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D. Paille, K. Baranton, C. Pedrono; Does Cyclodisparities Present in the Peripheral Field of View Affects Performance in Central Vision?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1824.
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Some studies suggested that cycoldisparities in the peripheral visual field could generate cyclovergence eye movements, even in the absence of any cyclodisparities in the center (Kertesz and Sullivan, 1978; Howard, Sun Shen, 1994). Furthermore, recent works showed that cyclodisparities impaired contrast sensitivity (Giraudet, Pedrono, 2006), posture stability (Giraudet, Van Driesche, unpublished data) and horizontal fusion and stereopsis (Georgievski et al., 2007). The current study aimed to determine whether cyclodisparities present only in the periphery may affect visual acuity in the central visual field.
Two subjects were involved in the experiment. They had to perform a visual acuity task in the central visual filed while being exposed to cyclodisparities in the periphery. Three different cyclodisparity values were considered: 4° of incyclodisparity, 4° of excyclodisparity and a control condition without cyclodisparity. In the 2° degrees of central field, visual acuity measurement consisted in 4 E letters, with different orientations; displayed for 250 ms. Subjects had to signal the position of the well oriented E with the keyboard arrows. Eleven letter sizes were considered (i.e. 11 logMAR acuities), with 100 repetitions per size condition. Before the experimentation an estimation of the amount of cyclovergence induced by the peripheral cyclodisparities was made for each subject.
The psychometric curves for each angle of cyclodisparity were computed and the results showed two different behaviours. For one subject central visual acuity decreased with cyclodisparities. The other subject had similar performances whatever the cyclodisparity angle. Nevertheless, the first subject responded to peripheral cyclodisparities with an important amount of cyclovergence (gain 0.5) whereas the second had a gain close to 0; so, for the last subject, fusion of disparities was entirely performed by the sensorial part of the visual system.
Our results showed that central vision performance may be deteriorated by cyclodisparities in the peripheral visual field, but only when the subject compensated for these disparities, at least partly, with vergence eye movements.
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