Higher-order aberrations from the internal optics of the eye

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Abstract
PURPOSE: To analyze the distribution of human higher-order wavefront aberrations (3rd- to 6th-order) from the internal optics (WAinternal) and the variations with age and to evaluate the degree of compensation that the internal optics provide for anterior corneal aberrations (WAcornea). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: With assumption of a simple model for the eye, the WAinternal were obtained by direct subtraction of the WAcornea from the ocular aberrations (WAeye). The WAeye were measured using the WaveScan system (Visx, Inc.), and the WAcornea were computed from the topographic data (Humphrey Atlas) using the CTView program (Sarver and Associates, Inc.). In 144 eyes of 114 normal patients (age 20 to 69 years), WAinternal were calculated for a 6.0 mm pupil and a compensation factor (CF) was computed, with positive values representing compensation of WAcornea by WAinternal and negative values indicating that the internal surfaces add aberrations to those of the cornea. RESULTS: There was wide individual variation in WAinternal. The mean coefficient for 4th-order spherical aberration (Symbol) was −0.145 μm ± 0.094 (SD) (95% confidence interval [CI], −0.160 to −0.130 μm); 95.1% of eyes had negative values. The mean root-mean-square value for HOAs was 0.334 ± 0.096 μm (95% CI, 0.319 to 0.350 μm). Moderate to high correlations were found between the right and left eyes in HOAs, 4th-order and 6th-order spherical aberration coefficients (Symbol and Symbol). With increasing age, the HOAs did not change, whereas the negative coefficients for Symbol tended to become less negative. Only the term Symbol had a CF significantly correlated with increasing age (r = −0.338, P<.05 with Bonferroni correction). Symbol Symbol CONCLUSION: WAinternal varied widely among patients, and a moderate to high degree of mirror symmetry existed between the right and left eyes. Internal surfaces compensated at least partially for the HOA and Symbol in most eyes, and this compensation decreased only mildly with increasing age.