The human eye is a small but complex organ that enables us to see the world around us. However, damage to the eyes can put our sight at risk.
The most common cause of blindness among people in the UK is a condition called retinopathy, which is caused by damage to the retina – the ‘seeing’ part at the back of the eye.
Most people affected by this are those who have diabetes, as retina damage can be caused by high levels of blood glucose, among other things.
About the eyes
The eye is a slightly irregular shaped sphere that consists of the following:
- The iris – the pigmented part of the eye
- The pupil – the black circular opening in the iris that lets light in
- The lens – the part behind the iris that helps to focus light on the back of the eye
- The cornea – a clear dome over the iris
- The conjunctiva – an invisible, clear layer of tissue covering the front of the eye, except the cornea
- The retina – delicate light-sensitive tissue at the back of your eye
- The sclera – the white part of your eye
How your eye works
When we look at something, a number of processes take place before we are able to actually “see”. Firstly, light passes through the pupil and is focused by the cornea and lens onto the retina.
The retina converts the light into electrical signals, which are then carried to the brain via the optic nerve. The brain then interprets these signals to produce the images that you see.
Another important part of the human eye is the macula It is a small, sensitive area within the retina that provides our central vision, i.e. allows us to focus for activities such as reading and writing, and to recognise colours. It is also essential for clear, detailed vision.
How diabetes affects the eyes
Diabetes can lead to the development of a number of eye conditions, which can affect your sight. These include:
- Diabetic retinopathy – Retinopathy is a common complication of diabetes and the most serious of all diabetes-related eye conditions. It occurs when persistent high levels of blood glucose cause leaks or blockages in the capillaries (small blood vessels) that provide the retina with a constant supply of blood. This damages the retina and stops it from working, thus affecting your vision. If left untreated, it an lead to total loss of sight.
- Temporary blurring – the abnormal changes in blood sugar levels caused by diabetes can affect the lens inside the eye, which can lead to short spells of blurred vision throughout the day.
- Cataracts – a cataract is an eye condition that is more commonly associated with older diabetics. It occurs when the lens becomes cloudy, causing vision to become blurred or dim as light struggles to pass through to the back of the eye.
Types of Diabetic Retinopathy
There are different types of diabetic retinopathy, which are based on the extent of the damage to the blood vessels in the retina caused by uncontrolled blood glucose.
Background diabetic retinopathy
This is early stage retinopathy that affects many people who have had diabetes for some time. It can cause the capillaries in the retina to bulge slightly ( microaneurysm ) and leak blood ( haemorrhages ) or fluid (exudates).Most people with this very mild form of retinopathy are unaware of their condition as it does not cause any noticeable symptoms. Eyesight remains unaffected but problems can occur if the condition progresses.
Annual retinal screening tests are offered to diabetics in England and Wales to help keep a close check on retinopathy during the initial stages and ensure that any signs of progression to more serious stages are detected early, and treated effectively.
More common in people with type 2 diabetes, maculopathy is a more serious type of retinopathy that affects the macula, the most used part of the retina. Fluid leaking around this area from the blood vessels causes swelling (oedema). This can affect your central vision, making it extremely difficult for you to read or see fine details. The amount of central vision that is lost varies from person to person, but if left untreated, it can cause blindness.
Proliferative diabetic retinopathy
Progression of background retinopathy can lead to more severe problems. The larger blood vessels in the retina can become blocked and damaged, starving the larger areas of the retina of vital oxygen (ischaemia).
This triggers a damage repair process called neo-vascularisatio, which stimulates the eye into growing new vessels to replace the blocked ones.
However, these newly formed blood vessels are very delicate, bleed easily and grow in the wrong place (on the surface of the retina and into the vitreous gel – a clear jelly-like substance inside your eye). The bleeding can lead to large haemorrhages that totally obscure vision in the affected eye.
Extensive haemorrhages can lead to scar tissue forming, which pulls and distorts the retina, causing it to become detached. This often leads to total sight loss. Fortunately, proliferative retinopathy is quite rare, affecting just 5 to 10% of all diabetics.
Looking after your eyes
Keeping your eyes in good health is vital for preventing conditions such as diabetic retinopathy and maintaining your eyesight. If you have diabetes, it is very important to control your blood sugar and cholesterol, and keep your blood pressure as close to normal as possible. Effective management of diabetes will reduce your risk of having problems.
Other steps you can take to help prevent retinopathy include:
- Informing your GP or diabetes care team of any changes to your vision
- Losing weight (if you’re overweight) and maintaining a healthy weight
- Eating a healthy, balanced diet and keeping fit through regular exercise
- Quitting smoking (if you smoke)
- Sticking to your prescribed medication plan
Diabetic eye screening
One of the most effective ways to prevent retinopathy-caused sight loss is to attend your diabetic eye (or retinal) screening appointments.
Each annual appointment involves a detailed examination of the eyes and is designed to help reduce the risk of vision loss in people with diabetes by identifying retinopathy at an early stage – research shows that early detection of retinopathy and appropriate treatment can prevent 90% of all those at risk from losing their eyesight.