The Absorption of Light by the Anterior Segment

Abstract

Purpose:: To determine, in vivo, the spectral transmission properties of the human anterior segment as they relate to age.

Methods:: This study is a prospective, non-randomized, cohort study approved by the IRB of the Harkness Eye Institute at Columbia University. A novel method to directly measure the in vivo absorption spectra of the human anterior segment is described. A 20-gauge fiber optic probe (Innovotech, Inc) was connected to a spectrophotometer to measure spectral transmission from 420 to 800nm with a standard halogen operating lamp as an illumination source. Recording with the probe outside the eye and then in the vitreous chamber, and correcting for both Rayleigh and Tyndall light scattering, allows calculation of the anterior chamber absorption curve according to the Beer-Lambert Law.

Results:: A total of 18 patients aged 18 to 93 years were enrolled. By stratifying for age and phakic status, the study confirmed that older, more yellow crystalline lenses reduce the amount of blue lighting reaching the retina in vivo (P < 0.01). Blue light reaching the retina was significantly increased by conventional intraocular lens implants (IOLs), and significantly decreased with "blue blocking" IOLs. Intraocular hemoglobin was also shown to substantially reduce transmission of light from 450 to 600nm.

Conclusions:: This study directly measured human anterior segment transmission spectra in vivo using a novel technique. The blue light transmitting capacity of the anterior segment decreases with age, and yellow tinted IOLs significantly decrease the transmission of blue light to the retina. This data holds important implications for retinal disorders including macular degeneration.

Keywords: aging: visual performance • anterior segment • vitreoretinal surgery