When it comes to our eyes, we have all heard of the term glaucoma in some way or other. We may know of family and friends who have glaucoma and are being treated for it. Some of us associate it with the air-puff test that measures our eye pressures inside our eyes during an eye exam. There are several types of glaucoma. In this article, I will only be discussing primary open angle glaucoma which forms about 90% of all glaucomas.
What is Glaucoma and what is the eye pressure inside the eyes? Glaucoma is one of the leading causes of blindness in the United States. Nearly 3 million people have it. Glaucoma is a group of eye diseases that damages the optic nerve inside the eye and thereby slowly and progressively causes vision loss. It is caused by an eye pressure that is higher than the eye can endure. This high eye pressure slowly damages the nerve cells in the optic nerve that is responsible for transmitting visual signals to the brain. As more and more nerve cells are damaged, one progressively loses more side vision. As the disease progresses, the loss in the side or peripheral vision gradually creeps into the central vision. It is only when central vision is affected, does one notice the symptoms of vision loss. Vision loss in glaucoma is irreversible. Therefore, early detection and treatment is the only way to prevent further loss. Glaucoma is also known as the “silent thief of sight”. Additional risk factors of glaucoma are family history of glaucoma, age, race and ethnicity and having hypertension or diabetes.
Inside the eye, there is a constant eye pressure that maintains and keeps the eye structures healthy. Fluid called aqueous humor is produced and it is drained through a structure called schlemm’s canal at the trabecular meshwork which is at the angle between the iris and cornea. The production and drainage of aqueous humor maintains a normal eye pressure. If more aqueous humor is being produced than can be drained or if there is an obstruction at the trabecular meshwork, the pressure inside the eye rises. If the optic nerve cannot tolerate this higher pressure, damage to its structure and nerve cells will result in glaucoma.
Check out this video on more on glaucoma:
How is glaucoma detected? Since there are no symptoms of glaucoma in its early stages, glaucoma is usually detected during an eye exam. The optometrist or ophthalmologist will look at the optic nerve with a special magnified lens with the use of a biomicroscope to detect any structural damage to the optic nerve. The eye doctor will also measure the eye pressures inside the eye. If there is any suspicion of glaucoma, a glaucoma workup visit will be scheduled so that additional testing and investigating can be done.
- Visual Field Testing: The patient has his or her head placed in an instrument and he or she pushes a button every time a presented light can be detected using one’s side vision. The purpose of the test is to map out any peripheral or visual field loss. This test forms a baseline and is compared to further tests that are done in the future. In glaucoma, one can have 50% nerve cell damage before it may start to affect the visual field.
- Dilated Exam: When the eye is dilated, the optic nerve and its structures can be better viewed with increased detail and magnification.
- Gonioscopy: A lens is placed on the patient’s eye so that the eye structures responsible for the drainage of fluid can be viewed for any obstruction that may be causing the increase in eye pressures.
- Central Corneal Thickness: The central cornea thickness is measured with an instrument called a pachymeter. Having a thin cornea is an increased risk factor for developing glaucoma.
- HRT, GDX and OCT: These are a group of instruments that scans and measures the nerve fiber layer, ganglion cell complex and optic nerve for any structural damage. Thickness values are quantified and they are used as a baseline to establish stability or progressive changes of the disease during future visits.
- Optic Nerve Photos: Photos are taken of the optic nerves to establish a baseline and they are used to compare them with photos taken in the future. Progressive optic nerve damage can be determined by this comparison.
How is Glaucoma treated and monitored? If glaucoma is diagnosed, treatment is usually started with eye drops that will decrease the eye pressures to a level that hopefully does not cause further vision loss and optic nerve damage.
How do we know that further vision loss and optic nerve damage is not occurring? Follow ups every 3 to 4 months are necessary to check on the eye pressures to ensure the pressures are at the level they are targeted to be at, and to make certain the patient is compliant with using the eye drops. Visual field testing and an OCT, HRT or GDX are done every 6 months to monitor for any progressive vision loss or optic nerve changes. If further loss is occurring, a second eye drop can be added to decrease the pressures further or a laser surgery procedure can be done. It is important to realize that glaucoma is a disease that needs to be managed, monitored and followed-up upon.
Since glaucoma is usually detected at a routine eye exam without the patient expressing any symptoms, it is crucial that we get our eyes examined once a year. In view of the fact that glaucoma is a progressive disease, it is imperative we remain compliant with using our drops and critical we do not miss our follow-up appointments.