Evaluation of an objective method for the in vivo measurement of changes in light transmittance of the human crystalline lens

Because the results of various vision tests and diagnostic methods are influenced by the amount of light transmitted by the lens, it would be useful to quantify changes in transmittance. We have developed a new method capable of following these changes objectively and quantitatively. The method is based on an increasing loss of fluorescence emitted by the lens substance as the probing volume is located more posteriorly along the lens axis. The loss of fluorescence is quantified by a parameter called the fluorescence reading ratio (FRR). In the present study, performed on postmortem human lenses, we evaluated the validity of our proposed in vivo method by comparing it with measurements of lens transmittance by spectrophotometry. The correlation of FRR with the transmittance between 420- and 500 nm (r > 0·7, P < 0·015) indicates that the measurement of FRR can provide information on the transmittance at these wavelengths. In addition, a correlation was found between age and transmittance at 440 nm (r = 0·93, P < 0·001) and FRR (r = 0·88, P < 0·001).