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R. Munger, L. Marchese, D. Priest; Equivalency of Optical Aberrations for Light Entering and Light Exiting the Human Eye . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2005.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: When patients perform visual tasks light is traveling from the real world into the eye towards the retina. In many clinical optical measurement techniques the optical properties of the eyes are assessed from light originating at the retina and traveling out of the eye. If the two situations are not equivalent, then diagnosis and treatments could be compromised. The purpose of this study is to determine if aberrations of the eye for light entering the eye are the same as the aberrations when the light exits the same eye. Methods: Two sets of 24 model eyes with different optical aberrations were created in ZEMAX; one set with a constant index (Gulstrand–LeGrand) and one set with a GRIN crystalline lens (Liu–Brennan). High order aberrations were introduced in each model eye by tilting/displacing the crystalline lens relative to the optical axis of the cornea. Monochromatic aberrations were measured at the exit pupil for: (A) light entering the eye from a point at infinity and traveling to the retina (C1); and (B) light exiting the eye from a point source on the retina (C2). Results: All results represent differences (C2–C1) or ratios (C2/C1). In all GRIN model eyes the high and low order aberrations for C1 and C2 were different. In emmetropic eyes, the difference in refractive states is not clinically significant (<+– 0.05D). In these same eyes, Coma (70 to 96%) and SA (68 to 110%) ratios show lower measurements for C2 than C1 in most eyes. When defocus is introduced, the differences in refractive states become significant (+0.25 to –0.75D for Rx of +4.00D to –8.00D respectively) and are well described by a second order polynomial. Furthermore, thedifferences in the high order aberrations for C1 and C2 generally increase non–linearly (each aberration is different) as defocus increases. Constant index crystalline lens results are consistent in trend but not identical to the GRIN results suggesting that the lens model used is important to determining full clinical impact. Conclusions: The monochromatic aberrations of the eye for light entering and light exiting the eye are different. These differences, which may be clinically significant, are consistent with current clinical results in wavefront guided (Hartmann–Shack sensor) refractive treatments.
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