Ophthalmomyiasis

Ophthalmomyiasis is the presence of dipteran fly larvae in the eye. It is believed to be caused by the sheep nasal botfly (Oestrus ovis) and the cattle warble fly (Hypoderma bovis). Larvae gain access to the eye via the blood or migrate directly through the eye. Larval migration and/or death causes mild to severe inflammation of intraocular tissues. Anterior uveitis with hyphema and retinal detachment may also occur with ophthalmomyiasis.

Cats are more commonly affected than dogs. The presence of arcuate or linear depigmented areas in the tapetal and nontapetal fundus may be caused by traumatic, degenerative, or inflammatory disease of the retinal pigment epithelium (Figures 1 and 2). The animals are usually visual, and clinical findings are often subtle.

History

A 13-year-old female Domestic Shorthair cat was presented to the University of Florida Veterinary Medical Teaching Hospital for a laceration of the tail that necessitated amputation.

Examination

During the patient's hospitalization, an ophthalmic screening examination revealed normal pupillary light reflexes in both eyes. The ocular examination of the left eye was normal for a cat of this age. Ophthalmic examination of the right eye revealed severe vitreal and retinal hemorrhage (Figures 1 and 2, white arrowheads) with multiple linear, arcuate tracks in the tapetal and nontapetal regions (Figures 1 and 2, arrows). A white, segmented, motile object was present in the vitreous (Figure 1, yellow arrowhead).

Ask Yourself...

The primary differential for vitreal and retinal hemorrhage in an aged cat is circulatory hypertension associated with renal disease. The tracks may be mistaken for a variety of inflammatory, traumatic, or degenerative diseases of the retina. The uniform width and apparent continuous nature of the tracks are strong evidence of larval migration, orophthalmomyiasis. Other causes of retinal and vitreal hemorrhage, anterior uveitis, retinal detachment, and chorioretinitis are found in the Tables.

Ophthalmomyiasis is evident as curvilinear tracks of retinal degeneration and retinal hemorrhage in cats. Larvae may be alive or dead, and free-floating in the vitreous. The actual incidence of this condition may be quite high in Florida, with many reports in cats particularly noted in the Daytona Beach area.

Most cases of feline ophthalmomyiasis are incidental findings and require no therapy. In this case, the retinal and vitreal hemorrhage resorbed without therapy over a 6-week period. The retinal tracks also became less obvious.

Causes of Retinal and Vitreal Hemorrhage

• Trauma

• Bleeding disorders

• Blood parasites

• Hyperviscosity syndromes

• Retinal inflammation, including ophthalmomyiasis

• Neoplasia and lymphoreticular diseases

• Congenital retinal/vascular anomalies

• Hypertension from kidney disease

• Severe anemia

Causes of Anterior Uveitis

Exogenous

• Trauma

• Perforating wounds or exogenous introduction of infection

• Intraocular surgery

Endogenous

• Extension of disease from cornea or sclera

• Ulcerative keratitis

• Interstitial keratitis

• Infection^TM Systemic mycoses (histoplasmosis,cryptococcosis)^TM FeLV, herpes, FIP, FIV, toxoplasmosis^TM Septicemia in general^TM Parasitism^TM Dirofilariasis^TM ToxoplasmosisIntraocular neoplasia (particularly lymphoma)IdiopathicImmune-mediated

• Lens-induced uveitis

• Auto-immune disease

Causes of Retinal Detachment

• Associated with congenital eye anomaly, retinal dysplasia

• Systemic infectious diseases (mycoses, FIP, FIV, toxoplasmosis, lymphosarcoma, FeLV)

• Neoplastic disease causing solid detachment

• Traction detachment associated with vitreoretinal adhesions

• Trauma

• Vitreal degeneration

• Sudden decreases in intraocular pressure (hypotony)

• Vascular disease resulting in serous or fluid detachment (vasculitis, uremia, vascular hypertension)

• Extraocular pressure from orbital neoplasia

• Retinal holes

Causes of Chorioretinitis

• Viral (FeLV, FIV, FIP)

• Bacterial (any septicemia)

• Fungal (cryptococcosis, histoplasmosis)

• Parasitic (toxoplasmosis, ophthalmomyiasis, ocular larval migrans)