We have developed new psychophysical approaches to measuring the regeneration kinetics of the human eye and done basic research into factors affecting these measurements. In addition we have used this technique to show that photopigment kinetics are altered in a number of retinal diseases, but only slightly in normal aging.
Elsner, AE, Burns, SA, Beausencourt, E, and Weiter, JJ, "Foveal cone photopigment distribution: small alterations associated with macular pigment distributions", Invest. Ophthalmol. Vis. Sci. 39,2394-2404, 1998
Elsner, AE, Burns, SA, and Weiter JJ, "Cone Photopigment in Older Subjects: Decreased Optical Density in Early Age-Related Macular Degeneration". J. Opt. Soc. Amer A 19: 215-222, 2002-(full text)
Prieto, P, McLellan, J.S., and Burns, S.A. Investigating The Light Absorption In A Single Pass Through The Photoreceptor Layer By Means Of The Lipofuscin Fluorescence. Vision Research 45 (15): 1957-1965, 2005(full text)
This is a note to indicate that while first order kinetics are convenient to use when modeling the photopigments they have been shown to deviate from the data obtained from both psychophysical and densitometric measurements. Burns and Elsner (1989) compare results using retinal densitometry to result obtained psychophysically to show that both techniques demonstrate the same departures from first order kinetics. The graph below shows measurements obtained using a color matching technique. Data obtained using an ascending series of retinal illuminances (allowing full adaptation between settings) are considerable steeper than the first order predictions (curve labeled ascending). We then examined data for a descending series of retinal illuminances (which is in some ways similar to the densitometry where measurements are often made after an initial "clearing" bleach). Here the data are shallower, but still steeper than the first order predictions.