Diabetes is a group of conditions characterized by chronic high sugar level in the blood. There are two types with type 1 (insulin dependent) occurring in young people and type 2 (non insulin dependent) accounts for 85% of diabetes in the developed world, and is particularly common in Asians, of whom up to 35% of elderly adults may be affected. Diabetes and its complications are a major cause of morbidity and mortality in the community. It is a major cause of heart attack, kidney failure needing dialysis, ulceration of foot or stroke two or three times the risk of general population. Classic symptoms of diabetes may include frequent thirst, urination, lethargy and weight loss but may also be asymptomatic. Very often, diabetes occurs concurrently with high blood pressure and high cholesterol. If the patient is also a smoker and pregnant, the risk factors are increased several folds. Overall mortality is increased 2-3 fold and life expectancy reduced by 5-10 years. Currently, a diabetic person is 10-20 times more likely to go blind than someone who is non-diabetic.
As the life expectancy of diabetics has increased with improved treatment so has the incidence of major complications including loss of vision. In the developed world diabetic eye changes is now the leading cause of blindness in adults under the age of 65.
Diabetes can affect almost all structures of the eye but most commonly involved are the retina and lens.
Diabetic retinopathy refers to changes at the back of the retina (like the film of a camera). It is a disease of the small blood vessels. Weakening of these small blood vessels results in retinal haemorrhage and leaking of fluid and lipid. These vessels will progressively shut down gives rise to areas of retinal ischaemia (i.e. lack of nutrient supply such as oxygen). In turn, a chemical substance is liberated to the formation of new vessels on the surface of retina and iris, the part which controls light aperture.
This is characterized by small dot and blot haemorrhages and lipid formation. This is normally found in elderly diabetics who have had the disease for several years. The vision may be normal at this stage.
The macular is the most sensitive part of the retinal. Gradual loss of vision can take place with vessels leaking fluid, lipid or obliterated.
This type of retinopathy is seen most frequently on long standing diabetics. New unhealthy vessels develop in cluster or diffused form on the retinal. These vessels bleed within the retinal or into the gel like structure called vitreous at the centre core of the eye which may obscure the vision for months or years. Later, adhesive tissue may form around these vessels and contracture gives rise to a traction retinal detachment. That is to say the film in the camera gets crumpled.
Diabetic retinopathy may also lead to the development of neovascular (new vessel formation) glaucoma. These new blood vessels, accompanied by a sheet of fibrous tissue, develop on the surface of the iris and obstruct the drainage system. Thus, the balance of fluid formation and out of the eye is upset, causing the eye pressure to rise significantly.
No specific treatment is required for background retinopathy. Laser application at different strength is used to either clear the fluid and fat accumulation or over a wide scattered area of retinal to increase the oxygen perfusion to the whole area. This will result in the prevention of chemical substance formation, thus leading to regression of new vessels.
Cataracts of the senile type occur more frequently in diabetics. Surgical removal is accompanied by an increased rate of complications and the visual result is frequently compromised by the presence of fluid formation.
Elderly diabetics may develop palsies affecting the nerves controlling the movement of the eye. The onset is acute and painful and full recovery can take several months.
Modern diabetic care now has a sound evidence base to advise a patient to achieve good blood sugar control, excellent blood pressure control, and attention to lipid profile, cardiovascular risk and weight reduction. If the current targets for medical treatment for diabetics can be achieved, many more people with diabetes will be alive and enjoy a better quality of life in the future. In the early stages, diabetic retinopathy is completely asymptomatic. It is common and can be detected by simple means and there is effective treatment available if detected early enough. It therefore fulfils the criteria for disease screening and this should be vigorously carried out. All diabetic persons should have a thorough eye examination every year.