The risks that diabetes poses for the eyes — and what to do about it

Diabetic retinopathy often has no early warning signals. But when it comes, vision could get blocked completely

Diabetes has emerged as a public health problem globally, more so in developing countries like India. According to projections made by the World Health Organization, the number of people with diabetes in India will rise to 79.4 million in 2030. It was 31.7 million in 2000.

Diabetes affects the eyes, among other parts of the body. However, vision-threatening complications occur when it affects the retina, causing diabetic retinopathy. Sankara Nethralaya in Chennai has been running the Sankara Nethralaya Diabetic Retinopathy Programme for nearly a decade. Major epidemiological studies done under the programme, have thrown up some salient findings.

In people aged above 40 years and living in urban areas like Chennai, nearly one out of four have diabetes. The situation is better in rural India, where among those aged above 40 years, one in 10 has diabetes.

Among those with Type 2 diabetes, nearly one in five in urban and one in 10 in rural India has diabetic retinopathy. Diabetes is more common in upper middle and upper socioeconomic classes. However, once a person has diabetes, everybody has the same chances of getting retinopathy.

Young males with suboptimal glycemic control, hypertension, anaemia and microalbuminuria (kidney damage) are at particular risk. The most significant risk factor among both rural and urban populations is duration of diabetes: the risk is 6.5 times more for those who have had diabetes for more than 15 years. People who get it before 40 have double the risk of developing retinopathy and sight-threatening retinopathy than those who develop it after 40.

Visual impairment occurs in 4 per cent of those with Type 2 diabetes. Diabetic retinopathy is the second most common cause of visual impairment. Cataract is the most common cause.

At the time a person is diagnosed with diabetes, one in 10 would have the kidneys affected (nephropathy) or the nerves (neuropathy). But one in 20 will have retinopathy. Obesity increases the risk. Pot belly, what is clinically called central obesity, increases the risk by two times. Diabetic retinopathy is more common among diabetics who take low-fibre diet (20 per cent) in comparison to those who take a high-fibre diet (15 per cent).

Genetic factors contribute to increased risk while some offer protection. Probably such genetic factors are what offer some protection against retinopathy.

People with suboptimal glycemic control (HbA1c>7) have a higher risk of diabetic retinopathy and those with poor control (HbA1c >8) of sight-threatening retinopathy. There is evidence to show that blood sugar control in the initial years of diabetes offers long-term protection against retinopathy. Abnormal serum lipids (especially serum cholesterol and LDL cholesterol) have a significant role in diabetic macular edema, which involves the swelling of the central part of the retina that results in blurred vision.

People with a combination of suboptimal control (blood sugar, blood pressure and lipids) have a higher risk of both retinopathy and sight-threatening retinopathy. Nearly one in three diabetics with suboptimal control will have retinopathy. In those with early kidney damage (microalbuminuria) the risk doubles. If he has advanced damage (albuminuria) the risk is six times more. In a person with diabetes who also has anaemia, the risk of developing retinopathy is two times more.

Framingham risk assessment scores which take into account age, smoking status, lipid levels and hypertension give a 10-year risk profile of cardiovascular disease. If a person has a high risk score, the chances of his developing sight-threatening retinopathy doubles as compared to people who have low risk.

Abnormal sleep patterns are related to neuropathy and nephropathy. Recent evidence suggests that sleep apnea is related to the severity of retinopathy.

Type 2 patients should have their eyes screened at the time of diagnosis and at least annually then. Children and adolescents with Type I diabetes should undergo dilated fundus photography five years after diagnosis and at least annually then. Both Type 1 and 2 diabetics need an eye examination soon after conception and then early in the first trimester. Thereafter the doctor recommends follow-up based on the severity of retinopathy.

Diabetic retinopathy often has no early warning signals. Blurred vision may occur when the macula, the central part that provides sharp vision, swells from the leaking fluid. This makes it hard to read or drive. As blood vessels bleed, there will be specks of dark spots or clouds, floating in your vision. Sometimes bleeding might be of a severe nature, blocking vision completely: this often happens during the sleep. Even in advanced cases, the disease may progress asymptomatically. Hence, regular eye examinations are important for people with diabetes.

Mild cases need no treatment. Regular examinations are critical. Strict control of blood sugar and blood pressure levels can reduce or prevent diabetic retinopathy. In advanced cases, treatment is needed to stop eye damage from diabetic retinopathy, prevent vision loss, and potentially restore vision.