Glaucoma is not a single disease but a group of eye disorders that progressively damage the optic nerve, which transmits visual information from the eye to the brain. This damage is frequently associated with elevated pressure inside the eye, known as intraocular pressure. Because the disease often causes no noticeable symptoms until significant and irreversible vision loss has occurred, testing is the only way to catch the condition early. A comprehensive glaucoma test involves several specialized measurements designed to detect the disease’s signs before they lead to permanent blindness. This process evaluates both the structural health of the optic nerve and the functional quality of a person’s vision.
Who Should Get Tested
Regular glaucoma screening identifies individuals who face a higher probability of developing the condition. The risk of primary open-angle glaucoma, the most common form, rises significantly after age 40. Certain ethnicities, including African American, Hispanic/Latino, and Asian populations, have a genetically increased predisposition to various forms of glaucoma. African Americans, for example, are up to four times more likely to develop the disease, often at an earlier age and with more aggressive progression.
A family history of glaucoma in a parent or sibling also substantially increases a person’s lifetime risk. Underlying health conditions, such as diabetes and high blood pressure, are additional factors that necessitate closer monitoring. For individuals aged 40 to 54 with no known risk factors, a comprehensive eye exam every one to three years is recommended. Those aged 65 and older, or those with known risk factors, generally need testing more frequently, sometimes every six to twelve months.
Measuring Intraocular Pressure
Measuring the pressure within the eye, tonometry, is a routine part of screening. Intraocular pressure (IOP) measures the fluid balance inside the eye, with a healthy range typically between 10 and 21 millimeters of mercury (mmHg). One common screening method is non-contact tonometry, often called the “air puff” test. This quick procedure uses a controlled burst of air to slightly flatten the cornea, calculating the pressure based on the cornea’s resistance.
If screening suggests high pressure, a more accurate method, such as Goldmann applanation tonometry, is performed. This technique involves applying numbing eye drops to the eye’s surface. A small, flat-tipped instrument then gently touches and flattens a small area of the cornea to directly measure the required force, providing a precise pressure reading. This contact method is considered the standard for IOP measurement.
A supplementary test is pachymetry, which measures the thickness of the cornea. Corneal thickness affects the accuracy of the tonometry reading. A thinner cornea can cause the tonometer to underestimate the true IOP, while a thicker cornea can lead to a falsely high reading. Pachymetry, which uses either an ultrasound probe or a non-contact optical device, ensures the pressure measurement is correctly interpreted.
Evaluating the Optic Nerve and Field of Vision
Beyond measuring pressure, a comprehensive test assesses the structure and function of the visual system. The structural health of the optic nerve is checked through a dilated eye exam, often called ophthalmoscopy. Dilating drops widen the pupil, allowing the doctor to use a magnifying tool and light to view the nerve at the back of the eye. The doctor looks for physical signs of damage, such as an enlarged cup-to-disc ratio or a pale appearance, which suggest nerve fibers have been destroyed.
The second assessment is the visual field test, or perimetry, which evaluates the functional impact of any damage by mapping the extent of peripheral vision. The patient is seated in front of a bowl-shaped instrument, looking directly at a central fixation point. Small, momentary lights of varying intensity are flashed in different locations across the field of vision. The patient presses a button each time they detect a light, generating a map of their sight and revealing any blind spots or areas of reduced sensitivity.
Glaucoma typically causes loss of peripheral vision first, often so gradually that the patient is unaware of the defect. The visual field test checks for these characteristic patterns of vision loss, confirming whether pressure-related damage has translated into a functional deficit. Structural imaging tests, such as Optical Coherence Tomography (OCT), may also be used to measure the thickness of the nerve fiber layer, providing a quantitative baseline for future comparison.
Understanding Your Results and Follow-Up
The diagnosis of glaucoma is rarely made based on a single test result, but rather on a combination of findings across all components of the exam. Elevated intraocular pressure alone may lead to classification as a “glaucoma suspect” if the optic nerve appears healthy and the visual field test is normal. Being a suspect means the patient is at a higher risk of developing the disease and requires close, ongoing surveillance. The most definitive diagnosis occurs when high pressure correlates with observable optic nerve damage and measurable loss in the visual field.
If all results are within normal limits, the recommended follow-up schedule depends on the patient’s individual risk factors, but a comprehensive check is advised every one to three years. For those classified as glaucoma suspects or who have mild damage, more frequent monitoring is necessary, often requiring repeat testing every six to twelve months. These follow-up examinations establish a reliable baseline and detect any subtle changes that indicate the disease is progressing.