Glaucoma is one of the most dreaded conditions affecting the eyes. When a person first confronts the diagnosis of glaucoma, the world almost crumbles all around him. And not without reason! Over the hundreds of years of its history, glaucoma is known to causes relentless, painless, progressive loss of vision. It is one of the conditions that has dodged science… we still don’t have a cure for it. It is the second most common cause of preventable blindness in the world. But within lies a ray of hope for all of us!
Preventable… yes… though permanent, it is preventable blindness.
What is glaucoma?
Also called Kala Motiya (hindi), Kach Bindu (Marathi), Jhamar (Gujrathi), causes gradual progressive painless loss of vision. There are myriad causes for glaucoma, some rare and some very common. Just like its many causes, there are many forms of glaucoma. In fact glaucoma is not just one disease but is a group of various conditions that have one thing in common – a typical form a damage to the optic nerve. The optic nerve sends the image signals from the eye to the brain. In glaucoma, this nerve starts getting damaged over a period of time.
Why does glaucoma occur?
Glaucoma occurs basically due to two different sets of causes. Either the defect lies in the eye (more common), or the defect lies in the optic disc (less common).
When the defect lies in the eye, it involves an increase in the eye pressure and the optic nerve gets damaged to the raised eye pressure. The raised pressure damages the optic nerve by reducing the blood supply to the optic nerve and well as direct pressure damage to the nerve cells.
Why does the eye pressure rise?
Normally there is fluid being constantly formed inside the eye and it constantly drains out. This fluid called Aqueous Humour, is different from tears. Tears are formed outside the eye while the aqueous is formed inside. When the drainage suffers, there results an imbalance in the formation and drainage of aqueous fluid inside the eye and the eye pressure rises.
Open angle glaucoma:
The structure of the eye through which the aqueous fluid drains out is called the angle. Open angle glaucoma is the most common type of glaucoma in the world. In this, the cells that form the angle are abnormal in a way that they do not allow adequate drainage of fluid. This results in increased eye pressure. So the angle is “open” but abnormal and hence it is called ‘Open angle Glaucoma’.
Closed angle glaucoma:
In closed angle glaucoma, as the name suggests, the drainage angle is closed mechanically and thus it interferes with the fluid drainage.
Closed angle glaucoma is more common in Asian, Mongols while open angle glaucoma is more common in white and black races.
Genetic influences in glaucoma:
Over the last few decades as we have started going deeper into the genetic aspects of various diseases that affect our body, we have uncovered various facts about glaucoma too. Many types of glaucoma have a strong genetic influence. It is very often inherited especially from the mother’s side. Some genes have been identified that are more common in glaucoma patients. Certain genetic syndromes have been identified that include glaucoma too. Some genetic influences cause glaucoma which appears right from the time of birth and sometimes even before the baby is born. But we are still in the infancy of research in this field. We still are unable to do genetic counseling to prospective parents about the chances of their children being safe from glaucoma. The best advice at this time is that all blood relatives of a person with glaucoma should get their eyes checked for glaucoma – preferably from a glaucoma specialist.
Other causes of glaucoma:
Other common causes of glaucoma are when the drainage structure of the eye, the angle, gets damaged due to injury, previous eye surgery, inflammation, swelling, medicinal side effects (e.g. steroids), diseases such as diabetes, complications of uncontrolled hypertension and hypercholesterolemia etc.
Glaucoma due to direct damage to the optic nerve:
This is a type of glaucoma that occurs despite the eye pressure being in the normal range. The normal range of eye pressure is considered to between 10 – 20 mm of Hg. This range covers about 80% of the normal population. Which means that if you look at the eye pressure of 100 people who do not have glaucoma, 80% of them will have an eye pressure that lies between 10 – 20 mm of Hg. So all people who have an eye pressure more than 20mm of Hg do not have glaucoma but they have an increased risk of developing optic nerve damage (and glaucoma) due to the high eye pressure. In a certain subset of people, typical glaucomatous optic nerve damage occurs even with the eye pressure being in the “normal” range. This is called Normal Tension Glaucoma. The exact cause of this condition is still unknown. There are various theories about why it happens. But the good news is that it is usually associated with slower rate of vision deterioration.
So we have briefly looked at various causes of glaucoma. In the next part of the series we will look at Management of Glaucoma.
Source by Ajit Hazari