Glaucoma is an eye disease that can cause blindness. If caught early, it can usually be controlled. But it often has no symptoms, so you need regular eye exams. Glaucoma usually begins when pressure builds up in the eye. This pressure can damage the optic nerve. The optic nerve sends messages to the brain so you can see. There are two main kinds of glaucoma: “open-angle” and “closed-angle.”
What is glaucoma?
A healthy optic nerve is necessary for good vision. Normal eye pressure readings range from 10-21 as a general guideline. Glaucoma is an eye disease that affects the optic nerve of the eye. The optic nerve is a bundle of more than one million nerve fibers and it connects the retina to the brain. It is the nerve fibers that can become damaged by glaucoma. Glaucoma can cause peripheral vision loss and/or blind spots that can be undetected by patients until it is significant and if untreated can eventually cause blindness. For this reason regular eye exams and specialized tests are recommended to catch changes early and ensure proper treatment.
In the front of the eye there is a space called the anterior chamber. This is the space between the cornea, the clear “windshield” on the surface of the eye, and the iris, the colored part of the eye behind the cornea. A clear fluid called aqueous humor flows continuously in and out of the chamber and nourishes nearby tissues. When the fluid reaches the angle where the cornea and iris meet, it flows through a spongy meshwork, like a drain, and leaves the eye. If the fluid does not circulate properly, it can build up inside the eye causing increased eye pressure that damages the nerve fibers.
How is glaucoma diagnosed?
There are several tests that may need to be performed, such as:
Tonometry – It is the measurement of the pressure inside the eye by using an instrument called a tonometer. Numbing drops are applied to the eyes for this test and the eye pressure is measured on the surface of the cornea.
Pachymetry – A pachymeter is a medical device that is uses an ultrasonic wave to measure the thickness of the cornea. This test is important because intraocular pressure may be underestimated in patients with a lower corneal thickness and overestimated in patients with a greater corneal thickness.
Visual field test – This test maps the field of vision by having a patient fixate on a steady light while responding to test lights of varying intensity in different areas of the test screen by pressing a button. Patients are able to blink normally but asked to stay fixed on the steady light and not to look around. The test is performed on one eye at a time.
Dilated eye exam – When the pupils are dilated, it allows the doctor to use a special magnifying lens to examine the optic nerve for symmetry, normal coloration, nerve fiber loss, and other signs of damage.
Is there more than one type of glaucoma?
There is more than one type of glaucoma and some conditions that are grouped in the glaucoma category.
Open Angle Glaucoma
The most common type of glaucoma is called open-angle glaucoma. In open-angle glaucoma, even though the drainage angle is open, the fluid passes too slowly through the meshwork drain. Since the fluid builds up, the pressure inside the eye rises to a level that can damage the optic nerve.
Not every person with increased eye pressure will develop glaucoma. Whether a patient develops glaucoma depends on the level of pressure the optic nerve can tolerate without being damaged. Some patients are diagnosed with ocular hypertension if they have higher ocular pressure readings but damage to the optic nerve has not occurred. These patients do not need treatment but they are monitored closely for changes that may occur.
Low-tension or normal-tension glaucoma
Some patients may have low or normal eye pressure readings but the amount of pressure in the eye is damaging the optic nerve. Lowering the eye pressure is necessary and the doctor will determine what target pressure will be the goal of treatment
Angle closure glaucoma
When the drainage angle is narrow it crowds the meshwork drain and fluid cannot drain and leave the eye. The iris blocking the angle results in an increase of eye pressure and causes damage to the optic nerve that cannot be reversed. THIS IS A MEDICAL EMERGENCY. Symptoms include severe eye pain, nausea, redness of the eye, and vision loss. A patient in this situation should go directly to their eye doctors’ office, nearest clinic or hospital. Usually prompt laser surgery and medication can clear the blockage, lower eye pressure, and protect vision.
When patients are examined, the anterior chamber angle is evaluated for depth. If a patient has narrow angles, a laser treatment can be performed to create a new drainage path for fluid to protect from an angle closure glaucoma attack. The laser is a painless procedure; however, patients need to be aware that eye drops will be used to constrict the pupil to allow the doctor to see the treatment area. These drops can cause a headache that ranges from mild to moderate. For this reason, we advise patients to make transportation arrangements for the laser appointment.
Pigmentary and pseudoexfoliation glaucoma
This occurs when pigment sheds off of the iris or extra material is produced and blocks the meshwork, slowing fluid drainage
Infants can be born with a defect in the angle that slows the normal drainage of fluid. Symptoms are usually obvious and conventional surgery is typically the suggested treatment.
How is glaucoma treated?
Treatment for early stage glaucoma can delay progression of the disease and that is why early diagnosis is very important. Glaucoma treatments include:
Medication – eye drops or pills are the most common early treatment for glaucoma. Some medicines cause the eye to make less fluid, while others lower pressure by helping fluid drain from the eye.
Laser treatment – this treatment helps fluid drain out of the eye.
Conventional surgery – a new opening is made for fluid to leave the eye by removing a small piece of tissue and a new channel is created allowing fluid to drain between the eye tissue layers. Surgery is often done after medication and/or laser treatment have failed to control pressure.