We quantitated blue-green light transmission and autofluorescence of the human crystalline lens in vivo, using an automated scanning fluorophotometer (Fluorotron) coupled with a lens system designed for high resolution of the ocular anterior segment. Lenses were scanned through the dilated pupil along the optical axis, generating a fluorescence profile consisting of anterior and posterior juxtacortical peaks and a central plateau. Fluorescence increased linearly with increasing age. We calculated percent transmission of excitation (410-500 nm) and emission (510-670 nm) as the ratio of posterior to anterior juxtacortical peaks. Light transmission decreased as a parabolic function of age and was correlated with both fluorescence increase and observed lens brunescence.