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Light Sensitivity (Photophobia) in Dogs

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • Sudden squinting in light usually means a painful eye and needs a vet promptly.
  • In older dogs, iris atrophy stops the pupil from shrinking and makes bright light uncomfortable.
  • Iris atrophy is harmless to vision but can't be reversed.
  • Some breeds inherit day blindness that starts in puppyhood.
  • Eye glow comes from a mirror-like layer; a clear difference between the eyes is worth a vet check.

Table of Contents

Research Causes Iris atrophy Day blindness Eye glow Home comfort FAQ Sources

Dog Eye Quicklinks

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A dog who squints, blinks a lot or turns away from bright light may have a painful eye, or pupils that can't shrink to block the glare.1,2 Pupils normally get smaller in bright light so the eye isn't dazzled.3 Sudden light sensitivity, especially in one eye, usually means pain from something like a corneal ulcer or inflammation inside the eye, and needs a vet promptly.4,1,5 Gradual light sensitivity in an older dog is often iris atrophy, a harmless aging change.2,6

See your vet the same day if your dog:

  • Suddenly squints or holds one eye shut, especially with redness, tearing or cloudiness4,1
  • Has pupils that are suddenly different sizes5
  • Has an eye that looks bigger, cloudy or bluish, which can mean glaucoma7,8
  • Seems to have trouble seeing5,1

What the Research Says

  • A dilated pupil shows most in bright light. A neurology specialist explains that a pupil that won't shrink is easiest to spot in bright light, and a pupil that won't widen is easiest to spot in the dark. That helps vets work out which eye is abnormal.3
  • Some unequal pupils clear up on their own. In about half of dogs with Horner's syndrome (a small pupil and drooping lid), no cause is found. These cases usually clear up within 1 to 6 months.3,9
  • Day blindness starts early. Inherited cone degeneration causes light sensitivity and poor daytime vision from about 8 to 12 weeks of age. A cheek-swab DNA test is available.10

Causes of Light Sensitivity

A painful eye

  • Corneal scratches and ulcers, often with squinting and tearing.4,11 See corneal ulcers.
  • Uveitis (inflammation inside the eye): most dogs avoid bright light, keep the eye shut and have a small pupil.1 See cloudy eyes.
  • Glaucoma, which also makes the pupil large.7,3 See glaucoma.
  • Conjunctivitis and eye infections.12
  • Something in the eye, or rolled-in eyelids rubbing the eye.13,14

Pupils that can't shrink

  • Iris atrophy in older dogs (below).2,15
  • Pupil-dilating eye drops, which can leave the eye light-sensitive for several days after you stop them.4
  • Nerve problems affecting the pupil, and some poisonous plants.3,6

Problems with the retina

  • Inherited day blindness (cone degeneration), described below.10

Some drops cause light sensitivity as a side effect.16 Flat-faced breeds are prone to ulcers, so squinting in these dogs should always be checked.17,11

Iris Atrophy in Older Dogs

Iris atrophy is a gradual thinning of the muscle in the colored part of the eye. It's a normal aging change. The pupil edge looks ragged or "moth-eaten," the pupils may be different sizes, and they stay larger and react slowly to light.2,6,15

  • Who gets it: middle-aged to older dogs of any breed, often from about 8 years. It's more common in small and toy breeds, Poodles and Cocker Spaniels.15,6
  • Is it serious? No. It doesn't affect vision, but it's slowly progressive, and bright light can be uncomfortable.6,2
  • Treatment: none is needed, and it can't be reversed.2,15

Iris atrophy has to be told apart from glaucoma and nerve problems that also cause a large pupil, so it's worth having an eye exam, ideally by an ophthalmologist.2,3

Inherited Day Blindness

In cone degeneration, the cells that work in daylight stop functioning. Affected puppies see well in dim light, but bright light is irritating and painful, and their daytime vision is poor. Signs start at about 8 to 12 weeks of age.10 The eyes look normal on a routine exam, so a special test of retinal function confirms it. Breeds include Alaskan Malamutes, German Shorthaired Pointers, Australian Shepherds and Siberian Huskies, and a DNA test is available for breeding dogs.10

Pannus, an immune disease of the cornea mostly in German Shepherds, is made worse by UV light. Vets may recommend UV-protective dog goggles along with lifelong drops.18,7

Why Do Dogs' Eyes Glow at Night?

Most dogs have a mirror-like layer at the back of the eye called the tapetum lucidum. It reflects light back through the retina to help them see in dim light, and that's the glow you see in headlights or flash photos.19,20

  • The glow can be green, blue, yellow or orange, and it often changes color in puppies during the first few months.19,20
  • Some dogs have little or no tapetum, most often blue-eyed dogs. Their eyes glow red in photos, because the camera sees blood vessels at the back of the eye.19,20
  • If the glow gets duller or brighter over time, or your dog's two eyes glow clearly differently, eye specialists recommend an exam, because it can be a sign of eye disease.19,20

A white or cloudy pupil in normal light can be a cataract. Only an exam can tell it apart from normal age-related clouding of the lens.21,22,2 See cataracts.

Keeping a Light-Sensitive Dog Comfortable

  • Walk early or late, and avoid midday sun (about 10 a.m. to 2 p.m.).7
  • Give your dog shady spots outdoors and a dim, quiet place to rest.15,7
  • A nightlight can help older dogs move around at night.15
  • Tinted dog goggles can cut glare if your dog accepts them. Introduce them slowly with treats, and never force them.7,6

Treat the cause when there is one. A painful eye needs your vet, not just shade.1,4

Frequently Asked Questions

Why is my dog's eye sensitive to light?

Usually a painful eye problem such as an ulcer or uveitis, or, in older dogs, iris atrophy that stops the pupil from shrinking.

Why does my dog squint in the sun?

It can be a painful eye, or pupils that can't shrink, as with iris atrophy. New squinting, or squinting in one eye, needs a vet check.

Is iris atrophy serious?

No. It doesn't affect vision and needs no treatment, but bright light may be uncomfortable.

Why do dogs' eyes glow at night?

A reflective layer at the back of the eye bounces light back through the retina to help them see in the dark.

Why does one of my dog's eyes glow red in photos?

Red glow can be normal in dogs with little reflective layer, but a clear difference between the two eyes is worth showing your vet.

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Sources and further reading

This article was rewritten and fact-checked on October 27, 2026 against current veterinary references and specialist guidelines:

  1. Hunter T, Llera R, Ward E. Uveitis in dogs. VCA Animal Hospitals, February 2023.
  2. American College of Veterinary Ophthalmologists. Signs of age-related change in the eye.
  3. Ives E. Problematic Pupils: A Logical Approach to Anisocoria. Southern European Veterinary Conference, Seville, 2019 (IVIS).
  4. Barnes C, Weir M, Ward E. Corneal ulcers in dogs. VCA Animal Hospitals, July 2025.
  5. Llera R, Hunter T, Yuill C. Anisocoria in dogs. VCA Animal Hospitals, February 2023.
  6. Hamzianpour N. Bilateral mydriasis in a senior neutered toy poodle. Vet Times, April 2017.
  7. Maharaj N. Eye protection for dogs: goggles, sunglasses, and more. American Kennel Club, March 2026.
  8. Gelatt KN. Glaucoma in dogs. Merck Veterinary Manual (pet owner version), updated September 2024.
  9. Hunter T, Llera R, Ward E. Horner's syndrome in dogs. VCA Animal Hospitals, February 2024.
  10. UC Davis Veterinary Genetics Laboratory. Cone degeneration. Accessed October 2026.
  11. Packer R. Eye problems in brachycephalic dogs. The Kennel Club. Accessed October 2026.
  12. Gibeault S. Dog eye infections. American Kennel Club, April 2026.
  13. Lort Smith Animal Hospital. Foreign body in the eye in dogs, updated March 2025.
  14. Giuliano EA. Eyelid Surgery Challenges. Southern European Veterinary Conference, Barcelona, 2017 (IVIS).
  15. Dayton L (reviewed by Morrison BJ, DVM). Iris atrophy in dogs: what it is and common causes. PetMD, April 2026.
  16. Hyland K. Fluoroquinolone antibiotic eye drops (drug information). VCA Animal Hospitals, May 2024.
  17. Plummer CE. Understanding and addressing brachycephalic ocular syndrome. Today's Veterinary Practice, April 2026.
  18. Weir M, Llera R, Ward E. Pannus in dogs (chronic superficial keratitis). VCA Animal Hospitals, September 2023.
  19. American College of Veterinary Ophthalmologists. Why do my dog's eyes shine at night?, December 2020.
  20. VCA Animal Hospitals. Why do your pet's eyes glow in the dark?. Accessed October 2026.
  21. Barnes C, Weir M, Ward E. Cataracts in dogs. VCA Animal Hospitals, May 2024.
  22. Gelatt KN. Disorders of the lens in dogs. Merck Veterinary Manual (pet owner version), updated April 2026.

About this article

Last updated : rewritten using the American College of Veterinary Ophthalmologists, VCA, the AKC, UC Davis and IVIS proceedings.

This page is for general information and is not a substitute for an exam by your veterinarian.