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Daniel V Palanker, Philip Huie, Seungjun Lee, Gavin Tan, Roopa Dalal, Daniel Lavinsky; Heat Shock Protein Expression Following Retinal Laser Therapy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5673.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the thresholds and activated area of the heat shock protein (HSP) expression after retinal laser therapy at energy levels ranging from conventional photocoagulation to non-damaging photothermal therapy.
Pigmented rabbits have been treated with 577nm PASCAL laser using EndPoint Management (EpM) software and retinal spot size of 200μm. Using 20ms pulses, laser power was first titrated to produce barely visible lesions, which was considered 100% energy on EpM scale. Laser exposures were then applied at 120%, 100%, 30%, 25%, 20% and 15% energy. Eyes were fixed 7 hours later, corresponding to peak expression of the HSP70. Immunohistochemistry was performed with histological sections and with whole-mount retinal preparation.
Exposures at 120% and 100% energy produced light and barely visible burns in acute ophthalmoscopic examination. Exposures at 30% energy and below did not produce any visible damage, even in histological analysis. In whole-mount imaging of RPE, the HSP expression in the 120% and 100% burns appeared as bright rings with the average outer diameter of 311 and 292μm, and the inner diameter of 186 and 138 μm, respectively. The 30%, 25% and 20% exposures appeared as bright discs with an average diameter of 176, 145 and 64 μm, respectively. There was no visible expression at 15% energy. In cross-section, the HSP expression in the visible burns (100% and 120%) appeared in the RPE surrounding the damage zone, and in the choroid below the retinal damage zone. In the 30% exposures, HSP was expressed only in the RPE.<br /> In the standard ETDRS pattern composed of light burns spaced by 2 spot diameters, the area activated with HSP expression corresponds to 22% of the treatment zone. With the 30% energy and 0.25 diameter spot spacing the activated area is 41%, and with zero spacing it increases to 64% of the treatment zone.
HSP expression, as a marker of the cellular response to thermal stress, indicates that cells surviving the hyperthermia express HSP around the conventional visible burns, as well as in the middle of the non-damaging spots, with energies ranging from 30% to 20% on EpM scale. Such a narrow therapeutic window of the HSP expression with non-damaging laser settings indicates that careful titration should be performed in each patient, and high density pattern is required to assure clinical efficacy of the non-damaging retinal laser therapy.
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