What is Glaucoma?
Glaucoma is a set of diseases characterized by progressive deterioration of the optic nerve. Glaucomatous damage to the optic nerve, a bundle of more than 1 million nerve fibres that transmits visual information from the eye to the brain, is often associated with increased pressure inside the eye. Increased eye pressure, or intraocular pressure, can occur when fluid inside the front part of the eye is not circulating properly. This fluid, called aqueous humor, normally flows out of the eye through a channel called the trabecular meshwork. If this meshwork becomes obstructed, the aqueous fluid builds up causing increased pressure and ultimately glaucoma if left untreated. Continued damage to the optic nerve can lead to permanent loss of vision. Glaucoma can be inherited, and the incidence of glaucoma increases with age. Glaucoma usually occurs in both eyes, although the severity of the disease may differ between the eyes.
Who is at risk for Glaucoma?
You are at an increased risk of glaucoma if you.
- Have a family history of glaucoma
- Are of African-American, Hispanic, Inuit, or Scandinavian descent
- Are over age 40
- Have a high prescription
- Have diabetes
- Take steroid medications, such as prednisone
- Have experienced trauma to the eye
Will I develop Glaucoma if I have increased eye pressure?
The presence of high intraocular pressure can indicate an increased risk for glaucoma, but not necessarily that the disease is present. Not every individual with glaucoma has increased eye pressure, and some optic nerves are able to withstand higher intraocular pressure than others without sustaining damage. For example, glaucoma can occur in the presence of normal and even low intraocular pressure, and this is called low-tension or normal-tension glaucoma.
How Many Types of Glaucoma are there?
There are a few main types of glaucoma:
- Open-angle Glaucoma: This is the most common type of glaucoma. Although the structures of the eye appear normal, the aqueous humor does not flow properly through the trabecular meshwork, causing a rise in the intraocular pressure.
- Closed-angle Glaucoma: In this type of glaucoma, the angle where the cornea and iris meet is too narrow and mechanically blocked by the iris, causing poor drainage of the aqueous humor. Closed-angle glaucoma can be either chronic or acute. In acute closed-angle glaucoma, the intraocular pressure rises rapidly and can cause a red eye, extreme discomfort, nausea, headache and decreased vision.
- Congenital Glaucoma: Babies can be born with a defect that inhibits the normal drainage of fluid in the eye. These babies often experience symptoms that are noticeable, such as excessive tearing, sensitivity to light, and cloudy eyes.
- Normal-tension glaucoma: In this type of glaucoma, glaucomatous damage occurs to the optic nerve in the absence of intraocular pressure that exceeds the normal range.
Glaucoma can also be caused by blunt force or chemical trauma to the eye, severe eye infection and inflammation, obstruction of intraocular blood vessels, and more rarely, surgery to correct another ocular condition.
What are the Symptoms of Glaucoma?
Glaucoma often does not present with symptoms in the early stages of the disease. Glaucomatous vision loss, usually gradual the loss of peripheral or side vision, commonly goes unnoticed until late in the disease and pain is rarely experienced. If left untreated, glaucoma can cause complete loss of peripheral vision, resulting in tunnel vision. In some cases, the intraocular pressure can rise to extreme levels, causing a red eye, intense pain, headaches, nausea, and blurred vision. Glaucoma can occur in one eye at a time or in both eyes simultaneously.
How is Glaucoma Detected?
The following tests are used for Glaucoma detection:
- Comprehensive eye exam – which includes:
- Visual acuity test – This test uses a standard eye chart to measure how well an individual can see at a variety of distances.
- Tonometry – During this test, an instrument is used to measure the pressure inside the eye. Numbing drops are usually applied prior to taking the test. Click here to learn more about non-contact tonometry.
- Pachymetry – The use of an ultrasonic wave instrument allows your optometrist to measure the thickness of the cornea. Numbing drops in the eyes are instilled beforehand.
- Dilated eye exam – Eye drops are used to widen or dilate the pupils for proper examination. A special magnifying lens is then used to examine the retina and optic nerve for signs of damage or disease. Your vision might be blurry for a few hours following the exam.
- Visual field test – this automated test is used to determine how well a person’s central and peripheral vision is functioning. This test maps the visual fields of each eye and allows your optometrist to determine if there has been a loss of peripheral vision.
- Optical coherence tomography – This is a non-invasive test that measures the thickness of the optic nerve and its fibres. In glaucoma, the nerve fiber layer (the fibers that make up the optic nerve) can thin as the disease progresses. Click here to learn more about OCT.
- Digital retinal photography – A photograph of the optic nerve can serve as a baseline to enable your optometrist to monitor changes over time. Click here to learn more about digital retinal photography.
How is Glaucoma Treated?
Immediate treatment can slow the progression of early stage open-angle glaucoma, hence the importance of early detection. One of the most common early measures for treatment of glaucoma is medicated eye drops. These drops work by either reducing the production of aqueous humor, or increasing its outflow, and may need to be taken several times per day. These drops may interact with other medications you are taking, so be sure to provide your optometrist with a list of your updated medications. If effective, the remaining vision might be preserved. If these drops are not effective in controlling the intraocular pressure, surgical options may be considered.