I have diabetes but my vision is fine. Do I really need an eye screening?

People with diabetes whose physician has asked them to see an eye doctor often wonder whether the visit is necessary when they can see well. The answer is yes, and the reason is simple: diabetic eye disease often has no early symptoms.

Good vision today tells you very little about the health of your retina. That sounds strange, so here is why.

Why your vision can be fine while damage is happening

Diabetes slowly weakens the small blood vessels of the retina, the light-sensing layer at the back of the eye. Those vessels can leak, close off, or grow abnormally. In the early and even moderate stages, this happens away from the centre of your vision, so you notice nothing. You read, drive, and work normally while the changes progress.

By the time vision blurs, the disease has usually reached the macula, the small central area we read with, or bleeding has occurred inside the eye. Treatment at that stage still helps, but it generally works better, and preserves more sight, when it starts earlier. Regular screening is how changes are found before vision is affected.

What a diabetic eye screening involves

The pupils are dilated with drops, which take about twenty to thirty minutes to work, and the retina is then examined thoroughly. Where needed, an OCT scan is taken, a non-contact imaging test that shows the retinal layers in cross-section and can show swelling at the macula before you would notice it yourself.

The drops blur your near vision for a few hours, so bring someone to drive you home, or plan for it. A screening visit involves no injection.

Who needs it, and how often

If you have type 2 diabetes, you should have a dilated retinal examination at the time of diagnosis, because the diabetes may have been present, unnoticed, for years before it was found. If you have type 1 diabetes, screening usually begins about five years after diagnosis.

After that, once a year is the usual rhythm if the retina is healthy. If early changes are found, you may be asked to return every three to six months. Pregnancy, poorly controlled sugars, high blood pressure and kidney disease all raise the risk, and the schedule is adjusted accordingly. A routine check of glasses power is not a substitute. The retina must be examined with dilated pupils.

What happens if something is found

Most of the time, early changes need no treatment at all, only closer follow-up and better sugar control, which remains the most important measure for the diabetic eye. Your physician and your eye doctor work as a team here.

If the disease progresses, there are established treatments. Laser is used to seal leaking areas or to treat the retina when abnormal vessels threaten to grow. For swelling at the macula, intravitreal injections of medicine into the eye, given under numbing drops, can reduce the swelling and in many cases improve vision. Results vary from eye to eye.

Advanced retinopathy needs prompt treatment. The purpose of screening is to find changes before that stage, when monitoring, laser or injections are most useful.

The habit that protects your sight

Think of the annual retinal examination the same way you think of your HbA1c test: not as something you do when there is a problem, but as the check that finds changes early, when they are easiest to treat. Disease without symptoms needs scheduled checking.

If you have diabetes and have not had a dilated retinal examination in the past year, ask an eye doctor for one.