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R. A. Linsenmeier, C. Lee, J. J. Kang Derwent, E. Budzynski, J. H. Smith; Damage to the Cat Choriocapillaris Caused by Argon Laser Photocoagulation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4167.
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To investigate the extent of damage to the choriocapillaris produced by lesions similar to those that are used to destroy the outer retina in panretinal photocoagulation (PRP).
Photocoagulation was performed in the retinas of 6 anesthetized cats with an argon laser. Small lesions, of 200 or 500 µm diameter, and larger lesions, made with several confluent 500 µm spots, were made in different cats. Cats were allowed to recover for 4 weeks and then indocyanine green dye (ICG) was used to image the choroid with a scanning laser ophthalmoscope (SLO). In a final procedure, 15 µm diameter fluorescent microspheres were injected into the heart, the choroid was removed and flat mounted, and the microsphere distribution was imaged. In some animals the retinal lesions were analyzed histologically.
The lesions destroyed the photoreceptors while leaving the inner nuclear and ganglion cell layers relatively unaffected. ICG angiograms showed that the choriocapillaris in the region under the large or 500 µm lesions was severely damaged or absent, but the larger vessels of the choroid remained intact. Damage could not be detected with the SLO in the 200 µm lesions. Severe damage was found by analyzing the microsphere distribution in all lesion sizes. In photocoagulated areas there were few if any microspheres, implying an absence of choriocapillaris blood flow.
Lesions similar to those placed in human PRP always produced damage to the choriocapillaris in cats. This is not surprising, because the choroid is so close to the major absorbers of laser energy. In other experiments, we showed that the intraretinal PO2 at the choroid was lower in lesioned areas than in normal areas of the retina, which is consistent with the damage observed here. We suggest that PRP may sometimes be ineffective in stopping neovascularization clinically because the expected elevation of inner retinal PO2 following photoreceptor loss is compromised by choroidal damage.
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