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Wavefront variation during accommodation: a comparison between myopes and non-myopes Pedro Serra, O.D. MSc* and Marisol Rubio ,O.D. PhD**

*PhD Student, Vision Sciences Research Group, University of Bradford, ** Director of Centro de Optometria Internacional (COI), Madrid, Spain

Purpose: To assess differences in optical aberrations between myopic and non-myopic eyes during accommodation. Introduction: Myopic eyes have a smaller lower accommodative gain when compared with emmetropic or hypermetropic eyes, as shown by the presence of higher accommodative LAGs in myopic eyes (1). The accommodative response increases the dioptric power of the eye, by a progressive steepening of the radius of the crystalline lens. In terms of wavefront analysis this variation means a change in the low order aberration coefficient (C20) that allows for vergence correction and in-focus near vision. However the anatomical changes in the lens shape also create change in higher order aberrations (HOA). Several studies have shown that spherical aberration is intrinsically related with the accommodative process, characterized by a decrease towards negative values (2). Other HOA have been advanced as possibly present in the accommodative process (3,4). To determine possible differences in the optical aberrations of myopic and non-myopic eyes, objective wavefront measures were made for two groups of subjects on a range of accommodative levels. Methods: Wavefront aberrations were measured in two groups, one with 9 myopic subjects (25.81±1.72 years-old) and the other with 7 non-myopic subjects (29.90±7.47 years-old). A total of 32 eyes were analyzed. The measurements were made monocularly using a Hartmann-Shack aberrometer with an internal Badal system that allowed for accommodation stimulation. Wavefront aberration was recorded in 0.2D steps of vergence stimulus from 0.00D (distance) to 0.33 m (near). Zernike coefficients were analyzed within a 5 mm pupil the smallest among all subjects. Results: Results show a statistically significantly lower accommodative response gain in the myopic group 0.42±0.28 [Dper D Acc] compared with the non-myopic group 0.71±0.18 [D per D Acc], (p<0.05). LAG amplitude, which was given by the Area Under the Curve (AUC) between the unit gain response and the measured accommodative response, showed higher LAGs for myopic eyes 3.06 ± 0.60 vs 2.13±0.92 in non myopic eyes, (p=0.038). Spherical aberration (C40) and horizontal coma (C31) were the only two HOA with a defined pattern among all subjects. C40 in non-myopic eyes decreased more rapidly -0.021 [μm/D] compared with the myopic group -0.013 [μm/D], but no statistical difference was found (p=0.074). Fur-




CIOCV'09 Proceedings  

Proceedings for the International Conference of Optometry and Visual Science 2009 (CIOCV'09). University of Minho, Braga, Portugal