What is diabetic retinopathy?
Diabetic retinopathy is a common eye condition caused by the damaging effects of diabetes. It is caused by persistently raised blood sugar levels. The retina is the layer at the back of the eye that is responsible for vision. The retina contains light-sensitive cells that receive information and converts these into signals which are then sent to the brain allowing us to see. Damage to the retina can alter parts of the retina, which in turn can affect the vision.
What causes diabetic retinopathy?
Diabetes is the inability to control blood sugar levels due to the inability to produce insulin or the resistance to it. A high level of blood sugar leads to the sugars to stick to the cells in the blood. These cells in turn stick to the side of the blood vessels and build up, causing narrowing of the blood vessels, very much like limescale building up in pipes and causing blockages and reducing the flexibility of the blood vessels, causing the blood pressure to go up. Also, the lack or resistance to insulin can change the way the body processes cholesterol, a fatty substance that is found in the blood. In diabetic patients, the amount of cholesterol in the blood also increases and this too can build up in the blood vessels, forming a plaque and contribute towards the narrowing of the arteries.
The retina is supplied by small arteries. In diabetes, as we can see from above, these small vessels can become clogged up with deposits, which can cause some inflammation of the blood vessels, causing the blood vessels to become leaky. This can lead to the leaking of fluid and blood into the retina which can build up in the macula, the part of the retina that is responsible for most of the central, colour and fine vision. Thus, a build-up fluid in this region, also known as macular oedema, can obscure or distort your vision. This is often considered early diabetic retinopathy or non-proliferative diabetic retinopathy.
The progression from early to advance diabetic retinopathy starts to occur when some of these small blood vessels become completely blocked by deposits. When this occurs, the natural response in the body is to create new blood vessels to restore the supply of oxygen and nutrients to the retina. This process is known as proliferation. These new blood vessels are fragile and can leak into the centre of the eye, which is comprised of a jelly like substance known as the vitreous humour, thus obscuring vision. Proliferation can also cause areas of the retina to become scarred and this, alongside the formation of new blood vessels, can lead to the retina detaching from the back of the eye, causing further vision problems. The formation of new blood vessels can also disrupt the balance of fluids entering and exiting the eye, if there is a disruption in the fluids exiting the eye, it can lead to a build-up of fluid inside, leading to an increase in Intraocular Pressure (IOP), which can lead to glaucoma (link to glaucoma).
The risk factors for diabetic retinopathy include poorly controlled blood sugar levels and uncontrolled blood pressure. Other risk factors include:
- High cholesterol
- Kidney disease
How is diabetic retinopathy diagnosed?
Since the relationship between diabetes and eye disease has been well established, checking for symptoms of any neuropathy (especially peripheral neuronopathy) is standard procedure of any regular diabetes check-ups that one undergoes. One such investigation is known as the monofilament test- where a soft monofilament is brushed over different areas of the skin, hands and feet in order to check if the sensation is intact. Another investigation is known as the nerve conduction study which can access for damage by measuring the speed of the electrical signals relayed through the nerves. Damaged nerves will mean that electrical signals will be relayed slower than normal. Another similar investigation is known as Electromyography (EMG), which measures the electrical signal produced in the muscles.
How common is diabetic retinopathy?
Diabetic retinopathy is present in about 35% of diabetic patients worldwide and seems to occur more commonly in type 1 diabetes in comparison to type 2 diabetes. Furthermore, it is more common in those that have had diabetes for longer periods of time and in those with poor control of both blood pressure and blood sugar levels.