Diabetic retinopathy is damage to the retina (retinopathy), specifically blood vessels in the retina, caused by complications of diabetes mellitus. Diabetic retinopathy can eventually lead to blindness if left untreated. Approximately 80% of all patients who have had diabetes for at least ten years suffer from some degree of diabetic retinopathy. The retina is the light-sensitive membrane that covers the back of the eye.
If diagnosed and treated early blindness is usually preventable. Diabetic retinopathy generally starts without any noticeable change in vision. However, an eye doctor (ophthalmologist) can detect the signs. Hence, it is important for diabetes patients to have an eye examination at least once or twice annually.
Anybody with either Diabetes Type 1 or Diabetes Type 2 can develop diabetic retinopathy. The risk is greater the longer a patient has diabetes and the less controlled his/her blood sugar is.
According to the National Institutes of Health (NIH), USA, approximately 16 million Americans have diabetes, of which half do not even know they have the condition. Unfortunately, only about half of the half who know they have diabetes receive appropriate eye care. Consequently, diabetic retinopathy is the leading cause of new blindness in American individuals aged 25 to 74 years - 8,000 new cases each year. Approximately 12% of all new cases of blindness in America are due to diabetic retinopathy.
According to the National Health Service (NHS), UK, diabetic retinopathy is the leading cause of blindness in adults under the age of 65 in the UK.
The NHS adds that an estimated 25% of individuals with Diabetes Type 1 will have some degree of diabetic retinopathy 5 years after their symptoms first develop, and 25% of those with Diabetes Type 2 who do not require insulin. For those who require insulin, approximately 40% are estimated to have some degree of diabetic retinopathy five years after the onset of symptoms (of diabetes).
Symptoms of diabetic retinopathy
A symptom is something the patient senses and describes, while a sign is something other people, such as the doctor notice. For example, drowsiness may be a symptom while dilated pupils may be a sign.
Diabetic retinopathy typically has no symptoms during the early stages. Unfortunately, when symptoms become noticeable the condition is often at an advanced stage. Sometimes the only detectable symptom is a sudden and complete loss of vision. The only way patients with diabetes can protect themselves is attend every eye examination their doctor tells them to go to.
Signs and symptoms of diabetic retinopathy may include:
- Blurred vision
- Both eyes are usually affected
- Color vision becomes impaired
- Floaters - transparent and colorless spots that float in the patient's field of vision. Sometimes they may appear as dark strings.
- Patches or streaks block the person's vision; sometimes described as empty or dark areas
- Poor night vision
- Sudden total loss of vision.
Risk factors for diabetic retinopathy
A risk factor is something which increases the likelihood of developing a condition or disease. For example, obesity significantly raises the risk of developing diabetes type 2. Therefore, obesity is a risk factor for diabetes type 2.
Anybody who has diabetes is at risk of developing diabetic retinopathy. However, there is a greater risk if the patient:
- Does not control blood sugar levels properly
- Suffers from hypertension (high blood pressure)
- Has high cholesterol
- Is pregnant
- Smokes regularly
- Has had diabetes for a long time
- Statistics in the USA indicate that Amerindians (Hispanics) and Afro-Americans with diabetes have a higher risk than other ethnic groups with diabetes (In America "Hispanics" usually means Amerindians from Latin America; while in the UK a Hispanic tends to mean a person from Spain).
Causes of diabetic retinopathy
The retina - this is a nerve layer that lines the inside of the back of the eye. It senses light and creates impulses that are sent through the optic nerve to the brain. At the center of the retina is a small area of very specialized and sensitive tissue called the macula - the macula allows us to see fine details clearly. The macula is used for activities which require careful focusing, such as writing and reading. It also helps us distinguish colors.
There is a network of tiny blood vessels which supply blood to the retina - without them it would not survive. Experts believe that these tiny blood vessels become damaged because of high glucose levels linked to diabetes, resulting in poor blood supply to the retina.
A diagram of the eye
Early diabetic retinopathy
(Non-proliferative diabetic retinopathy) - the walls of the blood vessels weaken and microaneurysms develop; these are tiny bulges in the walls of the blood vessels. Sometimes they leak blood and fluid - this does not generally affect vision. Eventually, however, the tiny blood vessels that nourish the macula may become damaged, leading to varying degrees of vision loss - the patient may find it hard to see things clearly at a distance and/or in fine detail, such as small print on paper.
Advanced diabetic retinopathy
(Proliferative diabetic retinopathy) - in the more advanced stages of diabetic retinopathy the blood vessels that nourish the retina may become blocked. The body tries to make up for this by producing new blood vessels in the area. These new blood vessels may be unstable and can bleed into the clear, jelly-like substance (vitreous) that fills the center of the eye, causing blurred and patchy vision as leaking blood obscures the patient's sight. In time the bleeding can result in the formation of scar tissue which may pull the retina out of position (retinal detachment) - vision gets darker, more floaters appear, and the patient eventually loses his/her sight if the condition is left untreated.
Diagnosing diabetic retinopathy
The following methods are commonly used to help diagnose diabetic retinopathy:
Dilated eye exam
The doctor places eyedrops in the patient's eyes which make the pupils dilate for several hours, allowing the doctor to get a good view of the interior of the eye. The drops may sting slightly. Photographs are taken of the interior of the eye - while the photographs are being taken the patient will see some bright lights. The bright lights may be startling, but they are not painful. It is normal for some people to experience blurry vision until the pupils go back to normal. During the eye examination the doctor can determine whether there are any:
- Abnormal blood vessels
- Abnormalities in the optic nerve
- Abnormalities in the retina, such as swelling, blood or fatty deposits
- Changes in eye pressure (glaucoma test)
- Changes in the patient's vision
- Growth of new blood vessels
- Retinal detachment
- Scar tissue.
Patients whose vision becomes blurry while the pupils are dilated should not drive. Sunglasses may help reduce photosensitivity. Very rarely, the eye drops may cause pressure within the eye to rise suddenly - this only occurs in high-risk individuals.
Drops are used to dilate the pupils, and then a special dye (fluorescein) is injected into a vein in the patient's arm. As the dye circulates through the eyes pictures are taken. If the blood vessels are abnormal, the dye may leak into the retina or stain the blood vessels.
This test can determine which blood vessels are blocked, leaking fluid or broken down, so that possible laser treatments can be accurately guided. Some patients' skin may turn a yellowish color for a few hours; their urine may also become dark orange for up to 24 hours as the dye is removed by the kidneys.
Optical coherence tomography (OCT)
This noninvasive imaging scan provides high resolution cross-sectional images of the retina, revealing its thickness. The doctor can then determine whether fluid has leaked into retinal tissue. Further scans may be used later on to check how effective treatment has been. OCT is similar to ultrasound testing, except that imaging is done by measuring light rather than sound. OCT can also detect diseases of the optic nerve.
Several countries with free universal healthcare have specific national programs for diabetic retinopathy prevention. In the UK there is a national screening program in which any patient aged at least 11 years is offered free annual (or twice a year) screening. Patients receive reminder letters from their GP (general practitioner, primary care physicians) or healthcare professional inviting them to attend a screening appointment.
Treatments for diabetic retinopathy
Treatment options depend on several factors, including the type of diabetic retinopathy, how severe (advanced) it is, and how the patient may have responded to previous treatments.
Treatment options for early diabetic retinopathy (nonproliferative diabetic retinopathy) - the patient may not need treatment straight away. The doctor may decide just to monitor the patient's eyes closely (watchful waiting).
Patients with poor blood sugar control will need to work with their doctor to seek ways of better controlling the diabetes. Good blood sugar control can significantly slow down the development of diabetic retinopathy.
Treatment options for advanced retinopathy (proliferative diabetic retinopathy) - in most cases the patient will require immediate surgical intervention. According to the National Health Service (NHS), UK, surgery is sometimes recommended for severe nonproliferative diabetic retinopathy.
Focal laser treatment
(photocoagulation) - the procedure is carried out in the doctor's office or eye clinic. Photocoagulation can either stop or slow down the leakage of blood and fluid in the eye. Laser burns treat leaks from abnormal blood vessels.
Patients will usually experience blurry vision for the 24 hours following the procedure. If you see small spots in your visual field for a few weeks, this is normal. Those who had blurred vision from swelling of the central macular prior to surgery may not recover normal vision.
Scatter laser treatment
(panretinal photocoagulation) - this procedure is also carried out in the doctor's office or eye clinic. Scattered laser burns are applied to the areas of the retina away from the macula, causing the abnormal new blood vessels to shrink and scar. Most patients require two or three sessions. Individuals may have blurry vision for the 24 hours following the procedure. There may be some loss of night vision or peripheral vision.
(vitreous surgery) - involves the removal of some of the vitreous (the gel) from within the eyeball. The surgeon replaces the clouded gel with a clear liquid or gas. The gas or liquid will eventually be absorbed by the body, which will create new vitreous to replace what was removed.
Any blood in the vitreous as well as scar tissue that may be pulling on the retina is removed. This procedure is done in a hospital and the patient receives either a general or local anesthetic.
The surgeon makes a small incision in the eye before removing the vitreous that exists in front of the retina (where the blood gathers). As well as removing any scar tissue from the retina, the retina may be strengthened in position with tiny clamps.
After surgery the patient may have to wear an eye patch so that they can gradually make more and more use of their eye, which can tire easily.
If gas was used to replace the removed gel the patient should not travel by plane until all of it has been absorbed into the body. The surgeon will tell the patient how long this should take.
Most patients will have blurry vision for a few weeks after surgery. In some cases it may take several months before normal vision returns.
Surgery is not a cure for diabetic retinopathy; it may stop progression or slow it down. Diabetes is a chronic (long-term) condition, and subsequent retinal damage and vision loss is always possible. Patients should continue attending their scheduled eye examinations.
Possible complications of diabetic retinopathy
Possible complications associated with diabetic retinopathy include:
(bleed) - a new blood vessel bleeds into the vitreous (gel substance in the eye), blocking light to the retina. The bleed specifically occurs in front of the retina in the back section of the eye. Symptoms may include eye pain, blurry vision, loss of vision, and sensitivity to bright light. In mild cases the patient may just see some dark spots or floaters, while in more severe cases vision may be blocked completely. In most cases, if the retina is not damaged, vitreous hemorrhage does not cause permanent vision loss and clears up within a few weeks or months, and previous level of vision is restored.
(retinal detachment) - scar tissue can pull the retina away from the back of the eye. This usually results in spots floating in the patient's field of vision, flashes of light, and even severe vision loss. If left untreated there is a significant risk of total vision loss.
Normal flow of fluid in the eye may be blocked as new blood vessels are created, causing an accumulation of pressure in the eye (glaucoma). When pressure inside the eye is high there is a risk of nerve damage inside the eye, resulting in vision loss.
Prevention of diabetic retinopathy
Diabetic retinopathy is an inevitable consequence of having diabetes for the majority of patients. However, the following measures can significantly help slow down its progression.
Controlling blood sugar levels - patients with diabetes who manage to control their blood sugar levels will definitely slow down the progression of diabetic retinopathy.
Hypertension (high blood pressure) - people with hypertension are more susceptible to blood vessel damage inside the eyes, raising the risk of developing advanced diabetic retinopathy. Patients with diabetes need to control their blood pressure by:
- Eating a healthy and balanced diet
- Taking regular exercise
- Maintaining a healthy body weight
- Quitting smoking
- Strictly controlling their alcohol intake
- Taking their antihypertensive medications according to their doctor's instructions.
Screening - make sure you go to all your scheduled eye examinations. Problems that are detected early on are much easier to treat successfully.