About the Author – This “Health Update” was written by John J. Mast, M.D., C.M.D., associate medical director, Masonic Village at Elizabethtown
Glaucoma is called the “silent thief of sight” because people usually do not have any pain or symptoms from glaucoma until it has stolen a significant amount of their peripheral vision. Glaucoma is the name for a group of eye diseases that are a common cause of blindness. All types of glaucoma can lead to damage to the optic nerve, and this vision loss does not come back.
More than half of the 2.5 million Americans who are blind have some vision loss from glaucoma, and it is the second leading cause of blindness. Two million Americans have been diagnosed with glaucoma. About another two million Americans have glaucoma but do not know it.
With glaucoma, problems with flow of fluid (called aqueous humor) can lead to increased pressure in the eye. The aqueous humor nourishes the eye, and is produced behind the iris and needs to flow out through a small area called the trabecular network. If the aqueous humor cannot flow out as fast as it is made, it leads to increased eye pressure. In addition, if too much aqueous humor is produced, it can also cause increased eye pressure. This increased pressure can cause damage to the optic nerve.
The elevated pressure of aqueous humor affects the eye at its weakest point. Think of the eye as a balloon that is being filled with more and more air. It stretches at the weakest point, which is behind the eye where the optic nerve leaves the eye.
The optic nerve is made of more than a million nerve fibers, bringing vision signals from the retina to the brain. As the pressure increases on this nerve, it causes some of these nerve fibers to die and degenerate slowly. This is why glaucoma can cause blindness.
Screening for glaucoma
The short answer to this question is simple: schedule an eye checkup at least every two years even if you are not having vision problems. The long answer to this question is more complicated.
Screening for glaucoma is complex because glaucoma itself is the name for a group of diseases that do not look the same early in the course of the disease.
Direct observation is the most important way your eye doctor checks for glaucoma. This is first done by dilating your eyes. The eye doctor then uses an ophthalmoscope to look directly at your optic nerve. The color and appearance of the optic nerve indicate if you have glaucoma damage, and how much damage has been done.
The main tool for glaucoma screening is the tonometer, which can measure your intraocular pressure rapidly and without pain. The readings the tonometer gives are important, but have limitations. If your corneal thickness is thin, you may have pressures in your eye that are higher than the readings given by the tonometer. If your corneal thickness is thicker than average, you can have an intraocular pressure that is lower than the readings given by the tonometer. Up to 70 percent of individuals with elevated intraocular pressure won’t ever get glaucoma. If tonometry alone is used, 50 percent of glaucoma cases will be missed.
When your eye doctor is concerned about loss of vision, he may order a visual field test. Your peripheral vision is affected first with glaucoma. If your visual fields are narrowing over time, it means that you are starting to lose nerve fibers in your optic nerve from the increased fluid pressure. In computerized visual field testing, you put your chin on a stand to keep it still and look forward. Flashes of light will appear at the periphery of your vision and you hit a buzzer whenever you notice one. After you are finished with the test, the computer analyzes the information for the doctor to interpret. Repeated visual field tests can measure loss of vision with glaucoma over time.
There is a painful, uncommon cause of glaucoma. Acute angle closure glaucoma occurs when the trabecular network is abruptly blocked and cannot release the aqueous humor. Symptoms include eye pain, blurry vision, halos around lights, nausea and vomiting. This condition cannot wait until the next day. It requires an immediate check so it can be urgently treated before blindness occurs.
Treatment
Treatments for glaucoma can include glaucoma surgery or eye drops. Eye drops are complicated to use: they need to be taken on a regular schedule, and if you are putting in more than one drop or more than one type of eye drop, you need to wait five minutes before you use your next eye drop. Improper or careless use of eye drops are major reasons for blindness caused by glaucoma.
Remember to schedule an eye checkup every two years. Glaucoma is treatable, but can go silently undetected.
