The Leading Cause of Blindness in Working-Age Adults Has No Symptoms Until It Is Nearly Too Late

Diabetic retinopathy is the leading cause of blindness among working-age adults. It is also, in its early and most treatable stages, completely silent.

That combination is the whole problem. Almost every other serious condition gives you something: pain, a lump, breathlessness, a symptom that sends you to a doctor. The retina gives you nothing. It deteriorates quietly, and the first thing many people notice is a change in vision that has arrived far too late in the process to be reversed.

What is actually happening in the eye?

Small blood vessels are being damaged by years of high glucose, and the retina is unusually dependent on very small blood vessels.

The early stage, called non-proliferative retinopathy, involves vessels that weaken, bulge and leak. An ophthalmologist can see microaneurysms and small haemorrhages on examination well before you can see anything wrong. Vision at this point is typically normal.

If it progresses, the retina becomes starved of blood supply and responds by growing new vessels. That sounds like a repair and is closer to a catastrophe. The new vessels are fragile and grow in the wrong places, and they bleed into the eye or contract and pull the retina away from the back of the eye. This is proliferative retinopathy, and it is how people lose sight suddenly after years of no symptoms at all.

Separately, and at any stage, fluid can leak into the macula, the small central part of the retina responsible for detailed vision. Diabetic macular oedema is the most common way diabetes damages reading vision, and it can occur while the rest of the retina looks relatively unbothered.

How often should someone with diabetes have their eyes screened?

The intervals are well established and widely ignored.

• Type 2 diabetes: screening should begin at diagnosis. This is not caution, it is arithmetic. Type 2 is frequently present for years before it is found, so retinopathy may already exist on the day someone is told they have diabetes.
• Type 1 diabetes: screening usually begins within three to five years of diagnosis, since the onset is normally identifiable and the clock starts from a known point.
• Thereafter: at least annually. Where there is no retinopathy or only minimal changes, some guidelines permit an interval of one to two years, and where disease is more advanced, far more frequently.

Note that this is a screening examination, not the sight test you have for glasses. A refraction check tells you nothing about the retina. The examination requires a dilated view or retinal photography, and asking an optician for one is a different request from asking for a new prescription.

Can it be treated?

Yes, and considerably better than a generation ago, which makes the detection failure more frustrating rather than less.