Flavins generate oxidants during metabolism and when exposed to light(
1). Here we report that the photoreceptor layer of retinas from black-
eyed rats is reduced in size by a dietary regime containing excess rib
oflavin. The effect of excess riboflavin was dose-dependent and was ma
nifested by a decrease in photoreceptor length. This decrease was due
in part to a reduction in the thickness of the outer nuclear layer, a
structure formed from stacked photoreceptor nuclei. These changes were
accompanied by an increase in photoreceptor outer segment autofluores
cence following illumination at 328 nm, a wavelength that corresponds
to the excitation maxima of oxidized lipopigments of the retinal pigme
nt epithelium(2).