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