What Is Glaucoma?

Glaucoma is an eye disease you’re likely to have heard of before – whether it’s in the media, from your eye care practitioner, or your Great Aunt Edna announcing to the family that she’s been diagnosed with “gloocoma”. In the United States, approximately 3 million Americans have glaucoma. Specifically, in the state of California, an estimated 300,000 people live with this eye disease.

Describing Glaucoma
Inside the eyeball, a fluid known as aqueous humour is constantly being produced. It must be drained from the eye at a similar rate, otherwise with an increase in volume of fluid in the confined space of the eyeball, basic physics tells us the pressure inside this eye is going to rise. As the pressure rises, again physics tells us that something is going to get squished, and in the case of glaucoma, this something is the optic nerve. The optic nerve responds to light from the world around us and is responsible for carrying these neural signals to the brain to produce what we call vision. If the optic nerve becomes damaged from an increase of intraocular pressure (that is, pressure inside the eyeball) it can result in irreversible loss of sight, typically beginning with peripheral vision. Because we are not always actively aware of our peripheral vision, glaucoma has been labeled as the sneak thief of sight as its effects on the peripheral vision are often not noticed until the disease is at an advanced stage. If left untreated, glaucoma can cause total blindness and in the US, 9 to 12 per cent of blindness is due to glaucoma. The best way to ensure you catch this sneaky bugger early is to schedule regular check-ups with your eye care practitioner even if you don’t feel your vision has deteriorated.
 

Eye Anatomy of Glaucoma

 
There Are Many Different Types and Causes of Glaucoma
The most common is known as primary open angle glaucoma – primary referring to a rather unsatisfactory “just happens for no real good reason”, and open angle meaning the drainage structure (known as the anterior angle) through which the aqueous humour leaves the eye is open but not functioning properly. This type of glaucoma accounts for about two-thirds of all glaucoma cases. Other types of glaucoma include closed angle glaucoma, in which the anterior angle of the eye narrows and impedes the removal of fluid; congenital glaucoma in babies with malformed eye anatomy; and glaucoma occurring secondary to other ocular issues, such as diabetic eye disease or certain types of inflammation in the eye.

 
Detecting Glaucoma
Glaucoma is sometimes incorrectly considered a disease only for the elderly, such as unfortunate Great Aunt Edna. As we’ve mentioned earlier, even babies can be born with glaucoma, often with severe consequences for their vision. Glaucoma can also be triggered by trauma to the eye, which can happen to anyone at any age. However, primary open angle glaucoma, the most common form, does become more prevalent with age. At age 69, African Americans were found to have a prevalence of open angle glaucoma of about 6 per cent; this increased to 12 per cent by age 80. In the US, African Americans had the overall highest prevalence of glaucoma at 3.4 per cent back in 2010; this compared to 1.7% of Caucasian Americans and 1.5% in Hispanics.

Other risk factors for glaucoma include:

  • Asian ethnicity
  • Age over 50
  • High intraocular pressures. Pressures outside the normal range may not necessarily result in glaucoma if an individual’s optic nerve is particularly robust; conversely, pressures within the statistically healthy range may still cause glaucoma in the presence of other risk factors in other individuals
  • Family history of glaucoma. Research has identified multiple genes associated with the presence of glaucoma; however this doesn’t mean an individual with a family member with glaucoma is doomed for the same diagnosis – it simply indicates an increased risk of developing glaucoma in the future
  • Long or short-sightedness
  • Presence of other health concerns such as diabetes, sleep apnea, or migraines
  • Use of corticosteroid medications

 
Diagnosis of glaucoma is often not as straightforward as performing a single “glaucoma test” and deciding from there that a patient does or does not have the disease. There is a battery of tests to perform, and even after that the conclusion could still remain as “glaucoma suspect” until further follow up and data can be achieved.

One of these tests is to measure the intraocular pressure of the eye. Like we mentioned before, normal for one person could still mean glaucoma for another, which is why the intraocular pressure value isn’t considered in isolation. The optic nerve also needs to be examined closely for its color, size, and structure. This is usually done behind the slit lamp when the eye care practitioner shines exceedingly bright lights into the eye (causing some temporary dazzle and vision loss – exactly what you came to the eye clinic for, isn’t it?). A retinal scan known as optical coherence tomography is now common practice in glaucoma testing as it gives further data about the optic nerve and nerve fiber layer that cannot be measured with other methods. If there is suspicion of glaucoma, a visual field test may also be conducted to produce a map of the sensitivity of the peripheral vision; this can highlight any areas of glaucomatous vision loss. In this rather soporific test, a patient sits in a dark room for about 10 minutes and clicks a button every time a point of light or flicker is seen in the machine (it’s all fun and games when you come to the eye clinic). Quite often, one or more of these tests will need to be repeated over time for a definitive diagnosis of glaucoma.

 
Treating Glaucoma
Treatment of glaucoma aims to reduce the intraocular pressure to a level that prevents further damage to the optic nerve and vision loss. This can be achieved through daily eye drops, a laser procedure, or surgery. The ideal treatment option can depend on multiple factors, such as the patient’s ability to instil/remember their own eye drops, any other medications that may react with the glaucoma drops, or the patient’s attitude towards surgical interventions.

In certain cases, an ophthalmologist may want to preventatively treat a patient who is at risk of developing glaucoma, specifically of the angle closure variety. If the drainage angles of the eyes are appearing very narrow, despite normal intraocular pressures and a healthy optic nerve, it may be wise to address this early before they close altogether and the pressures skyrocket. This is done by a quick and simple laser procedure in the consulting room which perforates a hole in the iris to allow the aqueous humour to drain through this new channel.

With the huge armory of treatment options available today, a diagnosis of glaucoma for you or a family member doesn’t need to spell doom and gloom. Unfortunately, a small 10 per cent of glaucoma patients receiving treatment will still lose some vision but for the vast majority, regular eye tests are your best bet at early detection and treatment before any vision loss occurs, or in some cases, even prevention of glaucoma altogether.

 

 

References
Vision Problems in the US. http://www.visionproblemsus.org/glaucoma/glaucoma-map.html
Glaucoma Facts and Stats. http://www.glaucoma.org/glaucoma/glaucoma-facts-and-stats.php
Glaucoma. https://www.lei.org.au/services/eye-health-information/glaucoma/
Glaucoma, Open-angle. https://nei.nih.gov/eyedata/glaucoma
Who Is At Risk of Glaucoma? https://www.glaucoma.org.au/about-glaucoma/who-is-at-risk/

 

 


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