The Anatomy of a Dog’s Eye

A dog’s eye is pretty similar to humans anatomically, with just a few differences. For one, dogs’ eyes have a third eyelid for additional protection. Their eyes also have more rods in their retinas that help process visual stimuli and help them see much better than us, especially in the dark.

Other than the mentioned differences, a dog and a human’s eye is practically identical. It has a clear outer protective barrier called the cornea and a white fleshy part called the sclera. Inside, the eyes are divided into two chambers: the anterior and posterior chambers. The anterior chamber has aqueous humor that provides nourishment for the other parts.

The two chambers are separated by the iris, pupil, and lens. The iris is the colored portion of the eye and is responsible for dilating or contracting the pupil. The pupil is the small opening of the eye that allows light to enter from outside. The entering light is focused by the lens and is received by the rods in the retina at the back of the eye for interpretation.

As mentioned, there are situations where eye color change is considered a normal process, but most cases are due to specific eye problems. All these parts can be affected by different eye conditions which can result in compromised visual function. Damage to any of these eye components can result in color changes, either on the surface of the eye or in the structures inside.

Common Eye Conditions that Cause Color Changes in Dogs

1. Heterochromia

Though not technically a color change that occurs as the dog goes through different life stages, it is still a condition that interests most dog owners, especially if their dog has it. Heterochromia is described as having two eyes of different colors. The color difference is observed in the dog’s iris, the pigmented part of the dog’s eyes.

Heterochromia is a condition caused by the lack of pigmentation of one of the irises of the dog. This results in one of their eyes being bluish or white. It is often hereditary and is passed on to the dog’s offspring. Breeds like Siberian Husky, Australian Shepherds, Australian Cattle dogs, Border Collies, Dachshunds, Chihuahuas, Shih Tzus, Great Danes, and Dalmatians are predisposed to developing this condition.

2. Nuclear Sclerosis

This is another eye condition that causes changes in the color of the dog’s eye but is considered normal. Nuclear sclerosis, also known as lenticular sclerosis, is described as the change in the color of the dog’s lenses. This is considered a normal process and happens as the dogs get older.

The lenses are mostly made of gel proteins, which become harder and change in color as the dog gets older. Nuclear sclerosis results in a hazy, gray, or bluish appearance which can be easily be confused with cataracts. Unlike cataracts, nuclear sclerosis is not a medical concern and does not affect the dog’s vision. It does, however, affect the dog’s ability to focus light and images.

3. Cataracts

Cataracts are characterized by the increase in the opacity of the lenses of the dog’s eyes. This occurs when the protein component of the lens clumps together and forms a cloud-like substance, preventing light from entering the eyes. Unlike nuclear sclerosis, cataracts in dogs cause vision impairment which can lead to total blindness if not managed properly.

Most cataracts in dogs develop as a complication to an underlying condition, such as diabetes mellitus. It changes the color of the lenses from transparent to almost white in severe cases. Other possible causes of cataracts in dogs are eye injury and old age.

4. Glaucoma

The aqueous humor found in the anterior chamber of the eye is constantly being produced and drained, maintaining a certain level of pressure inside the eye. Glaucoma develops when the drainage of the aqueous humor becomes obstructed, leading to a build-up of the fluid in the anterior chamber resulting in an increase in the pressure inside the eye, called intraocular pressure.

This results in symptoms involving pain, pawing of the eyes, lethargy, and decreased appetite. Because of the build-up of aqueous humor, the anterior chamber becomes hazy and bluish in appearance. Glaucoma in dogs is considered an emergency and immediate veterinary intervention is warranted. If not treated promptly, it can damage the eye’s nerve and cause blindness.

5. Scleritis and Uveitis

Inflammation of the outer part of the eye, called scleritis, or the inner structures, called uveitis, leads to color changes. In scleritis, the white part of the eye becomes bloodshot and the blood vessels become engorged, making the eyes red in appearance. This usually happens in response to corneal injury or irritation on the surface of the eye.

Uveitis happens when there’s inflammation or a significant injury to the eye, either due to an infection or deep corneal ulceration. Inflammatory cells migrate to the anterior chamber of the eye resulting in a hazy bluish appearance. This is usually accompanied by scleritis, conjunctivitis, and excessive tear production depending on the severity of the trauma.

Read more:

10 Facts About Your Dog’s Eyes

Dry Eye in Dogs and Cats

Why do my dog’s eyes look cloudy?

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