Definition of Narrow Angle Glaucoma
Narrow angle glaucoma is a group of glaucomas in which the intraocular pressure (eye pressure) is raised as a result of obstruction of the drainage pathway (trabecular meshwork). The obstruction may be mechanical with no evident pathology or it may be because of scarring in the angle where the trabecular meshwork resides.
Narrow angle glaucoma is also called angle closure glaucoma.
How Narrow Angle Glaucoma Affects Vision
Angle is a space in the eye formed between the cornea in the front and iris on the back. The fluid (aqueous) which is formed in the eye constantly drains into trabecular meshwork situated in the angle. Any partial or complete obstruction of the angle compromises the drainage of aqueous. This gives rise to accumulation of the fluid and high eye pressure consequently.
High pressure causes damage to delicate structures of the eye especially the nerve fibers. All the nerve fibers join to form optic nerve which transmits visual information to the brain. Damage to the optic nerve gradually leads to loss of peripheral vision first and then advances to central vision in the late stages.
Angle closure glaucoma is common among women. Other risk factors associated with narrow angle glaucoma are Chinese ethnicity, age more than 60 years, family history (it is hereditary), small eyes, some medications (anticholinergic and adrenergic) and emotional stress.
Narrow Angle Glaucoma Symptoms
- Acute angle closure glaucoma: The patient may have sudden pain, clouded vision, intolerance to bright light, colored halos around lights, headache, nausea and vomiting.
- Subacute angle closure glaucoma: Headache may occur or the person may be asymptomatic.
- Chronic angle closure glaucoma: The patient is largely without any symptoms.
Narrow Angle Glaucoma is more common that formerly thought. The loss of vision is more severe than what is caused by open angle glaucoma. Early diagnosis and treatment (with medication, laser and/or surgery) of narrow angle glaucoma is the key to prevent blindness and related morbidity.
More Details about Narrow Angle Glaucoma
The anterior chamber of the eye is filled with a fluid called aqueous humor. This substance constantly is produced from the blood in a structure called the ciliary body. It circulates first through the posterior chamber of the eye. This is the small space directly behind the iris but in front of the lens. It then enters the anterior chamber through the pupil and ultimately is returned to the bloodstream through the trabecular meshwork and Schlemm’s canal.
The main problem in primary glaucoma is that intraocular pressure increases because too much aqueous humor has accumulated in the anterior and posterior chambers of the eye.
Narrow angle glaucoma also is known by other names, such as primary angle closure glaucoma (the formal medical term) and angle recession glaucoma. In narrow angle glaucoma, the iridocorneal angle narrows and interferes with the normal circulation of aqueous humor. This increases intraocular pressure and, if left untreated, causes ongoing damage to the optic nerve.
When iridocorneal angles are within normal range, several structures can be seen in the anterior chamber through gonioscopy.
Who Is at Risk for Narrow Angle Glaucoma?
Although anyone can be diagnosed with narrow angle glaucoma, there are some characteristics that make people more susceptible than others. Major risk factors for narrow angle glaucoma include:
– Age: Angle recession glaucoma usually occurs in people that are over 40 years of age.
– Gender: Women more often are diagnosed with angle recession glaucoma than men.
– Ethnicity: People of Asian ethnicity are more frequently diagnosed with angle recession glaucoma. Additionally, I often see angle recession glaucoma in Latin American indigenous and mestizo people, whose eyes tend to be small.
How Many People Get Narrow Angle Glaucoma?
For every 1,000 people, approximately 50 of them will have narrow iridocorneal angles. But only 10% of those 50 (or 5 individuals out of 1000), will have iridocorneal angles that are so narrow that it results in angle closure glaucoma.
What Are the Symptoms of Narrow Angle Glaucoma?
It depends on whether the angle closure glaucoma is chronic or acute. In chronic angle closure glaucoma, people often do not perceive any symptoms at all. In some cases, they may notice redness of the eye, discomfort, blurred vision, or a headache, the intensity of which often is reduced with sleep. If you have any of these symptoms, you should visit an ophthalmologist.
An examination by your ophthalmologist may also reveal the following potential indicators of angle closure glaucoma.
– Narrow iridocorneal angles.
– Shallow anterior chamber.
– Hypermetropia (farsightedness).
– Small corneal diameter (normal diameter is 12 mm).
– Dense eye lens.
– Eye lens that is more anterior than normal.
Although chronic narrow angle glaucoma often does not present with any symptoms noticeable to patients, particularly in its early stages, it is important that you understand that angle closure in the anterior chamber of the eye is a serious problem that must be treated as soon as possible.
Acute Primary Angle Closure Glaucoma
Unlike chronic angle closure glaucoma and many other types of glaucoma, acute angle closure glaucoma presents with recognizable symptoms that often are very intense. The most common among these is severe pain that is constant and deep. It may occur suddenly and patients often describe it as the worst pain that they have ever experienced.
The quality of the pain is constant, meaning that it does not improve spontaneously, and it is deep because it can be felt around the entire eye. In fact, patients have reported pain so profound that it radiates into the middle of the face on the affected side and is accompanied by nausea and vomiting.
Another common symptom is decreased visual acuity. Blurring often occurs and vision loss can be significant. If the time elapsed since the start of the crisis has been short and the intensity of the pain not too extreme, decreases in visual acuity can improve in the next few days under treatment. However, if the time elapsed since the start of the crisis is significant, vision loss may be irreversible.
Seeing color halos around lights is another symptom that can accompany primary angle closure glaucoma, both in its acute and chronic forms. Other reported symptoms include excessive production of tears (lacrimation) and excess sensitivity to light (photophobia).
Mechanism of Narrow Angle Glaucoma
The most common mechanism of narrow angle glaucoma is something called a pupillary block. This happens when there is contact between the lens of the eye and the iris, causing the pupil to be fixed in one position (medium diameter) and it cannot open or close in order to adjust to light. Once this contact occurs, aqueous humor is unable to pass out of the anterior chamber through the trabecular meshwork.
In narrow angle glaucoma, the anterior chamber is more shallow and there can be contact between the iris and lens. Consequently, aqueous humor accumulates behind the iris and pushes it forward. This significantly narrows the drainage angle and obstructs the trabecular meshwork (the place of drainage). The inability of aqueous humor to exit the eye creates elevations in intraocular pressure, which can lead to optic nerve damage.
The lenses of young people are very flexible and therefore pupillary block does not normally occur in people under 40 years of age. But as we grow older, the lens of the eye becomes more rigid and loses some of its accommodation capability. Accommodation refers to the capacity of the lens to adjust in order to see objects at different distances, both close and far away. This is the reason why people above age 40 more often need corrective lenses.
In eyes that are predisposed to angle closure glaucoma, there is an increase in the thickness of the lens and advancement. This means that the lens moves forward in the anterior chamber, so that there is closer contact and spread between the iris and lens, resulting in increased difficulty of the passage of aqueous humor.
Closure of the anterior chamber angle is a serious event and needs to be addressed immediately. In addition to redness, the cornea may look cloudy or show evidence of edema (bulging due to fluid retention). Abnormalities of the cornea can lead to blurred vision, photophobia, and excessive production of tears.
The most dangerous situation for the occurrence of acute angle closure glaucoma is when the pupil is at a medium diameter. This means that it is not really open wide or closed to a small point. Some situations in daily life in which this happens is when we are in a semi-dark room or if we are in a stressful situation.