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Daniel Lavinsky, Thiago Rassi, Jose A. Cardillo, Michel E. Farah, Rubens Belfort, Jr., Daniel V. Palanker; Restoration Of Retinal Morphology And Residual Scarring After Photocoagulation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):548. doi: https://doi.org/.
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To measure initial sizes of retinal lesions with various clinical grades and their healing over time in order to assess the appropriate number of spots for coagulating the same total area, as well as residual scarring.
Patients undergoing panretinal photocoagulation received laser treatment over 3.5 mm from the fovea. Lesions were produced with 100, 200 and 400µm beam, and pulse durations of 20 and 100ms. Moderate lesions were white-gray burns, while the light and barely visible lesions were produced with power decreased by 25 and 50%. Laser burns were measured with SD-OCT immediately, 1 week, 1, 2, 4 and 6 months after treatment.
30 eyes of 22 patients have been treated. In moderate 100ms lesions acute OCT showed changes extending from RPE to the nerve fiber layer. In the 20 ms burns the damage was confined to photoreceptor layer. With aerial beam of 400µm (retinal spot 376µm) the acute lesion width was 524, 433, 372 and 279µm for 100ms moderate, and for 20ms moderate, light and barely visible burns, respectively. With aerial beam of 200µm (retinal spot size 188µm) the acute lesion width was 390, 281, 234 and 174µm for 100ms moderate, and for 20ms moderate, light and barely visible burns, respectively. To maintain the same total coagulated area as in 1000 standard burns (100ms, moderate grade) with 400µm beam one needs to apply larger number of 20ms lesions: 1464, 1979, 3520 of the moderate, light and barely visible grades, respectively. Due to stronger relative effect of heat diffusion with smaller beam, with 200µm this ratio becomes larger: for every 1000 standard burns it requires 1932, 2783, 5017 exposures of 20ms with the moderate, light and barely visible grades. During follow-up all lesions decreased in size. With 200µm beam the residual damage area at 6 months relative to the initial size was 71% for 100ms moderate burn, and 47, 33 and 20% for moderate, light and barely visible 20ms burns. 100µm burns demonstrated the most significant healing, with barely visible lesions presenting a residual scar area of less than 15% after 4 months.
Decreasing the pulse duration, spot size and clinical grade helps to limit the residual scarring and disorganization in photoreceptor layer. However, it is important to increase spot density reciprocal to the initial lesion size, in order to maintain the same total coagulated area.
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