Exophthalmos has been reported to occur spontaneously in at least one genus of otherwise healthy fish, Atlantic cod, Gadus morhua. The eyes from twelve, otherwise healthy rockfish, Sebastes sp., were enucleated, fixed, embedded in paraffin and sectioned in order to characterize the histologic changes associated with a unilateral, idiopathic exophthalmos.  Five of the twelve fish served as controls.  Seven fish were unilaterally exophthalmic.  All fish were members of a captive population for at least one year prior to ocular enlargement.

In all seven of the exophthalmic eyes, gross abnormalities were found in the choroidal layer consisting of large cysts filled with a clear, watery fluid and surrounded by dense, newly-formed connective tissue.  The choroid body in the control eyes was densely filled with erythrocytes, whereas in the exophthalmic eyes it contained markedly fewer erythrocytes and an abundance of a homogenous proteinaceous material along with focal accumulations of inflammatory cells.  The exophthalmic eyes also showed proliferation of scleral cartilage with disorientation of chondrocytes.  Some of the affected eyes showed pigmentary abnormalities with clumps of heavily pigmented cells present in the retina and choroid. Retinal degeneration and detachment was evident in some of the abnormal eyes.  The exophthalmos appeared to be due to development of the choroidal cysts.