Visual disturbance: where do I look?

Visual disturbances often signal serious ophthalmic disease. Comprehensive general medical and ophthalmic histories are most helpful. information about the animal's vision, based on Its performance In familiar and unfamiliar environments, should be obtained from the owner. As bilateral Involvement and visual disturbances are often associated with systemic diseases, a complete physical examination is Indicated. The ophthalmic examination consists of a series of diagnostic procedures to isolate and define the ophthalmic disorder. Several clinical tests can be performed easily In the examination room, including the light-Induced pupillary reflex, the dazzle or photic reflex, the menace reflex, the obstacle course test and, If indicated, the flash electroretinogram, the visual evoked response and, recently, the pattern electroretinogram. Ophthalmic diseases that produce visual disturbances In dogs often affect the cornea, aqueous pathways, lens and ocular fundus; In cats, they usually affect the uveal tract and are associated with serious systemic diseases. Orbital diseases are not usually associated with visual disturbance unless the optic nerve is Involved. Corneal diseases and cataract formation that involve the visual axis and puplliary aperture often cause visual disturbance. Inflammations of the iris and ciliary body can produce both acute and long-term visual disturbance and even blindness. Diseases of the retina and optic nerve usually present as visual disturbances In the absence of pain. SUMMARY The presentation of a small animal patient with a history of a visual disturbance requires a thorough search to identify and treat the basic disease. The patient's breed, age and sex, and medical and ophthalmic histories provide a foundation of information and often assist in suggesting possible diseases. As many systemic diseases may present initially as an ophthalmic condition and/or visual disturbance, a complete physical examination should be performed. The ophthalmic examination should carefully analyse the entire eye and higher visual centres. Any disease within the eye sufficient to cause obstruction to the ocular fundus can result in visual impairment or even blindness. Several simple reflexes can be performed in the examination room to evaluate the eye and provide some indication of the patient's vision. The light-induced pupillary reflexes should not be confused with vision but are important in assessing the overall integrity of the retina, optic nerve, parasympathetic system and iridal sphincter. The dazzle (photic blink) reflex is also a subcortical reflex, but seems to be positively associated with vision. The patient's vision should be tested within the examination room and with the assistance of the pet's owner. Not all pets cooperate, but the majority of the animals can provide a meaningful performance in both scotopic and photopic conditions. A makeshift obstacle course can provide useful information about the animal's ability to see. The flash ERG and the visual evoked response can provide additional information. A combination of the patient's medical and ophthalmic histories, the results from the physical and ophthalmic examinations, the ophthalmic reflexes and visual tests provide a foundation to determine the cause of visual disturbance. Additional ophthalmic diagnostic tests, radiographs, clinical pathology, serology and other procedures may be employed to establish the cause of the visual disturbance, prognosis and possible treatments.