EXTRAOCULAR-MUSCLE CHANGES IN EXPERIMENTAL ORBITAL VENOUS STASIS - SOME SIMILARITIES TO GRAVES ORBITOPATHY

Background: Graves' orbitopathy (GO) is generally considered to have a n autoimmune etiology. Recently, however, it has been hypothesized tha t orbital venous obstruction may contribute significantly to the clini cal manifestations. To determine whether such obstruction could induce histologic and clinical findings consistent with GO, we developed an animal model of orbital venous obstruction by ligating the draining op hthalmic veins of the right eyes of four cats. Methods: The branches o f the ophthalmic veins were isolated and ligated following a lateral o rbitotomy. Weekly photographs and echographs were taken of the cats; o ne cat was killed at each of four time points, namely 1, 2, 3, and 4 w eeks after surgery. Histologic stains were applied to isolated orbital tissues to characterize pathologic changes. Results: Clinically, ther e was onset of marked proptosis, chemosis, and exotropia. Histological findings within the extraocular muscles included activation and the p resence of acid mucopolysaccharides 1 week after ligation, increased c ollagen and the presence of lymphoid cells at 3 weeks after ligation, and persistent interstitial lymphocytic infiltrates the 3rd and 4th we eks after ligation. Conclusion: Without evoking a primary orbital infl ammation or inducing a systemic autoimmune disease, an animal model ha s been developed that closely mimics many of the advanced clinical and histologic changes that occur in GO.