If we were to play a word association game and I said "diabetes", chances are the first word that would come to your mind is "sugar".
It might seem strange to most people that a disease so intimately tied up with the control of glucose in our body, has complications that are mainly related to our blood vessels. (Most of the sugars in our food are metabolised to glucose, one of the basic building blocks of sugar.)
In fact, the complications of diabetes can be classified by the size of the blood vessels that are affected: macrovascular and micro-vascular.
Macrovascular complications involve the large blood vessels that supply the heart, brain and our limbs, resulting in coronary artery disease, stroke, and peripheral vascular disease respectively.
Meanwhile, diabetic retinopathy, nephropathy and neuropathy are caused by the microvascular complications of diabetes. They occur when the small blood vessels supplying the eye, kidney and peripheral nerves respectively, become defective.
Diabetes itself occurs when either our body is unable to produce insulin (type 1 diabetes mellitus) - which is the hormone that stimulates our cells to take in and store glucose from our bloodstream - or the cells themselves start to fail to respond to insulin (type 2 diabetes mellitus).
These two scenarios result in too much glucose floating around in our blood.
In turn, these high levels of blood glucose cause a chain of physiological reactions that eventually result in the weakening of our blood vessel walls.
This particularly affects the small vessels of the eye, among others.
One of the earliest detectable signs of diabetic retinopathy are microaneurysms, which can be picked up by looking at the eye through an ophthalmoscope.
These microaneurysms are small localised balloon-like dilatations of a blood vessel, caused by the weakened vessel wall.
When this occurs, the patient is considered to have mild to moderate non-proliferative diabetic retinopathy.
As the disease progresses, the chances of visual loss become higher.
Consultant ophthalmologist Dr Kenneth Fong says that there are usually two ways diabetes can result in blindness.
"Diabetic macular oedema, which is the more common condition, tends to lead to increased blindness in the working population," he says, adding that this condition can be present even though the patient feels quite well.
In diabetic macular oedema, the weakened blood vessel walls cause leakage of proteins and fluids into the eye, in particular, the macula, which is the most sensitive part of the retina.
This causes the macula to swell up, which may result in blurred vision.
However, it is also possible for patients to experience no symptoms at all, even though they have the condition.
This is why regular eye examinations are required in diabetic patients, as there are signs that doctors can pick up as the disease progresses, despite the lack of symptoms.
More blood vessels
The other cause of blindness from diabetes is proliferative diabetic retinopathy.
Dr Fong says: "The small blood vessels become leaky, and there is lack of oxygen to the eye.
"This hypoxia leads to increased VEGF (vascular endothelial growth factor), which is a critical factor that leads to the growth of new blood vessels."
Unfortunately, these new blood vessels are quite fragile, and can become leaky themselves quite easily, thus, triggering the whole cycle again.
This repeating process, if not treated, eventually leads to both vitreous and retinal damage, and eventually, loss of vision.
Again, as with diabetic macular oedema, proliferative diabetic retinopathy can also develop without any symptoms.
Some people might experience "floaters", which are dark spots, formed of blood, "floating" across their field of vision.
Sometimes, these spots go away by themselves, but if left untreated, will recur, as the haemorrhages that cause them will continue to occur.
Once you experience floaters, the next symptom would be blurred vision, followed by loss of vision.
Dr Fong shares that proliferative diabetic retinopathy usually occurs in patients who are quite ill, for example, those who are on dialysis.
Research has shown that there is a correlation between diabetic nephropathy and retinopathy, as the mechanisms that damage the small blood vessels supplying the kidneys and the eyes of diabetic patients are similar.
Control is the key
While there are various treatments available to treat diabetic retinopathy, Dr Fong says that the problem in Malaysia is that many patients come into the clinic too late.
"Diabetic retinopathy in Malaysia is still not being detected. Patients are still presenting with blindness in clinics."
In fact, diabetic retinopathy is the main cause of visual loss among working adults in the country.
Dr Fong adds that in his experience, many patients only start to seriously control their glucose levels once they've been diagnosed with a complication like diabetic retinopathy.
However, it is rather late for that to have an effect on their current condition.
"There is something called metabolic memory. For example, when you're younger, you didn't control your diet, then five years later, you start to better control it, but you will still have a higher risk of developing diabetic complications as your body still retains the metabolic memory of the time your blood glucose levels were uncontrolled," he says.
As diabetic retinopathy is an inevitable consequence of having diabetes - over 60 per cent of patients with type 2 diabetes mellitus have some degree of diabetic retinopathy 20 years after being diagnosed - the only way to delay it is to control your diet and take the medications as required.
Consultant dietitian Goo Chui Hoong notes that the Malaysian diet contains very high-glycaemic index food, making it more difficult for diabetic patients to exercise self-control.
Among the areas she advises diabetic patients to look out for are carbohydrates, fat, fibre and refined sugars.
"For carbohydrate intake, they shouldn't have large amounts in each meal.
"What you want to do is even out the blood sugar levels throughout the day, so they are not encouraged to skip a meal and eat a buffet after that."
Fibre intake should be increased, as it will help slow down the absorption of sugars during metabolism, while fat intake should be in moderation.
"I would encourage their fat intake to be of 'healthier' fat, for example, monounsaturated fats like vegetable oils, and polyunsaturated fats like omega-3 fatty acids."
The key, she adds, is moderation, and just choosing healthier options.
For example, in the book she co-authors with her husband, Dr Fong, recipes utilise brown rice, instead of white, and feature fresh ingredients, rather than processed ones.
The recipes are also tailored to produce moderate portions that satisfy one's hunger without overeating.
The book entitled Food For Your Eyes provides information on both common eye diseases and recipes to promote eye health.
Published by Star Publications (M) Bhd, the book is written in both English and Chinese.