Optical changes of the human cornea as a function of age
Faculty of Medicine and Health Sciences
Optometry and vision science. - Baltimore, Md
, p. 587-598
University of Antwerp
Purpose. To assess the changes of the surfaces and optical properties of the cornea as a function of age. Methods. The corneal shape of 407 normal eyes of 211 subjects with ages ranging from 4 to 79 years old was determined by means of Scheimpflug imaging. These data were analyzed by fitting their elevation topographies to a general surface model, which consists of a biconic plus a Zernike polynomial expansion. The analysis includes the computation of the position and orientation of the model in the three-dimensional space to determine the orientation of the optical axis and the apex coordinates. Results. Both average corneal surfaces show negative conic constant plus higher order aspheric terms (Z(4)(0) and Z(6)(0) are significant). These surfaces are misaligned between them and with the line of sight. Such misalignment increases with age as the cornea seems to rotate as a solid body. The apex curvature and the magnitude of the conic constant along the most curved meridian increase as well, but the largest change with age correspond to the aspheric terms Z(4)(0) and Z(6)(0). As a result, the spherical aberration ( SA) of the average cornea increases with age at a rate similar to the total SA of the eye. Conclusions. The average corneal surfaces are misaligned general aspheres. Corneal SA is higher than total SA, but both SAs increase with age at a similar rate. This confirms that the lens is partially compensating SA and that such compensation is preserved with aging. Misalignment and solid body rotation seem to reduce astigmatism and coma for young and middle-aged corneas.