Glaucoma is the second leading cause of blindness worldwide. It typically occurs when the intraocular pressure (IOP) of the eye becomes elevated, leading to optic nerve damage and eventually, vision loss. The vision loss is usually peripheral and unnoticeable at first, which is why glaucoma is called “the silent thief of vision.” Left unchecked, the vision loss can become central and symptomatic. This is usually when patients present to the doctor. Unfortunately, that vision loss is permanent. That is why routine eye exams are so important—catching glaucoma early allows us to treat it and halt any further damage. During your eye exam, we will check the IOPs, confrontational visual fields and examine the nerve. Should any of these signs be suspicious for glaucoma, extra testing of the visual fields with a Humphrey Visual Field or the optic nerve with an OCT or disc photos can be done.
The pressure of the eye is determined by how much fluid (aqueous humor) is produced and how much is drained through the angle (trabecular meshwork) of the eye. Producing more than you can drain results in a higher IOP, since the eye is not expandable like a balloon. Studies have shown that treating increased IOP has been shown to decrease the risk of nerve damage, or glaucoma.
If the angle of the eye appears grossly open in the setting of glaucoma, then we call it primary open-angle glaucoma. It would be the equivalent of seeing the drain of the tub, which appears able to drain, and yet is clogged deep within the pipes. It is the most common form of glaucoma and the primary cause of irreversible blindness in African Americans. Risk factors include family history, increased age, being African-American and diabetes mellitus, among other things. Treatment can include virtually all the options and include medications, selective laser trabeculoplasty, transscleral cyclophotocoagulation, iStents, Xen gel stents and Ahmed tube shunts.
If we see that the drain appears to be almost closed, then the person is said to have narrow angles. This would be the equivalent of seeing a bunch of debris in the drain of the tub, blocking the water from draining. This could be longstanding and result in chronic elevated IOPs or lead to a sudden, rapidly progressive, painful increase in IOP called angle-closure glaucoma.
If the lens pushes up against the iris and blocks the flow of fluid through the pupil, the angle can close abruptly and severely increase the IOP. This can be rectified by making a small hole in the peripheral iris, which can act as an escape valve. This is called a laser peripheral iridotomy (LPI).
If there is a specific identifiable cause of a patient’s glaucoma, then it is called secondary glaucoma. Since the causes are often very different, the treatments vary as well.
- Lens-induced glaucoma—A large cataract can either compress the angle or leak proteins that cause inflammation and increase inflammation. The main treatment for this is to do cataract surgery.
- Uveitic glaucoma—Chronic inflammation can create scarring which can effectively begin to close the angle. Sometimes an LPI is necessary but usual treatments include medications, TSCPC, Xen gel stent and Ahmed Tube shunts. SLT or iStents may be possible, if the angle is open enough.
- Traumatic Glaucoma—Previous trauma can cause changes to the angle. These changes can eventually cause increased IOP in one eye and an asymmetric glaucoma. Treatments include medications and TSCPC. SLT and iStents are not great options due to distorted anatomy and Xen gel stents and Ahmed tube shunts may not be as effective as in other conditions.
- Pigmentary Dispersion Glaucoma—If the iris is bowed, it can rub against the lens behind it and shoot off pigment that can clog up the angle. Treatments include medications, LPI, TSCPC, Xen gel stents, and Ahmed tube shunts. SLT tends to work very well for this condition.
- Pseudoexfoliation Glaucoma—Certain ethnic groups (Scandinavians and other groups in the northern latitudes) are more prone to this condition. The eye begins producing a material that deposits on the surface of the lens, in the angle and on the zonular fibers that hold the lens in place. This can cause a severe type of POAG. Medications, TSCPC, Xen gel stents, and Ahmed tube shunts are good treatments. SLT tends to work fairly well for this condition.
- Neovascular glaucoma—This type of glaucoma is caused by new blood vessels that grow in the angle. It can eventually cause a chronic angle closure glaucoma. The cause may be due to poorly controlled diabetic retinopathy, central or branch vein occlusions, among other things. The lack of oxygenated tissue causes the eye to secrete VEGF, a potent growth factor that promotes new blood vessel growth. As good as that sounds, many times the blood vessels are either fragile and bleed or grow in areas that do not benefit from the extra blood vessels. Medicine often fails as a treatment and it may require TSCPC, Xen gel stent or Ahmed tube shunt.
Multiple medications exist. They work in different ways so they can be used together, as they work synergistically. Their mechanism of action may be to decrease fluid production, increase drainage through the angle, or increase drainage through alternative pathways. Some drops work better for patients than others. Sometimes this is a trial-and-error process. Besides some issues with cost and inconvenience, virtually all these drops tend to cause dry eyes over time. The more drops the patient is on, the more likely this is to happen.
Acute angle-closure glaucoma occurs when the floppy iris pushes forward and completely closes the angle. For patients with anatomically narrow angles, it is recommended to have a hole placed in the peripheral iris to help equilibrate the IOP on either side of the iris. This keeps the iris pushed back and angle open. Laser can be used to make this hole (laser peripheral iridotomy), making this a quick procedure done in the office. Most patients go back to normal activity that day.
If a patient has POAG or a secondary glaucoma with open angle (e.g. pigmentary glaucoma or pseudoexfoliation glaucoma), laser trabeculoplasty can be an excellent option. The old procedure involved making permanent spots to the angle and could not be repeated. The new version of the procedure, selective laser trabeculoplasty (SLT) causes no permanent injury to the eye. Instead energy is used to promote drainage in the angle. This result usually wears off after a few years and can be repeated up to three times. Usually, we can get a decrease in IOP the equivalent of one medication and are successful with this approximately 2/3 of the time. This is a quick procedure done in-office. Patients may experience some temporary blurry vision but are able to resume normal activity that day.
Micropulse Transscleral cyclophotocoagulation involves using a laser to heat up the ciliary body, the cells that produce fluid in the front part of the eye. The laser passes through the white sclera of the eye and absorbs in the ciliary body due to its being pigmented. With decreased fluid production, the IOP should drop accordingly. It does not cause permanent injury to the eye when used at lower power settings and can be repeated multiple times. It can be used for virtually all types of glaucoma. The effects could last 3-12 months, but repeated treatments are expected. This procedure only takes a few minutes but is done in an outpatient same-day surgery center due to the need for anesthesia.
During cataract surgery, we can get patients more “drop-free” by adding on a simple 5-10 minute procedure called the iStent. This is a great option for patients on 1-2 glaucoma medications with mild to moderate open-angle glaucoma. Patients can experience some mild blurry vision for a day or two but the postoperative course is identical to cataract surgery without the iStent. This is done in the same-day outpatient surgery center.
Xen Gel Stent
For patients with moderate and severe glaucoma, the Xen gel stent can either be inserted from within the eye or externally. It can be done in conjunction with cataract surgery or as a standalone procedure in the surgery center. Essentially a tiny tube is placed in the eye allowing any extra fluid to be externally drained. This fluid eventually passes behind the eye and is absorbed the veins there. This is an extremely quick procedure that has a quick recovery time, though the IOP drop can be quite significant!
Ahmed tube shunt
We also reserve this for patients with moderate and severe glaucoma. There are more sutures and the recovery time is a little longer than for the other procedures. It can give quite a robust drop in IOP, even for tough neovascular glaucoma cases. This can be done with cataract surgery, or as a standalone procedure. We tend to do the Xen gel stent more frequently these days, since it is more minimally invasive, but if there is a concern about the pressure dropping too much, this is a great option as there is a valve which restricts too much fluid from draining out of the eye.