Posted by: Carolinas Center for Sight in Glaucoma
Approximately 1 in 100 people have Glaucoma and half are unaware of it. In developed countries, it is responsible for about 10% of the blindness. Unfortunately, glaucoma is not curable and often leads to visual loss, if not blindness. At present, only the eye’s “intraocular pressure” (IOP) can be altered for a more favorable prognosis. Yet although IOP may be controlled, vision already lost cannot be restored.
Glaucoma relates closely to the anatomy and physiology of the eye. The lens muscle, located behind the iris, produces clear watery fluid to nourish the lens and drain its waste products. This fluid ultimately flows forward through the pupil and leaves the eye through a drain where the cornea and iris meet.
Glaucoma is a set of diseases where the drain is blocked, raising the eye’s pressure. High IOP damages the superficial nerves of the retina which become the optic nerve and transmit vision to the brain.
Anyone can get glaucoma. However, certain birth defects and inherited diseases cause glaucoma in 1 of 10,000 American babies. African Americans have 15x greater chance of visual impairment and 7x more risk of blindness from glaucoma than others. Very near-sighted patients and patients on steroids have increased risk. Ocular trauma gives a lifetime higher risk of glaucoma. And all of us have increased risk for glaucoma as our drain slowly wears out with age.
There are different glaucomas categorized by what blocks the drain. The three main types are:
1) Open-angle glaucoma in which there is microscopic material blocking the drainage meshwork.
2) Closed-angle glaucoma wherein the iris blocks the drain, preventing fluid from leaving the eye.
3) Neovascular glaucoma, where decreased blood flow to the eye causes new blood vessels to invade and scar the drain.
If one has a family history, it is important to have yearly dilated eye exams and testing for glaucoma.
Since glaucoma is chronic, it must be monitored for life. Diagnosis and progression of the disease are evaluated by the same tests. Changes to the visual field test, examination of the optic cup, retinal nerve layer loss detected by OCT, and elevated IOP are the main reasons to diagnose and change treatment of glaucoma.
Generally speaking, IOP is lowered by taking glaucoma eye drop medications. Sometimes an oral medication is necessary to control IOP. However, new studies have revealed other helps:
1) Aerobic exercise,
2) Antioxidants: green leafy vegetables and beta-carotene,
3) Avoiding mineral supplements unless deficient,
4) Avoiding prolonged valsalva (e.g. breath-holding, inversion),
5) Avoiding low blood pressure at night,
6) Alternating which side you sleep on or elevating one’s head with a wedge pillow because the lower eye’s IOP may rise.
Treatments for glaucoma also include laser treatment like SLT and cyclophotocoagulation, as well as surgery. MicroInvasive Glaucoma Surgery (MIGS) can lower IOP and may decrease topical glaucoma medications. These include methods:
1) to bypass the drainage meshwork (like iStent);
2) expansion of Schlemm’s Canal (the conduit that fills with the clear fluid after it percolates through the drain’s meshwork), using a heavy gel (ABIC);
3) destruction of a large angle of the trabecular drainage meshwork (Trabectome, Kahook blade, disruption of the entire trabecular meshwork); or
4) inserting a stent through the drainage meshwork to an area between the lens muscle and the sclera (Cypass).
All of these methods decrease the IOP a modest amount – perhaps enough to discontinue one or two glaucoma drop medications.
If one needs a larger decrease in IOP, more involved surgery must be done.
Traditional surgeries such as Trabeculectomy and Aqueous Shunt (Baerveldt and Ahmed valve) surgery drain fluid from the eye to lower the IOP much lower than the above MIGS. They also have higher risk of visual loss due to postoperative extremely low IOP or elevated IOP. They are usually used when one cannot control the IOP by medications or the above MIGS.
One newer surgery approved by the FDA for lowering IOP, the Xen Stent, combines the effectiveness of the trabeculectomy and tube shunt surgeries with the relative safety provided by the above MIGS procedures. The Xen Stent is a tiny, 6mm hollow cylinder, about the size of a human eyelash, placed into the drainage meshwork and through the sclera to carry fluid from inside the eye to gather underneath the conjunctiva. Thus, it qualifies to be called a MIGS procedure. However, unlike the above MIGS, the Xen Stent lowers the pressure much more, like the traditional surgeries.
All of the glaucoma laser and surgical procedures have some risk of visual loss as well as complications which may require further intervention. However, the Xen Stent has some of the lowest risks for severe complications. Like the MIGS and unlike the traditional surgeries, the Xen has a very low rate of an extremely low IOP and its consequences – decreased vision.