Ophthalmic Manifestations of Systemic Diseases
Ophthalmic manifestations of systemic diseases are not uncommon with inherited, infectious, degenerative, and neoplastic disorders in animals. Often, ophthalmic examinations can assist in timely identification of the systemic disorder. Diseases affecting the vascular and nervous systems are likely to show ocular manifestations. Animals with bilateral ocular disease should be carefully evaluated for systemic diseases.
In dogs, ophthalmic diseases, such as retinal dysplasia, microphthalmia, and cataracts, have been associated with dwarfism, albinism, and merling. Infectious diseases often involve the uveal tract and present as iridocyclitis, choroiditis, and panuveitis. They may be caused by viruses (distemper, infectious hepatitis), rickettsial diseases (ehrlichiosis and Rocky Mountain spotted fever), bacteria (Brucella canis and Borrelia burgdorferi), fungi (Blastomyces, Coccidioides, Histoplasma, Cryptococcus, and Aspergillus), protozoa (Toxoplasma, Neospora, Leishmania, and Hepatozoon), algae (Prototheca), or parasites (Dirofilaria, Toxocara, and Diptera spp). Metabolic diseases associated with eye diseases in the dog include diabetes mellitus (cataract formation), hypocalcemia (cataracts), hyperadrenocorticism (corneal disease, cataracts, and lipemia retinalis), and hypothyroidism (keratoconjunctivitis sicca, intraocular hemorrhages from increased systemic blood pressure, and lipemia retinalis [hyperlipidemia]). Blood and vascular disorders may present as intraocular hemorrhage, retinal detachment, secondary glaucoma, and papilledema. Metastatic neoplasms, such as lymphosarcoma, most often affect the uvea, presenting as persistent uveitis, overt intraocular masses, intraocular hemorrhage, secondary glaucoma, or retinal detachment.
In cats, systemic diseases frequently affect the eye and associated structures. Eyelid inflammations are often associated with systemic Demodex cati and D gatoi, Notoedres cati (scabies), ringworm, and immune-mediated skin diseases. The pathogens that commonly cause infectious diseases of cats, eg, feline herpesvirus 1, Chlamydia, and Mycoplasma, frequently present as acute and recurrent conjunctivitis. Feline herpesvirus 1 is also associated with ulcerative and stromal keratitis, proliferative keratoconjunctivitis, corneal sequestrum, corneal symblepharon, and keratoconjunctivitis sicca. Feline infectious peritonitis, toxoplasmosis, feline immunodeficiency virus, and feline leukemia virus often present as anterior and posterior uveitis, chronic uveitis, retinal detachment, and secondary glaucoma. Acute vision loss with intraocular hemorrhage and retinal detachment in older cats may be secondary to systemic hypertension and is often associated with chronic renal failure or hyperthyroidism. Resolution of intraocular hemorrhages, repair of the retinal detachment, and possible restoration of vision depends on the successful lowering of blood pressure to normal levels, often using amlodipine, an oral calcium channel blocker.
In horses, systemic infectious diseases, such as adenovirus in immunodeficient Arabian foals, equine influenza, strangles (Streptococcus equi), Rhodococcus equi infection, leptospirosis, Lyme disease (Borrelia burgdorferi), and salmonellosis, may present as conjunctivitis, anterior uveitis, or posterior uveitis. Ophthalmic onchocerciasis can be markedly reduced by frequent administration of ivermectin but can present with anterior and posterior uveitis, peripapillary chorioretinitis, keratitis, keratoconjunctivitis, or lateral conjunctival vitiligo. Habronemiasis presents with inflammatory conjunctival masses of the periocular area (especially the medial canthus) associated with the aberrant migration of larvae of Habronema muscae, H microstoma, and Draschia megastoma. Therapy is usually systemic ivermectin.
In cattle, microphthalmia, cataracts, retinal dysplasia, and retinal detachments are associated with hydrocephalus and in utero infection of calves with bovine viral diarrhea. The same ophthalmic defects occur in lambs affected in utero with bluetongue virus. Vitamin A deficiency in piglets causes microphthalmia, and in calves blindness and optic nerve hypoplasia. Vitamin A deficiency in adult or growing cattle results in night blindness, mydriasis, and eventually total blindness. Ophthalmoscopic abnormalities include papilledema, retinal degeneration, and optic nerve atrophy. Vitamin A supplementation may restore vision in animals with night blindness only. Lymphosarcoma in cattle may present as bilateral progressive exophthalmia. Many infectious diseases, such as rhinotracheitis, malignant catarrhal fever, thromboembolic meningoencephalitis, and neonatal septicemia, may present with conjunctivitis or anterior or posterior uveitis. Intoxications such as male fern poisoning (Dryopteris filix), bracken fern poisoning (Pteridium aquilinum) in sheep, coumarin poisoning (sweet clover poisoning) in cattle, and phenothiazine toxicity in cattle present with clinical signs of blindness from retinal degeneration, intraocular hemorrhage, or corneal edema. (Also see Toxicology Introduction.)