We compared the maximum light output of selected 19- and 20-gauge continuous-fiber and detachable-tip endoilluminators to the retinal damage threshold for intravitreal fiber-optic light in the owl monkey. Because of cumulative light toxicity to the retina there is a substantial risk of retinal damage from endoillumination when the endoilluminator is close to the retina (for example, during membrane peeling procedures) and especially when the continuous-fiber endoilluminator with high light output is used.