performance in horizontal tracking may be attributable to 5 out of the 7 subjects had PRLs above or below central scotoma. If the target was in the scotoma, it seldom stayed in for long. On average, the target fell into the scotoma 10.1±5.8 times for each 35-sec tracking trial. The median dwelling time in the scotoma was 59.3±26.2 msec. Strategies such as different retinal locations for different target directions (Fig. a), skillful use of a small patch of intact retina (Fig. b) and moving the scotoma out of the target’s way were employed, sometimes in combination in the same trial.
Conclusion: Subjects with long standing CVL are able to keep a moving target visible most of the time. Even if the target falls into the scotoma, it is quickly brought out. Various scotoma evasion strategies may be employed to keep the target in sight.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure. (a) Using different retinal locations to track target moving in different directions. (b) Using a very narrow alley between scotomas for tracking.
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