Photophobia or light sensitivity in dogs

Photophobia is the term given to a hypersensitivity to light, which in dogs can indicate signs of a potential illness. A range of other symptoms may accompany the condition, which will all need to be considered in combination when making a diagnosis. Photophobia can cause pain and discomfort for the affected dog, and over the long term, a hypersensitivity to light can in fact cause permanent damage to the eyes. Because the condition is one that is not overly common or much discussed online, many dog owners are completely unaware that photophobia can affect dogs, making diagnosis more of a challenge.

It is a good idea for all dog owners to develop a basic understanding of the condition and its symptoms, in order to learn how to identify it. In this article, we will look at canine photophobia in more detail. Read on to learn more.

What causes photophobia in dogs?

There are a fairly wide range of different conditions that can lead to photophobia, and not all of them are directly related to the eyes themselves. The main causes of photophobia in dogs include:

• Corneal damage, affecting the external membrane of the eye.
• Damage to the retina of the eye itself.
• Cataracts.
• Ulcers on the eye.
• Problems or damage to the oculomotor nerve, which leads to an inability of the pupils of the eyes to constrict normally in bright light.
• Congenital or hereditary defects with the eyes themselves, which may be breed-related.
• Conjunctivitis in one or both eyes.
• Uveitis, or an inflammation of the uvea, the middle layer of the eye.
• Abscesses, tumours or other growths that affect the ocular nerves.
• Papillary dilation, which may occur spontaneously or be caused by the presence of irritants.
• Canine distemper.
• Toxicity or some forms of poisoning.
• Meningitis.
• Infections of the respiratory tract.
• Shock or trauma to the eyes themselves.
• Neurological conditions.
• Rabies, in countries that are affected by it, or in dogs that have visited such countries.
• Various types of medications including benzodiazepines and even chemotherapy for cancer can lead to light sensitivity too.

Symptoms of photophobia in the dog

Because there will often be no physical changes to the appearance of the eyes themselves in cases of photophobia, the symptoms of the disorder in dogs tend to be subtle and hard to spot. Photophobia means that being exposed to light, particularly very bright light will be uncomfortable and painful for your dog, and so your dog will likely go out of their way to avoid bright rooms and direct sunlight. If your dog appears to have turned into something of a vampire when it comes to going out in the sun but is perfectly happy in dim light and during the evening, photophobia may be the cause.

In some cases, your dog will squint or appear to be wincing when in bright light, in an attempt to minimise the brightness.

You can make an informed assessment of your dog’s sensitivity to light by taking them outside on a bright day and seeing how they react after a few minutes, once their eyes will have had a chance to adjust.

Diagnosing photophobia in dogs

If you suspect that your dog is suffering from photophobia, you should take them along to the vet for a thorough examination and definitive diagnosis. Your vet will use various tools including an ophthalmoscope and possibly a slit lamp to inspect the eyes, taking a good look at the whole of the eye, including the eyelids, iris, conjunctiva, sclera and cornea.

How your vet proceeds then will depend on the range of conditions that they have narrowed down the potential cause of photophobia to, which may include some of the following:

• A swinging lamp test, to reveal pupillary abnormalities and potential damage to the optic nerve. This test should also reveal the presence or absence of neurological problems.
• An intraocular pressure test, to detect any problems directly affecting the eye itself, such as glaucoma.
• If toxicity or poisoning is suspected, your vet may need to run a blood panel on your dog to look for toxins.
• If your dog has a discharge from their eyes, your vet will likely test this too, in order to diagnose problems such as conjunctivitis.
• If your dog is unvaccinated, the vet may need to consider and test for canine distemper.

What happens next?

Dogs that are diagnosed with photophobia will need to be kept in low light conditions and not exposed to bright light or full sunlight until the condition is resolved. Ascertaining and treating the underlying cause of the sensitivity is the key to resolving the issue, and preserving the dog’s sight, as well as addressing their discomfort and pain.

Some of the causes of photophobia, such as progressive conditions and infections can lead to irreversible blindness if left untreated, and so taking your dog along to the vet for diagnosis as soon as you spot a problem is vitally important.