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Fatema Firoz Ghasia; Visual exploration in Amblyopic patients. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2366.
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© ARVO (1962-2015); The Authors (2016-present)
Miniature eye movements such as microsaccades shift the image on the fovea and counteract visual fading. They are also thought to serve as an optimal sampling strategy while viewing complex visual scenes. The goal of our study was to assess visual search and microsaccade production in amblyopia.
24 amblyopes (mild =11;moderate= 9; severe=4) and 9 controls participated in the study. Eye movements were recorded using infrared video-oculography during amblyopic and fellow eye viewing while the subjects performed 2 tasks a) prolonged visual fixation b) identified picture differences.
Amblyopic subjects had comparable dwell time in the interest areas that had the picture differences during both fellow eye viewing (normal: 49.8%; mild: 48.4%; moderate: 45.9%; severe: 43.6%-one way ANOVA p=0.5) and amblyopic eye viewing conditions (normal: 49.8%; mild: 45.7%; moderate: 39.8%; severe: 47.3%- one way ANOVA p=0.5). Amblyopes were able to identify comparable picture differences during fellow eye viewing to controls (normal: 5.7; mild: 5.8; moderate: 5.2;severe: 4.3 one way ANOVA p=0.3). However, the ability to identify picture differences was diminished during amblyopic eye viewing condition (normal: 5.8; mild: 3.8; moderate: 2.7;severe: 0.8- one way ANOVA p<0.05). In amblyopes who were able to identify the picture differences the reaction time was increased during both fellow and amblyopic eye viewing condition. (Fellow eye viewing: normal: 8.5 sec; mild: 8.0 sec; moderate: 14.9 sec; severe: 11.9 sec- one way ANOVA p=0.03; Amblyopic eye viewing: normal:8.5 sec; mild: 7.4 sec; moderate: 16.7 sec; severe: 11.3 sec- one way ANOVA p=0.01;). There was a decrease in the frequency of microsaccades with increasing severity of amblyopia.
The brain increases the rate of microsaccades to aid visual exploration in demanding tasks. The relative increase in production of microsaccades while viewing crowded visual scene is diminished in severe amblyopes. These results suggest that central nervous system is unable to increase the microsaccade rate to aid viewing of a complex picture in amblyopia. Microsaccades could be a novel biomarker to assess severity/treatment response in amblyopia. Alteration in micro-saccades could explain the difficulty in perceiving details of a complex picture evident as crowding phenomenon in amblyopia.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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