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EYE, RETINA AND DIABETES:
Diabetes can affect the eye in various ways, the most often seen complication is diabetic retinopathy. The retina is the innermost layer of the eye. The health and high metabolic activity the retina depends upon the retinal capillary bed. This capillary bed extends lika a netlike throughout the retina except for a small area at the very centre of the macula known as the “Foveal Avascular zone”.
THE PROBLEM OF DIABETIC RETINOPATHY:
Diabetic retinopathy is the affection of the retina (back portion of the eye) due to diabetes. The risk of developing retinopathy is higher for patients who have diabetes for a long time. It has been estimated that about 60-70% of patients who have diabetes for 15 years would have some damage to their eyes due to diabetes. As the duration of diabetes increases further, the risk also increases. In those with duration of diabetes of 20 years or more the risk of retinopathy goes up by about 80%. Luckily however, not all patents who have diabetic eye changes have sight threatening forms of retinopathy and only a few patients ultimately become blind due to diabetes.
In a population based study done in Chennai using retinal photography, we showed that the prevalence of diabetic retinopathy was 17.6% i.e. one in 5 developed retinopathy due to diabetes.
Diabetic retinopathy can be basically divided into two stages, (a) non proliferative diabetic retinopathy and (b) proliferative retinopathy (advanced stage). In the early stages of diabetic retinopathy, there are small balloon like sacs called microaneurysms or dot haemorrhages in the eye. In the next stage, these sacs start leaking and water logging of the retina can occur. In early stages of diabetic retinopathy, usually no specfic treatment for the eyes is required. However, this is the warning sign that more serious stages may follow if diabetes is not controlled very tightly. Hence the patient should take extra precautions to control dabetes very carefully and intensify the treatment with frequent blood sugar estimations.
In some cases, the leaking fluid can collect in the critical central region of the retina which is called as the “macula”. The macula is the “seeing” portion of the eye. If this occurs we call it as the stage of Diabetic Macular Edema(DME). When the leaking fluids reaches the central portion of the eye, vision may become blurred and in some cases may actually progress to complete blindness. At the stage of DME, very often control of diabetes alone may not suffice. In order to stop this leakage, laser photocoagulation may be necessary. If left untreated, diabetic retinopathy may lead to severe visual loss.
In advanced stagess, abnormal “New Vessels” form on the retina. These new vessels are outgrowths from the normal vessels. The problems with the new vessels is that their walls are very friable and they have a tendency to bleed. For this reason, whenever new vessels are seen, immediate laser photocoagulation must be done. One could have extensive new vessels all over the retina and yet could be blissfully unaware of it because there are no symptoms. The sight could in fact be preserved till there is a massive bleed into the vitreous which can reduce vision overnight. Again, proliferatieve retinopathy if left untreated could lead to formation of fibrous bands. This could be the forerunner for a traction retinal detachment and sudden loss of vision.
How can one prevent blindness due to diabetes?
One of the most important things to do of course, is to control diabetes well. It is also mandatory to have periodic examination of the eyes done by a qualified retinal specialist atleast once a year. We have studied the families of patients with diabetic retinopathy and have published that the siblings of Type 2 diabetic patient with DR are 3.5 times more prone to develop retinopathy. Hence a family history of diabetic retinopathy is a definite indication for routine retinal examination. If there are already changes due to retinopathy more frequent examinations might be indicated. If Laser Photocoagulation is indicated, it must be done without much delay so that sight can be preserved.
Screening for Diabetic Retinopathy:
Every diabetic patient is offered an eye examination in the centre. This involves:
a. Checking the vision using the lastest equipments.
b. Measurement of the pressure of the eyes
c. Examination of the anterior portion of the eye by slit lamp.
d. Dilatation of the pupils using drops.
e. Retinal examinaition.
It is only wth the combined effort of diabetologists and ophthalmologists that implementation of a screening programme for diabetic retinopathy is possible in our country. Efficient, objective methods are available to detect high risk lesions and blindness can be prevented if appropriate laser treatment is instituted early.
Who should do the screening?
Ideally, screening for diabetic retinal disease should be done by an ophthalmologist trained for this purpose. When this is not feasible, screening should be the primary responsitibility of the doctor in charge of the diabetic patient. Screening should be carried out by someone fully competent in the use of an ophthalmoscope and in the recognition of fundus abnormalities. This has been endorsed by the 1990 convention on Diabetic Retinopathy by diabetologists and ophthalmologist of Europe.
When to screen?
It is mandatory that every patient should have a fundus examination at the time of diagnosis of diabetes. This is because, in NIDDM patients, diabetic retinopathy could be present even at the time of diagnosis of diabetes, due to the insidious nature of this disease and the long asymptomatic period.
In a study where we screened 1563 newly detected diabetics (i.e with a duration less than 1 year of diabetes), we have published that 7% of newly diagnosed Type 2 diabetic patients seen in the centre already had diabetic retinopathy at the time of diagnosis of diabetes (British Journal of Ophthalomology, 2001).
If the retina is normal, the follow-up examination should be done on an annual basis, but more frequently if lesions of diabetic retinopathy are already present.
In IDDM patients, the retina should be first examined at the time of puberty or within five years after the diagnosis of diabetes whichever is earlier and annually thereafter. If diabetic retinopathy is complicated by an ntercurrent illness or renal disease, more frequent examinations should be done.
The fundi should also be examined if patients complain of visual symptoms such as impaired central vision, distorted vision or seeing black floaters which may be caused by a vitreous haemorrhage.
Digital Colour Photography & Fundus Flourescein Angiography (FFA):
Newer techniques of screening by using digitalised retinal cameras are available.Retinal Colour Photography is used as a screening procedure especially in subjects with long duration of diabetes. Fundus Flourescein Angiography (FFA) is a procedure which involves intravenous injection of a dye in the arm and then taking rapid sequence photographs of the retina. This helps the ophthalmologist to have a complete assessment and a permanent record of the changes in the retina. It is also useful to pinpoint the specific areas in the retina which are diseased.
Laser Photocoagulation for diabetic retinopathy – When and Why Laser photocoagulation has been the single greatest hope of the century for patients with diabetic retinal disease. Several multicentric (Diabetic Retinopathy Study and Early Treatment Diabetic Retinopathy Study) studies all over the world especially in U.S.A. and Europe have conclusively demonstrated that laser photocoagulation, if instituted early and correctly, prevents blindness due to diabetes.
Newer Investigation Optical Coherence Tomography(OCT):
Is an imaging technique, using infrared light to visualize subsurface structure in biological tissues.Quantitative measurements of retinal morphology can be compared with a normative database to enhance diagnostic performance. Powerful adjunct to conventional fundus examination and FFA, not only for diagnosis, but also to track disease progression and monitor response to laser treatment.Useful in evaluation and management of DME and management of various retinal disorders.
What are lasers?
A laser generates and amplifies light energy, producing a powerful beam of light that is made up of light waves. The word “LASER” is an acronym for Light Amplification by Stimulated Emission of Radiation.
How does the laser work?
One of the major problems of diabetic retinopathy is that there is decreased oxygen supply to the retina (hypoxia). It is this hypoxia which is responsible for much of the damage due to diabetes in the retina. When there is hypoxia the body tries to form new vessels in an attempt to improve the blood circulation to the retina. Unfortunately, these new vessels are very fragile and can bleed easily. Laser photocoagulation effectively converts these areas of hypoxia into areas which do not need oxygen (anoxic). This ensures that there is no stimulus for new vessel formation.
Which diabetic needs laser photocoagulation?
Diabetic retinopathy is of several grades or stages. A qualified retinal specialist will be able to grade the lessions due to diabetic retinopathy very accurately. Not all patients with diabetic retinopathy need laser treatment. The following are some of the indications for laser treatment:
Proliferative retinopathy: When abnormal new vessels form on the retina they should be photocogulated. Laser photocoagulation will help to resolve these new vessels before they produce any damage. If left untreated there is a definite risk that they could bleed and lead to sudden loss of vision.
Diabetic Macular Edema: When there is accumulation of fluid near the macula (seeing portion of the eye) this is another indication for photocoagulation.
Are there any side effects of Laser Photocoagulation?
If done by a well trained retinal surgeon, laser treatment is an absolutely safe procedure and there are practically no side effects. Transient blurring of vission may occur in a few patients. There could be black spots floating in thefluid of the eye, which will settle down within a few days.
Will the vision improve after laser treatment?
This depends on the type of retinopathy for which the photocoagulation is performed. Often the patient does not have any visual problem even befre the treatment. In such cases, it is sometimes difficult to make the patient understand about the need for laser treatment. Photocoagulation ensures protection against this serious risk of loss of vision. Inshort, it is like taking an insurance policy against blindness ! In some patients, all that laser does is to maintain the same vision that the patients have at present. We have enough evidence based on studies all over the world that if left untreated the vision will deteriorate very rapidly, whereas if laser photocoagulation is performed the vision can be maintained at the same level. In very late stages, the rate of decline of vision can be at least slowed down. It must be emphasized that laser treatment is not a cure for diabetic retinopathy and there are unfortunately some forms of retinopathy that simply will not benefit from laser photocoagulation. With its obvious limitations, laser photocoagulation remains the single most effective treatment for diabetic retinopathy today.
Our experience with diabetic retinopathy:
At our centre, we have screened the eyes of several thousand diabetic patients. This is one of the few centres exclusively devoted to treatment and research in diabetic retinopathy in our country. We follow an internationally acepted system for grading of diabetic retinopathy (ETDRS Grading System) and decide which cases need treatment. We have currently registered 1,20,400 diabetic patients at our centre. Out of that, 30,000 patients were treated for diabetic retinopathy and 15,000 patients had undergone laser photocoagulation at our centre.
Cataract in diabetic subjects:
The development of senile cataract is earlier in diabetic patients as compared to the normal individual due to the metabolic disturbances. The indications for cataract surgery are the same and is related to the individual needs. Good control of diabetes and control of other systemic diseases and infections is mandatory for the success of surgery in a diabetic patient. A diabetic patient will have normal vision after cataract extraction and intra-ocular lens implant if the retina is normal.