Ocular Diseases

Considerable research interest has been directed toward amphibian retinal and central visual pathway physiology, retinal injury, and lens injury and repair. However, reports of spontaneous ocular diseases of amphibians are scarce. Mycobacterial panophthalmitis was reported in a South American Bullfrog (Lepto-dactylus spp.). Corneal edema and panophthalmitis have been noted in both natural and experimental infections of Leopard frogs (Rana pipiens) with Flavo-bacterium indologenes.

Severe panophthalmitis and otitis interna were reported in a large group of recently imported Fire-Bellied toads (Bombina orientalis). Corneal stromal infiltrates, scleritis, hyphema, hypopyon, iridocyclitis, cataract, and chorioretinitis were prominent. Opisthotonus, circling, head tilt, and loss of righting reflexes were associated with otitis interna. Several bacteria were cultured from affected eyes and normal viscera, including Aeromonas hydrophila, Citro-bacter freundii, Providencia alcalifaciens, Klebsiella oxytoca, and an unidentified oxidase-positive, Gramnegative bacillus resistant to tetracycline. Topical treatment of presumptive or proven bacterial ocular infections in amphibians must be undertaken with recognition of the potential for systemic toxicity. Gentamicin diluted to 2 mg/mL has been recommended.

Corneal opacities in amphibians have several potential causes. The most extensively reported and investigated disorder is lipid keratopathy. Originally discovered in Cuban Tree frogs (Osteopilus septentrionalis), it has since been identified in species of captive Hylid, Leptodactylid, and Ranid frogs either as a corneal and hepatic lesion or as part of a generalized xanthomatosis affecting the brain, some viscera, peripheral nerves, periarticular soft tissues, and digital pads. Hypercholesterolemia has been noted in animals with disseminated xanthomatosis. Clinically, dense white stromal opacities are seen, which are often raised with corneal thickening and surface epithelial irregularity (Figure 19.29). In advanced cases, the densest opacities are in the central cornea. Histologically, empty cholesterol clefts within keratocytes and between corneal collagen lamellae are present with occasional foamy macrophages in the stroma and between epithelial cells. Affected frogs have all been females, many with massive egg development, suggesting that excessive lipid mobilization associated with oogenesis may play a role. Dietary fat has been suggested as a factor, but affected animals have been fed several different diets.

Cataracts have been noted regularly by some observers, occurring both in conjunction with other ocular disorders of the anterior segment and alone. Phacoemulsification was successfully performed on a Loggerhead sea turtle (Caretta caretta).

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  • Category: Eye diseases