Health & Medical

It is half past nine, the hall light is off, and the dog stops dead at the bottom of the stairs. He has gone up those stairs every night for eleven years. Tonight he stands there, head low, waiting. You flick the light on and up he goes as though nothing happened. Most stories of canine vision loss begin somewhere around that moment, in the gap between something being not quite right and anybody putting a name to it.

Vision fails in dogs at two very different speeds, and they cause completely different amounts of alarm. Gradual loss is easily missed, because dogs memorise their homes with startling accuracy. A dog who has learned where the coffee table sits will walk past it confidently while seeing almost nothing, and the first real clue often comes on holiday, in a strange house, or in poor light where the memory map stops helping. Sudden loss is unmissable and terrifying, and it is far more likely to have a cause that needs handling today.

Cataracts are the change most owners think of first. A cataract is an opacity within the lens itself, and once it is dense it physically blocks light from reaching the back of the eye. The pupil looks white or crushed-ice grey rather than black. Some cataracts are inherited and appear in young dogs of predisposed breeds, others come with age or follow injury or inflammation. The version that catches people out is the diabetic cataract: in a dog whose blood sugar has been running high, lenses can go from clear to almost totally opaque within weeks, sometimes in a matter of days. It is one of the reasons a newly diagnosed diabetic dog needs their eyes looked at, not only their glucose curve.

Then there is the change that looks exactly like a cataract and is not one. Nuclear sclerosis is a normal hardening of the lens with age, and it gives the eye a hazy blue-grey depth from about seven or eight years onwards. It scatters a little light and may soften close focus slightly, but it does not blind a dog. Owners regularly convince themselves their old dog has cataracts and quietly grieve for their sight, when the vet can distinguish the two in seconds with the right light. If you can see haze in your dog's eyes, get it identified before you decide what it means.

SARDS, sudden acquired retinal degeneration syndrome, is a stranger one. The retina simply stops working, usually over days to a few weeks, and the eye itself looks entirely normal on casual inspection. The giveaways are widely dilated pupils that respond poorly to light and, often, a run-up of a month or two in which the dog was drinking more, eating more and putting on weight, which frequently gets investigated as a hormonal problem first. Middle-aged, slightly overweight small-breed females seem to feature more than most. Confirming it needs an electroretinogram at a referral centre, there is no treatment currently proven to restore vision, and the blindness is permanent.

Glaucoma deserves its own paragraph because it hurts and because it destroys sight quickly. Pressure inside the eye rises, and a badly affected eye can lose vision within a day or two. Look for a red, angry eye, a cornea that has gone cloudy or bluish, a pupil stuck wide open, squinting, tearing, or an eye that simply looks bigger than the other. Many of these dogs are not crying out; they just go quiet, withdrawn and off their food, which is easy to misread as a bad mood. Treat a painful cloudy eye as a same-day emergency. In the inherited form, the second eye is at real risk too, and preventive treatment for it is a genuine discussion to have.

Retinal detachment from high blood pressure is the one most people have never heard of, and it matters most in cats. An older cat with kidney disease or an overactive thyroid can develop hypertension severe enough to lift the retina away, and the result is an animal who was fine yesterday and today is walking into the fridge with pupils like saucers. Dogs get it too. Blood pressure measurement is quick and painless, and if the pressure is brought down promptly some of these patients regain useful sight, which is exactly why this needs seeing straight away rather than at the weekend.

Worth watching for at home: hesitating at kerbs, refusing stairs that were never a problem, bumping into furniture only in dim rooms, losing a thrown ball that lands in plain view, startling when touched, sticking closer to your legs than usual, sniffing along walls, or pupils that stay wide in bright light. Anxiety and clinginess in an older dog can be the first sign anybody notices.

The good news is that dogs handle blindness far better than owners expect, because scent and hearing were doing most of the work already. Keep furniture exactly where it is. Resist rearranging. Block stairs, ponds and pool edges, put a different textured mat at the top and bottom of steps, keep water and food bowls in fixed spots, and talk before you touch so nobody gets startled. Teach a simple verbal warning like step or careful. Use noisy or scented toys. Keep them leashed in unfamiliar places. Most blind dogs settle within a few months and go back to being unmistakably themselves.

Is surgery worth it? For cataracts, often yes, provided the retina behind the lens still works, which is checked with an electroretinogram and an ultrasound before anyone books a theatre slot. Success rates in suitable dogs are good, though it demands weeks of eye drops and repeat check-ups from you. Glaucoma is different: if an eye is blind and painful, removing it usually leaves a much happier dog than any amount of medication. For SARDS there is nothing surgical to offer, and the work is all in adapting the house.