You may notice that the pupils of your dog’s eyes are starting to look a bit bluer as he ages.  Is this a sign of cataracts?  Read on to find out more about a medical condition known as lenticular sclerosis and other interesting facts about your pet’s eye health.


Anatomy of A Dog’s Eye


A dog’s eye is comprised of three main sections, the anterior chamber between the cornea and iris; the posterior chamber between the iris and the lens; and the vitreous chamber between the lens and the back of the eye. When you bring your pet to our practice, you’ll see our doctors using an ophthalmoscope to view your pet’s eye and notice them adjusting a dial on the side of the device. This is changing the focus of the lens that they are looking through so they can see through these main areas of the eye to visualize the cornea, the lens, and the retina.



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What Does A Health Eye Look Like?

Eyes Should Be Symmetrical


When viewed straight on, your pet’s eyes should look symmetrical and if you gently rub your fingers over the top of your pet’s eye lids, the globes beneath should feel identical. It’s not uncommon for some dogs to have tear staining on the fur just below the tear duct on either side, but you should not see any dramatic changes in the size of the staining or the consistency of the tearing. Tearing is prevalent in some breeds because of their conformation; they are genetically pre-disposed to big eyes, short noses, crooked tear ducts or all of the above, consequently tears spill over the edges of the eyes instead of draining into the tear duct (nasolacramal duct) located in the corner of each eye next to the nose.




The eyelids of your pet should be open evenly on both sides and your pet should not be excessively blinking, often a sign of pain.


Whites of the Eye Or Sclera


The whites of the eyes are known as the sclera. You should not see prominent red veins in the sclera, an appearance that we refer to as ‘injected’ looking, or appearing as though the veins in your pet’s eyes are flush with blood.  Some breeds naturally have a bit of redness in the sclera, but the veins should not be pronounced.


Covering Of The Eye Or The Cornea


The cornea, or outermost covering of the eyeball should be moist and glossy. If the lighting is right, you should be able to see a reflection of yourself in it. Scratched corneas are a common eye injury that we see at Brookfield.  Pet’s with scratched corneas usually present with increased tearing in the affected eye, increased venation in the sclera, and a droopy eyelid or increased blinking. Because scratched corneas are painful, pets will often paw at their eyes and sometimes make the condition worse. Suspected injuries to the cornea must be treated by one of our veterinarians as soon as possible.


The Pupil


The pupil is the dark spot at the center of the iris, the light-controlling muscle of the eye that gives it color. Pupil size should be symmetrical in both of your pet’s eyes and both pupils should be equally responsive to changes in light, growing larger when the light dims and shrinking in size when the light brightens.


Bluish Color Change As Pets Age


As pets age, the fibers of the lens, located in the posterior chamber of the eye, become more compacted and scatter light in such a way to give it a bluish or cloudy appearance .  The condition is known as lenticular or nuclear sclerosis and may be visible as early as 7 years of age in dogs and cats. Interesting, humans can also suffer from nuclear sclerosis as they age. In dogs and cats, the condition does not significantly impact vision and is never treated. It is not the same as cataracts.




Unlike lenticular sclerosis, cataracts are deposits of protein on the lens, not due to changes in the lens.  Cataracts significantly affect a pet’s vision and can eventually lead to complete blindness. Pets may be genetically predisposed to cataracts, but they can also be a sign of more systemic disease like diabetes. Unfortunately, cataracts cannot be diagnosed merely by looking into your pet’s eyes; they must be diagnosed by a veterinarian using an ophthalmoscope. Pets that have cataracts may be eligible for corrective surgery.


Testing For Vision, the Menace Response Test


If you are interested in testing your pet’s sight, you can do something called the menace response test. Standing in front of your dog, cover one of his eyes with your hand, then push your other hand towards the open eye. If your pet is sighted, he should blink at the prospect of the ‘menace’, or your hand, coming towards his eye.


Why Do My Pet’s Eyes Glow At Night?


Have you ever noticed that your pet and other animals’ eyes shine at night when they are illuminated with the light of your car’s headlights or a flashlight? This is due to a structure located at the back fo the eye called the tapetum lucidum.  It’s a layer of cells positioned between the optic nerve and the retina that reflect light back onto the rods and cones (light sensory structures), essentially magnifying the light’s chances of stimulating the retina and allowing the animal to see better at night. In cats, the tapetum lucidum increases the sensitivity to light by 44% allowing them to see light that is imperceptible to humans.

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