Narrow Angle Glaucoma: Causes, Symptoms, and Treatments
Glaucoma is a complicated disease that causes permanent loss of peripheral vision and eventually to permanent blindness. It affects the pressure in the eye, called intraocular pressure. This intraocular pressure, or IOP, give the eye stability and rigidity, allowing it to keep its globe-like shape. But in some people, this pressure is higher than it should be, and this is called glaucoma.
There are several different types of this disease:
- Primary open angle
- Combined mechanism
There are two different fluids in the eye: the aqueous and the vitreous humor. The vitreous is a thick, jelly-like fluid found in the posterior chamber, or back of the eye and keeps the retina attached to the back wall of the eye.
Aqueous is a gel-like, clear fluid found in the anterior chamber or front of the eye between the iris (the color part of the eye that creates the pupil) and the cornea (a clear, dome-shaped structure that focuses 70 percent of the light entering the eye). Glaucoma affects the way the aqueous fluid drains from the eye. It can also affect how much aqueous is produced by the ciliary body.
The Flow of Aqueous Humor
Aqueous is constantly replenished by the ciliary body which is 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 out through the trabecular meshwork, a spongy tissue that creates a system of drainage tubes known as Schlemm’s canal and then the fluid flows out of the eye.
Sometimes the ciliary body produces too much fluid, or the fluid doesn’t drain properly through the trabecular meshwork. This causes the pressure in the eye to rise. When the pressure in the eye goes up, it damages the optic nerve.
The Optic Nerve and Visual Pathway
The optic nerve is a bundle of retinal nerve fibers found in the back of the eye. It connects the neurons that make up the retina 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 a collection of neurons that culminate into a very long axon or tail at the back of the eye and exits the back of the eye socket and travels to the lateral geniculate body and then to the occipital lobe of the brain. The optic nerve is one of the longest nerve endings in the body.
The Damage High Eye Pressure Causes
Normally, the optic nerve is flush with the retina, meaning it has a flat head where it exits the eye. But when the pressure in the eye rises, it forces the optic nerve to “cup.” The high pressure literally pushes the nerve fibers into the axon of the nerve, like when you punch a pillow. But unlike the pillow, the nerve fibers don't bounce back. 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?
Narrow angle glaucoma is not as prevalent as its sister disease primary open angle glaucoma, 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 the space between the back of the cornea and the front of the iris (see drawing below). It is also where the trabecular meshwork is found.
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 provides attachment for the suspensory ligaments that attach to and focus the lens.
Anatomy of the Angle
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.
The Iris and the Angle
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. But in a patient with narrow angles, the iris can get stuck in the angle and block the aqueous from draining through the trabecular meshwork.
When the iris gets "stuck" in the angle, it causes an extremely rapid rise in pressure. It's like a clogged drain in your bathroom, the water rises quickly. Intraocular pressure readings in patients with narrow angles can reach upwards of 70mmhg. In contrast, normal pressure is between 10 and 20mmhg. The highest I’ve seen in 22 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 blocks the angle resulting in 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)
- 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 for a 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 you may have already lost precious vision permanently. Always see an ophthalmologist for any eye problem. It is best to avoid the ER completely 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. Regardless of the situation, your vision is 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 treat with the 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 OSC