Glaucoma, nicknamed "the silent thief of sight," is a progressive eye disease that affects millions of people throughout the United States. Many have heard of the term glaucoma, but very few really know how this disease affects the eyes and if we ourselves are at risk. In this article, it is my goal to give the reader an overall idea of what glaucoma is, the risk factors for it, and the important signs I look for during a comprehensive eye examination. At the end, I will also briefly review treatment for glaucoma and what you can do to make sure your eyes are being properly cared for.
Glaucoma affects over 4 million people over the age of 40 in the United States, and it is approximated that half of those affected, over 2 million, don't know they have the disease. This is quite a large and disturbing number and the reason why glaucoma has the nickname "the silent thief of sight." Most patients are asymptomatic (not aware of anything bothering their eyes) when initially diagnosed with glaucoma, which can be problematic for myself as a clinician to convince patients they are potentially at risk.
Glaucoma is defined as a progressive eye disease that causes damage to the optic nerve of the eye. It is often associated with an increased intraocular pressure (IOP) and the most common type tends to be inherited and diagnosed after the age of 50. There are other types that include low tension, inflammatory, angle closure, and traumatic that are less common but have nearly the same effect on the eye. Without proper eye care glaucoma can lead to severe visual loss and depending on the aggressive nature of the case at times complete blindness.
During exams, I will often try to describe or explain eye diseases by comparing it to something we are all more familiar with. The best analogy I have found is comparing a glaucomatous eye to an over-inflated ball. If there is too much air inside of an inflated ball there is an increase of pressure on the inner walls, and the same applies to the eye. When there is a chronic increase of eye pressure over a period of time this can lead to damage of the nerves that live within the eye walls as well as the optic nerve. (see Image #1) If this pressure is not caught and/or treated it can lead to irreversible vision loss and periodically complete blindness.
It is important for everyone to know the risk factors for glaucoma. One of the most important and strongest risk factors for glaucoma is a positive family history. Glaucoma studies have shown that glaucoma can run in families, therefore it is important to know if a direct relative has ever been diagnosed. A direct relative includes a parent, grandparent, and siblings.
One constant in life that stands the test of time is that as long as the good Lord gives us breath we will continue to get older. Age is another risk factor for glaucoma. Outside of traumatic or inflammatory etiology, glaucoma generally reveals itself sometime after the age of 40-50 with risk increasing each passing year. If you have a family history of glaucoma it is important to get an annual eye examination especially if you are over the age of 40.
Other risk factors that are more controllable included diabetes, obesity, and sleep apnea. Although the studies are somewhat preliminary there is a small link of increased risk of glaucoma in those with diabetes and obesity. I would be hesitant to say, however, that lowering blood sugar and significant weight loss would be able to control glaucoma exclusively, as this is not scientifically proven. Sleep apnea is a common condition that causes one or more pauses in breathing while sleeping. These pauses or shallow breaths can significantly decrease the amount of blood flow and oxygen delivered to the brain and other vital organs, including the eyes, while you sleep. This lack of oxygen perfusion at night time can lead to increased risk of normal tension glaucoma when the optic nerve is basically starved at night from lack of oxygen perfusion. A sign of sleep apnea is shallow breathing, loud snoring or snorting, and pauses of breathing while asleep. If you have been told you have these symptoms it is important to ask your primary care doctor about sleep apnea.
Now that we have discussed what the risk factors are, let us discuss some important aspects I look for in a comprehensive eye examination as it pertains to glaucoma. During the initial health history work up you should be asked if you or anyone in your family has a history of glaucoma; as previously discussed this is an important factor of finding your risk. Intraocular pressure (IOP) is also a quantitative value I obtain during every full examination. There are several ways to obtain this value one of the most common and probably most feared is the NCT test or more commonly known as the "air puff." While this test is accepted in the medical community, it is not the gold standard and I know several grown men and women who ultimately dread the idea of having air puffed in their eyes.
Goldmann tonometry is considered the gold standard of testing the IOP, and what I personally use at my offices. Many will remember it as a little blue light that comes extremely close to your eye. It is a quick, efficient, and very comfortable procedure. The range for a normal IOP is between 8 and 21 millimeters of mercury (mmHg) and it is important that everyone over the age of 40 has an idea of where their eye pressures run. Just like blood pressure it can vary, usually a maximum of a couple points and is generally highest earlier in the day.
The third aspect I examine closely is the health of the optic nerve in the back of your eyes. The optic nerve is the pathway that sends the signal of sight to the brain. I often will compare it to a plug that plugs into the back of the eye. A healthy optic nerve will have a slight pink color and a small cup to disc ratio. If high eye pressures are present it can cause a change in the appearance of the optic nerve by thinning the tissue around the nerve as well as thinning the nerve itself which will, in turn, enlarge the cup to disc ratio. (see Images #2,3,4) An analogy I find effective to explain the cup to disc ratio of the optic nerve is as simple as a donut. The average cup to disc ratio of the optic nerve is a 0.3, or the cup is 30% of the entirety of the optic nerve. I often will have the patient picture a regular donut and explain that the cup would be the hole of the donut and the healthy disc with would be the actual dough. With advancing glaucoma the cup or donut hole with continue to grow in size leaving less and less healthy disc or dough behind. Any patient, especially over the age of 40, with a cup of over 55% is considered to be at higher risk for developing glaucoma. Several other more complicated assessments of the nerve are taken into consideration by your optometrist while observing the nerve as well to evaluate total nerve health.
After gathering these 3 main pieces of information I evaluate total glaucoma risk. Excluding a single finding that would place a patient into a high risk, an example would be an IOP of 25 or more or a cup to disc ratio of 0.75 or larger; I generally take the approach of 2 out of 3. If there are 2 of the 3 red flags or positive risk factors during the exam I will recommend getting some additional information to rule out glaucoma. Additional tests include visual field test and optic nerve imaging to get quantitative values of the tissue of the nerve.
The peripheral field of vision is affected first during the glaucoma disease process. An important diagnostic test is a peripheral visual field test to make sure there is not a depression of sensitivity at any point of the field of vision. Early detection is key when it comes to treatment, and often time early peripheral visual field loss cannot be sensed by the patient in day to day life. However, it is crucial to catch because of the risk of tunnel vision occurring with untreated advancing glaucoma over several years.
Optic nerve imaging, also known as optical coherence tomography (OCT), is on the forefront of managing glaucoma risk and advancement. At our Sugarcreek office, we have recently purchased this machine and use it nearly on a daily basis to help assess risk and advancement in those dealing with glaucoma. It has revolutionized the way we are able to care for our patients with glaucoma and also educate and inform those who are at risk. The OCT scan measures the thickness of the nerve fiber layer around the optic nerve; glaucoma is found with increasingly thinning values of that layer. Although I know the information is likely advanced, I included an OCT printout example of a moderate stage glaucoma right eye and a near normal scan for the left eye. Green values are normal, yellow outside of normal and red shows severe thinning.
Glaucoma is a disease that is better described as controlled with medications rather than cured. The first line of control is using daily eye drops that have an IOP lowering effect to take stress off the optic nerve. There are several classes of these medications available for you local eye care provider to use. When a patient is diagnosed with glaucoma it is crucial that their pressures be monitored 3 to 4 times a year to maintain a target goal. If there is advancement of the disease while on medications, a second and sometimes third drop can be used to reach the pressure lowering effect needed. More often than not glaucoma is well controlled with medication, however, in some of the aggressive forms of the disease, there may be a pressure lowering eye surgery needed to keep the eye from losing vision.
In conclusion, I hope I was able to clear up some common misconceptions about what glaucoma is and how it affects one's vision. My number one priority with a patient in my exam chair is to make sure they know I am an ally when it comes to their efficient and effective eye care and that all questions are answered. Glaucoma can be one of the more frustrating eye diseases for patients because of the fact there are no symptoms in the mild to moderate stages. Patients often times will have great vision with eyes that look and feel good as well, but they are still seeing the eye doctor 3 or 4 times a year. I hope through this article there is some extended understanding about the decision making and reasons why eye care practitioners watch for this "silent thief of sight" so closely.