The most common form of glaucoma (primary open-angle glaucoma) is usually not noticed until there are losses of peripheral vision. The condition may go unnoticed because the unaffected eye can “fill in” for the other one. Also, people tend to pay more attention to the detailed central part of their vision, which is not affected until later stages in glaucoma’s progression. Finally, many people assume that the loss of peripheral vision is a normal part of aging, which it is not.

Everyone older than 40 years should have regular general eye examinations at least every 2 years. Routine general examinations check for signs of glaucoma and other eye diseases that can cause vision loss or blindness. Several tests are particularly important for diagnosing glaucoma.

Measuring intraocular pressure, or tonometry: Measuring pressure inside the eye is usually done with the “blue light test,” which is formally known as Goldmann applanation tonometry. It is the most accurate method of measuring pressure, and it is painless. It involves administering anesthetic (numbing) eyedrops to allow the instrument to touch the surface of the eye.

A physician prepares to measure the internal pressure of a person’s eye. (Photo courtesy Jacqueline Griffiths, MD, Reston, VA)

Noncontact tonometry is another method used to measure internal eye pressure. It uses a measuring instrument that blows a puff of air at the eye (so-called puff test). It is painless and does not require an anesthetic agent. Noncontact tonometry is generally considered to be less accurate than the Goldmann method, and it is often used in glaucoma screening.

Measuring the thickness of the cornea, or pachymetry: The addition of pachymetry to the tests normally used to diagnose glaucoma is relatively recent. The thickness of the cornea, the clear outer part of the eye, affects the accuracy of methods used to measure intraocular pressure.

A technician uses an ultrasound instrument to measure the thickness of the cornea, the clear surface of the eye. The eye has been anesthetized, and the patient has no discomfort from the surface contact of the probe. (Photo courtesy Jacqueline Griffiths, MD, Reston, VA)

Examining the optic nerve with an ophthalmoscope: An ophthalmoscope, contact lens, or indirect lens is used to examine the inside of the eye, especially the optic nerve. In glaucoma, tissue from the center of the optic nerve is lost. This area of nerve loss is called the cup. In glaucoma, the cup becomes larger and larger. The procedure takes place in a darkened room, is painless, and requires no anesthetic drops. The examination allows the doctor to see the color and shape of the optic nerve. This is felt to be the most critical step in examining for glaucoma, and the one requiring the greatest skill and expertise.

Mapping the field of peripheral vision, or perimetry: Perimetry is used to map depressed or less sensitive areas of a person’s field of vision. Mapping the field can help establish the presence of optic nerve damage, and repeated examinations can document damage progression to see whether treatment needs to be altered.

Today, during automated perimetry, a person looks into a bowl-shaped surface and stares at a central target point. A computer-driven program flashes small lights at different locations within the bowl’s surface, and the person being tested presses a button when he or she sees the small lights in their periphery.

A patient looks into a dome-shaped automated perimeter that will map weak or blank spots in his field of vision. (Photo courtesy Haag-Streit INTERZEAG, Switzerland)

Examining the angle where excess fluid normally drains from the eye, or gonioscopy: This is a painless eye examination of the angle where the iris meets the cornea to grade the amount of closure of the angle, which indicates whether open-angle or closed-angle glaucoma is present. The test uses a special contact lens, the most common of which is the gonioscopy mirror. The lens is placed on the surface of the eye after the eye has been anesthetized.

Optic nerve and retinal imaging: This is a very new method of objectively measuring the shape and thickness of the optic nerve and surrounding retinal tissue by means of specialized, low intensity laser light. The laser has no effect on the eye, and is not harmful. This is similar to an MRI or CT scan, however no radiation is involved. The thickness of the nerve and retina can be determined (in glaucoma, the optic nerve and retina become thinner), and followed over time to detect changes.

All the tests described above are painless and can be performed in a single visit. It is important to have your eyes examined regularly.