The effect of melanin and hemoglobin on the dye laser photocoagulation in pigmented and albino rabbits

: Photocoagulation was performed in pigmented and albino rabbits using four different wave-lengths of the dye laser (577 nm, 590 nm, 610 nm and 630 nm), and each photocoagulated lesion was examined histologically. The 577 nm dye laser produced chorioretinal coagulation in albino rabbits, which was almost the same as that in pigmented rabbits. This result confirmed that the 577 nm dye laser was well absorbed by hemoglobin in the choriocapillaris, and could produce the sufficient coagulation even if there was no melanin pigment. The 590 nm dye laser produced chorioretinal coagulation in albino rabbits, but it was weaker than that in pigmented rabbits. It was considered that this was because the absorption by hemoglobin of the 590 nm dye laser was less than that of the 577 nm dye laser. The 610 and 630 nm dye laser could not yield appropriate coagulation in albino rabbits under the same conditions as in the 577 nm dye laser. More intense coagulation, that is longer duration and higher power, was required to make chorioretinal coagulation in albino rabbits using the 610 and 630 nm dye laser. In photocoagulation of normal fundus, melanin is the main substance of laser absorption, but in various disorders lacking melanin, the differences of the hemoglobin absorption rate becomes important.