Updated November 1, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
When a dog’s eye turns red or produces more discharge, infection is only one possibility. Corneal scratches, dry eye, abnormal eyelashes, allergies, inflammation and glaucoma can also cause redness or tearing. These conditions require different treatment; some can threaten sight if the wrong drops are used or care is delayed.
What discharge and redness can tell you
Clear tears may accompany irritation or poor drainage. Thick discharge can occur with infection or inadequate tear production. Squinting or holding the eye closed suggests pain and deserves particular attention. A veterinarian interprets the appearance alongside the dog’s history rather than diagnosing from discharge color alone.
Eye problems that need immediate care
Severe squinting, a cloudy or blue-looking cornea, obvious trauma, sudden vision loss, a bulging eye or marked pain warrants same-day or emergency care. A dog with a scratch or corneal ulcer may look as though it has conjunctivitis. Steroid-containing eye drops can worsen some ulcers, so leftover prescriptions are not safe substitutes for examination.
Tests that guide the treatment
The veterinary team may use fluorescein staining to detect corneal defects, measure tear production, assess eye pressure and inspect eyelids. Bacteria, dry eye and injuries are treated differently. The clinician can also explain when rechecking is necessary to make sure a corneal problem is healing.
What you can do in the meantime
Prevent rubbing if possible, avoid dust or chemical sprays and keep the dog calm. Do not use human redness-relief products or attempt to remove an embedded foreign body. Arrange help for persistent symptoms even if the dog otherwise seems well.
See when a dog’s eye symptoms require veterinary care and practical ways to reduce avoidable irritation.
Reference
Merck Veterinary Manual, ophthalmic disorders in dogs.
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.