This study evaluates the effects of exposure duration, beam diameter, and power on the safety, selectivity, and healing of
retinal lesions created using a continuous line scanning laser. A 532 nm laser (PASCALTM) with retinal beam diameters
of 40 and 66 μm was applied to 60 eyes of 30 Dutch-Belted rabbits. Retinal exposure duration varied from 15 to 60 μs.
Lesions were acutely assessed by ophthalmoscopy and fluorescein angiography (FA). RPE flatmounts were evaluated
with live-dead fluorescent assay (LD). Histological analysis was performed at 1 hour, 1 and 3 days, 1 and 2 weeks, and 1
and 2 months following laser treatment. Ophthalmoscopic visibility (OV) of the lesions corresponded to photoreceptor
damage on histological analysis at 1 hour. In subvisible lesions, FA and LD yielded similar thresholds of RPE damage.
The ratios of the threshold of rupture and of OV to FA visibility (measures of safety and selectivity) increased with
decreasing duration and beam diameter. Above the threshold of OV, histology showed focal RPE damage and
photoreceptor loss at one day without inner retinal effects. By one week, continuity of photoreceptor and RPE layers was
restored. By 1 month, photoreceptors appeared normal while hypertrophy and hyperpigmentation of the RPE persisted.
Retinal therapy with a fast scanning continuous laser achieves selective targeting of the RPE and, at higher power, of the
photoreceptors. The damage zone in the photoreceptor layer is quickly filled-in, likely due to photoreceptor migration
from adjacent zones. Continuous scanning laser can treat large retinal areas within standard eye fixation time.