Tools for monitoring glaucoma

 

When you first heard that you have glaucoma directly from your doctor, the world seemed to stand still. You may have heard horrible stories about glaucoma from either your relatives or friends, thinking that you are about to go blind. You might also start thinking about which actions you had done in the past that may have contributed to your glaucoma. All of these racing thoughts only raise your anxiety further.

 

With this article, I hope to reassure you regarding the tools we have to monitor the status and progression of your glaucoma. In the next article, we will discuss what conservative lifestyles we can adopt, in addition to medical treatments to potentially stifle the vision loss from glaucoma. As a reminder, it is important to remember that everybody is different. Each patient’s glaucoma progresses at a different rate, with a majority having a relatively stable condition, while the progression of glaucoma is worse in some others.

 

Glaucoma is a condition that initially affects the structure of the optic nerve, and then affects the peripheral field function as the condition worsens. End stage glaucoma will eventually lead to tunnel vision or blindness. Therefore, it is intuitive to have tools that can study both the structure of the optic nerve, as well as the pattern of one's peripheral vision. Not surprisingly, we have three predominant tools to monitor glaucoma.  

 

Optical Coherence Tomography (OCT)

 

This is a non-invasive imaging technique that uses light waves to measure the thickness of the retinal nerve fiber layers (RNFL) around the optic nerve. RNFL is an important parameter for glaucoma specialists because all of us are born with healthy RNFL that are responsible for transmitting light information from inside the eye to the brain. Early signs of glaucoma usually begin with the thinning of RNFL thickness. At this early stage, we label the condition as pre-perimetric glaucoma, in which the patient has not yet lost any field of vision from glaucoma. This is a great stage for glaucoma specialists to intervene to protect the patient’s eyesight from future damage, but we will reserve this topic for the future.

Your glaucoma specialist will most likely utilize OCT at least once a year, and compare the current result with previous ones. The parameters that are compared include the contour of your optic nerve, the thickness of the RNFL, as well as surrounding structural changes. If your eye pressure is higher than expected but all of your imaging tests are stable, then it is okay to delay treatment until further changes occur.

 

Fundus Photography (FP)

 

Fundus photography allows your glaucoma specialist to take a live photograph of your optic nerve. This is crucial because although exam findings are subjective from visit to visit, a picture speaks a thousand words and is more objective, especially when comparing side by side. Parameters that are monitored include the presence of disc hemorrhage, optic nerve contour, and RNFL loss. To top it off, FP also captures the status of the macula, where age related macular degeneration takes its effect. 

 

Humphrey Visual Field (HVF) 

 

As glaucoma progresses, one's visual field will slowly constrict until tunnel vision occurs. HVF is the most important test in measuring the integrity of your peripheral vision. In this test, you will look through the machine's interface at a fixated point; light of varying intensity will flicker in your peripheral vision, and the doctor will instruct you to hit the clicker when the flicker is seen. The length of the HVF test and the need for good attention span can make this test difficult for some individuals. Sometimes, patients will feel like they have flunked the test, when in reality they have tested consistently compared to their previous tests. This is because the purpose of the test is to give gradually weaker signals or flickers in your peripheral vision until you cannot see them anymore. Although it takes some mental resilience to go through with the whole test, your effort will pay off because your glaucoma specialist will usually place the most emphasis on the HVF test, compared to OCT and FP. Your glaucoma doctor will compare your current HVF result with the previous ones, and at least one visual field test per year is necessary to monitor the progression of glaucoma. Please do not skip this test.

 

To recap, the goal of this article is to help familiarize you with the tools that we have at our disposal in diagnosing and monitoring glaucoma. I hope that the next time you are face to face with your eye doctor, that you can ask them what they think about the tests you have done. In addition, you will now have a better understanding of why a clinical visit with a glaucoma specialist can take longer than visits with other ophthalmologists. The longer visit is worth it because the time spent on getting good imaging gives your glaucoma specialist the data necessary to treat your condition.