Lens fluorescence and accommodative amplitude in pre-presbyopic and presbyopic subjects (original) (raw)

2007, Experimental Eye Research

Accommodative amplitude (AA; the difference, measured in diopters, between the near and far points of vision) declines steadily with age such that, by midlife, most individuals are unable to focus clearly on near objects and, thus, are said to be presbyopic. Conversely, intrinsic lens fluorescence (LF) increases steadily with age. Previous studies have suggested that AA and LF are negatively correlated, independent of age. Were this to be the case, it might suggest that the biochemical modifications underlying increased tissue fluorescence (for example, glycation of lens proteins) contribute to presbyopia. We used quantitative techniques to re-evaluate the relationship between AA and LF in 161 healthy volunteers aged between 25 and 70. Our data confirmed that AA decreases with age, becoming essentially zero by age 55, and LF increases with age. However, in marked contrast to previous reports, statistical analysis failed to detect any correlation between LF and AA independent of age. Thus, the biochemical processes responsible for increased LF observed in the aged lens are unlikely to contribute directly to presbyopia. Accommodation, the ability to focus clearly on near objects, is lost progressively with age. Classic early studies by Donders (Donders, 1864) and Duane (Duane, 1912) demonstrated that accommodative amplitude (AA; the difference, measured in diopters (D), between the near and far points of vision) decreases almost linearly with age. In young children, AA may exceed 13 D (Jimenez et al., 2003; Leat and Gargon, 1996) but, by midlife, only a few diopters of AA remain. When the accommodative range is insufficient to allow an individual to read comfortably, that person is said to be presbyopic. According to Helmholtz's widely accepted theory of accommodation, the increase in refractive power of the eye during accommodation is accomplished through a change in the shape of the lens (Helmholtz, 1855). During accommodation, contraction of the ciliary muscle releases tension on the suspensory zonules allowing the lens to adopt a more spherical shape. Elastic forces, generated in the posterior choroid, return the lens to a flattened shape during disaccommodation. Presbyopia, the age-related failure of the accommodative mechanism, has