Diabetic Eye Disease
If you have diabetes mellitus, your body does not use and store sugar properly. High blood-sugar levels can damage blood vessels in the retina, the nerve layer at the back of the eye. The retina is responsible for sensing light as it enters your eye and then transmits signals via the optic nerve to your brain. The brain is then able to generate an image.
Diabetes can cause the tiny blood vessels in the retina to swell and leak blood or fluid around the retina. As they heal scar tissue forms and can damage the retina so its function is less effective and consequently, vision is impaired. This disease process is known as diabetic retinopathy.
There are two types of diabetic retinopathy:
- Non-proliferative diabetic retinopathy (NPDR)
- Proliferative diabetic retinopathy (PDR)
NPDR is commonly known as background retinopathy and is an early stage of diabetic retinopathy. In this stage, the tiny blood vessels within the retina leak blood or fluid. Signs of NPDR seen in the retina may include dot and blot hemorrhages (tiny bleeds in the retina), microaneurysms (balloon-like swelling of capillaries), and exudates (retinal deposits occurring as a result of leaky vessels).
Many people with diabetes have mild NPDR. Most people do not notice any symptoms at this stage, however damage may be occurring. Therefore it is important to have regular eye examinations as early detection is the best protection against vision loss.
PDR is seen in advanced stages of diabetic retinopathy. The main cause of PDR is widespread closure of retinal blood vessels, called ischemia, preventing adequate blood flow. The retina responds by growing new abnormal blood vessels in an attempt to supply blood to the area where the original vessels have closed. This is called neovascularisation. These new blood vessels are often accompanied by scar tissue that may cause wrinkling or detachment of the retina. The abnormal blood vessels have thin, fragile walls and often leak blood or fluid into the retina or vitreous, resulting in severe vision loss.
PDR may cause more severe vision loss than NPDR because it can affect both central and peripheral vision. Diabetic retinopathy can affect your vision in the following ways:
- Macular oedema: This is swelling or thickening of the macula. The macula is a small area in the centre of the retina that allows you to see fine details clearly and perform activities involving depth perception and colour vision, such as reading and driving. Macular oedema is caused by fluid leaking from the retinal blood vessels and may result in blurred or distorted vision. It is the most common cause of visual loss in diabetes and can occur at any stage of the disease, although it is more likely to happen as the disease progresses. Vision loss may be mild to severe, but even in the worst cases, peripheral vision continues to function
- Macular ischemia: This occurs when the small blood vessels close. Vision blurs because the macula no longer receives sufficient blood supply to function normally.
- Vitreous hemorrhage: In PDR the abnormal, fragile blood vessels may bleed into the vitreous, the jelly-like substance that fills the middle of your eye. If the vitreous hemorrhage is small, a person might see a few new, dark floaters. A very large hemorrhage might block out all vision. It may take days, months, or even years to reabsorb the blood. If the eye does not clear the vitreous blood adequately, then vitrectomy surgery may be recommended
- Vitreous hemorrhage alone does not cause permanent vision loss. When the blood clears, vision may return to its former level unless the macula is damaged.
- Traction retinal detachment: When PDR is present, scar tissue associated with neovascularisation can cause the retina to shrink, wrinkle or pull away from its normal position. Macular wrinkling can cause visual distortion. More severe vision loss can occur if the macula or large areas of the retina are detached.
- Neovascular glaucoma: Occasionally, extensive retinal vessel closure with PDR will cause new, abnormal blood vessels to grow on the iris (the coloured part of your eye) and block the normal flow of fluid out of the eye. Pressure in the eye builds up, resulting in neovascular glaucoma, a severe eye disease that causes damage to the optic nerve which, in turn, can lead to loss of vision.
Unfortunately, diabetic retinopathy usually does not cause problems in your vision until its later stages. This means that by the time vision changes do occur, there has already been a large amount of damage to the retina.
Symptoms of diabetic retinopathy can include:
- Decreased vision
- Blurred vision
A medical eye examination is the only way to detect changes inside your eye. Your ophthalmologist can often detect and treat serious diabetic retinopathy before you are aware of any visual symptoms. Your eyes will be dilated for a thorough eye examination and colour photographs may be taken.
A special test called a fluorescein angiogram may also be required to assess your retina. In this test a dye is injected into your blood stream and photos are taken of the retina as the dye travels through highlighting the blood vessels. Ocular Coherence Tomography (OCT) is also used to assess your macula. This is a non-contact, non-invasive imaging technique used to obtain high resolution, cross-sectional images of the macula.
The best treatment is to prevent the development of diabetic retinopathy as much as possible. Strict control of your blood sugar will significantly reduce the long term risk of vision loss. Once diabetic retinopathy develops and progresses to later stages then your ophthalmologist may recommend treatment to help slow the progression. Early detection of diabetic retinopathy is crucial for effective treatment.
There are 3 common treatments of diabetic retinopathy:
- Laser Treatment: The goal of laser treatment is to stop the leakage of blood and fluid in the retina and thus slow the progression of diabetic retinopathy and vision loss. Laser treatment may be recommended for macular oedema, severe non-proliferative diabetic retinopathy (NPDR), proliferative diabetic retinopathy (PDR) and neovascular glaucoma.For macular oedema, the laser is focused on areas where blood vessels are leaking near the macula. This is called focal laser. This is usually completed in one session; however more sessions may be needed. The goal of focal laser is to seal leaking blood vessels near the macula and prevent further loss of vision. It is uncommon for people who have blurred vision from macular oedema to recover normal vision, although some experience partial improvement. A few people may see the spots in their central vision following focal laser. These spots usually fade with time but may not completely disappear. For severe NPDR and PDR, the laser is focused on all parts of the retina except the macula. This is called panretinal photocoagulation and causes the abnormal blood vessels to shrink and disappear. Hence it reduces the chances of a vitreous hemorrhage and traction retinal detachment. Panretinal photocoagulation is usually done in two or more sessions and usually works better before the fragile, new blood vessels have started to bleed. After panretinal photocoagulation you may notice some loss of peripheral vision and difficulties with night vision. This is a sacrifice to save as much of your central vision as possible.Laser treatment can be useful in slowing the progression of diabetic retinopathy. However it is not a cure and does not always prevent further loss of vision.
Complications with Laser Treatment:
- Vision can be blurred for several weeks, although in most patients it usually improves within hours or days.
- Night vision and colour vision may be reduced.
- Some loss of side vision, this may reduce the ability to drive safely, especially at night.
- Increased sensitivity to glare; sun glasses often help.
- A slight risk of damage to the macula, this may reduce central vision.
- Vitrectomy: If a vitreous haemorrhage does not clear on its own then a vitrectomy may be needed. This is a surgical procedure where the vitreous, the jelly-like substance that fills the middle of your eye, is removed and replaced with a salt water solution. This salt solution is absorbed over time and slowly replaced by fluid produced naturally by your eye. By removing the vitreous and the haemorrhage your vision can be restored to its former level unless the retina is damaged. Laser treatment may then be required to seal leaking blood vessels. A vitrectomy is also used to remove scar tissue when it begins to pull the retina away from the back of the eye. This allows the detached retina to settle back into its normal position.
- Steroid or anti-VEGF Injections: An injection of the steroid, Triamcinolone, into the eye can be beneficial for some patients with diabetic retinopathy. Steroid medications aim to reduce inflammation as well as tighten and strengthen blood vessels thus reducing leakage and swelling of the retina. An alternative to a steroid injection is an anti-VEGF treatment known as Avastin. It works by blocking a substance known as vascular endothelial growth factor or VEGF. The blocking or inhibiting of VEGF helps to prevent further growth of unwanted and abnormal blood vessels that are fragile and are prone to leaking or bleed into the macula and surrounding areas resulting in swelling. Triamcinolone and Avastin are administered by injection into the vitreous or jelly-like substance in the back chamber of the eye. Your pupil will be dilated and the eye is also numbed with anesthesia. It is important that this treatment is promptly delivered before extensive damage has occurred. All injections and laser treatments have risks including thermal damage or serious infection causing blindness or loss of the eye.
Details regarding risks and complications will be provided by your treating ophthalmologist when discussing treatments and proceeding with consent. At this time, your Brisbane Eye Clinic Ophthalmologist will be pleased to answer any queries you may have.
People with diabetes should have a thorough eye examination every 12 months. More frequent eye examinations may be necessary after diagnosis of diabetic retinopathy.
Pregnant women with diabetes should schedule an appointment in the first trimester, as retinopathy can progress quickly during pregnancy.
Rapid changes in your blood sugar levels can cause fluctuations in your vision even if retinopathy is not present. You should have your eyes checked promptly if you have visual changes that:
- Affect only one eye
- Last more than a few days
- Are not associated with changes in blood sugar