Compensation of monochromatic aberrations in older eyes

Abstract

We wished to verify and characterize the nature of the compensation of corneal astigmatism and high order aberrations of the eye by its internal optics as a function of age. The corneal and total optical wave aberrations of 22 subjects whose refraction was within − 4.6 to + 2.5 D (mean = − 1.25±0.38 D) spherical equivalent, and whose mean age was 49.7±16.5 SD years were measured using a Topcon KR 9000PW Wave-Front Analyzer. For each subject, the Zernike coefficients describing the wave aberration of the internal optics of the eye were computed by subtracting the corneal aberration coefficient from the total ocular coefficient. These were examined across the aging population (divided into two groups < or ≥50 years of age) to see if internal aberrations had compensated the corneal aberrations, as indicated by an absolute value of the total aberration coefficient being less than the absolute value of the corresponding corneal aberration coefficient. A further test of the nature of the compensation was performed by examining the correlation between the magnitudes of the corneal aberration and its compensation. It was found that oblique astigmatism, horizontal coma, and spherical aberration (Z3, Z8, Z12) were compensated by the internal optics of the eye in subjects under 50 years of age, but only horizontal coma was compensated in persons >50 years. Furthermore, the average total higher order RMS deviation from a perfect wave front increased with age (r² = 0.41, p = 0.0013). Corneal oblique astigmatism, horizontal coma, and spherical aberration are significantly compensated for by the internal optics of the eye, in younger subjects but these compensations decrease with age. We did not find evidence for a magnitude-dependent compensative process for oblique astigmatism; however, we did find some for horiz./vert. astigmatism, horizontal coma and spherical aberration. The internal optics of the eye generally fail to compensate monochromatic aberrations of the cornea after 50 years of age.