ABSTRACT
The central cornea maintains reasonable optical quality throughout life, although there are some structural and other changes with age, particularly a reduction in endothelial cell density (Abib and Barreto, 2001) and in sensitivity (Millodot, 1977). There is little change in axial direct spectral transmittance, which shows a sharp cutoff below about 320 nm (Beems and Van Best, 1994; van den Berg and Tam, 1990), but there is often some loss of transparency in the peripheral cornea, near the limbus, where fatty and other deposits may build up to form arcus senilis. Corneal light scattering normally increases only slightly with age (Allen and Vos, 1967; Olsen, 1982). Corneal power and aberrations change slowly (Oshika et al., 1999; Guirao et al., 2000). There is a gradual shift from generally with-the-rule (vertical meridian more myopic) toward against-the-rule (inverse) astigmatism with age (Fledelius, 1984; Saunders, 1988; Hayashi et al., 1995), due largely to a steepening of the cornea in the horizontal meridian (Baldwin and Mills, 1981). More recent studies using Scheimpflug imaging (Dubbelman et al., 2006; Navarro et al., 2013a,b) have examined the shape of the anterior and posterior surfaces, and their effects on aberration, in more detail. Navarro et al. (2013b) find a small increase in corneal power, amounting to about 0.75D between the ages of 20 and 80 years: corneal aberrations appear to increase with age at a similar rate to total eye aberrations (see in the following text).
