Diabetes and Your Eyes (2)
Retinopathy – Diabetic Eye Disease
It is now universally accepted that having diabetes can lead to a number of eye diseases. Most commonly cited, is ‘diabetic retinopathy’, in which damage to the small blood vessels at the back of the eye may lead to significant loss of vision.
In addition to retinopathy, diabetes can cause changes in vision requiring new prescription glasses, and it can also lead to other problems, including glaucoma and cataracts; these are considered in “Diabetes and Your Eyes – Part 1“.
What’s included on this page:
Diabetic retinopathy is the most common cause of new cases of blindness in adults in most developed countries. 20 years after diagnosis, almost 100 per cent of people with Type 1 and more than 60 per cent of people with Type 2 diabetes will have developed some degree of retinopathy. That said, however, early intervention can save your sight – which is why it is so important to have regular eye examinations.
Stages/Types of Retinopathy
The disease progresses from mild abnormalities in the retina (with little change in vision) to moderate or severe ‘nonproliferative’ retinopathy. Numerous changes occur as a result of damage to the tiny blood vessels that supply the retina. Changes in vision may not be noticed until it is too late to save sight – therefore, it is vital to have regular screening in order to detect these changes before loss of vision occurs (see, “Eye Examinations“). Sight is rarely restored, but further loss of sight can often be prevented with timely intervention, usually laser treatment.
|No Evident Retinopathy||Depending on the duration of diabetes, the lining of the blood vessels supplying the retina may already be under attack (see below)|
|Nonproliferative Diabetic Retinopathy (NPDR)
No noticable changes in vision
Tiny swellings in blood vessels (‘microaneurysms‘)
Leaky blood vessels
The macula is the area of the eye responsible for central and ‘sharp’ vision. Disease of the macula (i.e. “maculopathy”) is therefore potentially sight-threatening.
Maculopathy is defined by the presence of dot or blot haemorrhages and and yellow-white spots or plaques (deposits of lipid or lipoprotein material, known as ‘hard exudates’) in the macula.
Diabetic Macular Edema* (DME) is characterised by ‘thickening’ of the retina, and accumulation of fluid and other material as a result of leakage from damaged blood vessels. DME can develop during any of the stages of retinopathy.
Clinically significant macular edema (CSME) represents a high-risk state with respect to vision loss.
This potentially serious condition usually requires focal laser treatment to seal leaky vessels.
Sometimes grid laser treatment is used if macular edema is diffuse.
Sometimes this stage is referred to as: “moderate or severe nonproliferative retinopathy”
Blood vessels close off and starve retina of oxygen & nutrients; this localised ischaemia is seen as ‘cotton wool spots’. Preproliferative stage defined by 6 or more in one eye.
Scattered laser treatment may possibly be indicated at this stage (can reduce risk of macula edema)
|Proliferative Diabetic Retinopathy (PDR)||New fragile blood vessels grow, which can bleed severely into the eye. Vision may be relatively unaffected until bleeding occurs (vitreous haemorrhage)
Scattered laser treatment usually indicated
Contracting scar tissue can result in retinal detachment
So What Happens to the Retina?
High blood glucose levels damage the lining of the blood vessels that supply the retina with oxygen and nutrients. This happens through a number of mechanisms, some of which are described in more detail in, “Hyperglycaemia – Long Term Effects“.
The damaged blood vessels become weak and leaky. Very small vessels (called capillaries) may become blocked, leading to a loss of blood supply to some areas of the retina. Such areas of ‘nonperfusion’ become starved of oxygen and nutrients – this is known as ischaemia. In response to ischaemia, production of growth factors (substances that promote growth) – such as Vascular Endothelial Growth Factor, or VEGF – results in the formation of new blood vessels. This process is called ‘neovascularisation’.
Complications of Retinopathy
The new blood vessels that form in the proliferative stages of diabetic retinopathy are fragile and bleed easily. Bleeding into the clear hollow part of the eye is called a ‘vitreous haemorrhage‘ and even a small bleed can significantly affect vision (see below).
In time, neovascularisation results in the formation of fibrous scar tissue, which tends to contract, and can tear the retina, sometimes detaching it from the back of the eye. This is known as ‘retinal detachment‘ and can lead to loss of sight (see below). If the new blood vessels grow into the vitreous gel, this may ultimately result in shrinkage of the gel, which may result in ‘wrinkling’ of the retina or even complete detachment (‘traction’ detachment).
|Neovascularisation occurring at the iris can block the drainage network of the eye; the resulting accumulation of fluid increases pressure in the, causing neovascular or ‘rubeotic’ glaucoma.|
One of the most frightening aspects of developing long term complications of diabetes is the threat of losing one’s sight.
|The most common causes of vision loss are:
There are various degrees of vision loss. Severe or total visual loss is less common these days – with timely and appropriate treatment, some sight can usually be saved. Moderate visual loss is still more common than it should be – or could be. However, people who are ‘legally’ blind may still be able to walk around unaided and carry out daily activities as usual.
Bleeding into the cavity of the eye between the retina and the lens is called a vitreous haemorrhage. The vitreous cavity is normally clear, allowing light to be focused by the lens at the front of the eye on to the retina at the back of the eye (See, “How The Eyes Normally Work” in Part 1). When blood seeps into the normally clear, jelly-like vitreous, vision can be obscured.
A bleed into the vitreous of the eye can happen without warning, and you may suddenly lose a large part of your vision. Eventually the blood clears, although it may take some time before vision is restored.
It can take weeks for the blood to clear. Sometimes it is necessary to remove the vitreous in an operation called a vitrectomy (see below) – this may be necessary if urgent laser treatment is needed to seal the bleeding vessel(s).
WHAT SHOULD I DO?
If you do have a bleed into the eye, don’t panic. It’s not usually that serious in itself – but it does indicate that some laser treatment may needed. If you do not already have an eye specialist, contact your doctor or a member of your diabetes team for advice.
The centre of the retina is called the macula, and this is the area that is responsible for ‘sharp’ vision. It is the most important area of the eye, and disease in this area can render you legally blind, even if the rest of your eye is okay.
Damaged blood vessels leaking into the macula can result in the accumulation of fluid and “hard exudate” (fatty material, which may clump together). This condition is known as macula edema. It can result in decreased blood supply to the macula, ‘wrinkling’ of the normally smooth surface of the macula, and sometimes tears or holes may appear.
Early macular disease results in a distortion of vision. If it is treated in good time with laser, then significant loss of vision can usually be prevented.
|It is important to realise that laser treatment cannot restore lost vision – therefore it is important to have laser treatment in order to prevent imminent loss of vision before it is too late. Don’t wait until you notice changes in your sight – get your eyes checked – and treated if necessary – NOW!|
The new fragile blood vessels that grow during the proliferative stage of retinopathy (see table) form a web that may contract like scar tissue, after a bleed. This tightening can pull on the retina and may cause it to tear or come away from the back of the eye. When this happens at or close to the macula, significant vision may be lost.
Sometimes the damage can be successfully repaired in one or a series of operations (see the section on “Eye Surgery” below). Operations to repair detached retina are most frequently successful in restoring some vision if the detachment is away from the macula or centre of vision.
Laser Treatment and Eye Surgery
What Does Laser Treatment Consist Of?
Laser is simply a very powerful and focused light, where the light rays are all of the same type. It can be accurately directed on to a tiny spot area of the retina and is used to burn blood vessels in order to seal them.
Laser treatment usually happens in the outpatient clinic. You sit in a darkened room, at a slip-lamp, with your chin on the rest, just as if you were having your eyes routinely examined. Anaesthetic drops may be put in your eyes, then you will have a contact lens placed on the eye – this stabilises the eye and helps to focus the laser beam.
You are required to keep very still. Bright lights will be flashed into your eye, and you will probably hear some ‘clicks’ at the same time. Each flash lasts less than one tenth of a second. Depending on the type of treatment, and your own individual case, you may just have a few burns or you may need multiple lasering across the eye.
Laser Treatment for Macular Edema
Does the macular edema need lasering? Your eye(s) may first need to be thoroughly evaluated with a dilated eye examination and fluorescein angiography. Digital photographs will probably be taken of your eye(s). These investigations will enable the ophthalmologist (specialist eye doctor) to pinpoint specific areas of leakage.
Multiple laser burns are applied close to your centre of vision. The very centre of vision (known as the ‘fovea‘) is avoided, however, as a burn in this area would lead to immediate loss of sight. Usually about 100 burns are made, but this can vary depending on the individual; anything from a few up to 250 is possible. You may be asked to look in certain directions at certain times. This type of focal laser treatment is not too painful, although you may experience some stinging. The treatment will probably take less than half an hour (?) from start to finish. Often more than one laser session is necessary; usually you will be embarking on a course of treatment, as opposed to a single session.
Your eyesight may be dim or blurry after a session of laser treatment, however this should improve during the following week. You may notice black specks in your vision; these may take some months to fade away.
Laser Treatment for Preproliferative and Proliferative Retinopathy
The laser treatment used to treat advancing preproliferative or proliferative retinopathy is applied in a slightly different way to that described above for treating macular edema. This type of laser is often referred to as PRP – panretinal photocoagulation – or scatter laser treatment.
Each PRP laser treatment may consist of 1000 or more short burns. The laser is directed around the periphery of the retina, not in the central area. Several sessions may be needed.
This type of laser treatment tends to be more painful; the treatment itself may sting, and afterwards the eye may ache for many days (anti-inflammatory eye drops may help this). As more and more laser sessions are endured, the treatment can become more painful. A local anaesthetic injection may be given under the eye, at the side, in order to reduce the pain of PRP.
Night and/or colour vision may be affected, and some degree of peripheral (side) vision may be lost after repeated sessions of PRP laser; but remember that ultimately this is a sight-saving exercise, and you may be sacrificing a little of your side vision in order to retain a major part of your central vision.
A vitrectomy may be needed:
- if the vitreous shrinks and significantly pulls on the retina
- if a severe bleed has clouded the normally clear vitreous
- if sight is threatened by macular edema
Your eye doctor may be unable to see the retina if the vitreous is severely clouded from a haemorrhage; an ultrasound scan can indicate whether the retina is in place or whether it has become detached. (An ultrasound is a simple and painless scan, using a probe which is placed over the eye).
Vitrectomy surgery may be performed under a local or general anaesthetic and is performed in the operating theatre (although a hospital stay is not always necessary). Three tiny holes are made in the side of the eye to be operated on. A light is placed in one, so that the eye surgeon can see what’s happening. A cutting suction needle is then placed inside the eye and used to cut up and remove clots, fibrous material and fluid. Scar tissue is also removed, and any thickened membranes present are carefully ‘peeled’ away from the retina. The third opening takes an infusion line, which runs clear fluid in, replacing the vitreous that was removed. The surgery may take anything up to 6 hours, depending on how difficult it is to remove fibrous material and scar tissue from the retina. Sometimes laser treatment is then required to repair small tears in the retina.
|A vitrectomy operation may cause a cataract to develop in the lens (a cloudy area in the normally clear lens) … this may then require a cataract operation (see “Cataracts” in Part 1).|
You will probably leave the hospital with an eye patch and some medication to help prevent infection setting in, and to reduce inflammation. It may take 3-6 months before results of the operation are evident in terms of vision.
The landmark study known as the DCCT (Diabetes Control and Complications Trial) clearly demonstrated that it was possible to slow down the progression of retinopathy with good control of blood glucose levels. Good blood pressure is also vitally important in order to reduce progression of the disease.
In the short term, a sudden and significant improvement in glycaemic control (HbA1c down from 9 to 7 per cent, for example) may cause a worsening in retinopathy, requiring immediate laser treatment. Again, it is important to remember that the laser is good for the long term, and in the meantime, the improved control is good for your general health and for the delay or prevention of other diabetes-related problems (see “Introduction” page to “Long Term Complications” section).
HbA1c target 6.5 – 7.0 %
Blood pressure target < 130/75
References and Resources
Recommended Book: The Diabetes Eye Care Sourcebook
by Donald S. Fong & Robin Demi Ross. Paperback published by Contemporary Books Inc (November 1999)
Recommended Website: http://medweb.bham.ac.uk/easdec/
an excellent Website for patients and professionals, maintained by eye expert David Kinshuck [http://www.diabeticretinopathy.org.uk will re-direct you there and is easier to remember!]
Ministry of Health publication: National Diabetes Retinal Screening Grading System and Referral Guidelines 2016