Health & Medical

Ask a Vet: My Dog Has Red Eye and Prescribed Eye Drops Aren’t Working

Red Eye in Dogs Shih Tzu | Vanillapup

Brachycephalic breeds like Shih Tzus are susceptible to Red Eye due to severe eye exposure and poor tear production. Dr Rui shares with us the causes and diagnosis.

Q: My Shih Tzu has Red Eye. We have visited a vet several times. He advised to use Tobradex and Ciloxan, but they weren’t effective. Human eye drops seem to work but are they safe?

To treat “Red Eye” (eye redness), there is a protocol to follow to help us determine the possible condition causing it before advising the appropriate treatment.


The most common conditions causing eye redness would be dry eye, conjunctivitis, keratitis (inflammation of the cornea) and corneal neovascularization, scleritis or episcleritis, and glaucoma.

Shih Tzus are prone to having “Red Eye” caused by conjunctivitis due to their severe eye exposure, brachycephalic syndrome, and frequent dry eye conditions.

These characteristics of the breed make them suffer frequent conjunctivitis and keratitis and it is crucial to diagnose this in due time.

Other frequent conditions affecting Shih Tzus (and other brachycephalic breeds) are:

1. Medial canthus entropion – inward inversion of the eyelids

If the lower eyelid rotates inwards and sufficiently covers up or occludes the lower tear duct openings, it will cause tears to overflow under the eye.

2. Trichiasis – eyelashes deviating towards the cornea

In this case, eyelashes will chronically irritate the eye surface. Even if the dog does not show discomfort, it can contribute to keratitis and pigment deposition on the cornea.

3. Distichiasis – presence of an extra row (or more) of eyelashes

This is also a common anomaly of the eyelid in the Shih Tzu. The rigidity and direction of these abnormally placed lashes vary from dog to dog.

If the lashes are soft and the tear film is normal, they may cause a few lesions. But, when the lashes are coarse and stiff and the tear film is inadequate, or the hairs are growing towards the cornea, then considerable discomfort and corneal irritation may result causing a red eye condition.

This condition may prevent even a minor corneal abrasion from healing or may cause it to worsen leading to a corneal ulcer.

4. Reduced corneal sensitivity compared to non-brachycephalic breeds

While afflicted dogs may not exhibit acute or severe corneal pain, diminished innervations can contribute to delayed recognition of the problem. It can also contribute to ongoing damage that leads to impaired corneal wound healing.

5. Quantitative or qualitative tear deficiencies

Tear deficiencies can further aggravate a corneal injury and be the cause of a chronic red eye situation.

6. Shallow orbits (eye sockets)

Shallow eye sockets offer considerably less protection to the globe (eyeball) than the deeper eye sockets of the non-brachycephalic breeds.

This orbital anatomy, especially when combined with excessively long eyelid openings will greatly increase the potential for traumatic proptosis. It is a globe-threatening condition in which the eyelid margins become entrapped behind the equator of the globe. As a result, it is impossible for the patient to blink and protect the front structures of the globe.


First of all, a vet should start the veterinary examination by measuring the tear production of your Shih Tzu through the Schirmer’s tear test.

It is also important to have her intraocular (eye) pressure checked by using a tonometry test. This is to rule out primary glaucoma, of which the breed is susceptible. This is especially relevant if your vet has ruled out all the above-mentioned conditions and the eye redness still persists.

If the eye redness is persistent and your regular vet has not diagnosed a specific cause, I would recommend you to consult a Veterinary Ophthalmologist.

Photo credit: Brad Montgomery via / CC BY

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Dr. Rui Oliveira
Veterinary Ophthalmologist at Amber Vet
DVM CertVOphthal MRCVS

Dr. Rui Oliveira graduated from the Technical University of Lisbon in 1999, followed by an intensive Postgraduate Diploma in Veterinary Ophthalmology in Barcelona in 2002. He attained the Certificate in Veterinary Ophthalmology awarded by the Royal College of Veterinary Surgeons London (RCVS) in 2012.

He has since practiced in multiple countries and worked in veterinary teaching, and advised several zoos, aquariums, and wild animal centres in Portugal.

He is currently the Consultant Ophthalmologist at Amber Vet and enjoys treating eye cases and performing surgery for cataract, glaucoma, and conditions of the eyelids, cornea, and retina.
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