Foveal cone densitometer and changes in foveal cone pigments with aging

A foveal cone densitometer was built for measuring the kinetics of foveal cone pigments in human eyes. The light from a 500-W xenon lamp was divided into reference, measuring, and bleaching beams, and projected through an optical fiber leading to a modified fundus camera. After the light was projected into the ocular fundus, the reflected light (central 1°) was measured by a photomultiplier and the regeneration time and the two- way density were abstracted from the records. The two-way density, which is the decadic logarithm of the measuring-reference beam ratio under bleached conditions divided by the measuring-reference beam ratio under dark conditions, eliminated the artifacts caused by eye movement of blink. Reliable curves were obtained in 45 eyes out of 53 healthy Japanese subjects (age range, 9 to 82 years). The mean ± standard deriation SD of the two-way density (log) and the time constant (sec) were 0.34 ± 0.09 and 139.9 ± 79.3, respectively. The time constant significantly increased with aging.