A comparative study of the effects of argon and diode laser photocoagulation on retinal oxygenation

Background: The purpose of this study was to compare the effects of diode and argon laser photocoagulation (DLP and ALP) on the preretinal oxygen tension (P-O2): (1) directly over photocoagulated retina and (2) in between laser lesions. Methods: DLP or ALP was applied to avascular rabbit retina to produce grade II lesions. On the day of the oxygen measurement, a droplet of perfluorotributylamine was placed into the preretinal vitreous space over the lasered area of retina and the steady-state P-O2 was measured in normoxic animals using F-19 magnetic resonance spectroscopy. To determine the P-O2 directly over laser lesions, small (5-mu l) droplets were placed over large (approximate to 4 mmx5 mm), confluent areas of treatment (burn area approximate to 95% of the treated retinal surface area). To determine the P-O2 in between laser lesions, a larger (10-mu l) droplet was placed over a field of scatter photocoagulation (burn area approximate to 30% of the treated retinal surface area). The theoretical basis for this approach is discussed. Results: Untreated eyes had a preretinal PO2 of 22 +/- 9 mm Hg (mean +/- SD, n=15 eyes), The preretinal P-O2 was significantly higher over confluent, 12-day-old ALP or DLP lesions (51 +/- 13 mm Hg, n=8 eyes; P<0.01) compared to untreated eyes. However, at that time, DLP lesions had significantly higher P-O2 values (60 +/- 13 mm Hg, n=4 eyes) than did ALP lesions (42 +/- 6 mm Hg, n=4 eyes; P=0.04). The preretinal space in between laser lesions generally showed no significant increase in P-O2 (P>0.05) over controls on post-treatment days 1, 5, 14 and 47. The only exception was in the DLP group of eyes, in which a significant increase in P-O2 over untreated or ALP-treated eyes occurred on post-treatment day 5 (41 +/- 7 mm Hg, n=5 eyes; P=0.01). Over photocoagulation lesions in this study, DLP produced a greater increase in preretinal P-O2 compared to control values than did ALP. Conclusions: These results support the use of DLP as an alternative to ALP for the treatment of retinal vascular diseases in which hypoxia is suspected to play a role.