Diabetes is a systemic disease that can affect various organs in the body like the heart, brain, kidney, nervous system, and also the eye. But, many people are not aware of this fact and present to ophthalmologists very late. Excess blood sugar decreases the elasticity of blood vessels and causes them to narrow, impeding blood flow. This narrowing of blood vessels can lead to a reduced supply of blood and oxygen and thereby damage large and small blood vessels. Microvascular damage can affect the eye and may cause:

1.Senile cataract [clouding of the lens];

2.Diabetic retinopathy - When blood sugar levels cause damage to the blood vessels in the Retina [inner layer of the eye]

3.Nerve palsy [affecting the extraocular muscles],

4.Glaucoma [damage to the optic nerve]

Among all the above conditions, Diabetic retinopathy [DR] is the most common cause of vision loss. Blindness due to DR is preventable with active screening and timely management of underlying diabetes. 

Causes and Risk factors

1. Any person with diabetes is a potential candidate to develop retinopathy.

2. Risk of retinopathy increases if associated with the following:

•         Uncontrolled blood sugar levels.

•         Prolonged diabetes.

•         High blood pressure.

•         High cholesterol.

•         Anemia.

•         Chronic smoking.

•         Pregnancy.

 Symptoms 

In the early stages or the non-proliferative stage, the patient may be asymptomatic until retinopathy affects the Macula [centre of the Retina]

As retinopathy worsens, one can see:

• The blurring of vision

• Difficulty seeing colours

• Floaters

• Total loss of vision

Signs  

Signs vary according to the severity of retinopathy. 

DR can be classified into Non-proliferative and Proliferative retinopathy based on severity. 

1.       NPDR [Non Proliferative Diabetic Retinopathy] : In this stage, intra-retinal vascular changes are present, such as, Micro-anuerysyms [outpouching of capillaries], Dot and Blot Hemorrhages, Hard-exudates, and Cotton wool spots.

2.       PDR [Proliferative Diabetic Retinopathy] : This stage is characterised by presence of new immature retinal vessels that develop over the surface of the Retina due to ischemia. This may cause bleeding over the Retina, into the vitreous or may even cause a pull over of the Retina causing tractional retinal detachment. 

DME [Diabetic Macular Edema]: DME can be present in any stage of retinopathy. It is characterised by fluid collection in the centre of the Retina, i.e, the Macula,  due to leakage from blood vessels and may cause vision loss.

Diagnosis 

Early diagnosis of these changes in the Retina through proper screening helps in preventing vision-threatening complications.

Screening: Needs to be made mandatory for all people with diabetes.

Type-2 diabetic patients should be screened immediately after the diagnosis of diabetes. This initial screening should be followed by a check-up based on the severity of Retinopathy as advised by the Ophthalmologist. 

Type-1 diabetic patients should be screened 5 years after the diagnosis of diabetes. The Ophthalmologist may recommend more frequent check-ups based on the severity of retinopathy.

Pregnant women with diabetes are to be screened for DR immediately after conception and early in the first trimester.

INVESTIGATION

1. Dialated Eye Examination: Topical dilating drops (Tropicamide with or without phenylephrine drops) are routinely instilled in the eye to dilate the Pupil and examine the Retina under a slit lamp with 90D lens or with 20D lens for more peripheral examination. 

2. Optical Coherence Tomography (OCT): It is a non-invasive high-resolution cross-section imaging of Retina, especially useful for quantitative and qualitative assessment of the Macula.

3. Fluorescein Angiography (FFA): Like Cardiac Angiography FFA is done to evaluate the blood flow in the retina. A special dye is injected into a patient’s Retina, and sequential pictures are taken as the dye circulates in the eye. This is done in patients where we are not able to clinically judge the stage of retinopathy to plan further management. 

4.  B-scan Ultrasound of the eye is done in eyes with dense media opacities like cataract or vitreous hemorrhage to assess the status of the Retina that lies behind.

Treatment options

Strict control of blood sugar levels must be maintained. This is done by monitoring the blood HbA1C value. This value is the 3-monthly average value of blood sugar and is more appropriate than fasting and post-prandial blood levels alone. Beside an Ophthalmologist’s check-up, regular follow-up with a physician for the treatment of diabetes and other risk factors plays a key role in managing diabetic retinopathy.

1. Intra-vitreal anti-VEGEF injections: These are given under strict aseptic precautions in the operation theatre for sight-threatening retinopathy causing macular oedema.

2.Laser photocoagulation: It is a simple outpatient procedure and is painless. If done promptly, it can prevent 90% of vision loss. It can stop or slow down leakage of blood or fluid and shrink abnormal blood vessels.

3.Vitrectomy+ Endolaser: Surgery is done in a patient with vision loss due to non-resolving vitreous hemorrhage. This surgery is performed to remove the blood in the eye. This surgery is also performed in patients with vision loss due to retinal detachment. In this case it helps to relieve traction and reattach the Retina. 

Diabetes is a life-long condition that may cause subsequent retinal damage and vision loss. Hence getting an early diagnosis and following a treatment plan that involves regular medical care, lifestyle changes, early screening for diabetic retinopathy and also proper care of other risk factors can help limit the progression.

Thus the role of a Physician, Ophthalmologist, and the patient is equally important in controlling vision loss due to this disease.