Diabetic retinopathy is the name for damage to the retina at the back of the eye caused by diabetes.
Diabetic retinopathy is one of the most common causes of visual impairment and blindness in New Zealand. However, if picked up early, treatment can help prevent or slow vision loss.
Keeping good blood glucose control and having regular diabetes eye examinations, even if vision seems normal, are needed, together with control of blood pressure, blood cholesterol, and measures such as not smoking.
Vision problems in diabetes
Diabetes is the commonest cause of blindness and vision impairment in the age group 20 to 60 years.
- Compared to the general population, people with diabetes have about 25 times greater risk of vision impairment.
- At least one-third of people with diabetes have retinopathy.
- Retinopathy threatens vision, or has already destroyed sight, in 10% of people with diabetes.
Early detection of retinopathy means treatment can be given to slow or prevent vision loss.
What happens in diabetic retinopathy?
Diabetes damages the blood vessels that supply the retina of the human eye. When signs of damage are detected, you have retinopathy.
The retina is a very thin and complex layer which lines the back and inner wall of the eye. It contains the special photoreceptor cells, which convert light to chemical and electrical energy which is conveyed to the brain via other retinal cells, the optic nerve and the visual nerve pathways to produce, after much further processing, our sense of vision or seeing things in our environment.
The retina is likened to the film of a camera. If the retina is damaged, especially in its central area, the macula, there is irretrievable loss of sight.
The macula with its central areas, the fovea and foveola, contain the cone shaped photoreceptors responsible for colour and detailed vision, eg, reading. Light is focused on the central macula by the lenses of the eye.
The rest of the retina is principally rod photoreceptors which enable us to have some vision in low light levels. It is vital in treating diabetic retinopathy that the central macula area is preserved.
The inner half of the retina receives its blood supply from the central retinal artery which enters via the optic nerve. Diabetes causes the small blood vessels within the retina to close and/or leak blood, fats, and fluid, all of which are toxic to the retina, which causes two types of major damage:
- proliferative retinopathy
Closure of small blood vessels leads to proliferation of abnormal blood vessels which are fragile and may bleed into the vitreous, the ‘jelly’ of the eye which fills the space between the retina and the lens, and may eventually cause the retina to detach.
Leakage within the macula, especially of fluid and fat, destroys the retinal photoreceptor and ‘nerve’ cells, and reduces visual acuity, ie, ability to see the vision test chart.
Grading of retinopathy
Retinopathy is graded according to severity and your ophthalmologist may tell you about these:
- Minimal/ mild/ moderate – no immediate threat to sight.
- Pre-proliferative, proliferative/ pre-maculopathy/ maculopathy – sight threatened or already lost. Usually needs laser treatment to control.
- Advanced – irretrievable sight loss.
Who is most likely to develop retinopathy?
Those most likely to develop retinopathy are:
- people who have had diabetes for many years – the risk increases progressively each year from the time of diagnosis, and after 15 years, three out of four people will have retinopathy
- people whose diabetes is poorly controlled – strict blood glucose control is the most important factor in the prevention of both the development and progression of retinopathy
- people with hypertension (high blood pressure) and abnormal blood fats, and pregnancy, which can make retinopathy progress faster than usual
- people with associated kidney disease.
This treatment is the only effective way of controlling sight-threatening retinopathy. It is most effective if able to be undertaken before retinopathy is advanced, and when vision is threatened by signs of impending vision loss rather than already reduced.
Macula laser treatment
This ‘dries up’ the fluid and exudates – but may take several months, and two to three treatments to be effective.
Overall retinal laser treatment
A laser burns throughout the retina, causing the fragile abnormal blood vessels to disappear, or never develop. Again, several treatments may be necessary to each eye. Where treatment has to be extensive there will be some loss of side vision and night vision. (Also see ‘Questions about laser treatment’ below.)
How to preserve vision in diabetes
Measures to preserve eye sight include the following:
- Minimise the risk of retinopathy by strict control of blood glucose.
- Have treatment for abnormal blood pressure and fats in the blood (lipids) which cause additional harm to eyes if not controlled. Also see high blood cholesterol
- Once someone is diagnosed with diabetes, you need a retinal eye screen test at least every 2 years.
- Once changes are found, this may become every year or less. Remember, vision may be normal, but retinopathy could be present.
- Follow medical advice about diet, exercise, medications for diabetes, blood pressure and abnormal blood lipids.
- Do not smoke – this causes strokes, heart attacks and poor circulation in the legs which may result in amputation. Also see quitting smoking
Regular eye examinations for retinopathy
Once you have diabetes, make sure you get regular retinal examinations at least every two years because there is no other way of detecting retinopathy. This is done:
- By photography for those under 66 years of age with good vision who do not have significant cataract, or who do not have one of the more severe grades of retinopathy. Age 66 is an arbitrary age cut-off: lens opacities, or cataract, tend to occur in older persons preventing good photographs of the retina.
- By ophthalmologist (eye doctor) for those with more severe retinopathy, or cataract which prevents photography. This examination requires drops to be used to enable the doctor to see the retina well, and is usually more frequent than two-yearly for those with retinopathy (possibly every three to six months).
Do not wait until you have any eye symptoms or vision problems. This can be too late.
Also be aware that retinopathy can get worse more quickly for people with diabetes who also:
- are pregnancy,
- have poor diabetes control (this means the average blood glucose level is higher than it should be)
- have high blood pressure.
Benefits of regular eye examinations
Benefits of regular eye examinations include:
- Picking up retinopathy early.
- Making sure you get treatment at the right time to prevent visual loss or blindness.
- With early detection and adequate treatment, up to 98% of severe vision loss (bilateral blindness) can be prevented.
Questions about laser treatment
Is laser treatment painful?
Most people who have macula treatment do not experience pain. If you need treatment to the peripheral retina, this may cause mild pain and a dull ache for a few hours following treatment. The ophthalmologist (eye specialist) will talk with you about what can be done to minimise this as much as possible.
Does laser treatment cause blindness?
No, if people present too late, then the damage has already occurred. In these cases, laser treatment may still be offered in an attempt to retain some sight.
Like most treatments, laser treatment can have complications. In some advanced proliferative cases, bleeding into the vitreous may occur and/or retinal detachment and this may be associated with laser treatment. However, such complications would have occurred without treatment, and the eye is in a better state if some laser has been undertaken should surgery be necessary to remove blood from inside the eye and re-attach the retina.
Make sure to ask your eye doctor what the risks and benefits of all treatment options are for you.
How soon do the benefits of laser treatment become evident?
Laser is extremely effective in most patients treated, but benefits may not occur for some months after it is finished. Vision may improve for a long time as the retinopathy stabilises.
After laser treatment is finished, will it need to be repeated each year?
For those with macular disease, treatment may need to be repeated if the disease remains active and recurs in new areas of the macula.
For those with proliferative disease, further treatment is rarely needed once all the abnormal blood vessels have gone.
Questions about eye checks in diabetes
Are eye checks necessary if diabetes is mild and controlled by diet?
Yes. The risk is only slightly less in diet-controlled diabetes.
Are eye checks necessary if diabetes control is very good?
Yes, the risk is much less, but other factors can influence retinopathy development, so eye checks are still needed.
Is fluctuating vision a sign of developing retinopathy?
Yes, it can be due to retinopathy or due to fluctuating (high) blood glucose affecting the lens of the eye. However there are other possible causes such as the onset of presbyopia (the need to wear glasses for close work) which usually starts to occur from age mid-40s onwards.
Can a person with diabetes tell if it is affecting their eyes?
In early retinopathy there are no symptoms, and visual acuity (how well you can read an eye chart) is normal (unless cataract or other eye problems have developed). Hence, the need for routine retinal examinations.
Is there any point in putting a big effort into diabetes control if a person with diabetes already has retinopathy?
Yes, there is! There is strong evidence that progression of retinopathy can be slowed by about 50% in many patients with mild or moderate disease. However, retinopathy is not slowed by improved blood glucose control when it is advanced, but response to laser treatment may be better.
The National Diabetes Retinal Screening Grading System and Referral Guidelines Ministry of Health, NZ, 2006
Quality Standards for Diabetes Care Toolkit 2014 Standard 9 retinal screening Ministry of Health, NZ
Diabetic retinopathy screening in New Zealand requires improvement: results from a multi-centre audit, Australian & NZ Journal Public Health 2012