Dr Sambuddha Ghosh, Associate Professor of Ophthalmology in West Bengal Medical Education Services, elaborates on the ocular complications caused by diabetes
Diabetes mellitus is a common disorder affecting multiple systems including the eye. Prevalence of diabetes is increasing globally. India has the world’s largest diabetic population. At present, India has 31.7 million diabetic subjects and the number is expected to rise to 57 million by 2025.
Ocular complications of diabetes include refractive errors, recurrent infection of eyelids, non healing corneal ulcer, cataract, glaucoma, loss of ocular movement and damage to retina — the all important light sensitive neural membrane inside the eyeball. This retinal damage, also known as retinopathy, is the commonest ocular complication of diabetes. Diabetes is the fourth leading cause of blindness in world today. Worldwide 2.5 million people are blind due to diabetes. The cause of blindness among diabetics is diabetic retinopathy. The prevalence of retinopathy among diabetics is alarmingly high. 25 per cent of diabetic population has retinopathy. It occurs both in type I and type II diabetes mellitus and has been shown that nearly all type I and 75 per cent of type II patients develop retinopathy after 15-year duration of diabetes. In India, with the epidemic increase in type II diabetes mellitus as reported by the World Health Organization (WHO), diabetic retinopathy is fast becoming an important cause of visual disability. Even well controlled diabetics are not immune. Diabetic retinopathy is often asymptomatic until it reaches an advanced stage. Even at the time diagnosis, about 21 per cent of type II diabetics suffer from retinopathy. It is important to diagnose the disease in its early stage so that this can be properly managed.
The single most important risk factor is duration of diabetes. Many studies have shown an increased prevalence of retinopathy as the duration of diabetes increases. The risk increases also with age. There is strong evidence to suggest that the development and progression of DR is influenced by the level of blood sugar level. The other contributing factors are hypertension, anaemia, dyslipidemia, nephropathy, pregnancy and genetic factors.
Pregnancy and retinopathy: Diabetic women starting pregnancy without retinopathy has increased chance of developing retinopathy during pregnancy. Those who start with retinopathy show increase in severity during pregnancy with regression after child birth.
Genes and retinopathy: Some patients develop retinopathy despite good control of diabetes while others escape retinopathy despite poor control. This suggests the role of genetic factors in susceptibility to retinopathy.
In addition to the clinical examination, colour fundus photography, fluorescent angiography and optical coherence tomography (OCT) scan contribute in the evaluation and management of diabetic retinopathy. High quality OCT machines are now available in our city. This generates cross sectional scan of retina with great details.
The management of diabetic retinopathy has undergone a sea change over the last two decades. It is based on a multidimensional approach consisting of prevention, early diagnosis, treatment and disability limitation. While medical intervention and life style modifications are the mainstay of the preventive measures; laser treatment has greatly changed the outcome. Surgical approaches like vitrectomy are necessary in complicated cases with advanced disease state.
- Strict control of blood sugar: Aggressive glycemic control has long been known to reduce the risk of retinopathy in diabetic patients and also slow the progression of the ongoing retinopathy changes. Glycemic status of the patient is measured in terms of HbA1c which is a marker of glycosylated haemoglobin in the body. Continuous augmentation of pharmacological therapy with other agents and/or insulin is also warranted to maintain the HbA1c level below seven per cent.
- Tight control of blood pressure achieves clinically significant reduction in progression of retinopathy. Patients of diabetes mellitus should be treated to systolic blood pressure of <130 mmHg and diastolic blood pressure of <80 mmHg.
- Correction of anaemia and dyslipidemia
Laser: Laser photocoagulation has long been the only acceptable treatment modality for diabetic retinopathy which was administrable across the spectrum of the disease. Different types of laser treatment are employed at different stages of the disease. The rate of visual loss is greatly reduced after laser. However, it must be remembered that laser will not cure the disease. It will prevent progression to blindness.
Intra-ocular injection: Intravitreal injection of anti vascular endothelial growth factor (anti VEGF) has made a sea change in visual outcome of patients with diabetic retinopathy, particularly those with diabetic macular edema. However, cost of the medicine is a concern.
Vitreoretinal surgery: Despite medical and dietary modifications and timely laser therapy, a significant proportion of retinopathy cases progress to a stage when complex vitreoretinal surgery is the modality of treatment. Nowadays, with the most modern vitrectomy machines being available with us, many patients in our city are getting back useful vision even in very advanced disease state.
Cataract with retinopathy: Sometimes cataract is present along with retinopathy. Cataract surgery may worsen retinopathy. So, laser photocoagulation is recommended in these situations prior to cataract surgery. However, sometimes cataract is so dense that it may interfere with the laser procedure. In these situations cataract surgery has to be undertaken before retinopathy can be treated.
Right time to see your doctor for retinopathy screening
If age of the patient at the time of diagnosis is more than 31 years, he/she needs immediate examination by an ophthalmologist. If no retinopathy is detected, follow up should be done annually. If retinopathy is detected, follow up schedule will depend on the level of retinopathy in any particular case.
If age of onset is below 30 years, patient needs ocular check-up five years after onset of the disease. (If there is no other ocular problem in the mean time).
In pregnancy with diabetes, ocular check-up should be done in the early first trimester. Then, bimonthly ocular check-up is advocated.
Many studies are being done in different parts of the world to find solution to this huge problem. The preliminary results with a new drug (anti vascular endothelial growth factor) have been encouraging. Many of our patients in Kolkata are now getting the benefit of this very recent management technique.
However, cost of the drug remains a deterrent factor.
Early detection of retinopathy can lead to marked reduction of morbidity due to visual loss. Careful screening of diabetic population is therefore necessary so that retinopathy can be detected and treated before serious complications ensue.