Abstract
Abstract: :
Purpose: To study the effect of experimental glaucoma (EG) on the optic nerve blood flow response to flicker stimulation. Methods: In 8 anesthetized male cynomolgus monkeys who underwent argon laser photocoagulation of the trabecular meshwork in one eye 2 months earlier, a 30° diameter field centered at the temporal edge of the optic disc was illuminated with diffuse green light (590 nm). This light was alternated between constant (30 s duration) or sinusoidally modulated (100%, 40 s duration) at the same mean retinal illuminance. The blood flow response (Rflow) was measured at the lower temporal rim of the optic nerve head using laser Doppler flowmetry (670 nm) and expressed as the percentage change between the flow measured during 10 s immediately before flicker (baseline) and the last 10 s during flicker. Three readings of Rflow were obtained and averaged at each of 6 flicker frequencies (4, 8, 15, 20, 25 and 50 Hz) and 5 light levels (2, 10, 20, 50 and 100% maximum illuminance of 2100 lux) in a randomized sequence for each eye. Results: The intraocular pressure in the EG eye was 45 ± 16 [30, 74] mm Hg. We found no significant difference in the baseline blood flow between the EG eye and the fellow control eye. The Rflow in both the EG and control eye showed a highly significant increase (14.1 ± 5.3 % and 13.9 ± 5.4 %, respectively, paired t–test, p < 0.001). The Rflow had a bandpass–like shape as a function of flicker frequency. However, this response was not significantly different between eyes (paired t–test), although a difference in Rflow of 1.4 % or more would have been detectable in this group of animals. Conclusions: Our results suggest that baseline flow and Rflow are still normal after 2 months of EG. Previous reports showed that baseline flow in the EG eye is significantly decreased compared to the control eye after 3 years of EG (Percicot et al., ARVO 1996) and that the optic disk tissue pO2 is significantly increased after 2 months of EG, but decreased after 6 years of EG (Ferrez et al., EVER 2003). We conclude that blood flow changes lag behind changes in the optic disk oxygenation in the early stages of EG. A longer follow–up is required to characterize the time course of these changes.
Keywords: optic disc • blood supply • intraocular pressure