You may have heard that diabetes causes eye problems and may lead to blindness. People with diabetes do have a higher risk of blindness than people without diabetes. But most people who have diabetes have nothing more than minor eye disorders.
With regular checkups, you can keep minor problems minor (see our Eye Care page). And if you do develop a major problem, there are treatments that often work well if you begin them right away.
To understand what happens in eye disorders, it helps to understand how the eye works. The eye is a ball covered with a tough outer membrane. The covering in front is clear and curved. This curved area is the cornea, which focuses light while protecting the eye.
After light passes through the cornea, it travels through a space called the anterior chamber (which is filled with a protective fluid called the aqueous humor), through the pupil (which is a hole in the iris, the colored part of the eye), and then through a lens that performs more focusing.
Finally, light passes through another fluid-filled chamber in the center of the eye (the vitreous) and strikes the back of the eye, the retina.
The retina records the images focused on it and converts those images into electrical signals, which the brain receives and decodes.
One part of the retina is specialized for seeing fine detail. This tiny area of extra-sharp vision is called the macula. Blood vessels in and behind the retina nourish the macula.
People with diabetes are 40% more likely to suffer from glaucoma than people without diabetes. The longer someone has had diabetes, the more common glaucoma is. Risk also increases with age.
Glaucoma occurs when pressure builds up in the eye. In most cases, the pressure causes drainage of the aqueous humor to slow down so that it builds up in the anterior chamber. The pressure pinches the blood vessels that carry blood to the retina and optic nerve. Vision is gradually lost because the retina and nerve are damaged.
There are several treatments for glaucoma. Some use drugs to reduce pressure in the eye, while others involve surgery.
Many people without diabetes get cataracts, but people with diabetes are 60% more likely to develop this eye condition. People with diabetes also tend to get cataracts at a younger age and have them progress faster. With cataracts, the eye’s clear lens clouds, blocking light.
To help deal with mild cataracts, you may need to wear sunglasses more often and use glare-control lenses in your glasses. For cataracts that interfere greatly with vision, doctors usually remove the lens of the eye.
Sometimes the patient gets a new transplanted lens. In people with diabetes, retinopathy can get worse after removal of the lens, and glaucoma may start to develop.
Diabetic retinopathy is a general term for all disorders of the retina caused by diabetes. There are two major types of retinopathy: nonproliferative and proliferative.
This is the most common type of diabetic retinopathy and many people who have had diabetes for some time will have this early type.
The blood vessels in the retina are only very mildly affected, they may bulge slightly (microaneurysm) and may leak blood (haemorrhages) or fluid (exudates). As long as the macula is not affected, vision is normal and you will not be aware that anything is wrong.
Your retinal screening test will keep a close check on these early changes and ensure that any signs of progression to more serious stages of retinopathy are detected early.
The most serious complication of diabetes for your eye is the development of diabetic retinopathy. Diabetes affects the tiny blood vessels of your eye and if they become blocked or leak then the retina, and possibly your vision, will be affected.
The extent of these changes determines what type of diabetic retinopathy you have. Forty per cent of people with type 1 diabetes and 20 per cent with type 2 diabetes will develop some sort of diabetic retinopathy.
In nonproliferative retinopathy, the most common form of retinopathy, capillaries in the back of the eye balloon and form pouches. Nonproliferative retinopathy can move through three stages (mild, moderate, and severe), as more and more blood vessels become blocked.
Although retinopathy does not usually cause vision loss at this stage, the capillary walls may lose their ability to control the passage of substances between the blood and the retina. Fluid can leak into the part of the eye where focusing occurs, the macula.
When the macula swells with fluid, a condition called macula edema, vision blurs and can be lost entirely. Although nonproliferative retinopathy usually does not require treatment, macular edema must be treated, but fortunately treatment is usually effective at stopping and sometimes reversing vision loss.
In some people, retinopathy progresses after several years to a more serious form called proliferative retinopathy. In this form, the blood vessels are so damaged they close off. In response, new blood vessels start growing in the retina.
These new vessels are weak and can leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina or pull it out of place, a condition called retinal detachment.
If diabetic retinopathy progresses, it can cause the blood vessels in the retina to become blocked. These blockages, when affecting a significant part of the retina, can result in areas of the retina becoming starved of oxygen.
This is called ischaemia. If this happens your eye is stimulated into growing new vessels, a process called neo-vascularisation. This is the proliferative stage of diabetic retinopathy and is nature’s way of trying to repair the damage by growing a new blood supply to the oxygen starved area of your retina.
Unfortunately, these new blood vessels are weak, and grow in the wrong place – on the surface of the retina and into your vitreous gel. As a result, these blood vessels can bleed very easily which may result in large haemorrhages over the surface of the retina or into the vitreous gel.
These types of haemorrhages can totally obscure the vision in the affected eye as light is blocked by the bleed and the blood in the vitreous gel. For many people, with time, the blood can be reabsorbed and their vision can improve.
But for others these haemorrhages may keep happening and the blood may not fully reabsorb. This can lead to more permanent loss of sight.
Extensive haemorrhages can lead to scar tissue forming which pulls and distorts the retina. This type of advanced diabetic eye disease can result in the retina becoming detached with the risk of serious sight loss.
Only between 5 and 10 per cent of all people with diabetes develop proliferative retinopathy. It is more common in people with type 1 diabetes than type 2. Sixty per cent of type 1 diabetics show some signs of proliferative disease after having diabetes for 30 years.
Diabetic maculopathy means that your macula is affected by your diabetes. This may occur either with background, or proliferative retinopathy. If this happens, your central vision will be affected and you may find it difficult to see detail such as recognising people’s faces or seeing small print clearly.
The amount of central vision that is lost varies from person to person. However, the vision that allows you to get around at home and outside (peripheral vision) is not affected.
Some people develop a type of maculopathy called diabetic macular oedema. This causes fluid to collect in your macula which can cause further problems with your central vision.
Most diabetic maculopathy can be treated with a laser, and more recently injections. These treatments aim to stop your sight getting worse, although some people may notice an improvement in their vision.
Risk factors for developing diabetic retinopathy can be divided into those you are able to control and those you cannot. Good diabetic control significantly lowers your risk of retinopathy.
You can reduce your risk of developing retinopathy or help to stop it from getting worse by:
- controlling your blood sugar (glucose levels)
- tightly controlling your blood pressure
- controlling your cholesterol levels
- keeping fit, maintaining a healthy weight and giving up smoking are all part of good diabetes control. Nerve damage, kidney and cardiovascular disease are more
- likely in smokers with diabetes. Smoking increases your blood pressure and raises your blood sugar level which makes it harder to control your diabetes. Diabetes UK can offer you information and support on living with diabetes
- regular retinal screening (there is more information about this in the following section). The most effective thing you can do to prevent sight loss due to diabetic
- retinopathy is to attend your retinal screening appointments. Early detection and treatment prevents sight loss.
Risk factors that cannot be controlled:
- The length of time you have had diabetes. This is a major risk for developing diabetic retinopathy.
- Your age affects the progression of diabetic retinopathy.
- Your ethnicity. If you or your family are from India, Pakistan, Bangladesh or Sri Lanka you are more at risk of developing diabetes and the sight-threatening conditions diabetes can cause.
- If you have diabetes and plan to have a child, your GP will discuss with you how to manage the pregnancy. Retinal screening is carried out more often during pregnancy and for a while after you have had your baby.
Similarly if you develop gestational diabetes during pregnancy, you will also have more regular retinal screening during pregnancy and after your baby is born.
- Annual diabetic eye screening
- If you have diabetes this does not necessarily mean that your sight will be affected. If your diabetes is well controlled you are less likely to have problems, or they may be less serious.
However, if there are complications that affect your eyes, this can sometimes result in serious loss of sight.
- Most of the complications that diabetes causes in the eye can be treated, but it is vital that they are diagnosed early. They can only be detected by a detailed examination of your eye carried out at a specialist screening centre.
If you have diabetes your GP or hospital clinic should arrange for you to have annual retinal screening. At this appointment you will have eye drops put into your eyes which dilate the pupil and allow the specialist a good view of the retina.
A picture is taken using a digital retinal camera and this is looked at in detail to see if there are any changes caused by diabetes.
- As you may not be aware that there is anything wrong with your eyes until it is too late, having this regular test is essential. Research shows that if retinopathy is identified early, through retinal screening, and treated appropriately, blindness can be prevented in 90 per cent of those at risk.
If you have not had this type of test, ask your GP or diabetic clinic as soon as possible. You should also go for an annual eye test with the optometrist (optician) as the retinal screening test does not replace the regular eye examination.
- Some optometrists will take a photograph of the back of your eye as part of your regular eye examination. This photograph does not replace your retinal screening appointment. It is very important to attend both your retinal screening appointment and your regular eye test with the optician.v
How is it Treated?
Huge strides have been made in the treatment of diabetic retinopathy. Treatments such as scatter photocoagulation, focal photocoagulation, and vitrectomy prevent blindness in most people. The sooner retinopathy is diagnosed, the more likely these treatments will be successful. The best results occur when sight is still normal.
In photocoagulation, the eye care professional makes tiny burns on the retina with a special laser. These burns seal the blood vessels and stop them from growing and leaking.
In scatter photocoagulation (also called panretinal photocoagulation), the eye care professional makes hundreds of burns in a polka-dot pattern on two or more occasions.
Scatter photocoagulation reduces the risk of blindness from vitreous hemorrhage or detachment of the retina, but it only works before bleeding or detachment has progressed very far. This treatment is also used for some kinds of glaucoma.
Side effects of scatter photocoagulation are usually minor. They include several days of blurred vision after each treatment and possible loss of side (peripheral) vision.
In focal photocoagulation, the eye care professional aims the laser precisely at leaking blood vessels in the macula. This procedure does not cure blurry vision caused by macular edema. But it does keep it from getting worse.
When the retina has already detached or a lot of blood has leaked into the eye, photocoagulation is no longer useful. The next option is vitrectomy, which is surgery to remove scar tissue and cloudy fluid from inside the eye.
The earlier the operation occurs, the more likely it is to be successful. When the goal of the operation is to remove blood from the eye, it usually works. Reattaching a retina to the eye is much harder and works in only about half the cases.
There are two types of treatment for macular edema: focal laser therapy that slows the leakage of fluid, and medications that can be injected into the eye that slow the growth of new blood vessels and reduce the leakage of fluid into the macula.
The importance of early treatment
Although your vision may be good, changes can be taking place in your retina that need treatment. Most sight loss due to diabetes is preventable if treatment is given early. The earlier the treatment is given the more effective it is.
- early diagnosis of diabetic retinopathy is vital
- attend your annual retinal screening appointment
- have an annual eye examination with the optician (optometrist). Eye examinations are free for people with diabetes.
- The importance of early treatment of diabetic retinopathy cannot be stressed enough.
Remember, however, that if your vision is getting worse, this does not necessarily mean you have diabetic retinopathy. It may simply be a problem that can be corrected with glasses. So check it out.