Overview
The retina is the thin, light sensing layer lining the back of the eye. It is fed by very fine blood vessels, and blood sugar that stays high over years damages them, so they leak or close off and the retina is left short of blood.
This happens in stages. At first the changes are small and sight is unaffected. In the most advanced stage, fragile new vessels grow on the retina and bleed easily. Fluid can also collect in the macula, the central patch of retina used for reading.
Symptoms
For a long time there are none. Sight feels normal while the vessels quietly change, which is why the condition is found by examination rather than by the person noticing it.
When symptoms do appear they may include blurred or patchy vision, trouble reading, difficulty seeing in dim light, faded colours, and dark floating spots or streaks like cobwebs. A sudden bleed can cause a shower of floaters, a dark shadow or sudden loss of sight.
When to see a doctor
See a doctor within a few days if vision has become blurred or patchy, if reading or seeing in dim light has become harder, or if colours look different. Book an eye examination if you have diabetes and have not had one in the past year.
Causes
The cause is glucose in the blood staying above the healthy range over a long period. Sugar damages the walls of the smallest vessels, so they leak into the retina and some of them block. Where the retina is starved of blood it signals for new vessels to grow, and those new vessels are weak, bleeding into the eye or pulling on the retina as scar tissue forms.
Risk factors
- Having had diabetes for many years
- Blood sugar that is often above target
- High
- High
- Pregnancy in a woman who already has diabetes
- Smoking or chewing tobacco
- Diabetic kidney disease
Complications
- Swelling of the macula, which blurs central vision
- Bleeding into the jelly of the eye
- Scar tissue pulling the retina away from the back of the eye
- Raised pressure inside the eye from abnormal new vessels
- Permanent loss of sight
Prevention
- Keeping blood sugar as close to the agreed target as possible
- Treating high and high
- Attending every eye examination, even when sight seems perfect
- Stopping smoking and chewing tobacco
- Arranging an eye check when pregnancy is planned or confirmed
Diagnosis
The main test is an examination of the back of the eye after drops are used to widen the pupil. Photographs of the retina are often taken so that changes can be compared over time, and vision stays blurred for a few hours afterwards.
If the centre of the retina looks swollen, a scan measures its thickness. Sometimes a dye injected into a vein in the arm shows on photographs which vessels are leaking or blocked.
Treatment
Early changes usually need no eye treatment at all. What is treated is the diabetes itself, along with and , and the eyes are watched more closely.
For advanced disease or swelling of the macula, treatment may include injections into the eye of medicines that reduce leaking and abnormal vessel growth, slow release steroid implants, and laser treatment. Surgery clears blood and scar tissue from inside the eye when bleeding does not settle or the retina is being pulled away.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“My eyesight is fine, so my eyes cannot have been affected by diabetes.”What is true?
Fact
The early stages of diabetic retinopathy usually cause no symptoms at all. Damage is found by looking at the back of the eye, not by how well a person can see, which is why the examination is offered to everyone with diabetes rather than only to those with blurred vision.
Myth“Only people on insulin, or people whose sugar is very high, get eye problems.”What is true?
Fact
Anyone living with type 1, type 2 or pregnancy related diabetes can develop retinopathy, whatever their treatment. The longer a person has diabetes the more likely it becomes, and high blood pressure and high cholesterol add to the risk.
Myth“If my sight goes, the doctor can always bring it back.”What is true?
Fact
Laser, injections and surgery can stop diabetic retinopathy getting worse and can save the sight that remains, but they usually cannot undo damage that has already happened. That is the reason for finding it early, before vision is lost.
Myth“Blurred vision in diabetes just means I need new spectacles.”What is true?
Fact
Blurring can come from fluid swelling the central part of the retina, and no pair of spectacles can correct that. Vision that changes in someone with diabetes is a reason for an eye examination first, and a new prescription only after the retina has been checked.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
My sugar has been well controlled for years. Do I still need eye checks?
Yes. Good control lowers the risk a great deal but does not remove it, and the early changes cause no symptoms. The examination is quick and is the only reliable way to know what is happening at the back of the eye.
Do the injections into the eye hurt?
Numbing drops are used first, so most people feel pressure rather than pain. The eye may feel gritty and look red for a day or two afterwards. Increasing pain, worsening vision or a sticky discharge after an injection should be reported the same day.
Why does my vision blur when my sugar swings a lot?
Vision in diabetes can change for more than one reason, including fluid collecting in the central retina. Any new or changing blurring should be looked at by an eye doctor rather than assumed to be temporary, especially if it lasts more than a few days.
Can diabetic retinopathy be cured?
It can be controlled rather than cured. Treatment can stop it progressing and protect the sight that is left, and steady control of blood sugar, blood pressure and cholesterol keeps it from returning quickly, but vision already lost usually cannot be restored.
