Acute Vision Loss in Small Animals

Acute loss of vision is associated with diseases in three broad categories:

• opaque ocular media (eg, diffuse corneal edema or cataracts)

• retinal dysfunction

• optic pathway disease

Many ocular diseases (eg, anterior uveitis and keratitis) can cause vision loss to the affected eye because of loss of transparency to the cornea, anterior chamber, or lens. If the opposite eye is blind, then the patient may be presented for evaluation because of vision loss, although the owner may also notice the change in the appearance of the eye. Thus, this discussion focuses on acute bilateral vision loss when the ocular media are clear.

A complete history is critical because ivermectin can cause retinal toxicity as well as central blindness in dogs and cats, and enrofloxacin can cause acute retinal degeneration in cats. For acute vision loss, a thorough neuro-ophthalmic examination that assesses the menace response, dazzle and palpebral reflexes, and pupillary light reflexes (PLRs) is critical. Because large amounts of the retina must be involved, a fundic examination is also important to rule out diffuse retinal detachment or progressive retinal degeneration. Lesions of the optic nerve can also cause blindness, and the optic nerve head may appear normal if retrobulbar lesions are present.

If the retina appears normal and the patient is blind, then referral to an ophthalmologist is recommended. The ophthalmologist should perform an electroretinogram to diagnose sudden acquired retinal degeneration syndrome (SARDS) if retinal function is absent or should strongly suspect optic pathway disease if retinal function is present. If retinal function is normal, then a neurologist may need to perform a thorough neurological examination, and additional testing may be necessary.