National Glaucoma Awareness Month provides a perfect opportunity to learn more about glaucoma, a leading cause of vision loss that affects more than 3 million people in the United States. Glaucoma often is called “the sneak thief of sight” for good reason: Many people are unaware that glaucoma has few symptoms or warning signs in its early stages. Early treatment for glaucoma can usually (but not always) slow the progression of the disease. However, as of yet, there is no cure for glaucoma.
Because glaucoma has no obvious initial symptoms, a comprehensive dilated eye exam is critical to detect early glaucoma changes. People who are over 40 should have a dilated eye examination from an ophthalmologist or optometrist at least every two years. African Americans; people who are over 35 and have a family history of glaucoma; and everyone age 60 or older should schedule a comprehensive eye examination every year.
What Is Glaucoma?
Glaucoma is a group of eye diseases that can lead to blindness by damaging the optic nerve, which transmits information from the eye to the brain, where it is processed and interpreted. The eye continuously produces a fluid, called the aqueous, that must drain from the eye to maintain healthy eye pressure. Glaucoma is particularly dangerous to your vision because there are usually no noticeable initial symptoms or early warning signs.
The Different Types of Glaucoma
Primary Open Angle Glaucoma
The most common type of glaucoma is Primary Open Angle Glaucoma (POAG). In POAG, the eye’s drainage canals become blocked, and the fluid accumulation causes pressure to build within the eye. This pressure can cause damage to the optic nerve, which transmits information from the eye to the brain.
Vision loss is with this type of glaucoma is usually gradual, and often there are no early warning signs. There is a strong genetic predisposition for this type of glaucoma.
Angle Closure Glaucoma
Angle Closure Glaucoma is much less common than POAG in the United States. In this type of glaucoma, the aqueous cannot drain properly because the entrance to the drainage canal is either too narrow or is closed completely. In this case, eye pressure can rise very quickly and can be triggered by pupil dilation.
Symptoms can include sudden eye pain, nausea, headaches, and blurred vision. If you experience these symptoms, you should seek immediate medical treatment.
Normal Tension Glaucoma
In this type of glaucoma, also called low-pressure glaucoma, there is damage to the optic nerve, even though the eye pressure is not elevated excessively. A family history of any type of glaucoma, cardiovascular disease, and Japanese ancestry are a few of the risk factors for this type of glaucoma.
This type of glaucoma is treated much like POAG, but the eye pressure needs to be kept even lower to prevent progression of vision loss.
The typical progression of vision loss from glaucoma
Source: National Eye Institute
How Is Glaucoma Detected?
Because glaucoma can begin to develop without noticeable symptoms, the best way to protect your sight is to schedule regular comprehensive dilated eye examinations, which should include all of the following components:
- A health and medication history
- A vision history
- Visual acuity testing
- Basic visual field testing
You can read more about each of these eye examination components at What Is a Comprehensive Dilated Eye Examination?
Additional Tests for Glaucoma
If your eye doctor suspects that you may have glaucoma, you will need to undergo additional testing that can help your doctor make a more definitive glaucoma diagnosis:
- This test uses a probe that emits an ultrasonic wave to measure the thickness of your cornea. Thicker than normal corneas can give eye pressure readings that are inaccurately high, while thinner than normal corneas can give readings that are inaccurately low.
- To measure your corneal thickness, the doctor will touch the tip of the pachymeter probe to the surface of your cornea. The probe emits a painless ultrasound wave that measures your corneal thickness. The doctor will numb the surface of your eye with an anesthetic drop for this test.
- This test measures and maps your visual fields. Perimetry testing can draw a map of your visual fields and show you where you may have lost vision, especially your peripheral (or side) vision, which is the vision usually affected by early damage to the optic nerve from glaucoma.
- The most commonly used test for perimetry is the Humphrey Field Analyzer (pictured at left). The machine resembles a large bowl.
- One eye is covered with a patch and the other eye remains stationary and focused straight ahead. Small white lights of varying sizes and intensities will flash at different locations around the bowl. You will be instructed to press a button whenever you see a flashing light.
- By recording which lights you see and which ones you do not, it creates a map of your visual field.
- This test assesses the angle, or drainage canal, that is formed between your cornea and iris. Because angle-closure glaucoma requires immediate medical attention, it is important to examine the drainage canals, or angles, to ensure that they are functioning properly.
- Because the drainage angle is located around a “corner” of your cornea, the doctor can’t see whether your angle is open by looking directly into your eye.
- Gonioscopy uses a lens with a mirror to view the angle. During the exam, the doctor places this lens, called a gonioscope, on the surface of your eye like a large contact lens. The doctor will numb the surface of your eye with an anesthetic drop for this test.
For more detailed and patient-centered information about ophthalmoscopy, tonometry, pachymetry, perimetry, and gonioscopy, see Discovering the Sneak Thief: Diagnosing Glaucoma in VisionAware’s Patient’s Guide to Living with Glaucoma and El descubrimiento del ladrón silencioso: El diagnóstico de glaucoma in Guía del Paciente: Vivir con Glaucoma.
What Is the Treatment for Glaucoma?
Glaucoma is a chronic condition that must be monitored for life. With proper monitoring and compliance with treatment, glaucoma can be managed – but not cured. Current treatments include eye medications, laser treatment, surgery, and several newer surgical alternatives.
- Prostaglandin Analogs
- Carbonic Anhydrase Inhibitors
- Alpha-Adrenergic Agonists
- Beta-Adrenergic Blockers
- Combination Drugs
For tips, adaptations, and assistive devices to help you take your glaucoma medications, see Tips for Taking Glaucoma (and Other) Eye Drops by Ira Marc Price, O.D.
If eye drop medications do not adequately control your glaucoma, the next step is a treatment called a laser trabeculoplasty. In this procedure, laser energy is directed at the trabecular meshwork, which is the drainage system of the eye. The laser treatment lowers pressure by increasing the drainage of the fluid from the eye. The procedure is relatively short, painless, and usually performed in the doctor’s office.
Three types of lasers can be used for the procedure:
- Argon laser trabeculoplasty (ALT) has been used for more than two decades.
- Selective laser trabeculoplasty (SLT)
- Micropulse laser trabeculoplasty (MLT)
- SLT and MLT are two newer laser treatments now available.
- Side effects from all types of lasers include mild inflammation in the eye and a possible temporary pressure rise. A short course of a mild steroid or non-steroidal anti-inflammatory eye drop is used to treat any resulting inflammation.
- Other lasers are available, but these are reserved for people with particular types of glaucoma that narrow or completely close the drainage system of the eye.
Surgery to treat glaucoma is usually undertaken only as a final step for people who have not achieved adequate pressure control with either eye drop medications or laser treatment.
Depending on the type of glaucoma and associated risk factors, two types of surgeries are available:
- Filtering Surgery: Trabeculectomy: In a trabeculectomy, a small incision is made in the sclera (the white of the eye). Fluid slowly leaks from this incision into a “bleb,” which is a covered space made in the conjunctiva (the thin, transparent tissue that covers the outer surface of the eye). The fluid in the bleb is slowly reabsorbed by the eye. This surgery provides a “natural” alternate drainage for aqueous to flow out of the eye.
- Drainage Device Surgery: Drainage device surgery partially inserts an artificial tube implant into the eye. Fluid drains through the tube and out to a reservoir. This surgery provides an “artificial” alternate drainage for aqueous to flow out of the eye.
Both types of surgeries have been proven effective in lowering eye pressure. Some people may still need to use post-surgery eye drop medications to maintain healthy eye pressure.
Several new surgical options have been developed recently:
- Express mini-shunt: A small stainless steel device the size of a grain of rice is implanted in the eye to drain the fluid.
- Trabectome: A device is inserted into the eye through a very small incision at the edge of the cornea. A small portion of the eye’s trabecular meshwork, which is responsible for fluid outflow, is removed, which improves drainage. This is usually done as part of cataract surgery.
- Canaloplasty: An incision is made in the eye and a microcatheter is inserted into the eye drainage system to encourage fluid outflow. This is usually done as part of cataract surgery.
- Other newer procedures, called MIGS (minimally invasive glaucoma surgeries), are receiving attention from eye surgeons. The currently available iStent is very small and recommended for use at the time of cataract surgery.
You can find more information about these surgical procedures at the Glaucoma Research Foundation.
- Follow glaucoma research on the VisionAware blog.
- For patient-centered information about glaucoma detection, treatment, and everyday management, see VisionAware’s Patient’s Guide to Living with Glaucoma and Guía del Paciente: Vivir con Glaucoma.