Diabetes, Hypertension and the Eye FAQ

Diabetes affects the eye in a myriad of ways, affecting almost all structures of the eye. Eye affection increases with duration of diabetes and with poor control. Both factors are important. This means that if you have diabetes of say 20 years duration, you have greater than 50% chance of developing eye affection, even though you have had it in superb control for all those years! Your risk however increases even further if you have been a ‘naughty’ diabetic who has paid scant regard to your doctor’s advice on diet, medication and exercise.

As soon as you are made aware of your diabetes or hypertension, you should have a complete eye examination. If the diabetes or hypertension has not affected your eye, your eye doctor may recommend annual visits. The frequency of visits may increase if you are detected to have diabetic or hypertensive eye disease.

The commonest affections due to diabetes are retinal problems, glaucoma, cataract and the increased risk of eye infections. Other, less common problems are paralysis of one or more eye muscles, dry eye and affections of the optic nerve (the nerve of sight).

That may be being penny- wise and pound-foolish. Many a problem can be detected and treated even before symptoms develop. Treating it later may be more expensive and more importantly, less effective! The blood vessels of the retina are the only blood vessels in the whole body that can be viewed with a simple non-invasive technique (ophthalmoscopy). These blood vessels mirror the changes taking place in the rest of the body’s blood vessels. This is why, an eye doctor can tell you are a diabetic or hypertensive simply by examining your retinal blood vessels. At the next check-up, he can tell if your retinal blood vessels are showing progressive changes of diabetes or hypertension and warn you to discuss stricter control with your treating physician.

The tiny retinal blood vessels in diabetics are more prone to leakages. This can result in leakage of blood in the retina (retinal haemorrhage) or into the jelly of the eye in front of the retina (vitreous haemorrhage). In case fluid containing protein leaks out into the retina, it tends to collect in the centre i.e. the macular area causing macular oedema. Fatty material, cholesterol etc may also leak into the retina, either in the centre or in the periphery. All leakages, whether of blood, fluid or cholesterol in the macular area will result in distorted vision or a drop in vision. This may be sudden, such as when bleeding occurs, or gradual, when fluid oozes slowly into the macular area. The patient will detect this provided he has been educated to examine his vision at home at regular intervals, covering one eye at a time. This vision testing should be done with the correct glasses worn, for both distance and near. He should obviously visit his eye doctor, the moment he detects this fall in vision. However, if the same leakages are not in the centre of the retina, the patient may not notice them till much damage has occurred. Therefore it is essential that he visit his eye doctor at regular intervals as suggested by him. The eye doctor will dilate his pupils as required and carefully examine the macula and periphery of the retina using an instrument called an ophthalmoscope. If he does detect these leaking areas, he may ask for a fluorescein angiography test to detect the site of leakage. He may decide to use laser treatment to treat these leakages.

The aim of laser treatment is to preserve whatever vision there is left, rather than improve it. Also, as the duration of diabetes increases, especially if it is poorly controlled, fresh hemorrhages and leakages can occur. This may necessitate repeated sittings of laser. Unfortunately, our retinal cells do not have the capacity to grow. Hence, whatever cells are damaged, will result in permanent loss of vision in the affected area.

In certain cases, diabetes affects mainly the central area of the retina, called the macula, causing an increase in its thickness (detected by a special machine called OCT or Ocular Coherence Tomography-see chapter on ‘investigations’)). This results in poor central vision. These can now be treated with intra-vitreal injections (injections into the jelly in front of the retina) of certain new medicines. These usually have to be given as a course of 3 injections, at intervals of 4-6 weeks. These have shown good results in selected cases, even improving vision in these patients. The actual drugs used have unpronounceable names, so I will not mention their names here for fear of twisting your tongue. Yes, these drugs are expensive but the costs are coming down as their usage is increasing. In certain cases, long acting steroids are ‘implanted’ into the back of the eye by injection techniques which continue to work for 3-6 months before needing a second sitting.

This is a very common tactic employed by patients – I call it the ‘ostrich’ approach. Stick your head in the sand and pretend the problem is not there or will not affect you or will somehow become better with time! Unfortunately, the problem only gets aggravated if not tackled in time. The diabetic retinopathy (affection of the retina) which only consisted of a few haemorrhages and/or cholesterol deposits on the surface of the retina – called background diabetic retinopathy can gradually lead to the formation of new, fragile tiny blood vessels in the retina. These repeatedly burst, giving rise to fresh haemorrhages. The vessels can ultimately burst into the jelly in front of the retina, giving rise to a vitreous haemorrhage, with tremendous drop in vision. Worse still, formation of scar tissue by nature may cause a pull or traction on the retina causing a traction retinal detachment. Proliferation of these new vessels on the retina or into the vitreous is known (quite obviously) as proliferative vitreo-retinopathy. This condition requires complicated (and therefore expensive!) vitreoretinal surgery, carrying a much-reduced visual prognosis. In advanced cases, permanent blindness can result.

The simple fact is, in most cases, with timely intervention during the background diabetic retinopathy stage, progression of the disease to the next stage can be arrested or at least markedly delayed. All it takes is for the diabetic patient to visit his eye doctor at regular intervals as advised, so that the retina can be examined, instead of simply going once a year to his neighbourhood optician for a new pair of glasses.

You have a remarkably short attention span – I did mention in answer to an earlier question that diabetics are more prone to cataract, glaucoma and dry eye. This is another reason why a diabetic should have at least an annual check up with an eye doctor. He will not only look at the retina, but will also check the pressure of the eye and look at the optic disc to rule out glaucoma, examine the eye on a slit lamp biomicroscope to rule out early cataracts and test you for dry eye. The adage ‘a stitch in time saves nine’ was possibly dreamt up for a diabetic!

Most eye surgery is done under local anaesthesia; hence you need not starve yourself before the surgery. If you are on oral anti-diabetic agents, we usually recommend discontinuation of the medication on the morning of surgery. You may resume the medication along with your next major meal. In case you are on insulin, it is best you follow the advice of your diabetic specialist. You should find out from your eye doctor the time of surgery and inform your physician, so that he can alter your insulin schedule accordingly. For hypertensives, it is very important that they continue their medications as per their schedule and not miss a single dose, especially on the morning of the surgery. They should of course, inform their eye doctor about the medications they are on and the fact that they are hypertensive. He may wish to avoid the use of adrenaline and similar compounds during surgery as they may cause a rise in blood pressure.

It is important to tell your eye doctor about the fact that you are on blood thinners. Depending on what blood thinner you are taking, he may ask you to stop this a few days before and after surgery. However, if your physician feels that it is not safe to stop the blood thinners, your eye surgeon may operate you without stopping them either before or after the surgery. In modern phaco-emulsification surgery, with a corneal incision there is almost no blood loss. Many eye surgeons operate patients like you without stoppage of the blood thinners at all.