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 (PO2): (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 PO2 was measured in normoxic animals using 19F magnetic resonance spectroscopy. To determine the PO2 directly over laser lesions, small (5-microliter) droplets were placed over large (approximately 4 mm x 5 mm), confluent areas of treatment (burn area approximately 95% of the treated retinal surface area). To determine the PO2 in between laser lesions, a large (10-microliter) droplet was placed over a field of scatter photocoagulation (burn area approximately 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 PO2 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 PO2 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 PO2 (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 PO2 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 PO2 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.