Glaucoma Glossary

For your reference, we have assembled an alphabetical list of terms and phrases relating to glaucoma and its diagnosis and treatment. These are words that you may encounter on our website, in our educational materials, and at your doctor’s office.

Angle-Closure Glaucoma or Primary Angle-Closure Glaucoma: A type of glaucoma in which the angle is closed in many or most areas, causing increased eye pressure, which leads to optic nerve damage, and possible vision loss. This rise in eye pressure may occur suddenly (an acute attack of angle closure) or gradually.

Aqueous Humor: The fluid filling the front part of the eye.

Bleb: A bubble in the eye tissue that lays over the new drainage opening created during surgery.

Central Vision: What is seen when you look straight ahead or when you read.

Ciliary Body: Tissues located around the lens of the eye that supply fluid to nourish the eye.

Congenital Glaucoma: A rare form of glaucoma that occurs in babies and young children. This condition can be inherited. It is usually the result of incorrect or incomplete development of the eye’s drainage canals during the prenatal period.

Conjunctiva: A thin, clear membrane that lines the inner surface of the eyelids and the outer surface of the eyeball, except for the cornea.

Cornea: The clear part of the eye located in front of the iris. Part of the eye’s protective covering.

Drainage Canals: Small openings around the outer edge of the iris. These canals provide the final pathway for fluid to leave the inside of the eye. Sometimes referred to as the trabecular meshwork or Schlemm’s canal.

Glaucoma Suspect: An adult who has one of the following findings in at least 1 eye: an optic nerve or nerve fiber layer defect suggestive of glaucoma, a visual field abnormality consistent with glaucoma, or an elevated IOP greater than 21 mm Hg.

Gonioscopy: In this diagnostic procedure a contact lens that contains a mirror is gently placed on the eye. The mirror lets the doctor look sideways into the eye to check whether the angle where the iris meets the cornea is open or closed. This helps the doctor decide whether Open-Angle or Angle-Closure Glaucoma is present.

Intraocular Pressure (IOP): The inner pressure of the eye. Normal intraocular pressure usually ranges from 12-22 mm Hg, although people with relatively low pressures can still have glaucoma (see Normal-Tension Glaucoma).

Iris: The colored part of the eye that can expand or contract to allow just the right amount of light to enter the eye.

Laser Surgery: A type of surgery in which a tiny beam of light energy is used to modify tissues in the eye. There are three common forms of laser surgery for glaucoma.

Laser Peripheral Iridotomy: Creates a new drainage hole in the iris, allowing the iris to fall away from the outflow channel so fluid can drain out of the eye.

Laser Trabeculoplasty: In this procedure, the laser is aimed toward the normal drainage channels of the eye, in an attempt to open those channels so fluid can leave the eye more efficiently.

Laser Cyclophotocoagulation: This laser procedure is usually used in people who have severe glaucoma and are not responding to standard glaucoma surgery. The laser is used to partially destroy the tissues that make the fluid in the eye.

Lens: Located behind the iris, this helps light focus onto the retina.

Microsurgery: Surgery performed under a microscope.

mm Hg: An abbreviation for “millimeters of mercury,” which is a scale for recording intraocular pressure.

Normal-Tension Glaucoma: Also called low-tension glaucoma. A type of glaucoma in which intraocular pressure stays within the normal range (12-22 mm Hg), but damage still occurs to the optic nerve and visual fields.

Ocular Hypertensive: When the pressure inside the eye (intraocular pressure or IOP) is higher than normal, but the optic nerve looks normal and there are no signs of vision loss. People with ocular hypertension may be considered Glaucoma Suspects.

Open-Angle Glaucoma or Primary Open-Angle Glaucoma: The most common form of glaucoma in the western world. This form of glaucoma usually develops very slowly as the eye’s drainage canals gradually become clogged. There are no early warning signs for Open-Angle Glaucoma, which is why it is often called the “sneak thief of sight.”

Ophthalmoscopy: An exam used to look at the inside of the eye, especially the optic nerve.

Optical Coherence Tomography (OCT): Measures the reflection of infrared light off eye tissues to produce an image of the retina and optic nerve and to measure the thickness of the retinal nerve fiber layer.

Optic Nerve: The nerve in the back of the eye that carries visual images to the brain.

Perimetry: Also known as the visual field test. A test that produces a map of the complete visual field, to check whether there is damage to any area of vision.

Peripheral Vision: The top, sides, and bottom areas of vision. These are usually the first areas of vision affected by glaucoma.

Pupil: The opening that controls how much light enters the inner part of the eye.

Retina: The retina converts the light images into electrical signals, and the retina’s nerve cells and fibers carry these signals to the brain through the optic nerve.

Sclera: The tough, white, protective outer covering of the eye.

Secondary Glaucoma: A form of glaucoma that can occur as the result of an eye injury or inflammation. Includes forms such as Pigmentary Glaucoma and steroid-induced glaucoma.

Tonometry: The use of a device to measure the pressure in the eye.

Trabecular Meshwork: The formal name of the mesh-like drainage canals surrounding the iris.