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Y. Hirohara, T. Tanabe, T. Fujikado, H. C. Howland, T. Mihashi; Compensation of Off-Axis Aberrations, Especially Coma, in the Human Eye. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3324.
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We investigated the off-axis wavefront aberrations (WAs) of the whole eye and the cornea of the human eye.
Ten normal right eyes of ten subjects were included in the study. Ocular and corneal WAs were analyzed with Hartmann-Shack wavefront sensor and with a corneal topographic analyzer (Wavefront analyzer, Topcon Corp, Tokyo, Japan). Subjects fixated five different points on the inner fixation target (center, and 4.5 degrees off-axis at the top, bottom, right-side, and left-side of the target plane). WFAs were analyzed using normalized Zernike polynomials up to the fourth order defined over a 4-mm diameter area in the center of the pupil. The coefficients of the ocular and corneal WAs were compared at each target direction.
Only comatic aberrations were altered with changes in target direction. Corneal vertical coma for the top and bottom targets was changed 0.088 and -0.094 µm from that of the center target respectively. Corneal horizontal coma of the left-side and right-side was changed 0.088 and -0.083µm from that of center respectively. Ocular vertical coma for the top and bottom targets was changed 0.037 and -0.047µm from that of center respectively. Ocular horizontal coma of left-side and right-side was changed 0.026 and -0.026µm from that of center respectively. All of these differences were statistically significant at the p< 0.001 level. The variations of ocular coma were smaller than those of the cornea. We found a statistically significant proportional compensation for horizontal corneal coma (i.e. the amount of compensation of corneal coma by the internal optics of the eye was proportional to the magnitude of corneal coma). However we failed to demonstrate similar proportional compensation for vertical coma.
We found that the magnitudes of both corneal and total optical coma change away from the visual axis. As in the central retina, we failed to demonstrate proportional compensation for vertical coma in the near peripheral retina.
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