Retina damage needs quick action to save sight

The retina is a layer of tissue at the back of the eye that collects light relayed through the lens. Special photoreceptor cells in the retina convert light into nerve impulses, which are transmitted to the brain. At the retina’s centre is an especially critical area called the macula, which enables you to see anything directly in front of you, like words on a page, a person’s face, the road ahead or the image on a screen.

When blood flow through the retina is blocked or when the retina pulls away from the wall of the eye, getting the problem properly diagnosed can be an emergency. Modern treatments can do wonders if they are begun before the damage is irreversible. But a delay in getting to a retinal specialist can diminish the ability of even the best therapy to preserve or restore normal vision.

As with all living tissue, the retina is highly dependent on a constant supply of oxygen-carrying blood. Should anything disrupt that, vision is at risk. Two retinal mishaps, retinal-vein occlusion and retinal detachment, can occur at any age, but both are more common among older people.

In July, David Bronson of New York, an avid reader at age 82, realised that the vision in his left eye was a little cloudy. He thought a developing cataract was the cause, but when he saw an ophthalmologist two weeks later, he learned that the problem was more serious: a partial blockage in the central vein that drains blood from the retina. The blockage caused pressure to build in the capillaries that take blood to the retina, which then leaked into the centre of the eye, clouding Bronson’s vision. The blockage and its consequences are analogous to a clogged sink drain; if water keeps running into the sink, it will eventually spill over the top.

Retinal-vein occlusion is a common cause of vision loss in older people, second only to diabetic retinopathy as a blood vessel disorder of the retina, according to a report last year in The New England Journal of Medicine. Unlike Bronson’s experience, retinal-vein occlusion most often involves a branch vein, which is less serious and in half of cases resolves on its own within six months. If treatment is needed, most, though not all, patients respond well to laser therapy, the journal authors reported.

Leading risk factor

High blood pressure, Bronson’s only other health problem, is the leading risk factor for this disorder, but retinal-vein occlusion is also associated with diabetes, elevated blood lipids, smoking, kidney disease and glaucoma.

Typically, patients develop sudden painless vision loss in one eye. The extent of vision loss depends on how much of the retina is affected and whether the macula is involved. Most of the time, the diagnosis can be made based on a clinical exam, although a test called fluorescein angiography is often performed to assess the severity.

Retinal detachment, which occurs in about 18 out of 100,000 people a year, is much less common than retinal-vein occlusion but more likely to cause permanent vision loss if not promptly treated.

The longer the retina remains detached, the less likely vision can be restored, so it is vital to recognise the symptoms and seek an ophthalmologist’s care without delay.

Retinal detachment is painless but nearly always causes symptoms, often before the detachment starts: a sudden appearance of many “floaters” – spots, hairs or strings – in your vision; sudden brief flashes of light even when your eyes are closed; or a shadow over part of your visual field.

In addition to age, risk factors for retinal detachment include extreme nearsightedness, a family history of the problem, a prior detachment in one eye, cataract surgery and a severe eye injury, as can occur in an auto accident or from a paint ball, a BB gun or a bungee cord, said Dr Donald J D’Amico, chief of ophthalmology at Weill Cornell Medical College.

In an interview, he outlined the usual treatments. The simplest, called pneumatic retinopexy, can be done in the doctor’s office under local anesthesia. A gas bubble is injected into the vitreous cavity. As the gas expands, it presses the retina against the wall of the eye and closes the break. The patient must remain face down for most of several days to weeks to keep the bubble in the right place. The retinal break is often permanently sealed with a freezing probe or laser.

Another common treatment is scleral buckling, done in a hospital under anesthesia but usually on an outpatient basis. A permanent silicone band is sewn to the outside wall of the eyeball, creating an indentation that presses the retina back in place.