A theory of retinal burns

Abstract

Retinal burns may be accidental in origin (eclipse blindness, flash burns) or intentional (in the operative technique of photocoagulation). An attempt is made to come to a quantitative understanding of the thermal events involved in the production of these burns. The results of experiments by Hamet al. (Am. J. Ophth.,46, 700–723, 1958) on retinal flash burns in rabbit eyes were therefore analyzed. It is concluded that the findings of these authors cannot be explained in the simple terms of a critical temperature beyond which burns are produced: the temperature is raised beyond the boiling point of the tissue fluid, and the production of steam must be taken into consideration. In fact, it appears from the computed amount of steam production. However, it is also obvious that functional damage might occur at a much lower level of irradiation too, since somewhere between 45° and 60°C. the albumins begin to coagulate. It even seems plausible that a still smaller temperature increase of only a few degrees centigrade might produce at least temporary lesions after prolonged exposure, by the process of “metabolic poisoning,” which occurs when the waste products of the accelerated metabolic processes cannot be removed quickly enough.