Acute Vision Loss
Acute loss of vision may occur with many ophthalmic and CNS diseases, usually with abrupt onset of blindness, anisocoria, mydriasis, and loss of both direct and indirect pupillary light reflexes. Bilateral loss of vision is more common, but unilateral vision loss can occur particularly when the other eye is blind. For acute vision loss, large amounts of the retina must be involved; lesions of the optic nerve can cause blindness, because the disease process can be quite localized. The rod or cone photoreceptors may be preferentially affected initially and cause either night or day vision loss. Evaluation includes thorough ophthalmic and general physical examinations, because many systemic diseases may cause blindness. Because visual field evaluations cannot be performed in animals, subjective tests for vision are necessary and include the menace test, dazzle reflex, maze test in both light and dark illumination, electroretinography, and visual evoked potentials.