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S.K. Dorairaj, C. Oliveira, V. Barocas, N. Ragusa, C. Tello, J.M. Liebmann, R. Ritch; Iris Contour Changes During Accommodation . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3891.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the alterations in iris contour following the onset of accommodation in eyes with narrow angles and normal eyes.
Eyes were imaged using high–frequency, high–resolution, anterior segment ultrasound biomicroscopy. A radial perpendicular image in the horizontal temporal meridian detailing the iris configuration was obtained for the right eye by having the subject focus on a distant (∼ 6 m) target (unaccommodated state) with the fellow eye under standardized room lighting conditions. The subject was then instructed to focus on a near (∼ 0.33 m) target (accommodated state) and to continue focusing on the same target for three minutes. Images were acquired at 0, 1, 2, and 3 minutes. Images were imported to the NIH image–analysis program ImageJ, and iris curvature was determined by measuring the maximum distance between the posterior iris surface and a line drawn from the iris root to the pupil margin.
For control subjects (n = 19), the iris curvature decreased immediately after accommodation, but not significantly (p > 0.25), from 272 ± 36 µm (mean ± SEM) to 257 ± 67 µm; curvature increased significantly (p < 0.05) after three minutes of accommodation to 356 ± 53 µm. Eyes with narrow–angles (n = 6) performed similarly, with curvatures of 457 ± 47 µm when unaccommodated, 485 ± 61 µm immediately after accommodation (p > 0.25), and 589 ± 45 µm (p < 0.05) three minutes later. Not surprisingly, the narrow–angle subjects had significantly greater iris curvature at all times.
The results confirm the time–dependent nature of iris contour response, with significant differences observed between the initial observation after accommodation and the observation three minutes later. The observations of normal subjects were generally consistent with previous theoretical analysis (Heys and Barocas, IOVS 43:700, 2002), which predicted an initial decrease in curvature followed by a steady increase over the next three minutes.
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