THEORETICAL ESTIMATE OF THE TEMPERATURE WITHIN IRRADIATED RETINAL VESSELS

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Abstract
Temperature within irradiated retinal vessels is calculated on the basis of a relatively simple heat transfer model. Two mechanisms of heating are considered, on the one hand by direct absorption of radiation, on the other by conduction from the pigment epithelium which is heated by irradiation. The effects of the high‐pressure xenon are lamp and the argon ion laser are compared, and cooling by blood flow is taken into account. Since the irradiation time as used in practical vessel occlusion technique is long compared with the relaxation time of both conduction and convection losses, the resulting temperature is roughly that of the steady state. Whereas for clear preretinal media it should theoretically be possible to reach temperatures near the boiling point for practically all vessels with the argon laser, even at high values of blood velocity, such temperatures are obtainable with the xenon are lamp only for intra‐ and epiretinal vessels. Of intravitreal vessels relatively far from the pigment epithelium, only big ones with slow flow will respond satisfactorily. It should, however, be noted that vessel occlusion can by no means be predicted in terms of temperature alone.

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