Dr. S.M.Sadikot.
Hon. Endocrinologist,
Jaslok Hospital and Research Centre,
Mumbai 400026

In India, today, diabetes ranks the second most common cause of blindness, right after cataracts! In many Western countries, it is already the most common cause of blindness.

Almost all patients with Type 1 DM, as well as in patients Type 2 DM which occurs in the younger age group, in whom diabetes has been present for around 15 years will have some evidence of retinopathy, and about half have proliferative retinopathy. Type 2 diabetics in whom the diabetes starts at a slightly older age have less risk for retinopathy, but in many of these patients retinopathy may be the first sign of diabetes. In these older patients, those who require insulin are at higher risk for retinopathy than those who do not require insulin. Amongst insulin requiring Type 2 patients, 80% will show evidence of retinopathy as compared to 20% in those who do not require insulin. The corresponding figures for proliferative retinopathy are 40% and 5% respectively. The risk of clinically important macular edema is 10 to 15 percent after diabetes has been present for 15 to 20 years, regardless of the age at onset or whether insulin is required.

Blindness occurs not only as a result of the sequelae of proliferative diabetic retinopathy and macular edema, but also because of an increase propensity for cataracts and glaucoma.

Due to the fact that retinopathy can be present in many Type 2 diabetes patients, it is essential that all patients have a baseline visual evaluation. This MUST include:

• History of visual symptoms.
• Measurement of visual acuity and intraocular pressure : refractive errors should always be corrected after a period of stable control ; cataract and glaucoma (with special focus on open angle glaucoma) are more common in diabetics and should be actively looked for.
• Ophthalmoscopic examination through dilated pupils.

This examination should be done at the time of diagnosis and repeated on an annual basis. It should be carried out by a person killed in diagnosing diabetic eye involvement.

Patients at special risk, and those who show the presence of abnormalities, may require more frequent checkups; these patients should be seen along with a specialist.

• Women who are planning a pregnancy, must have a detailed eye examination.
• All pregnant women must have a detailed eye examination for the presence of retinopathy at the time of diagnosis and then as frequently as warranted.
• Patients with unexplained visual symptoms deterioration in visual acuity increased intraocular pressure any retinal abnormalities any other ocular abnormality that threatens vision.
• Patients with preproliferative retinopathy (multiple cotton wool spots, multiple intraretinal hemorrhages, intraretinal microvascular abnormalities venous beading).
• Patients with proliferative retinopathy (retinal neovascularisation, preretinal or vitreous hemorrhage, fibrosis, traction retinal detachment).
• Macular oedema (hard lipid exudates and/or retinal thickening in side the temporal vascular arcades).
• Presence of microalbuminuria, hypertension and smoking.

I personally feel that doctors who have many patients with diabetes, must learn to use an ophthalmoscope, so that they can diagnose the presence of retinopathy, especially in the early stages. If this is not possible, then expert help should be taken for the retinal examinations.

Often when I ask patients whether they have their eyes examined, they say that their eyes have been examined recently. What they usually mean is that they have had their vision checked to see if they need "glasses" or if there is a change in the "number". Such an examination in no way examines the retina and therefore, it is essential that the patient be told what a retinal examination means. They must also be told that it is possible that the doctor who examines the eyes may put some drops in them and that the vision would be blurred for a few hours. Therefore, it would be better for them to be accompanied by someone and it is obvious that they should not be driving a car!

I feel that patients with Type 1 diabetes should have their retina checked 5 years after diagnosis or at puberty, (which ever is earlier) and annually thereafter. Patients with Type 2 diabetes should have their retina checked at the time of diagnosis and annually thereafter. The annual checkup recommendation is only valid if there is no significant problem. If the patient does show significant changes, then the frequency would have to be individualized. Diabetic women who are planning a pregnancy should have their retina checked before conception. If this is not possible, it should be done as soon as possible after she gets pregnant and should be carried out every semester at the very least.

In case you do examine the retina with an ophthalmoscope, what would be looking for?

This is what one would see with an ophthalmoscope

If the patient has non-proliferative or background retinopathy, this is what you would see.

The small red dots are 'microaneurysms', tiny damaged capillaries. The red lines are small haemorrhages, little flecks of blood.

The number of microaneurysms, the little red dots the doctor sees, indicate the likelihood of more severe problems in the years to come.

The patients may have more serious form of a diabetic retinopathy. In the preproliferative stage, the retina has been damaged by the higher than normal sugar levels over several years. Small haemorrhages (flecks of blood) and tiny abnormal blood vessels are present.

If this progresses and many new vessels start developing in the retina, one has progressed to the proliferative stage. These new vessels are weak and can leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina or pull it out of place -- this is called retinal detachment.

New blood vessels growing on the retinal surface and slightly in front of the surface.

If the macula is involved, this is a very serious matter, as the very central part of the vision would be affected!

There are usually no symptoms in the early stages of diabetic retinopathy. Vision may not change until the disease becomes severe. An exam is often the only way to diagnose changes in the vessels of your eyes. This is why regular examinations for people with diabetes are so important. But it may not be feasible to carry out a retinal examination at every visit. Thus, one should tell the patient to look out for signs and symptoms which may herald a serious problem and they should be told that they should seek medical attention urgently.

• vision becomes blurry
  
• trouble reading signs or books
• see double
• one or both of the eyes hurt
• the eyes get red and stay that way
• feel pressure in your eye
• see spots or floaters
• straight lines do not look straight
  
• can't see things at the side as you used to The macula is an area of the retina very near the optic disc. It seems to be devoid of blood vessels but is one of the most important areas of the retina as it is responsible for "central" vision. One can well understand the role of central vision if one reflects that if the macula is affected and one tries to see or read anything, the very central part on which the eyes would focus would appear either distorted or as a black spot! When the vessels surrounding the macula are affected by diabetic microangiopathy the condition is known as diabetic maculopathy or diabetic macular edema. I consider this as an acute emergency and immediate corrective steps need to be taken to rectify the problem.

When the retina is examined, the macular area would also be looked at. But the next examination may be a year away and what happens if there is any problem in the meantime. Often the initial signs and symptoms may be very subtle and in my opinion, most of the patients who have macular problems come to us at a relatively late stage when the chance of normalising the vision may be that much harder. I usually give patients an Amslers Chart which they can use to test for macular vision. This chart is given alongside. I ask the patients to test central vision daily or at least twice a week and to seek immediate attention if there seems to be any problem. I have found that this is an extremely useful chart and allows the patient to be diagnosed at the every early stages of macular involvement.

1. Look at the square (grid).

2. Wear your reading glasses (if you use one) and cover one eye.

3. Focus on the center dot for one full minute.

4. While looking directly at the center, be sure that all the lines are straight and clear, and all the small squares are the same size.

5. Repeat the test in the other eye.

6. If any lines or squares appear distorted, wavy, blurred, discolored, or otherwise abnormal, call your eye doctor right away.

7. In healthy eyes the lines are straight.

The Amsler's chart is very useful for early detection of macular problems and thus is very important as this may be an early sign of macular problems and lead to a loss of central vision! But one must know its limitations.The Amsler grid will NOT detect proliferative diabetic retinopathy, most preproliferative changes and other types of damage that may threaten vision, nor is it useful for detecting any of the early changes. Remember: a normal Amsler grid test does not rule out the presence of retinopathy that can threaten your vision. It cannot replace routine eye exams. Only regular eye exams can do this.

Meticulous management of the risk factors and an early diagnosis would go a long way towards averting diabetic retinopathy or retarding the progression of the retinal changes even if one is not able, to revert the changes that have occurred. The risk of retinopathy is directly related to the degree and duration of hyperglycemia. The prevalence of proliferative retinopathy - and of blindness related to this condition - is directly associated with the duration of diabetes and the degree to which blood glucose concentrations have been elevated.

Thus, all efforts must be made to keep a "tight" control on the blood glucose levels. Many studies have shown the importance of a good glycemic control. If one does not have diabetic retinopathy but does not keep the blood glucose under optimal control, one would have FOUR times the chances of getting retinopathy as compared to someone who does keep the blood glucose well controlled! Moreover, in people who already have retinopathy, the condition progresses in those with good control only half as often as those not well controlled.

In fact, it has been shown that for each 1% rise in the HbA1c, the retinopathy gets worse at the rate of 32%. So if one's HbA1c is 9%, the retina is getting damaged twice as fast as someone with a level of 6% (3 x 32% = 92% additional deterioration).

High blood pressure is fairly common in people with diabetes. Again one should aim for a good control of the blood pressure 130/80 or less (lower still if there is protein in your urine). With blood pressure, for each 10mmHg rise, the retinopathy gets 11% worse. So if one's blood pressure is 150/90, their retina is getting 22% worse that someone whose pressure is 130/80.

Patients with diabetes who have high serum lipid concentrations have an increased risk of both proliferative retinopathy and vision loss from macular edema and associated retinal hard exudates. Reducing the hyperlipidemia may lower this risk.

Similarly Smoking literally doubles the rate of damage that diabetes causes to the bodies larger arteries, making amputations and heart disease far more likely. Smoking triples the rate of retinopathy progression. These impressive results show that we can do a tremendous amount to prevent serious deterioration of the diabetic retinopathy.

Lifestyle	30-60 minutes exercise a day, moderate alcohol consumption only, avoid obesity if possible, balanced diet including 5 portions of vegetables or fruit a day, with the minimal of animal or 'hard' vegetable fats, and very low salt.
Blood Pressure	130/80 or less125/75 or less if protein in urine present
HbA1c	6.5% or less with very few or preferably no hypos. If hypos develop, see expert advice. ACE inhibitors or AT11 unless young/pregnant/very low blood pressure/poorly tolerated
Cholesterol	<5.0mmol/l, and statins recommended for most adult patients
Smoking	Smoking 20 a day triples retinopathy (passive smoking: room-mates inhale at least 25%)

Prevention of retinopathy is the best approach to reducing the risk of blindness among patients with diabetes, but this is not yet possible in many patients.

At the outset it should be made clear that there are no drugs available to treat diabetic retinopathy. Hopes raised previously by a group of drugs called the Aldose reductase Inhibitors have not been borne out and neither has antioxidant treatment. Treatment with aspirin did not affect the progression of retinopathy, the risk of visual loss. The two treatments are laser surgery and vitrectomy. They are very effective in reducing vision loss from this disease. In fact, even people with advanced retinopathy have a 70-80% chance of keeping their vision when they get treatment before the retina is severely damaged.

Which again brings into focus the importance of regularly examining the retina of the patients! Laser photocoagulation therapy is effective in reducing the risk of further visual loss and is generally useful in preventing blindness in diabetics with high risk proliferative retinopathy and macular edema. There is now evidence that early treatment with laser photocoagulation, without waiting for the development of severe changes, may lead to a better prognosis in preventing vision loss.

Vitrectomy may restore vision in some patients with recent traction retinal detachment or vitreous hemorrhage. It is important to note that although these treatments are successful, they do not cure diabetic retinopathy.