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M.B. Nehemy, E. Magalhães, R. Mattos, M.S. Pedrosa; Transpupillary thermotherapy inpigmented rabbits : a histopathologic study of threshold and decrescent sub–threshold doses . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1817.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To evaluate, in rabbits, the chorioretinal effects of threshold and decrescente sub–threshold transpupillary thermotherapy (TTT) in order to help to stablish optimal treatments parameters. Methods: TTT was performed in 30 pigmented rabbits using a 810 nm diode laser with spot size of 3.0 mm. The power used at the first application, in order to stablish the exposure time, was 300 mW. The exposure time was determined individually interrupting the irradiation immediately after any visible change was present. In the subsequent pulses the laser power was decreased in 20, 40 and 60% (240,180 and 120 mW, respectively). Color and red free retinography, and histologic examination, by light microscopy (LM) and transmission electron microscopy (TEM), were performed 24 hours, 7 and 30 days after treatment. Results: Immediately after TTT and 24 hours later , retinal whitening was detected when powers of 300 and 240 mW were used. These lesions were pigmented at 7 and 30 days. No visible change was clinically detectable at any examinations, when 180 and 120 mW were used. When 300 and 240mW were used, LM showed significant lesions in the retina and choroid, 24 hours after TTT, and a glial scar after 30 days. The powers of 180 and 120mW caused significant lesions on LM, but TEM demostrated outer segment photoreceptor cell damage and ultrastructural cells lesions, at all examinations. Conclusions: Slightly sub–threshold evolves into thereshold TTT a few minutes after treatment. Threshold (300 mW) and slightly sub–threshold (240 mW) TTT causes significant chorioretinal damage detectable by LM. Sub–thereshold with a decrease of 40% and 60% of the thereshold laser power show lesions on TEM that are undetectable on LM.
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