As a dog enters the clinic or examination room, the veterinarian will watch how the dog walks to look for any obvious signs of vision difficulties. The initial work-up will include an evaluation of pupil size and symmetry and an assessment of the dog’s pupillary light reflexes. The veterinarian probably will check the “menace reflex” by moving one hand swiftly toward the dog’s face, then stopping abruptly, checking for a blink reaction. Another test frequently done to detect vision deficiencies is to throw a cotton ball onto the floor while watching to see if the dog follows the movement. Blood and urine glucose levels will likely be assessed as well, to determine whether diabetes mellitus is a contributing factor to the dog’s vision problems.
The intraocular pressure of the eyes will be assessed to rule out glaucoma. The veterinarian tests the pressure inside the eye using an instrument called a tonometer. Assuming that intraocular pressure is normal, the veterinarian normally will dilate the pupils and use a penlight or other light source to characterize the nature and extent of the cataract and to evaluate for possible concurrent uveitis. Anesthetic drops are normally applied to the eyes before these tests to ensure a painless examination and accurate test results.
Other tests that veterinarians commonly use to diagnose eye conditions include the Schirmer tear test and staining the eye with a fluorescein dye. These two tests are used to check the moisture level of the eye, look for foreign bodies and determine whether damage to the cornea has occurred. Advanced testing may include ocular ultrasound and electroretinography to evaluate the retina and rule out concurrent retinal degeneration. These tests are usually performed if surgery is anticipated. Most of these advanced diagnostic tests typically are performed by a veterinary eye specialist.
If your dog shows signs of vision disturbances, contact your veterinarian. Cataracts usually are quite treatable surgically.