Diabetic retinopathy

The retina is the one place in the body where blood vessels can be seen from outside, simply by looking into the eye. Diabetes damages small vessels everywhere, but here the damage shows up earliest and here it costs the most, because what is at stake is sight. The awkward thing about retinopathy is that for years it produces no pain, no blurring and nothing else to be uneasy about; by the time someone notices they are seeing less well, the easy part of the treatment is already behind them. Which is why this whole page comes down to a single idea: it has to be looked for while nothing is wrong.

Why diabetes goes for the retina

Glucose that stays high changes the wall of the capillaries, making it leaky and brittle at the same time. Some vessels block off, leaving patches of retina without oxygen. Fluid, proteins and fats seep through the weakened walls into the tissue, tiny haemorrhages appear, and the vessel wall bulges here and there. A starved retina responds by releasing substances that make new vessels grow. The body's logic is understandable; the result is not good. The new vessels are fragile, they grow where they are not wanted, they bleed easily and they drag scar tissue along behind them.

How fast this goes depends on more than glucose alone. High blood pressure, raised cholesterol, smoking, kidney damage and pregnancy all speed it up, and so, inevitably, does time: after fifteen or twenty years of diabetes, most people with type 1 and a good half of those with type 2 have changes at the back of the eye. In type 2 the retinopathy is often found on the very day of diagnosis, because the diabetes had already been there for several years and nobody knew.

The early stages keep quiet

While the changes stay out at the edge of the retina, sight is unaffected. People read, drive and pass the eyesight test for a licence with retinopathy already under way. The brain also fills in the missing parts of the visual field, which is why a gradual loss of side vision is noticed last of all, sometimes only when the good eye happens to be covered.

From that follows the central rule: the diagnosis is made by examination, not by symptoms. Everyone with diabetes should have the back of the eye examined regularly with the pupil dilated, or the retina photographed. The age at which this starts and the interval between examinations are set differently from country to country, so check the timing with your own doctor; the principle, though, is the same everywhere. The first examination is arranged soon after the diagnosis, it is repeated on a planned basis, and once changes are found it is repeated more often.

Pregnancy needs a word to itself. Retinopathy can accelerate sharply during pregnancy, so the back of the eye is checked when a pregnancy is being planned, again early in the pregnancy, and afterwards as the doctor advises. Diabetes that appears for the first time during pregnancy is not covered by this rule.

What the examination involves

There is nothing unpleasant in it. Drops go in to widen the pupil, you wait about half an hour, and the retina is then examined through a lens or photographed. Sometimes a scan is added that shows the thickness of the retina layer by layer at the centre: a couple of minutes, and very good at catching swelling. If new vessels are suspected, pictures are taken with a dye injected into a vein.

Two things are worth knowing beforehand. Once the pupil is dilated, everything close up stays blurred for several hours and light feels harsh, so it is best not to drive that day and worth bringing sunglasses. And the letter chart, the test used when glasses are prescribed, does not detect retinopathy at all, since it can be present with perfect vision. What is needed is an examination of the back of the eye.

Stages: from the first dots to new vessels

The changes build up gradually, usually over years, and something can be done at every point along the way.

• Early. The retina shows isolated microaneurysms and dot haemorrhages. Sight is unaffected, no treatment is required, and all that is needed is control of glucose and blood pressure plus the scheduled examination.
• Moderate and severe. More haemorrhages, patches where vessels have stopped working, veins that look irregular. Sight may still be excellent, but the chance of moving on to the next stage within a year is high, so examinations become more frequent and treatment is sometimes started ahead of trouble.
• Proliferative. Fragile new vessels grow on the retina and on the iris. This is the stage at which sight is lost: a vessel can bleed into the jelly filling the eye, and the scar tissue that forms can pull the retina off. Treatment by an eye specialist is needed, and it cannot be put off.

The names given to the stages differ between countries and between doctors, so the term matters less than the answer to two questions: are there new vessels, and is there swelling at the centre of the retina. Those two decide whether you are treated now or watched.

Swelling at the centre, the commonest way sight is lost

The centre of the retina, an area the size of a pinhead, handles everything sight is actually used for: reading, faces, close work. When fluid from damaged vessels soaks into that area it thickens, and the picture degrades. Letters blur, straight lines look wavy, a smudge appears in the middle, colours go dull. It can happen at any stage, including the earliest, and it bears no relation to how widespread the changes are further out.

The good news is that this swelling responds well to treatment, and when treatment starts in time, sight is often not merely preserved but partly recovered. The bad news is that it comes on slowly and in both eyes at once, so people adapt to it and turn up late. A simple habit at home: once a week cover each eye in turn and look at something with straight lines in it, a door frame, a window frame, a line of tiling. A bend or a smudge is a reason to book an examination without leaving it.

When there is no time to lose

See an eye specialist urgently, or go to emergency care if that is not possible, if any of this comes on suddenly:

• a sharp drop in vision in one eye over hours or a day;
• a sudden shower of black dots, a cobweb, or a reddish veil across the eye, which is what a bleed into the jelly of the eye looks like;
• flashes of light, sparks or streaks at the edge of the visual field;
• a dark curtain creeping in from one side, the sign of the retina detaching;
• pain in a red eye with rainbow rings around lights and failing vision, which happens when vessels grow on the iris and the pressure inside the eye rises steeply; without quick treatment the eye can be lost.

Noticeably bent lines or a new smudge in the centre do not count as emergencies in that sense, but they are no reason to sit in a routine queue for six months either. The right interval here is measured in days.

How it is treated

Treatment aims to stop the process and clear the swelling. Retina that has already died cannot be brought back, but with swelling at the centre some of the sight usually returns.

• Injections into the eye. The mainstay when the centre is swollen. Anti-VEGF drugs, which suppress the growth of vessels, are put into the eye through a fine needle under anaesthetic drops; it takes minutes and is easier to sit through than it sounds. Regularity is the key condition, since injections are frequent in the first months and missed appointments undo the result.
• Steroid implants. A tiny depot that releases an anti-inflammatory substance slowly; used when the injections above have not worked or cannot be given as often as they should be.
• Laser. Where new vessels have appeared, the outer retina is treated with laser to make them regress. The method has decades of evidence behind it and reliably prevents blindness, but the price is narrowed side vision and poorer vision in the dark, which is worth knowing in advance.
• Surgery. If blood in the jelly of the eye does not clear, or the retina has begun to detach, the jelly is removed and the retina laid back into place surgically.

One more thing people are rarely warned about: if glucose has been very high for a long time and is then brought down quickly, retinopathy can get temporarily worse over the first months. That is not an argument against control, which wins clearly in the long run, but it is an argument for lowering glucose gradually and for having the back of the eye examined before any radical change of regimen.

What genuinely lowers the risk

The list is short, and every item on it has proven effect behind it.

• Steady glucose without wild swings, which matters more than everything else put together.
• Blood pressure in range. For the retina this comes second in importance, and plenty of people forget about it entirely.
• Cholesterol and triglycerides within the limits agreed with your doctor.
• Stopping smoking, since it accelerates vessel damage at every level.
• Attention to the kidneys: protein in the urine usually means things are going worse in the eyes as well.
• Scheduled examinations of the back of the eye even when sight is excellent. This is the only item on the list that catches the disease while the treatment is still simple.

The reverse is worth remembering too: retinopathy by itself is no obstacle to an ordinary life. Exercise, work and reading do not damage sight. Restrictions come in only at the proliferative stage, and they mainly concern heavy lifting and straining, which are discussed individually with an eye specialist.

Online consultation

Remotely it is convenient to go through what usually stays unexplained: what the report after an eye examination actually says, which stage you are at, whether anything needs doing now and when the next appointment should be. A doctor can look at your test results and blood pressure figures, explain which of them weigh most heavily on the eyes, help you set out a schedule of examinations and tell you what should raise concern between them. Pregnancy with diabetes belongs here as well, along with the question of how to bring long-standing high glucose down safely. Treating the retina itself needs an examination and equipment, and a sudden loss of vision, flashes or a dark veil are reasons to be seen in person straight away.

This material is for information only and does not replace medical advice.