Glaucoma is a very serious disease of the eye that can slowly and silently take away one's vision. It is thought to be the second leading cause of blindness in the world, with approximately 67 million people affected. Although there are many risk factors that can contribute (see below), glaucoma's most basic definition is damage of the optic nerve. More appropriately, damage or cell death of the individual nerve fibers that make up the optic nerve.
The optic nerve, the hard wire that takes what you see back to your brain, is made up of millions of small nerve fibers that collect the information that you see. In glaucoma, just as in natural selection, the weakest of these nerve fibers are destroyed first. The weakest being those that control your more peripheral vision. Due to our brains ability to fill in micro-gaps in our vision, these small nerve fiber deaths may go unnoticed. In fact, approximately 50% of nerve fibers must be dead in a specific region to show any visual field loss.
Types of Glaucoma - There are two main types of glaucoma, Primary Open Angle Glaucoma (POAG) and Angle Closure Glaucoma. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye. When optic nerve damage has occurred despite a normal IOP, this is called normal tension glaucoma (NTG). Secondary glaucoma refers to any case in which another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss. Read more about the types of glaucoma here.
Risk Factors - There are many different risks factors associated with glaucoma. If a patient has one or more of these factors it is not indicitive of glaucoma unless there is actual optic nerve damage. But, patients with one or more must be watched closely, at the discression, of your optometrist to be sure that no optic nerve damage occurs. View complete list of glaucoma risk factors.
Increased Intra-Ocular Pressure (IOP) - The historic magic number in IOP has always been 21mmHg. Every point higher increases the risk of glaucoma. There are many people whose pressure runs high (greater than 24mmHg) but show no signs of glaucoma damage. This is called Ocular Hypertension. How do optometrists measure IOP?
Optic Nerve Appearance - Optometrist evaluate the optic nerve and measure what is called the cup-to-disc ratio. If you imagine your optic nerve like a cantelope, and the more seeds that are scooped out, the less catelope there is. The same applies to the optic nerve. The larger the cupping in the center of the nerve (the seeds removed), the less healthy nerve fibers are left (the cateloupe), thus the more fragile the optic nerve may be. How does your optometrist evaluate your optic nerve?
Medical Conditions - High blood pressure and Diabetes have traditionally been thought to increase the risk of glaucoma. Other conditions such as vitamin B12 deficiency and anemia are proven to increase the risk of NTG.
Family History / Race - Having a family history of glaucoma does not mean that you will get it. But, as we learned about our optic nerve appearance, the genetic anatomy of your optic nerve is inherited, and that can increase one's risk. Race is proven to be a risk factor as well. One study proved the prevalence of glaucoma in African-Americans was four times higher.
Testing for Glaucoma
During a routine eye exam your optometrist will perform such tests as IOP measurement, Visual Field testing, and assessing the optic nerve. How are these test performed?
Your optometrist may discover one or more of these risk factors during your complete eye exam, and may want you to return for extra testing. Most insurances do not allow this extra testing on the same day as a complete eye exam. Extra testing is a necessary step to complete the "glaucoma suspect puzzle". What are these extra tests?
"The Glaucoma Suspect Puzzle"
Just because your optometrist may find one or more glaucoma risk factors does not necessarily mean you have glaucoma. Nor does it mean you will get glaucoma. It simply means that you are more "at risk" for developing glaucoma than the next person. At-risk patients or Glaucoma Suspects must be monitored closely to assure that these risk factors do not damage the optic nerve, i.e. develop into glaucoma.
What Can I Do?
The first step is to have a routine eye exam every year. Even if you have great vision, only your eye doctor can detect these risk factors.
Diet and Exercise - always an important part of healthy vision.
Is Glaucoma Curable? - The simple answer is No, but it is preventable and treatable. Because glaucoma is nerve fiber death, and nerve fibers cannot regenerate the same as muscle and skin cells, any damage is not reversible. But, if caught early enough by the proper tests your optometrist can stop or slow glaucoma dead in its tracks by many different means.
How is Glaucoma Treated? - Glaucoma can be treated with medications, lasers, or surgery, depending on the severity and risks. The first line of treatment is typically using an eye drop, but new studies are showing that laser treatment may be a beneficial alternative to eye drops.
If your optometrist prescribes an eye drop to lower your IOP, he/she may perform a monocular trial (using the drop in only one eye) to test the drugs efficiency. Never stop using the prescribed medicine without first consulting with your optometrist, and always follow-up at the scheduled times. This will assure that the proper steps are being followed to reduce the risk and/or prevent the vision loss of glaucoma.
At Gahanna Vision Center, Dr. Miller performs a Glaucoma Evaluation on every patient as part of the Lifestyle Eye exam.
Primary Care of the Glaucomas by Murry Fingeret and Thomas L. Lewis . 2001