Eye Diseases and Disorders
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OphthalmologyAn ocular examination is best performed in a quiet, well-lit room that can also be darkened. The initial examination of the eye and orbit should assess for symmetry, normal conformation, and the presence of any gross lesions. The patient should initially be viewed from 2–3 feet (~1 meter) away, in good light, and with minimal restraint of the head. The menace response, pupillary light reflexes (PLRs), and dazzle reflex should be assessed with a strong light and magnification in both bright and dim lighting. Routine baseline tests like the Schirmer tear test (STT), fluorescein staining, and tonometry (intraocular pressure [IOP] measurement) are generally performed next. An STT should be performed before any drops are placed on the eye or the eye is cleansed. If indicated, a culture should be taken before any other routine baseline test. If indicated, corneal or conjunctival cytology can be performed after topical anesthesia is administered. The adnexa and anterior segment should then be evaluated in both bright and dim lighting with a strong light and magnification. Depending on the type of tonometer used, prior instillation of a topical anesthetic may be required. Tonometry should be performed before dilation of the pupil; the pupil should not be dilated if the IOP is elevated, because pupillary dilation may further increase the IOP. Diseases of the lens, vitreous, and ocular fundus are best evaluated by direct and indirect ophthalmoscopic examination (usually performed after inducing mydriasis with tropicamide); without dilation, examination of these structures is challenging and they cannot be fully evaluated. Vision can be further evaluated by maze testing in both bright and dim lighting. If indicated, the nasolacrimal duct can be flushed. If fluorescein stain is visible in the nostril after the cornea is stained, then the nasolacrimal system is patent and functioning (positive Jones test).
- Physical Examination of the Eye in Animals
- Eyelids in Animals
- Nasolacrimal and Lacrimal Apparatus in Animals
- The Conjunctiva in Animals
- The Cornea in Animals
- The Anterior Uvea in Animals
- Glaucoma in Animals
- The Lens in Animals
- The Ocular Fundus in Animals
- The Optic Nerve in Animals
- The Orbit in Animals
- Prolapse of the Eye in Animals
- Ophthalmic Manifestations of Systemic Diseases in Animals
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Chlamydial ConjunctivitisChlamydial conjunctivitis refers to an acute, chronic, or recurrent infection of the conjunctiva of a variety of animals with intracellular bacteria of the family Chlamydiaceae. Although often asymptomatic, infection may also lead to acute or chronic purulent inflammation of the conjunctiva with or without the presence of keratitis or other pathologies. Antimicrobial treatment typically involves administration of tetracycline-class antibiotics. Systemic administration is preferred because chlamydial conjunctivitis may arise as a result of systemic infection and/or involve shedding at other anatomic sites.
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Equine Recurrent UveitisEquine recurrent uveitis (ERU) is an important ophthalmic condition, with a reported prevalence of 2%–25% worldwide. The classic form of ERU is characterized by episodes of active intraocular inflammation followed by variable quiescent periods. However, some horses experience insidious ERU, in which subclinical ocular inflammation persists without obvious signs of discomfort. With chronicity, the inflammatory bouts cause secondary ocular changes such as cataracts, lens luxation, glaucoma, phthisis bulbi, and retinal degeneration. As a result, ERU is the most common cause of blindness in horses in the world.
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Eyeworm DiseaseThelaziases are caused by spirurid nematodes (also known as eyeworms), which cause infestation of the orbital cavities and associated tissues of several animal species. These whitish nematodes are transmitted by nonbiting dipteran muscid flies or drosophila fruit flies (intermediate hosts) while feeding on the lacrimal secretions of infected animals. Adults of Thelazia spp localize under the eyelids and the nictitating membrane, as well as in nasolacrimal ducts, conjunctival sacs, and excretory ducts of lacrimal glands, depending on the species targeted. Thelaziases may be responsible for eye disease, with signs and symptoms of varying severity (eg, lacrimation, ocular discharge, epiphora, conjunctivitis, keratitis, and sometimes corneal opacity or ulcers). Levamisole and ivermectins (eg, doramectin) administered either subcutaneously or intramuscularly, are useful for the treatment of thelaziasis in cattle and horses. Some Thelazia spp may also infect humans.
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Infectious KeratoconjunctivitisInfectious keratoconjunctivitis of cattle, sheep, and goats is a common ocular condition characterized by blepharospasm, conjunctivitis, lacrimation, and varying degrees of corneal opacity and ulceration. In severe cases, ocular rupture leading to blindness can result. Affected animals can present at any age, but young stock are most commonly affected. The disease can occur at any time of year, but outbreaks are most often associated with warmer times of year, when risk factor exposure is greatest.
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Neoplasia of the Eye and Associated StructuresThe various tissues of the eye and associated structures can be the site of primary or metastatic neoplasms. Ophthalmic neoplasms vary in histologic type, frequency, and importance in different species, and they are an important group of diseases in veterinary ophthalmology.
