Many pet owners ask, "How well does my pet see? Does it see in color?"

Animal vision varies among the species. Most animals don’t see as well as do humans. Except for birds and primates, such as monkeys, the animal eye is not as well developed as the human eye.

For most animals, the clear cornea, or window of the eye, is not as curved as in people. This results in astigmatism and distorted images. The lens is larger and unable to change its shape as well as in humans. Thus, accommodation, or focusing, is also poorer in most animals.

The light-sensitive retina is not as well developed in pets, except in birds. The retina contains visual cells called rods and cones. Cones are needed for color vision and are concentrated in the macula, the part of the retina that provides sharp, straight-ahead (central) vision. Rods are needed for night vision and side (peripheral) vision. Birds have more cones in their retinas than do humans and thus have excellent color vision. They also have well-developed maculas, so most birds have better central vision than humans.

Except for birds, most domestic animals have mainly rod cells with few cones in their retinas. Their maculas are not as developed as in humans. Thus, color vision and central vision in these animals is not good. But most animals have better peripheral vision and can spot something immediately if it moves even slightly to the side.

Animals' eyes excel over humans’ in ability to see at night. This is because they have extra rods and something people don’t have; the tapetum lucidum. This specialized layer next to the retina intensifies and reflects lower levels of light, and is present in all animals except birds and monkeys. This layer is what makes animal eyes shine in the dark.

How common are eye problems in pets?
Pets experience most of the same eye conditions as humans. Glaucoma, cataracts, corneal ulcers (resulting from scratches) and retinal degenerations are just some of these common eye conditions.

One main eye problem that is not treated in pets is refractive error (near- and farsightedness and astigmatism). Most dogs are farsighted and astigmatic. However, since they don’t read the newspaper, they seldom complain.

Many of the eye problems in pets are inherited. Inbreeding (mating closely related animals) increases the chance of inherited eye defects. Most breeds tend to have at least one inherited eye problem.

Among dogs, poodles tend to inherit cataracts and retinal degenerations; collies often develop retinal detachments. Cocker spaniels are subject to cataracts, glaucoma, retinal degenerations and eyelid deformities. When you’re shopping for a purebred dog, it is important to know if the breeder screened the animal’s parents for inherited eye defects. The Canine Eye Registry Foundation (CERF) registers most purebred dogs with normal eyes.

Pets have other common eye problems. Cats are prone to viral infections that affect the eye. The most common is feline herpes virus. You should suspect this virus if your new kitten is sneezing and has a discharge from its eyes. Less common but more serious viruses include feline leukemia virus and feline immunodeficiency virus (feline AIDS). Fortunately, people are not affected by these viruses.

Eye trauma also occurs frequently in pets. Corneal lacerations (cuts to the outer surface of the eye) from cat claws are common. If you want to keep a dog and cat in the same house, it is recommended to have the cat’s front claws removed.

Short-nosed, prominent-eyed dogs (Pekinese, Pug, Shih Tzu and Lhasa Apso) are prone to corneal injuries such as ulcers, which can lead to blindness if left untreated.

In hunting dogs, plant debris often penetrates the cornea or gets trapped under the nictitating membrane ("third eyelid"). This type of injury results in painful ulcers on the cornea. Always check your dog’s eyes after a run in the field.

Pets are living longer now (15-18 years) and have more problems related to aging. High blood pressure is common in older pets, especially cats. It generally causes retinal hemorrhages (bleeding inside the eye), which can quickly progress to retinal detachment and blindness if untreated.

In older dogs, corneal edema (swelling) is common. Drug treatment can control the swelling and prolong vision. Cataracts also are common in older dogs. Usually cataracts can be removed if the dog is healthy enough to withstand surgery. Most people undergoing cataract surgery have an artificial lens implanted to replace their cloudy, natural lens removed during surgery. Animals, however, do not routinely get a lens implant after cataract surgery. Because most animals normally have poor accommodation and central vision, they seem to see well enough after cataract surgery without a lens implant.

How can I tell if my pet has an eye problem?
There are many signs or symptoms that suggest your pet has an eye problem.

If your pet has a discharge from its eyes, especially if present more than two days, have your veterinarian check it. If your pet has a discharge and squints or rubs its eye, the problem could be serious. Compare the animal’s two eyes. Is the white of the eye inflamed or does the eye have a cloudy, bluish cast? If so, these could be symptoms of an inflammations, such as iritis, or a corneal ulcer or glaucoma. You should take the animal to your veterinarian right away.

Also go to the vet if your pet acts confused and bumps into people or objects. This behavior usually indicates loss of vision.

Most veterinarians can recognize and treat the majority of eye problems your pet may have. If your vet is not sure about the diagnosis or treatment needed, he or she will generally refer your pet to a veterinary ophthalmologist in your area. These veterinary eye specialists have several years of advanced training in eye disease and are members of the American College of Veterinary Ophthalmologists.

How are my pet's eyes examined?
A veterinary ophthalmologist will most likely give your pet the same eye examination you would receive, including glaucoma testing. Exceptions are visual correction for glasses or other tests requiring the patient’s cooperation.

The doctor uses special lighted equipment to look at your pet’s eyes. It is the same as that used for people (ophthalmoscope and slit-lamp biomicroscope.) Most large dogs (Great Dane, St. Bernard) are examined on the floor rather than a table.

Pets rarely need sedation during an eye exam. Most pets are naturally a bit afraid of some of the procedures, but an owner’s touch and reassurance most often calms them. If the animal is a biter, a muzzle may be required.

Sometimes the veterinary ophthalmologist needs to touch the animal’s eye or tissues around the eye. In this case, he or she applies an anesthetic drop to numb that area. Since the animal feels no pain and gets a treat afterward, most pets don’t mind these exams.