Thirty-eight retinal burns were inflicted by a modified xenon-arc photocoagulator in the eyes of eight human volunteers. The ophthalmoscopic characteristics of these lesions were correlated with the degree of histopathologic damage. Definitive clinical criteria that helped to predict the severity of the retinal burns were established. The dose of radiant energy received was further correlated with the histopathologic changes in determining the threshold of safety standards of bright flashes of white light to the human eye. Lesions from patients with blue irises were produced by considerably higher dose rates than comparable lesions from patients with brown irises and the fovea was more susceptible to damage than the rest of the retina.