The condition was unknown 50 years back, when most diabetic patients used to die before the diabetic retinopathy could cause blindness. However,today by effective control of blood sugar diabetic patients can be helped to live to ripe old age. Unfortunately, supplementing insulin does not seem to solve all problems for the diabetic. The most disturbing of these unsolved problems being D.R.

With the increasing longevity of the diabetic patients through modern medical care, the number of diabetics going blind due to D.R. is increasing rapidly. As a result D.R. has become one of the most important reason for blindness in western countries. The problem is slowly assuming disturbing proportion in India too. It is so, specially among the urban population of well-to-do families. With our public hospitals running effective diabetic clinics , the problem will sooner or later appear among all sections of the population.

Since D.R. develops whether or not diabetes is kept under control, it is clear that the abnormalities in diabetes are not confined to insulin deficiency alone. What these abnormalities are, we do not know. What we do know, is that the longer the diabetic patient live, the higher are the chances of developing Retinopathy. For instance, it has been estimated that if, say, 100 patients of diabetes are kept under watch for signs of D.R. 90% will develop retinopathy after 18 years and all will develop the disease in 25 years.

Diabetes occur more in females than in males in the ratio of 3:2. They are also prone to develop retinopathy (ratio 4:3). Therefore, till the exact cause of diabetic retinopathy is known - so that the process can be prevented or even reversed (which unfortunately remains a distant dream)- the only alternative left is to try to ensure useful vision for as long as possible, preferably as long as the person lives. In choosing the best method of treatment available today 4 excellent multicentric clinical trials funded by National Institute of Health USA ( Diabetic Retinopathy study -DRS ; Early Treatment Diabetic Retinopathy Study - ETDRS; Diabetic Retinpopathy Vitrectomy Study- DRVS; and Diabetes Control and Complication Trial- DCCT) have helped immensely.

Diabetic retinopathy is an expression to describe a series of dangerous changes in the retina which ultimately lead to gross visual loss or total permanent blindness.

The early and the most fundamental changes take place in the finest blood vessels- the capillaries of the retina. Because of weakness developing in the walls of these blood vessels, small outpouchings develop known as microaneurysms. Through these weakened wall blood and serum leak out, causing small haemorrhages -and white exudates. The retina becomes edematous. In other forms of D.R. over small areas the capillaries close down, as a result, the retina deprived of normal oxygen , stimulates the growth of new blood vessels, presumably through the release of vasoformative substances.

The retina, like brain, is protected from many toxic substances in the circulating blood by substances in the circulating blood by special arrangement of cells in the capillary walls and special protective layers- known as blood-retinal barrier. The newly formed blood vessels are on the other hand extremely thin walled and lack these special qualities of normal retinal blood vessels. These vessels fail to maintain the barrier. These blood vessels not only leak protein and fat rich fluids but also toxic substances, on there way to be excreted through the kidney or detoxicated in liver, into the sensitive retina. Often these ruptured vessels produce hemorrhages into the eye ( vitreous haemorrhages).

While retinal edema specially in the central area of the retina (Macular edema ) deteriorates vision , vitreous haemorrhage when massive can cause serious impairments of vision-even blindness. Often the haemorrhage gets absorbed partly or fully to improve vision. But unfortunately, the haemorrhage, recurs again and again, usually resulting in lost of vision. If the vision is not lost because of vitreous haemorrhage, a peculiar growth of scar tissue on the surface of retina and later its shrinking does so when retina is pulled up causing retinal detachment. In some severe cases new vessels may grow in the front part of the eye, leading to a difficult to treatment glaucoma, known as a neovascular glaucoma (high eye pressure).

Left to itself, the process inexorably proceeds to near loss of vision or total blindness.

Very good control of diabetes may help in delaying the development of diabetic retinopathy, and once developed may slow down the process of deterioration. However, no treatment with drugs have been found useful in treatment in D.R. Sooner or later photo-coagulation will be needed in most cases, often a new advanced surgical system - vitreo-retinal surgery is proving sight savings.

Photocoagulation can be carried out by Xenon arc, Argon laser, Diode laser, krypton laser, Dye laser, frequently doubled Yag laser. In experienced hands all are effective. Besides, retinal cryo ablation can be very useful when used as a supplement to photo-coagulation in difficult cases where sufficient photocoagulation cannot be carried out because of cataract, vitreous haemorrhage etc.

It is possible to produce a burn on the retina an underlying tissue ( choroid) by focusing a strong source of light. The light energy on being absorbed by the dark pigment of the choroid and in a pigment layer close to the retina, produces enough heat to coagulate the tissue-normal or diseased. Subsequently the area heals to form a scar. Thus, diseased leaking blood vessels can be destroyed. The retina can be made to stick to the choroid (as if welded). Various forms of energy have been used in the construction of the photocoagulator using laser as source of energy proved to be unsafe. However, lately, argon gas laser has been successfully used in certain photocoagulator and are as safe as Xenon photocoagulator.

The most important use of photocoagulation is to destroy the newly formed blood vessels, which when rupture lead to sudden loss of vision through massive bleeding inside the eye .

While eliminating these dangerous sources of vitreous haemorrhage the risk of blindness can be considerably reduced. However, just destroying the newly formed blood vessels will not be of much use in the long run, unless the stimulus for the regrowth is eliminated.

The only way one can attempt to do is to turn the oxygen starved ( hypoxic) retina into scars which need no oxygen. This is done by what is known as multiple spot scatter photocoagulation or selective retinal ablation also known as panretinal photocoagulation (PRP)

Understanding the retinal areas turned into scars do not function anymore.

However, by cleverly and carefully placing, the photocoagulation marks over the areas of retina which are least useful to man, the restrictive effect of the treatment can be so minimised that the patients usually do not realise the difference and do not complain. All the aspects of fine vision ( as required to read or write ) and colour vision are confined to a highly sensitive tiny area- macula, situated at the centre of the back of the eye. The rest of the retina serves to give what is known as field of vision and night vision. When a person walks or drives in a busy road looking ahead he is also aware of the people and vehicles on either side. This is possible due to the field of vision, and function of the peripheral retina, the retina is endowed with rods, which can become 1000 times more sensitive in darkness by a remarkable process of adaptation so that a man can see in darkness.

Therefore , when parts of peripheral retina are destroyed by photocoagulation, it is expected that both field of vision and night vision will be affected to some extent. The reasons why patients do not usually feel the difference after treatment at the hand of a careful and experienced retina surgeon could be :

• spots of photocoagulation scars are so distributed as to leave functioning retinal areas all over the treated area thereby minimising the effect of field defects.
• since a diabetic patient with retinopathy rarely ventures in dark night he does not notice the difference.
• the retina with diabetic retinpopathy has poor sensitivity as a part of the disease. Therefore, the selective destruction of their poorly functioning retina is not as significant as it would have been in a normal retina; and
• the improvement of central vision ( which one needs the most ) as a result of peripheral treatment is often so encouraging and pleasant that such other minor functional losses involving field of vision or night vision do not bother the patients. However, these are facts, a more sensitive patient or a patient whose treatment has to be intense and extensive as in cases where the retinal disease is more advanced, before the treatment has been started. These limitation of visual function could be disturbing. It is always advisable that all patients are informed about the good, as well as not so good, aspects of treatment with photocoagulation.

The best that has been claimed about this treatment is that it helps to preserve useful vision for a longer period; it staves off disaster in the form of blindness. But, does it eliminate such possibility? The answer is : though it considerably reduced the chances of gross visual loss, it does not eliminate the possibility. It has been found that when treated early it significantly slows the process of diabetic retinopathy and long term prognosis in maintaining good vision is far better than treatment started late.

Photocoagulation of the retina seems the only practical form of treatment in diabetic retinopathy. This form of therapy has gain widespread acceptance all over since its introduction by Prof. Mayer-Schwickerath ?( the inventor of the first photocoagulater) of West Germany in 1959. Though the majority reported encouraging results , visual deterioration and loss of vision during and after the treatment were frequently observed. With increasing experience the result continued to improve. However, it is not possible to answer such anxious and searching question of the patients of D.R. as " what are my chances of regaining good vision? For how long? What are the risk I’m taking?" etc.

The reasons are many:

• The natural progress of the disease is not uniform and therefore , not entirely predictable.
• Patients vision may fluctuate; sometimes even the retinal picture changes as visualised by the opthalmologists.
• Because of the complexity of retinal changes in D.R. no visual recordings can be accurate. Yet it is absolutely necessary that the patient should know the odds, specially when the treatment by photo-coagulation is essentially destructive. One destroys certain part of retina, certain potential sources of bleeding in order to preserve the functioning of the rest of retina, specially the central one, used for fine vision.

In order to obtain an unbiased and objective evaluation of effect of photocoagulation in D.R., in a multicentric clinical trial conducted on 1700 diabetic patients by Diabetic Retinopathy Study Research Group, USA
( 1971). Their other eye serve as control. The events were analysed by independent ophthalmologists and advanced statistical evaluation proved:

• Photocoagulation reduces the chances (rate) of development of serious visual loss by 57%
• It inhibits the progression of all varieties of diabetic retinopathy; and
• Recovery of visual loss because of retinopathy is more frequent in treated than untreated eyes.

Thus it appears that the original optimism about the usefulness of the photocoagulation in the treatment of this otherwise hopeless disease is to a great extent justified.

A person with a massive vitreous haemorrhage which does not clear, or with a diabetic membrane in front of the retina or a retinal detachment caused by contraction of such a membrane was considered to have too advanced stage of D.R. for effective treatment.

Lately a system of surgical techniques in the vitreous, have been developed. These techniques have been well taken up by many retina surgeons in our country too, providing world call service.

The blood filled vitreous is cut and sucked away in tiny bits while the vitreous removed is replaced by a suitable clear fluid and membranes peeled by special microforceps under operating microscopes. From among the hopeless cases, vision is restored in increasing percent of cases by vitreous surgery. With accumulating experience and improved equipment and technique the results are bound to improve.

In conclusion, it may be said that till we understand the mechanism of development of diabetic retinopathy and find its specific treatment to prevent or treat it, photocoagulation provides the best and only meaningful treatment in most cases. Vitreous surgery is the only hope for the advanced and traditionally hopeless cases.

Fluorescence Photography

Before planning photocoagulation complete picture of the abnormalities in the retina is obtained by a special photographic system -Fluorescence Photography,which are important prerequisites to execution of accurate and adequate photocoagulation. Finest micro-aneurysm, capillaries and neovascular areas are outlined with amazing clarity.

Sodium fluorescein, a dye, when illuminated by blue light, emits a strong light in yellow green spectrum. The dye is non toxic, and is eliminated through kidney when injected intravenously. Normally the dye does not leak into the retina or the brain. However, in diseased conditions of the blood vessels, as in D.R. the leakage becomes remarkable ,the dye while in circulation in the blood vessels or leaking out to stain the retina can be directly visualised with an opthalmoscope with blue light ( angioscopy). With a special camera fitted with special filters, circulation of the dye can be recorded ( photography or video), known as Fluorescein angiography.

Ultrasonography ( USG)

When examination of the retina is not possible because of advance cataract or vitreous haemorrhage, ultrasonography is helpful in detecting grosss abnormalities of the retina. That helps in predicting prognosis or referral to a vitreo-retinal surgeon. It is superfluous when retina is visible by opthalmoscope.

Besides these two tests, colour Fundus Photography and Fluorescence Angioscopy are useful in the management of diabetic retinopathy.

Diabetic retinopathy appears and progresses at different pace in different individuals. Very often the vision remains good till the retinopathy has progressed too far. Since the results of treatment started early is far more gratifying than when started late in the disease process, it is clear that diabetic retinopathy must be detected at a suitable moment. Therefore, the logical steps a diabetic patient must take is to get himself examined by a retina specialist at regular intervals.