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An immunohistochemical study of the ‘snowbank’ in a case of pars planitis

Purpose: To characterize the extracellular matrix and cellular components of a ‘snowbank’ removed during vitreous surgery for treatment of retinal detachment complicating pars planitis. Methods: The ‘snowbank’ was examined using immunohistochemical techniques and a panel of monoclonal and polyclonal antibodies directed against glial fibrillary acidic protein (GFAP), cytokeratin, alpha smooth muscle actin, tenascin, laminin, fibronectin, and collagen types I, II, and III. Results: The ‘snowbank’ was acellular except on the uveal side where there were cytokeratin-positive retinal pigment epithelial cells. There were no cells positive for the glial cell marker GFAP and the myofi- broblast cell marker alpha smooth muscle actin. The extracellular matrix of the ‘snowbank’ contained tenascin and collagen types I, II, and III. There was no immunoreactivity for laminin and fibronectin. Conclusion: These results on the immunohistochemical components of the ‘snowbank’ may be useful in clarifying the nature of the chronic inflammatory process in pars planitis. They indicate extensive tissue repair and remodeling, leading to major loss of function.