Comparison of pre-retinal oxygen pressure changes after selective retina therapy versus conventional photocoagulation in the rabbit eye.

PURPOSE: To evaluate oxygen consumption by photoreceptors, we estimated changes in pre-retinal oxygen pressure (PO2 ) after selective retina therapy (SRT) compared with conventional photocoagulation (PC) in rabbits.

METHODS: One eye of each of 10 Chinchilla Bastard rabbits received both 144 laser SRT spots and 144 laser PC spots. Color fundus photography, optical coherence tomography (OCT), and fluorescein angiography were used to evaluate the lesions after treatment. Fiber-optic sensors (optodes) were used to determine the pre-retinal PO2 levels of untreated, SRT-treated, and PC-treated areas of laser-damaged eyes 7 days after treatment. The pre-retinal PO2 was measured in the other five eyes (controls). The same procedures were applied to these remaining five eyes 4 weeks after treatment. Light microscopy (LM) was used to evaluate histological changes 7 days and 4 weeks after treatment.

RESULTS: We found no significant difference in the mean pre-retinal PO2 values among untreated, SRT-treated, and control eyes 7 days after treatment. However, the mean pre-retinal PO2 value in PC-treated regions (24.3 ± 4.9 mmHg; mean ± SD) was higher than those in untreated regions (17.0 ± 1.8 mmHg; P = 0.019), SRT-treated regions (16.7 ± 2.6 mmHg; P = 0.015), and controls (16.9 ± 2.4 mmHg; P = 0.018). Similarly, the mean pre-retinal PO2 of only PC-treated regions (25.2 ± 4.7 mmHg) was higher than those of the untreated regions (16.3 ± 2.5 mmHg; P = 0.006), SRT-treated regions (17.7 ± 3.1 mmHg; P = 0.023), and controls (16.4 ± 2.4 mmHg; P = 0.007) 4 weeks after treatment. OCT and LM revealed selective retinal pigment epithelium damage with the sparing of photoreceptors in SRT lesions.

CONCLUSIONS: SRT treatment did not induce changes in the oxygen consumption of photoreceptors, or the pre-retinal PO2 .