Diabetes effect on Eyes, Part I, Diabetic Retinopathy

KEEP YOUR EYES ON THE FUTURE!

Look at the picture below on the left hand side. This is what you would see if you were walking along the road. Now look at the picture on the right. This is what you would see if your eyes are affected with severe diabetic retinopathy!

Terrible, is it not?

Normal Vision
Normal Vision

Vision affected by diabetic retinopathy

This is in no way meant to frighten you. But you must realize that unless you are careful about managing your diabetes, this could happen to you.

If you have diabetes this does not necessarily mean that your sight will be affected, but there is a higher risk. If your diabetes is well controlled then you are less likely to have problems, or they may remain at a mild level.

Although giant strides have been made in the treatment of diabetic retinopathy, the best treatment still remains “prevention” and even if one cannot completely avoid getting the retinal complications, one can definitely slow down its progression, so that it never reaches a level serious enough to cause “blindness“!

But a large part in saving your eyes lies in your hands!

Before, we discuss these aspects, let us first understand what is diabetic retinopathy.

Diabetic retinopathy is a general term for all disorders of the retina caused by diabetes. This is commonest complication of diabetes to do with the eyes. It is a progressive disease that destroys capillaries (the smallest blood vessels linking arteries to veins) in the eye by depositing an abnormal material along the walls of the tiny blood vessels in the retina. Blurred vision and often blindness follows

How can diabetes affect the eye?

Your eye has a lens and an aperture (opening) at the front, which adjust to bring objects into focus on the retina at the back of the eye. The retina is made up of a delicate tissue that is sensitive to light, rather like the film in a camera.

At the centre of the retina is the macula which is a small area about the size of a pinhead. This is the most highly specialised part of the retina and it is vital because it enables you to see fine detail and read small print. The other parts of the retina give you side vision (peripheral vision). Filling the cavity of the eye in front of the retina is a clear jelly-like substance called the vitreous.

The retina is a light-sensitive tissue at the back of the eye. When light enters the eye, the retina changes the light into nerve signals. The retina then sends these signals along the optic nerve to the brain. Without a retina, the eye cannot communicate with the brain, making vision impossible.

How does the eye “see”?

Thinking of a camera can help you understand how the eye works. macular or retinal damage.


The lens of the camera in yellow,
the film in blue

The lens of the eye in yellow,
the retina in blue

A camera lens focuses a picture onto a film inside the camera. In our eyes the same thing happens, but the film is replaced by the retina. The retina ‘makes’ the pictures of the world that we see, converting the light into electrical signals that are then sent on to the brain.

The eye as a camera. Above, the image of the house focusing on the retina. The central part of any image, a house or a person’s face for instance, will be clear if the macula is healthy.

The retinal cells stand next to each other, a bit like houses in a street. The main cells are the rods and cones: these are the cells that take up light and convert it into electrical messages, which are then sent onto the brain.

These cells receive their oxygen and other nutrients from tiny blood vessels nearby. These blood vessels are like pipes which pass nearby the cells; imagine a largish pipe passing past your house, containing blood. The walls of these pipes/blood vessels are very thin, and so nutrients can pass through them. These nutrients are the ‘food’ for the cells.


Light …in yellow… falls onto the retina. The retinal cells are rods (the long straight cells) and cones (the cells with the pointed end). There are tiny blood vessels (capillaries) on the surface of the retina …the red ovals.

As you read on, you will understand the major role played by a part of the retina called the “macula”

The macula is the most sensitive part of the retina. It makes out the fine details of the things we look at, peoples’ faces, bus numbers, reading and writing, and everything lese we see.

If the macula is damaged all these things you see in fine detail are misty. The picture is still there but you cannot make out any of the detail.

A healthy retina will produce a clear image, like a normal film in a camera. But in macular damage the image will not be clear.

For example if the film was scratched in the middle, the ‘scratch’ would show up in the middle of the photograph like a black mark or blot of ink. This is similar to damage caused by macular disease such as diabetic maculopathy.

Everything will appear blurred of the macular area of retina is damaged. This shows the importance of the “macula”.

Diabetes causes damage to the blood vessels that nourish the retina, the seeing part at the back of the eye.

What is Diabetic Retinopathy?
There are two types of diabetic retinopathy, non-proliferative or proliferative.

Nonproliferative retinopathy is the common, mild form. It accounts for about 80 percent of all cases.It usually has no effect on vision and needs no treatment. But after it is diagnosed, have your eyes checked at least yearly to make sure it’s not getting worse.

In nonproliferative retinopathy, capillaries balloon and form pouches. Although retinopathy does not usually cause any vision loss at this stage, the retinal vessels weaken and develop bulges (microaneurysms) that may leak blood (hemorrhages) or fluid (exudates) into the surrounding tissue.

A healthy capillary, a tiny blood vessel . Nutrients pass out of the capillary to reach the retinal cells, and waste products from the retina pass into it to be taken away. In diabetic retinopathy the damaged capillaries start to leak fluid.

The ability to control the passage of substances between the blood vessels and the retina may be lost. As a result, the retina becomes swollen and fatty deposits form within it. If this swelling affects the center of the retina, the “macula”, this called macular edema and vision loss can result, as we have seen above.

Your doctor must have either sent examined the inside of your eyes or sent you to an “eye” specialist to have a fundus examination. This is nothing but examining the retina in your eye with the help of an instrument called the “ophthalmoscope” .

This is how the retina appear to the doctor if your eyes have not been affected by diabetes.


A Normal eye

In order to understand this more clearly, this is a schematic view of a normal eye

When you have non proliferative, (or “background”) retinopathy, this is what the doctor would see.

 


The small red dots are ‘microaneurysms’, tiny damaged capillaries. The red lines are small haemorrhages, little flecks of blood.
The number of microaneurysms, the little red dots the doctor sees, indicate the likelihood of more severe problems in the years to come.

If you are not careful in some people, retinopathy progresses to a more serious form called proliferative retinopathy.

Initially, there is a stage which has been variously thought of as being a late non proliferative stage or as an early proliferative stage.

Let us call it a prepropliferative stage.

In this stage the retina has been damaged by the higher than normal sugar levels over several years. Small haemorrhages (flecks of blood) and tiny abnormal blood vessels are present.

If this progresses and many new vessels start developing in the retina, one has progressed to the proliferative stage.

The blood vessels can make a special growth chemical (VEGF= vascular endothelial growth factor) that makes other tiny, tiny blood vessels grow. These are called ‘new’ blood vessels.These new vessels are very delicate and very easily bleed, and this blood can (if the eye is not lasered) damage your eye badly.


The damaged capillaries start to make a special growth chemical that makes other capillaries grow.

If the blood vessels are severely damaged, they close off. In response again, new blood vessels start growing in the retina.


The capillaries start to close up and block. The retinal cells nearby can become damaged, and the sight reduced.

New blood vessels growing on the retinal surface and slightly in front of the surface

This is ‘proliferative retinopathy’.

Usually in this condition, without laser treatment ( see below), the sight is very badly affected and people may become blind.

laser: 1000 burns in a typical session Usually in this condition, without laser treatment, the sight is very badly affected and people may become blind. proliferative retinopathy
proliferative retinopathy ‘new blood vessels’ grow on the surface of the retina and can bleed. This process is shown in the animation (exaggerated).

These new vessels are weak and can leak blood, blocking vision, which is a condition called vitreous hemorrhage. The new blood vessels can also cause scar tissue to grow. After the scar tissue shrinks, it can distort the retina or pull it out of place — this is called retinal detachment.

If the macula is involved, this is a very serious matter. We have seen above that when the macula is involved, the central vision is affected!

But this can still be treated in its early stages with laser therapy.

An excellent composite view of the changes which take place in the vessels as retinopathy progresses is given below.

To be continued………
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About Anuj Agarwal

I am a professional with varied working experience of more than 18 years in India, USA and Middle East. My areas of work and interest are Information Technology, Corporate Social Responsibility, Health and Wellness. Please feel free to contact me through the blog or write me at agarwalanuj@yahoo.com
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