DOSE AND TEMPORAL PARAMETERS IN DELAYING INJURED OPTIC-NERVE DEGENERATION BY LOW-ENERGY LASER IRRADIATION

Low-energy laser irradiation has been reported to postpone the degener ative processes in crushed optic nerves of rats, which are part of the nonregenerable mammalian central nervous system. In the present study , we evaluated the optimal irradiation parameters for this purpose. Op tic nerves of 141 rats were subjected to crush injury and then irradia ted through the eye, starting at different points of time before or af ter the injury, for different durations and periods, using various int ensities of either helium-neon laser or noncoherent infrared light (90 4 nm). The effect was evaluated by measurements of the compound action potentials of the nerve segments between the site of injury and the o ptic chiasm. The compound action potential amplitude of the crushed no nirradiated nerves, as measured 2 weeks after the injury, was found to be 0.51 +/- 0.30 mV, in contrast to 3.10 +/- 1.03 mV measured in 232 normal nerves. Irradiation with a 10.5 mW helium-neon laser for 2 and 3 min once a day for 14 consecutive days resulted in maximal preservat ion of action potentials (1.78 +/- 0.72 and 1.95 +/- 0.71 mV, respecti vely). Irradiations beginning immediately prior to the injury were as effective as irradiations beginning soon after it. Irradiations for lo nger than 3 min or twice a day aggravated the damage. Noncoherent infr ared light was ineffective or adversely affected the injured nerves. O ur experiments suggest that optimal delay of posttraumatic optic nerve degeneration in rats is attainable with 10.5 mW helium-neon laser irr adiations for 2 or 3 min once a day for 14 consecutive days. (C) 1993 Wiley-Liss, Inc.