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Jesson Martin, Norberto Lopez-Gil, Tao Liu, Arthur Bradley, Larry N. Thibos; Effect of Pupil Miosis on Accommodation Measurements. Invest. Ophthalmol. Vis. Sci. 2011;52(14):831.
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Accommodative miosis is a natural decrease of pupil size during accommodation. We investigated the effect of miosis on the measurement of refractive state and accommodation.
An optical bench fitted with a modified aberrometer (COAS, Wavefront Sciences Inc.) was used to obtain wavefront aberration measurements in the right eyes of 5 non-presbyopes during accommodation. Vergence of the visual stimulus (Landolt C) ranged from +0.5 to -4.5 D relative to the eye’s far-point. To ensure accurate accommodation during aberrometry, measurements were obtained when the subject was correctly reading letters near their own personal resolution limit. The experiment was performed monocularly with and without pharmacological dilation of the pupil. Pupil dilation without cycloplegia was achieved by instilling one or two drops of phenylephrine. Refractive state of the eye was measured 2 ways: (1) by the Zernike coefficient C20 for defocus (which specifies the target vergence required for optimal focusing of the circle-of-least-confusion on the retina); and (2) by the Seidel coefficient W20 (which specifies the target vergence required for optimal focusing of paraxial rays).
On average, the natural pupil constricted 1.9 mm in diameter for the nearest target. For dilated pupils, the change in refractive state produced by the accommodative stimuli was higher for the Seidel criterion than for the Zernike criterion. This finding is consistent with the reversal of sign of spherical aberration (Zernike coefficient C40) when the crystalline lens changes shape during accommodation. For natural pupils this discrepancy between Zernike and Seidel measures of accommodative response decreased as a consequence of a reduced impact of spherical aberration for naturally constricted pupils.
Measured changes in ocular refractive state during accommodation depend on the method of measurement and also pupil size. Different methods converge to a common value as the pupil constricts due to accommodative miosis. Thus pupil size will affect traditional measures of accommodative amplitude, accommodative gain, lead and lag.
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