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Atanu Ghosh, Michael J. Collins, Scott A. Read, Brett A. Davis, D.Robert Iskander, Payel Chatterjee; Changes in Ocular Aberrations during a Near Task in Downward Gaze for Emmetropes and Myopes. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6314.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the influence of accommodation (0 D, 2.5 D and 5 D) on ocular aberrations in downward gaze over a period of time in myopes and emmetropes.
Twelve emmetropes (mean -0.29 ± 0.36 D) and fourteen myopes (mean -3.26 ± 1.60 D) with normal ocular health, aged from 19 to 30 years were recruited. Subjects performed a control task (watching TV at 5 meters distance in primary gaze) for 10 minutes prior to each trial, then a binocular distance task (watching TV at 5 meters) in downward gaze (250) and a near task (watching video on a portable LCD screen) at two different accommodative demands (2.5 D and 5 D) in downward gaze (250) in a randomized order. Immediately after (<1 minute), 5 and 10 minutes from the commencement of each trial, measurements of ocular aberrations were taken in downward gaze (250) using a modified Shack-Hartmann aberrometer. Zernike coefficients up to the 8th radial order were analysed for natural pupil diameters.
Repeated measures MANOVA revealed a significant influence of accommodation stimulus (p<0.001) and time (p=0.001) on the changes in mean refractive power (M), indicative of a reduction in accommodative lag over time. Primary astigmatism (J0) was shifted in the with-the-rule direction with accommodation (p=0.014). Of the higher order coefficients, vertical trefoil C(3,-3) [p=0.008], horizontal coma C(3,1) [p<0.001], secondary astigmatism C(4,-2) [p=0.001] and primary spherical aberration C(4,0) [p=0.005] all changed significantly with increased accommodation level. There was also a significant interaction between accommodation and refractive error group for the changes in C(3,-3) [p=0.03], C(4,0) [p=0.03] and C(6,0) [p=0.04]. Mean higher order RMS increased (p<0.001) with accommodation which was significantly greater (p=0.04) in myopes than emmetropes for 5 D accommodative demand.
Significant changes in refractive power and higher order aberrations occurred with accommodation as a function of time in downward gaze. This highlights the dynamic characteristics of visual optics during a near task.
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