Melanin granule models for pulsed laser induced retinal injury.

Two models for retinal threshold injury on exposure to intense light (laser) pulses ranging from 0.1 see to 10(-8) sec, are discussed. In both models, the melanin granules in the retina are considered as the primary absorption site-the site of greatest energy absorption per unit volume in the retina. The single mechanism granule model considers that a specific temperature must be reached in the perigranular region to produce injury. The two-mechanism model assumes that production of steam is not required for injury at long pulse durations-that is, injury at long pulse durations is essentially thermal-but that once steam is produced, injury is related to steam production. The models agree with experimental observations that indicate that the energy for threshold injury decreases as the pulse duration is shortened to the Q-switched range.