Light stimulation of iris tyrosinase in vivo.

Although exposure of epidermal melanocytes to ultraviolet radiation is known to increase tyrosinace activity, a similar effect has never been demonstrated for the iris. This paper presents evidence that light stimulates tyrosinase activity in iris melanocytes in rabbits. Levels of iris tyrosinase were found to be greater in eyes of rabbits exposed to light for 6 weeks than in eyes of rabbits maintained in darkness. Despite increasing tyrosinase levels, exposure to light produced to no clinically observable change in iris color.