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Jenny Wang, Daniel Lavinsky, Philip Huie, Roopa Dalal, Dae Yeong Lee, Seung Jun Lee, Daniel V Palanker; Determining the therapeutic window of non-damaging retinal laser therapy by protein expression. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5845.
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© ARVO (1962-2015); The Authors (2016-present)
“Sub-threshold” laser therapy has been used in several configurations to treat macular disorders with promising but inconsistent results and unknown therapeutic mechanism. In this study, we use a titration algorithm, Endpoint Management (EpM), to deliver specified thermal dose to the retina and define the therapeutic window for non-damaging laser therapy by measuring the thresholds of (a) cellular toxicity and (b) expression of heat shock protein (HSP70) and glial fibrillary acidic protein (GFAP).
Dutch-belted rabbits (n=15) were irradiated with a 577 nm PASCAL laser using the EpM titration algorithm to set experimental pulse energies relative to a barely visible lesion. Grids of laser spots at 20, 25, 30, 40, 100 and 114% energy settings were applied and the RPE was analyzed at 7 hours after laser application using live/dead staining and whole-mount immunostaining for HSP70. Histology (t = 1 day) and scanning electron microscopy (t = 1 hr) were also performed to confirm damage threshold. Immunohistochemistry for GFAP (t = 1 month) was used to measure long-term glial cell activation. Results were compared to a computational model of the retinal heating.
Energy setting of 30% (n = 250) was non-damaging while 40% (n =250) was damaging in 69% of laser spots. HSP expression in the retinal pigment epithelium (RPE) was observed at 25% energy and above, with activated area at 30% measured as 0.75 (0.62 – 1.02) mm2 per 100 spots. HSP expression area increased through 40%, but at higher settings, the HSP expressing cells appeared only at the edges of the central damage zone. Our computational model matched experimentally observed HSP expression patterns for cells where Arrhenius integral was in the non-damaging therapeutic window (0.1< Ω < 1). Activation of GFAP in Muëller cells 1 month after the laser treatment was observed with energy settings of 30% and higher.
Retinal laser therapy with 30% energy on EpM scale can avoid tissue damage within normal variations of pigmentation and it activates two different types of tissue response: heat shock protein expression in the RPE and activation of Müller cells in the retina. Lack of tissue damage allows (a) macula therapy at much higher spot density than conventional photocoagulation, which should boost clinical efficacy, (b) treatment of the fovea, and (c) periodic retreatment in chronic diseases.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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