Background: Transcleral retinopexy may be applied with either a cryoprobe or the newer contact laser delivery systems. Tissue responses to these modalities are studied. Methods: Transcleral 1064-nm continuous wave neodymium-ytrium-aluminum garnet (CW Nd:YAG) laser retinopexy lesions were compared with retinopexy lesions produced by a cryoprobe in a pigmented rabbit model. Equatorial transcleral CW Nd:YAG laser retinopexy or cryoretinopexy was applied. Rabbits were killed 1 day, 3 days, 1 week, or 1 month after treatment. Hematoxylin and eosin stains and immunohistochemical studies were conducted to determine the level of retinal damage and glial reaction. Antibodies against Muller cells (vimentin and glial fibrillary acidic protein), astrocytes (glial fibrillary acidic protein and S-100 protein), retinal pigment epithelial (RPE) cells (cytokeratin 8, 18, and 19 [5D3]), and macrophages (HAM 56) were used. Results: Lesions produced by cryotherapy showed significant overlying retinal destruction with intravitreal RPE cell (5D3 positive) migration. Lesions produced by transcleral CW Nd:YAG laser showed reaction primarily at the level of choroidal melanocytes and RPE. Marked expression of both glial fibrillary acidic protein and vimentin epitopes with a normal expression of S-100 was seen in the chronic lesion made with cryotherapy and with less intensity in lesions made with CW Nd:YAG laser. Conclusion: Although less inner retinal destruction and no intravitreal RPE migration was observed in lesions formed by transcleral CW Nd:YAG laser, similar deep retinal Muller cell reaction occurred in lesions formed by both cryotherapy and laser as demonstrated by immunohistochemical studies.
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