Narrow Angle Glaucoma: Causes, Symptoms, and Treatments
Glaucoma is a complicated disease that can lead to permanent loss of peripheral vision and can eventually lead to permanent blindness. There are several different types of this disease:
- Primary open angle
- Narrow angle
Glaucoma affects the way the aqueous fluid drains in the eye. Aqueous is a gel-like, clear fluid found in the anterior chamber, which is located between the iris and the cornea.
Aqueous is constantly replenished by the ciliary body located behind the iris next to the lens (see the above diagram). The fluid flows from behind the iris through the pupil and then drains through the trabecular meshwork, a spongy tissue that allows the fluid to flow through a system of drainage tubes known as Schlemm’s canal and then out of the eye.
Sometimes the ciliary body produces too much fluid, or the fluid doesn’t drain properly, and this causes the pressure in the eye to rise. When the pressure in the eye rises, the optic nerve becomes damaged.
The optic nerve is a bundle of retinal fibers that exit the eye and travel to the occipital lobe of the brain. Each area of the retina corresponds to a specific section of the optic nerve. Essentially, the retina is one big neuron with a very long axon, or tail.
When the pressure in the eye rises, it forces the optic nerve to “cup.” This creates a bowl-like appearance to the optic nerve, which results in the loss of peripheral vision because it damages the fibers that create the nerve.
If we think of the optic nerve as a doughnut, the center hole would be the cupping created by the increased pressure, and the doughnut would be the rim of the optic nerve. The size of the doughnut hole grows as the pressure in the eye rises, which leads to permanent vision loss (see photo below).
Optic Nerve Cupping
What Is Narrow Angle Glaucoma?
Unlike primary open angle glaucoma, narrow angle glaucoma is not as prevalent—but it is much more aggressive. It is the result of a structure in the eye called the angle being too narrow, as its name suggests. The angle is where the trabecular meshwork is found; it is the space between the back of the cornea and the front of the iris (see drawing below).
The Structures of the Angle
Trabecular Meshwork - Area of tissue near the iris that allows the drainage of aqueous humor from the eye through the sclera (white part of the eye).
Aqueous Humor - One of two fluids in the eye that give the eye its shape and stability and provides nutrients to various avascular structures (parts of the eye without blood flow like the cornea).
Ciliary Process - Structure of the eye that produces aqueous humor and provide attachment for the suspensory ligaments that attach to and focus the lens.
In most people, this angle is wide open, as in the drawing. Those of us in ophthalmology describe it as “wide enough to do the backstroke in.” In some patients, however, this structure is very narrow.
Patients who are hyperopic (farsighted) have very short eyes, and this naturally puts them at risk for narrow angles because the structures of the eye are essentially compressed together. Myopic (nearsighted) patients have long eyes, causing the anatomical structures to be spread out.
When the iris dilates, it folds like an accordion. In a patient with open angles there is plenty of room to accommodate the bunched-up tissue of the iris. On the other hand, in a patient with narrow angles, the iris can get stuck in the angle and block the aqueous from draining through the trabecular meshwork. This meshwork is essentially a series of drains that allow the aqueous that is constantly produced to flow out of the eye.
When the iris gets "stuck" in the angle, it causes an extremely rapid rise in pressure. Intraocular pressure readings can reach upwards of 70mmhg. In contrast, normal pressure is between 10 and 20mmhg. The highest I’ve seen in 20 years was over 85mmhg, and the tonometer stops at 88mmhg.
The iris can also be bowed forward either by a cataract, or by a buildup of aqueous. When this occurs, the iris occludes, or blocks, the angle—and the result is a narrow angle glaucoma attack. In this instance, the occlusion may be progressive and happen slowly, rather than striking suddenly. But once the iris fully blocks the angle, symptoms will occur as in a narrow angle attack and may be more severe since the pressure will already be higher when the attack starts.
Symptoms of Narrow Angle Glaucoma
Because of the rapid rise in pressure, acute angle closure is extremely painful. “My eye is going to explode,” is generally how most patients describe the sensation. The rapid rise in pressure also causes swelling in the cornea, which causes several distinct symptoms including:
- The appearance of rainbows around lights
- Nausea and/or vomiting
- Excruciating pain (which can be a sharp pain, or a feeling of extreme pressure that many patients say feels like their eye is going to explode)
- Extremely red sclera (the white part of the eye becomes very bloodshot)
- Blurred, foggy, or hazy vision (caused by the swelling of the cornea)
- Pupil dilation (which is typically the cause of the narrow angle attack)
If not treated promptly, permanent vision loss typically occurs within 24 to 48 hours. It's important to seek treatment from an ophthalmologist, not an emergency room, as soon as these symptoms occur. Doctors in an emergency room are not equipped to handle this condition, and waiting in an ER waiting area for diagnosis is a waste of precious time and can cause permanent vision loss.
The ER doctors will eventually send you to an ophthalmologist, but by then it may be too late to save the vision. Always see an ophthalmologist for any eye problem. It is best to avoid ERs completely, if at all possible, when it comes to the eye.
See an Eye Specialist Right Away
Always go directly to an ophthalmologist for ANY eye problem. When it comes to the eyes, it is best to avoid ERs completely because you could lose precious time. Depending on the situation, your vision may be at stake.
When Do Narrow Angle Attacks Occur?
Most attacks occur after a patient enters a dark room, such as a movie theater, and the eye fully dilates, which is usually in about 30 minutes. It can also occur when the eye is dilated artificially with drops such as Mydriacyl® or Cyclogyl®, which is why your technician should perform a slit lamp examination prior to instilling any dilating drops.
YAG Peripheral Iridotomy
Treatments for Narrow Angle Glaucoma
Unlike primary open angle, narrow angle glaucoma has only two treatments:
- Peripheral Iridotomy
- Peripheral Iridectomy
The most common of these is an Nd: YAG Peripheral Iridotomy, or YAG PI (it is sometimes also called an LPI or laser peripheral iridotomy).
This procedure involves using an Nd: YAG laser (neodymium—doped yttrium, aluminum, and garnet laser) to punch a small hole through the periphery of the iris.
This allows the aqueous to reach the trabecular meshwork. An argon laser can also be used for this purpose; however, the YAG laser is much more common.
The YAG PI is performed in the office after the patient has been given a drop of Pilocarpine. This drop is used to constrict the iris (make the pupil smaller) so that the doctor can find the thinnest part of the peripheral iris to laser.
Because the drop forces the pupil to constrict by stimulating the iris sphincter muscle, it can cause the ciliary muscles to spasm which can cause a headache. This is a very common side effect of the drop and can be alleviated with typical headache remedies such as ibuprofen or acetaminophen.
The procedure only takes about 10 minutes and can be painful. I have seen a number of patients flinch during the procedure when the hole is actually made despite the use of topical anesthetics. But the pain only lasts a few seconds.
It is also not unusual for the doctor to hit a blood vessel in the iris when performing an LPI. If this happens you may notice what looks like a red streak on the iris when you look in the mirror. The body will eventually reabsorb this blood within a week or so; it's nothing to be alarmed about.
Because the procedure is not invasive, antibiotic eye drops are not necessary. Most doctors will, however, prescribe a steroid eye drop such as Omnipred (generic name Prednisolone Acetate) to prevent any inflammation. Typically, only one eye is done at a time.
The peripheral iridectomy is a surgical procedure performed in a surgery center or hospital that involves cutting out a wedge-shaped section of the peripheral iris. This serves the same purpose as the YAG PI and is usually used after a failed peripheral iridotomy, as a last resort.
Surgical Peripheral Iridectomy
If you are treated for narrow angle glaucoma with a YAG PI it’s important to have regular eye exams to make sure the PI remains patent, or open. Although rare, there is the risk that the PI will become occluded by cellular debris or pigment from the iris. If this occurs, the patient will experience an acute angle closure. For this reason, many doctors put in an extra PI to act as a “safety valve.” If one becomes occluded, it’s highly unlikely both of them will become occluded at the same time.
Remember to see your eye doctor if you suspect you have an eye problem. Seeing the ophthalmologist as quickly as possible can mean the difference between permanent blindness and a lifetime of clear vision. Don’t hesitate to call your eye specialist if you think something is wrong. If they won’t see you within 48 hours, it’s time to find a new doctor.
© 2013 Melissa Flagg COA OSC