Neuro-ophthalmology in Horses

Neuro-ophthalmology in Horses: A complete neuro-ophthalmologic assessment is part of every ophthalmic and neurologic examination. Cranial nerves II, III, IV, V, VI, VII, and VIII and a portion of the sympathetic and parasympathetic innervation to the head can be evaluated on or near the eye by general observation, by vision assessment, by assessing the menace response, ocular reflexes (pupillary light, dazzle, and palpebral), and by observing globe and lid movement, positions and response to touch. Neuro-ophthalmic assessment of the equine patient begins with a routine general history that should also include questions related to use of the horse, performance, and visual acuity in bright and dim light situations. The neuro-ophthalmic examination should be performed, whenever possible, in a well-lit environment that can be darkened completely as required. Some patients require sedation before any portion of an ophthalmic examination can proceed but ideally the examination is completed without sedation and without the use of any topical or local anesthetic agents. Equipment needs are minimal: a focal halogen or other bright light source such as a Finhoff transilluminator or otoscope light (nonmagnified) and a towel to use, if needed, as a blindfold. The clinician is cautioned to never use an LED penlight or other LED light source unless its brightness has been previously assessed on a human, as some LED penlights are sufficiently bright as to create discomfort similar to that of looking at the sun and leave a retinal afterimage that may persist more than 24 hours.