Iris Atrophy in Dogs: What It Is and Common Causes

Iris atrophy in dogs is a common, age-related eye condition that causes thinning of the iris and changes in pupil shape—usually without affecting vision. While it often looks concerning, most cases are harmless, though some dogs may develop light sensitivity. 

If you notice your dog’s pupil looks irregular or the eye appears “moth-eaten,” it’s important to have your veterinarian evaluate it. In some cases, iris atrophy can be linked to underlying eye conditions like uveitis or glaucoma, which may require treatment. 

What Is Iris Atrophy in Dogs?

Iris atrophy in dogs is a condition that occurs when the muscle of a pup’s iris starts to thin. This usually occurs around the edge of the iris, causing a misshapen pupil.  

It can also occur within the iris itself, leading to a moth-eaten appearance of the colored portion of the eye. 

Types of Iris Atrophy in Dogs 

There are two types of iris atrophy in dogs: 

• Primary (Senile) iris atrophy: This is the most common type of atrophy, which tends to show up in older dogs as a slow and natural process.  

• Secondary iris atrophy in dogs: This type occurs when the muscle thins due to pressure within the eye caused by inflammation from an underlying eye condition such as chronic uveitis, glaucoma, or trauma to the eye. This type of iris atrophy can be painful and require medical treatment. 

Symptoms of Iris Atrophy in Dogs

Iris atrophy in dogs may have few or even no symptoms.  

In some cases, dogs will become sensitive to light because the iris can no longer close the pupil in brighter conditions.  

In secondary iris atrophy, you might notice your dog squinting and winking more often. 

Other symptoms include: 

• Irregular edges of the pupil (not smooth) 

• Areas of less color laced in the colored part of the eye 

• Anisocoria (different pupil sizes) 

• Slow or absent light reflex in the eye (pupil will not constrict properly in bright light) 

Causes of Iris Atrophy in Dogs

There is no known cause for primary iris atrophy. 

Like many changes that come with age, it can just happen naturally. Small, toy breed dogs can be more predisposed, but any dog can develop the condition. 

In some cases, secondary iris atrophy is caused by uveitis, or inflammation of a layer in the eye called the uvea. Uveitis has many causes, ranging from systemic disease to ocular trauma. 

How Veterinarians Diagnose Iris Atrophy in Dogs

Iris atrophy in dogs is commonly diagnosed during a routine ophthalmology exam.  

When a light is shined into the eye, vets look for holes in the iris or an abnormally shaped pupil. Your vet may also do a pupillary light reflex test. For this test, a bright light is shined in the eye, which should cause the pupil to contract. An abnormal or delayed response from the pupil may be a sign of iris thinning. 

If any underlying condition is expected, your vet may perform tests to identify conditions including uveitis or glaucoma. X-rays may be performed on dogs who have experienced trauma that is possibly contributing to the iris atrophy. 

Treatment for Iris Atrophy in Dogs

There is no treatment for primary iris atrophy in dogs. As a normal part of aging for some dogs, it can’t be reversed.  

The good news is that, for most dogs, iris atrophy won’t affect their vision, although they may become more sensitive to light. 

Secondary iris atrophy is treated by addressing the underlying condition. 

• Uveitis is treated with using antibiotics both systemic/oral (Doxycycline) and topical (drops/ointment such as Neo-Poly-Dex), anti-inflammatories (prednisone or NSAIDs), and atropine eye drops to help with eye pain.  

• Glaucoma in dogs can be a medical emergency and needs to be treated by your vet right away with eye medication (Latanoprost and Dorzolamide) or even enucleation surgery. 

Eye trauma treatment can vary, from oral and topical medications to surgery, depending on the severity of the condition and the pain. 

Recovery and Management of Iris Atrophy in Dogs

With primary iris atrophy there is nothing to worry about!  

Due to the light sensitivity caused by iris atrophy, it’s recommended that you keep your dog out of bright light  and protect their eyes with goggles when they have to be outdoors during peak sunlight. 

At nighttime, they might appreciate a dim nightlight to help them navigate around easier. 

If your dog has secondary iris atrophy, make sure your pup wears a recovery collar. 

This helps them to not scratch, rub, or retraumatize the eye.  

Following all your vet’s instructions for home care is important, including giving all medications on time and for the length prescribed.  

It’s also important to continue to go to follow-up appointments with your vet to ensure your dog is healing properly.  

Prevention of Iris Atrophy in Dogs

For older dogs, preventing age-related primary iris atrophy is not possible. Since it doesn’t affect their vision, it’s just a cosmetic issue that most pups are completely unaware they have.  

With secondary iris atrophy, routine veterinary visits for physical eye exams are very important.  

Dogs should see their vet once a year for a healthy checkup to include vaccines, fecal checks, and a physical exam to look for any changes that can promptly be addressed.