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D.M. Benderson, S.L. Bernstein; Turning Down the Heat on PRP . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5722.
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Despite more than 40 years of pan–retinal photocoagulation (PRP) therapy for proliferative diabetic retinopathy, there is still no consensus regarding how much visible scarring is needed for adequate treatment. While it is assumed that photoreceptor layer destruction is necessary for clinically effective therapy, the power required to achieve this is not entirely clear. We sought to determine whether high laser power is essential for effective PRP, or whether lower powers can generate the same effect.
Retinae from 4 Long–Evans Hooded rats were treated with argon laser photocoagulation (500 Microns; 0.1 sec, 535 nM). Power was varied from 50–250 mW. A minimum of 12 burns/retinae were performed. Fundus photographs were taken pre–, immediately post–, and 21 days post–treatment. Animals were euthanized 21 days post–treatment, and paraformaldehyde–fixed eyes were sectioned and stained with H&E. Histological analysis of the photoreceptor layer, RPE layer, and choriocapillaris was performed. Clinically effective treatment was defined as a loss of the photoreceptor layer.
Retinal blanching occurred at powers as low as 80 mW. However, photoreceptor loss (signifying effective tissue damage) was only achieved with powers of 130 mW and greater. Higher powers resulted in more damage, but did not result in greater photoreceptor loss.
Effective PRP may be achievable with lower powers than are conventionally utilized. Visible blanching does not necessarily correlate with the degree of histological damage. These results are important in terms of minimal–maximal responses to treatment, patient comfort and compliance.
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