Figure 1. This demonstrates a generalized anatomy of a human eye.
Remember that annoying air-puff test you received at your last eye exam? You may have heard that the air-puff test “looks for glaucoma,” but what does that really mean? How does a person know that they have glaucoma and what does it mean if you do? Can one prevent glaucoma? This article is going to talk about all of these things, and shed some light on a potentially visually devastating eye disease. However, before we understand why an eye is said to have glaucoma, we have to understand the cause of glaucoma itself.
Figure 2. Because the amount of fluid being created at the back of the eye is equal to the amount of fluid draining at the front of the eye, this eye is considered healthy.
Just as the body has a blood pressure, the eyes have an eye pressure. This pressure, called the intraocular pressure, is thought to be related to the cause of glaucoma. Depending on the type of glaucoma, the intraocular pressure may be high or low. Fluid is created by the ciliary body behind the iris (See Figure 1). This fluid is then drained through the pupil, and out through the anterior chamber drainage angle. When the system works as it should, the amount of fluid created at the back of the eye equals the amount drained through the front of the eye (See Figure 2). If there is an imbalance in this system, intraocular pressure rises and that increased pressure may cause permanent damage to the eye (See Figure 3).
Figure 3. This images depicts an eye with more fluid production occuring at the ciliary body than is draining at the anterior chamber drainage angle. The result will be increased intraocular pressure and possible glaucoma.
In angle-closure glaucoma, the anterior chamber drainage angle is sealed shut. Because fluid is still being created at the back of the eye, but not draining at a similar rate at the front of the eye, the overall pressure goes up –sometimes dramatically. Angle-closure glaucoma is less common than primary open angle glaucoma (glaucoma where the angle is open to drainage), though it is more frequently associated with pronounced symptoms. Patients with angle-closure glaucoma may report red eyes, immobile pupils, blurred vision, haloes around lights, and generalized (sometimes quite severe) eye pain. Angle closure glaucoma is considered an ocular emergency and the eye pressure needs to be lowered very quickly, often by a combination of oral and topical medications –and sometimes by emergency surgical procedures.
Figure 4. The optic nervehead is the structure viewed by ophthalmoscopy to determine if glaucomatous damage might be present. A. shows a normal optic nervehead. B. shows some suspicion for early glaucoma. C. shows end-stage glaucoma with very pronounced changes.
Primary open angle glaucoma is the more common type of glaucoma. In its earliest stages, primary open angle glaucoma frequently carries with it no symptoms for patients to mention. In primary open angle glaucoma, the anterior chamber drainage angle is open. But while the angle is technically open, on a microscopic level, the tiny openings in the tissue of the angle close and prevent fluid from exiting the eye. The result is an angle that is open, but one that doesn’t drain fluid very well. The eye pressure goes up, and with that rising pressure, the damage associated with glaucoma occurs.
In all types of glaucoma, the damage to the eye results in a loss of the side vision. In angle closure glaucoma, this damage can happen very quickly (hence the need to be diagnosed and treated immediately if angle closure is suspected) though in primary open angle glaucoma, the damage is slow, building up over years and decades. The physical changes to the eye include damage to the peripheral retina (the part of the retina that perceives peripheral vision). Because the retina is transparent, this loss is difficult to clinically visualize, though the damage to the retina includes a change in the appearance of the optic nerve at the very back of the eye (See Figure 4). The optic nerve changes shape in glaucoma, hinting at the damage to the rest of the retina. It is interesting to note that not all patients with glaucoma have high eye pressures. Intraocular pressures can be high or low and a patient can still be diagnosed with glaucoma. Glaucoma historically tends to be associated with high eye pressures, though sometimes patients will have a high eye pressure but no damage to the eye. These patients are typically watched closely and labeled ocular hypertensive. No matter what a patient’s eye pressure was at the time of diagnosis there is only one way to treat glaucoma, and that is to lower the intraocular pressures.
Lowering the intraocular pressure can be accomplished with topical medications. Some medications act to decrease the amount of fluid being produced by the ciliary body, while others act to increase the eye’s ability to drain fluid. Some patients are prescribed a combination of medications to achieve both effects. Surgery can be used to increase the drainage of the eye as well, with trabeculectomy creates an opening in the outer layers of the eyes to help drain fluid, and drainage implants can be used to help relieve the eye of its increased pressure. Laser surgeries such as a selective laser trabeculoplasty can help relax the tissue in the anterior chamber drainage angle, allowing fluid to pass through it more easily. Topical eye medications are the easiest and the least invasive of these choices, and are often an excellent option for the first line of glaucoma treatment.
Detecting glaucoma involves looking at a combination of things, and diagnosing the disease isn’t always as clear cut as one might like. Intraocular pressure can be measured with non-contact tonometry (or as our patients know it, the “air-puff test”), or with Goldmann applanation tonometry which is slightly more accurate and used in glaucoma management because of its accuracy as compared to the air-puff test. Every routine eye exam at Vista Eye Care measures the patient’s intraocular pressures. Every eye exam also involves care assessment of the optic nerve head by means of ophthalmoscopy –visualizing the back of the eye through the biomicroscope. A dialogue between the doctor and patient will help determine if there is a family history of glaucoma. A side vision screening is also performed at each comprehensive eye and vision exam. If anything looks funny during the eye exam, further testing may be warranted.
If an annual eye check-up finds high pressures, a strong family history, side vision problems, or suspicious optic nerveheads, our doctors may request that the patient return for a glaucoma workup. This work-up will go a bit more in depth than the comprehensive exam, looking specifically for evidence of glaucoma in the patient’s eyes. The intraocular pressures are measured carefully and the anterior chamber drainage angle is inspected with a specially-mirrored contact lens (called a goniscope) to assess the eye’s ability to drain fluid (and thus to determine if the glaucoma is open or closed-angle). The side vision is measured with an automated visual field test. This test takes about five minutes per eye and very carefully and systemically maps out the sensitivity of the patient’s side vision. If results from these tests suggest glaucomatous changes and are repeatable, and the optometrist has reason enough to diagnose a patient, treatment is initiated. While a patient is being treated, they are seen back periodically to have their eye pressures and side vision re-measured. If necessary, we will have patients seen by an eye surgeon for advanced diagnostics (including retinal scans) and possible surgical treatment for those patients with an intolerance to anti-glaucoma medications or in those patients where the drops are not having a dramatic enough pressure reduction effect.
Even if glaucoma is detectable with regular eye care, and even if it is treatable, it would sure be nice not to have to get in the first place though, right? Glaucoma is a unique disease in that it is largely not preventable. Genetics and overall systemic health play a larger role than a patient’s nutrition, for example. That said, patients with health problems, such as diabetes, tend to have more serious cases of glaucoma than those without systemic disease. Certain types of glaucoma can be caused by other diseases such as diabetes, uveitis, or use of corticosteroids.
The best method of keeping glaucoma from affecting your eyes is to have regular eye care to look for it. Dr. Brian Abert, O.D., FAAO, and Dr. Deanna Pedroza, O.D., take great pride in providing their patients thorough eye examinations that look for the early signs of glaucoma. Be sure to discuss your family history with your doctor, and be sure to ask any questions you may have regarding your own ocular health. Keeping your eyes healthy is our goal, and sometimes that process starts with a little puff of air.