Glaucoma affects over 70 million people worldwide and is the leading cause of irreversible blindness. Open-angle glaucoma is the most common type of glaucoma — an eye disease that damages your optic nerve and causes reduced vision and even blindness. Closed-angle (or angle-closure) glaucoma accounts for less than 20 percent of glaucoma cases in the United States. In most cases, closed-angle glaucoma is more severe than open-angle glaucoma.
Both diseases involve changes in the eye that obstruct proper drainage of fluid. As a result, a buildup of pressure occurs inside the eye, which progressively damages the optic nerve. While glaucoma does not have a cure, early diagnosis and treatment can help manage and prevent glaucoma from progressing to vision damage.
The difference between open- and closed-angle glaucoma
The front part of your eye, between the lens and cornea, is filled with a fluid called the aqueous humor. The aqueous humor plays a role in maintaining the spherical shape of the eye and nourishing the eye’s internal structures. New aqueous humor is continually being produced and then drained out of the eye. To sustain proper pressure inside the eye, there must be a balance between the amount of liquid produced and the amount drained out.
Glaucoma causes damage to the structures that let the aqueous humor drain out. Two outlets allow the aqueous humor to drain, including the:
- Trabecular meshwork
- Uveoscleral outflow
Both of these structures are near the front of the eye. The difference between open-angle glaucoma and closed-angle glaucoma depends on which of the two drainage pathways is damaged.
- In open-angle glaucoma, the trabecular meshwork provides elevated resistance to fluid outflow, which causes the pressure to build up inside the eye.
- In closed-angle glaucoma, both the trabecular meshwork and the uveoscleral outflow experience blockage. Typically, a damaged iris (colored part of the eye) blocking the outlet is the cause.
The blockage of either of these important outlets leads to an increase in pressure inside the eye. The fluid pressure inside the eye is called intraocular pressure (IOP).
Differences in angle
The word “angle” in open- and closed-angle glaucoma refers to the angle that the iris makes with the cornea. The iris is in the right position in open-angle glaucoma, and the uveoscleral outflow canals are clear. However, the trabecular meshwork is not draining properly. On the other, the iris is squeezed against the cornea in closed-angle glaucoma, which blocks the trabecular meshwork and the uveoscleral drains.
Symptoms of open- and closed-angle glaucoma
Glaucoma in its early stages usually does not cause any symptoms. Damage to your vision can arise before you become aware of it. When symptoms appear, they often include:
- Poorer vision
- Loss of peripheral vision
- Swollen cornea
- Redness in the white of the eye
- Pupil dilation to a medium size that does not change with increasing or decreasing light
- Nausea and vomiting
These symptoms primarily manifest in acute cases of closed-angle glaucoma, but they can also appear in open-angle glaucoma. Additional symptoms that may only develop in closed-angle glaucoma are:
- Severe eye pain
- Seeing bright halos appearing around objects
It is not fully understood why some people get glaucoma while others do not. Glaucoma has a link to genetics, although these account for less than 10 percent of all cases. Glaucoma may also be a result of trauma to the eye. This is referred to as secondary glaucoma.
The risk factors of open-angle glaucoma include:
- Increasing age
- Family history of glaucoma
- African ancestry
- Low blood pressure, but high blood pressure carries other dangers
- Use of topical corticosteroids
- Having a tumor in the eye
- High IOP
The risk factors of closed-angle glaucoma are:
- Older age
- Being female
- Family history of glaucoma
- Being Asian
A high IOP can accompany glaucoma, but it is not a sure sign. According to a 2015 study, 25 to 50 percent of men and women with glaucoma have normal IOP.
To diagnose open-angle glaucoma or close-angle glaucoma, you need to undergo a comprehensive eye exam with your eyes dilated. Some of the tests a glaucoma specialist or optometrist will use are:
- Visual acuity test with an eye chart.
- Visual field test to examine your peripheral vision. and help confirm the diagnosis.
- A dilated eye exam may be the most important test. An optometrist will use drops to dilate (open up) your pupils to see into the retina and optic nerve at the back of the eye. The procedure is painless. You may experience blurred close-up vision and sensitivity to lights for a few hours.
- Tonometry. An optometrist will apply numbing drops to the eyes and use a specialized machine to measure the pressure near the cornea. This procedure is painless, but you may feel a very slight sting when the doctor applies the drops.
- Pachymetry. After an optometrist applies numbing drops to the eyes, they will use an ultrasonic wave instrument to gauge the thickness of your cornea.
Treatment for open-angle glaucoma and closed-angle glaucoma
Reducing the fluid pressure inside your eye is the one proven method for treating glaucoma. The treatment begins with hypotensive drops to help reduce the pressure.
Next, a doctor will use the pressure levels from your tonometry exam to determine a target pressure to best address your glaucoma. Eye doctors will aim for a 20 to 50 percent decrease in pressure as a first target. They will lower the target if your vision continues to worsen, or if the doctor notices changes in the optic nerve.
The first-line of pressure-lowering drugs is prostaglandin analogs, which are fatty acids found in almost every tissue. They can improve the flow of blood and bodily fluids and enhance drainage of aqueous humor through the uveoscleral outlet. You need to take this drug once at night.
Other drugs that a doctor may use as a second line of defense include:
- Alpha agonists
- Carbonic anhydrase inhibitors
- Cholinergic agonists
Other treatments are:
- Selective laser trabeculoplasty (SLT). This procedure involves a laser aimed at the trabecular meshwork to address the drainage issue and lower eye pressure. On average, SLT can lower pressure by up to 30 percent. It is successful in about 80 percent of patients. SLT is replacing eyedrops in some cases. The effect can last from three to five years, and you may repeat the procedure in the future.
- Trabeculectomy. This is a complex type of surgery that involves creating a new drainage pathway for the aqueous humor.
Know your options
If you are experiencing symptoms of glaucoma or have not seen an eye doctor in years, now is the time to act. Glaucoma can cause permanent blindness without immediate treatment. Do not let that happen to you. Call us now at 623-474-3937 (EYES) to schedule an eye exam. We are a leading provider of exemplary retinal medical and surgical care for the eyes of clients in Sun City and the surrounding areas.