Effect of Transpupillary Thermotherapy (TTT) on the Normal Mouse Retina

Abstract

Abstract: : Purpose: To evaluate the histological effect of transpupillary thermotherapy (TTT) on the normal mouse retina using visible and non-visible thermal burns. Methods: TTT (power 50, 60 or 70 mW, spot size 0.5 mm, duration 60 s) was delivered to the fundus of 42 pigmented C57BL/6 mice using a diode laser (emission wavelength 810 nm) and a slit lamp delivery system with a handheld contact lens. Eyes were enucleated at 1, 3, 5, 7, 10, 14 and 28 days, respectively, after treatment and histological sections were prepared and stained with hematoxylin-eosin. Results: No visible effect was seen in the retinas after TTT treatment with a power of 50 mW whereas the retinas of all eyes treated with a power of 70 mW showed moderate whitening. Histological analysis showed no damage to the retina, RPE or choroid at any time point using a power of 50 mW. In contrast, the retinas of eyes treated with a power of 70 mW exhibited progressive retinal damage that was almost exclusively located to the photoreceptors. In those cases, early damage to the photoreceptor outer segments was seen one day after TTT and after 5 days the outer nuclear layer had degenerated. At the same time-point an accumulation of pigmented cells, presumably macrophages, was seen in the subretinal space. No apparent damage was seen in the RPE or choroid. Conclusions: The close correlation between visible thermal retinal burns showing whitening and photoreceptor damage underscores the importance of using sub-threshold effects when applying TTT to patients with neovascular age-related macular degeneration.

Keywords: age-related macular degeneration • animal model • choroid: neovascularization