What are the Different Types of Glaucoma Screening Tests?

C. K. Lanz

Different types of glaucoma screening tests include the commonly performed air puff test that measures intraocular pressure as well as a test for optic nerve damage and a visual field test. Doctors also often measure the thickness of the cornea, perform a gonioscopy and use optic nerve imaging. Most of the available glaucoma screening tests are painless, harmless and quickly administered to patients in the optometrist’s office, often as part of a routine annual eye exam.

Glaucoma tests are typically performed during eye exams.
Glaucoma tests are typically performed during eye exams.

The air puff test is the most common of the glaucoma screening tests and is usually administered during routine eye exams. The patient looks into a device that resembles binoculars and focuses on a small light. The device releases a controlled burst of air that hits the surface of the eyes and measures the eyes’ resistance to air pressure. This allows optometrists to measure how much pressure is inside a patient’s eyes.

Glaucoma causes a person to lose vision gradually.
Glaucoma causes a person to lose vision gradually.

Eye pressure can also be measured with an applanation tonometer, in which a patient’s eyes are anesthetized, and the optometrist touches the eye’s surface to determine how much pressure is needed to flatten the cornea. Doctors also use the electronic indentation method. This procedure accomplishes the same task with a digital instrument similar to a pen that is also used to press on the surface of the eye.

Patients with thick corneas may have eye pressure readings that are higher than normal even though they do not have glaucoma. A thick cornea can also mask glaucoma. Glaucoma screening tests such as pachymetry use an ultrasonic wave instrument to measure the thickness of a patient’s cornea. Determining the thickness of the corneas can help make eye pressure evaluation more accurate.

Ophthalmoscopy is a glaucoma screening test that begins with pupil dilation. Once the pupil is sufficiently enlarged, the doctor can look inside the eyes and examine the back of the eyeballs. Any optic nerve damage typically will be visible. A visual field test can also help determine if a patient is suffering from glaucoma by evaluating his or her peripheral vision.

Additional glaucoma screening tests include gonioscopy and optic nerve imaging. Gonioscopy involves examining the front part of the eyeball to see if the iris is closer to the back of the cornea than it should be. If it is, closed angle glaucoma is a likely diagnosis. Optic nerve imaging can be any one of four imaging methods used to document changes to the optic nerve that occur over time: scanning laser polarimetry, confocal scanning laser ophthalmoscopy, optical coherence tomography and disc photography.

Glaucoma is not just one eye condition but a group of related diseases caused by optic nerve damage. This optic nerve damage is typically caused by unusually high pressure inside the eye. The vision loss caused by glaucoma can be so gradual that patients rarely notice this symptom until the disease is advanced. Glaucoma screening tests are crucial because an early diagnosis and intervention can significantly reduce optic nerve damage and even prevent vision loss.

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