What is glaucoma?
Glaucoma is a condition in which the normal fluid pressure inside the eyes (intraocular pressure, or IOP) slowly rises as a result of the fluid aqueous humor – which normally flows in and out of the eye – not being able to drain properly. Instead, the fluid collects and causes pressure damage to the optic nerve (a bundle of more than 1 million nerve fibers that connects the retina with the brain) and loss of vision.
What causes glaucoma?
While physicians used to think that high intraocular pressure (also known as ocular hypertension) was the main cause of optic nerve damage in glaucoma, it is now known that even persons with normal IOP can experience vision loss from glaucoma. Thus, the causes are still unknown.
What are the different types of glaucoma?
Open-angle glaucomaWith this most common type of glaucoma, the fluid that normally flows through the pupil into the anterior chamber of the eye cannot get through the filtration area to the drainage canals, causing a build-up of pressure in the eye. Nearly 3 million Americans – half of whom do not know they have the disease – are affected by glaucoma each year.
Low-tension or normal-tension glaucomaWhile normal intraocular pressure ranges between 12 to 21 mm Hg, an individual may have glaucoma even if the pressure is within this range. This type of glaucoma presents optic nerve damage and narrowed side vision.
Angle-closure glaucomaIn angle-closure glaucoma, the fluid at the front of the eye cannot reach the angle and leave the eye, because the angle becomes blocked by part of the iris. This results in a sudden increase in pressure and is generally a medical emergency, requiring immediate treatment to improve the flow of fluid.
Childhood glaucomaChildhood glaucoma is a rare form of glaucoma that often develops in infancy, early childhood, or adolescence. Prompt medical treatment is important in preventing blindness.
Congenital glaucomaCongenital glaucoma, a type of childhood glaucoma, occurs in children born with defects in the angle of the eye that slow the normal drainage of fluid. Prompt medical treatment is important in preventing blindness.
Primary glaucomaBoth open-angle and angle-closure glaucoma can be classified as primary or secondary. Primary glaucoma cannot be contributed to any known cause or risk factor.
Secondary glaucomaBoth open-angle and angle-closure glaucoma can be classified as primary or secondary. Secondary glaucoma develops as a complication of another medical condition or injury. In rare cases, secondary glaucoma is a complication following another type of eye surgery.
What are the symptoms of glaucoma?
Most people who have glaucoma do not notice any symptoms until they begin to lose some vision. As optic nerve fibers are damaged by glaucoma, small blind spots may begin to develop, usually in the side or peripheral vision. Many people do not notice the blind spots until significant optic nerve damage has already occurred. If the entire nerve is destroyed, blindness results.
One type of glaucoma, acute angle-closure glaucoma, does produce noticeable symptoms because there is a rapid build-up of pressure in the eye. The following are the most common symptoms of this type of glaucoma. However, each individual may experience symptoms differently. Symptoms may include:
Blurred or narrowed field of vision
Severe pain in the eye(s)
Haloes (which may appear as rainbows) around lights
The symptoms of acute angle-closure glaucoma may resemble other eye conditions. Consult a physician for diagnosis immediately if you notice symptoms, as this type of glaucoma is considered a medical emergency requiring prompt medical attention to prevent blindness.
How is glaucoma diagnosed?
In addition to a complete medical history and eye examination, your eye care professional may perform the following tests to diagnose glaucoma:
Visual acuity test – the common eye chart test (see above), which measures vision ability at various distances.
Pupil dilation – the pupil is widened with eye drops to allow a close-up examination of the eye's retina.
Visual field – a test to measure a person's side (peripheral) vision. Lost peripheral vision may be an indication of glaucoma.
Tonometry – a standard test to determine the fluid pressure inside the eye.