Abstract
Purpose :
Study of the papillary performance is increasingly interesting in myopia research because the pupil size directly influences optical quality of the retinal image and the iris is closely connected with the anterior chamber structures. The iris profile changes from one eye to another during accommodation, with a substantial individual variation in a bowing of the iris profile. The purpose of this study was to test the effect of iris bowing on pupil size during accommodation.
Methods :
Accommodative responses to 0D and 6D stimuli were measured for16 young adults (age ranged 22 to 27 years, Rx from -0.50 to +1.00D) by using a customized AS-OCT system, and the accommodative changes in the lens shape and refractive power have been previously reported. In this study, the OCT images were re-processed to derive the pupil size and the iris profile by outlining the posterior profile of the iris after correcting refractive distortion with a customized ray tracing procedure. A 2nd order polynomial function was used to fit the iris profile, and the coefficients were derived to assess slope and curvature of the iris profile.
Results :
For all subjects, as the eyes accommodated from 0D to 6D, the mean pupil size was reduced from 5.94±0.59 mm to 4.06±0.70 mm, and the mean curvature coefficient of the iris profile was changed from 0.035±0.027 in a convex shape to -0.036±0.022 in a concave shape. The iris curvature coefficient changed from one eye to another, and the more negative was the coefficient, the larger area of a contact between the iris and the lens surfaces was resulted. While the pupil size was not significantly correlated to the iris curvature coefficient at 0D (r =-0.09, n.s.), it was significantly correlated to the iris curvature coefficient at 6D (r=-0.62, p<0.02). However, the iris coefficient was not correlated to ACD at either 0D or 6D accommodation conditions.
Conclusions :
There is a substantial individual variation in the performance of iris constriction during accommodation, which is inepended on the ACD. While the iris is constricted in a forward way with a slightly contact with the lens at the pupil margin in some eyes, it constricts in a backward way with a close contact between the iris and the lens in a large area in other eyes. The contact between the iris and the lens surfaces produces the iris bowing which generates a resistance to the iris constriction and thus influences pupil size control.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.