Glaucoma is a potentially blinding disease that affects 66 million persons worldwide. It is the second leading cause of blindness worldwide. On the basis of the available data, we estimate that there are approximately 11.2 million persons aged 40 years and older with glaucoma in India. The disease is characterized by typical changes in the optic nerve (the nerve that connects the eye to the brain) with associated visual field defects.
Glaucoma refers to a group of related eye disorders that all cause damage to the optic nerve that carries information from the eye to the brain. The increased pressure, called intraocular pressure, can damage the optic nerve, which transmits images to your brain. However, with early detection and treatment, you can often protect your eyes against serious vision loss.
The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina to the brain. The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision.
It’s the result of high fluid pressure inside your eye. This happens when the liquid in the front part of the eye doesn’t circulate the way it should.
Normally, the fluid, called aqueous humor, flows out of your eye through a mesh-like channel. If this channel gets blocked, the liquid builds up. That’s what causes glaucoma. The reason for the blockage is unknown, but doctors do know it can be inherited, meaning it’s passed from parents to children.
Less common causes include a blunt or chemical injury to your eye, severe eye infection, blocked blood vessels inside the eye, and inflammatory conditions. It’s rare, but sometimes eye surgery to correct another condition can bring it on. It usually affects both eyes, but it may be worse in one than the other.
The two major categories of glaucoma are open-angle glaucoma (OAG) and narrow angle glaucoma. The “angle” in both cases refers to the drainage angle inside the eye that controls the outflow of the watery fluid (aqueous) that is continually being produced inside the eye.
If the aqueous can access the drainage angle, the glaucoma is known as open angle glaucoma. If the drainage angle is blocked and the aqueous cannot reach it, the glaucoma is known as narrow angle glaucoma.
Variations of OAG include: primary open angle glaucoma (POAG), normal-tension glaucoma (NTG), pigmentary glaucoma, pseudoexfoliation glaucoma, secondary glaucoma and congenital glaucoma.
Variations of narrow angle glaucoma include include acute angle closure glaucoma, chronic angle closure glaucoma, and neovascular glaucoma.
Glaucoma often is called the “silent thief of sight,” because most types typically cause no pain and produce no symptoms until noticeable vision loss occurs.
For this reason, glaucoma often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss.
But with acute angle-closure glaucoma, symptoms that occur suddenly can include blurry vision, halos around lights, intense eye pain, nausea and vomiting. If you have these symptoms, make sure you see an eye care practitioner or visit the emergency room immediately so steps can be taken to prevent permanent vision loss.
Your eye doctor will use drops to open (he’ll call it dilate) your pupils. Then he’ll test your vision and examine your eyes. He’ll check your optic nerve, and if you have glaucoma, it will look a certain way. He may take photographs of the nerve to help him track your disease over time. He’ll do a test called tonometry to check your eye pressure. He’ll also do a visual field test, if necessary, to figure out if you’ve lost your side, or peripheral, vision. Glaucoma tests are painless and take very little time.
An abnormally high IOP reading indicates a problem with the amount of fluid (aqueous humor) in the eye. Either the eye is producing too much fluid, or it’s not draining properly.
Normally, IOP should be below 21 mmHg (millimeters of mercury) — a unit of measurement based on how much force is exerted within a certain defined area.
If your IOP is higher than 30 mmHg, your risk of vision loss from glaucoma is 40 times greater than someone with intraocular pressure of 15 mmHg or lower.
Immediate treatment for early-stage, open-angle glaucoma can delay progression of the disease. That’s why early diagnosis is very important. Glaucoma treatments include medicines, laser trabeculoplasty, conventional surgery, or a combination of any of these. While these treatments may save remaining vision, they do not improve sight already lost from glaucoma.