A dog's eyes show trouble quickly and, unlike many other body systems, they forgive delay poorly. The signs fall into two groups: changes you can see in the eye itself — redness, cloudiness, discharge, swelling — and changes in what he does, such as squinting, pawing at his face, or misjudging a step he has taken a thousand times. One eye or both matters, too. A single red, painful eye that appeared today points down a different path from both eyes slowly growing hazy over a year in an elderly dog, and being able to say which pattern you are seeing helps your veterinarian enormously.
What the surface of the eye is telling you
Compare the two eyes directly, in good light. Look for a white of the eye threaded with angry red vessels, a cornea that has lost its glassy clarity and looks cloudy, steamy, or blue-gray, and any discharge — clear and watery, stringy mucus, or thick yellow-green material collecting in the corner. Check whether both pupils are the same size, whether the third eyelid is showing more than usual, and whether one eye looks larger, smaller, or more prominent than the other. A small speck, scratch, or something stuck under a lid can drive intense irritation in an otherwise healthy-looking eye.
Pain and vision signs in his behavior
Squinting, holding an eye closed, blinking repeatedly, tearing, rubbing the face on the carpet, or pawing at the eye all suggest discomfort, and a dog doing any of these is telling you the eye hurts now, not eventually. Vision change is quieter: bumping into chair legs in a rearranged room, hesitating at curbs and stairs, missing a tossed treat, or startling when a hand comes from one particular side. In a senior dog, a gradual blue-gray haze in both eyes can be a normal aging change in the lens, but only an examination can distinguish that from a cataract or another problem, so gradual still deserves a check.
What to do, and what not to do, at home
Prevent more damage first: stop him rubbing, using a protective cone if he is determined, because a paw can turn a minor irritation into a serious surface injury in minutes. Note when it started, anything that preceded it — a walk through long grass, a scuffle, shampoo at bath time, a dusty car ride with his head out the window — and whether it is improving or worsening. Do not use leftover eye medication from a previous problem or another pet, and do not borrow human drops; the wrong product can seriously harm an eye with an unseen surface defect. Photographing the eye daily in the same light gives an honest record of change.
Eye signs that are same-day urgent
Treat as urgent: an eye held shut or obviously painful, sudden cloudiness, a visible injury or something embedded, one eye bulging, a pupil of a different size, sudden vision loss, or any chemical or shampoo splash into the eye — rinse a chemical splash gently with clean water on your way to getting help. Eye conditions can deteriorate within hours, so a painful eye is never a wait-until-next-week problem. Call your veterinarian or an emergency clinic and describe exactly what you see; they will tell you how fast to come in.
A dated eye record for a system that changes fast
Because eye history guides treatment — a recurring redness each spring is different from a first episode after an injury — writing down dates, which eye, triggers, and what was prescribed builds a genuinely useful pattern over a dog's life. Keeping those eye notes in KinsLe's Pet Passport with the rest of his health packet means any veterinarian, including an emergency clinician meeting him for the first time, can see his full eye history without you reciting it under stress.