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Maria Vinas, Pablo De Gracia, Carlos Dorronsoro, Lucie Sawides, Gildas Marin, Martha Hernandez, Susana Marcos; Visual performance under natural, corrected and Adaptive Optics induced astigmatism: meridional and adaptational effects. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1281.
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© ARVO (1962-2015); The Authors (2016-present)
To study the extent to what prior adaptation to astigmatism affects visual performance, whether this effect is axis-dependent, and the time-scale effect of potential changes in visual performance in the presence of astigmatism following its correction. To study whether the effect of possible positive interactions of aberrations (astigmatism & coma) on visual performance might be altered after long-term adaptation to correction of astigmatism.
Measurements of visual acuity (VA) were performed under induction of astigmatism and a combination of astigmatism and coma, while controlling the low and high order aberrations (HOA) of the subject with an Adaptive Optics (AO) system, in 25 subjects classified in 3 groups: non-astigmats, habitually-corrected and uncorrected astigmats. Astigmatism (1.00D) was induced at 3 different orientations: at the natural axis, at the perpendicular orientation, and at 45deg for astigmats, and at 0, 90 and 45deg for non-astigmats. Experiments were also performed with coma (0.41µm at a relative angle of 45deg) combined with the mentioned amount/orientations of astigmatism. VA was measured in a total of 14 different conditions, using an 8-Alternative Forced Choice (8AFC) procedure with tumbling E letters and a QUEST algorithm. Uncorrected astigmats were provided with proper astigmatic correction immediately after the first session. Measurements were performed during 6 months following correction.
In non-astigmats, inducing astigmatism at 90deg, under full AO correction, produced a statistically (p<0.01) lower reduction in VA (29%) than at 0 (40%) or 45deg (41%). In astigmats, the lower decrease was for astigmatism induced at the natural axis (24% for corrected astigmats, 28% for non-corrected astigmats). 6-months of astigmatic correction wear did not reduce the insensitivity to astigmatism induction along the natural axis. Visual benefit of adding coma to astigmatism over astigmatism alone improved significantly only in non-astigmats, and only for some orientations of astigmatism.
The impact of astigmatism on VA is greatly dependent on the orientation of the induced astigmatism, even in non-astigmats. Prior experience to astigmatism plays a significant role on visual performance in the presence of both astigmatism and combinations of astigmatism and coma, with a strong bias towards the axis of natural astigmatism.
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