How is glaucoma diagnosed?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

Generally, glaucoma can be diagnosed through a comprehensive examination of the eyes. In this exam there are many different steps that test for vision, pressure, and overall health of the eyes. Before any tests begin your doctor will numb your eyes through a procedure called pachymetry. After the numbing, the preliminary test for glaucoma involves measuring the pressure inside the eye with an instrument called a tonometer. The next basic steps to the exam are a visual field test, for your peripheral vision, and a visual acuity test, for your distance vision. Your doctor can also check for optic nerve damage through a dilated eye exam.

Regular eye examinations by your ophthalmologist are the best way to detect glaucoma. A glaucoma screening that checks only the pressure of the eye is not sufficient to determine if you have glaucoma. The only sure way to detect glaucoma is to have a complete eye examination.

During your glaucoma evaluation, your ophthalmologist will:

  • Measure your intraocular pressure (tonometry)
  • Inspect the drainage angle of your eye (gonioscopy)
  • Evaluate whether or not there is any optic nerve damage (ophthalmoscopy)
  • Test the peripheral vision of each eye (visual field testing, or perimetry)

Photography of the optic nerve or other computerized imaging may be recommended. Some of these tests may not be necessary for everyone. These tests may need to be repeated on a regular basis to monitor any changes in your condition.

No single test is 100% effective in determining whether you have glaucoma. To diagnose the disease, your healthcare professional will ask you questions about your medical history. You should receive a comprehensive eye examination, which may include any of the following painless tests:
  • Visual acuity. This test measures the ability of your central vision to distinguish details and shapes. You will be asked to cover an eye and read a chart to measure how well you see at various distances.
  • Tonometry. This is a test to measure your intraocular pressure. It can be performed in a variety of ways. In Goldman applanation tonometry, you are given drops to numb your eye, and a pressure-sensitive tip is placed against the eye to measure its pressure. This method is the most accurate way of measuring pressure but is limited when there is an irregularity of the corneal surface.
  • Gonioscopy. In this test, a special lens containing a mirror is placed lightly on the front of your eye. It allows the healthcare professional to examine the angle between the cornea and the iris inside the eye.
  • Pachymetry. This test uses a measuring device to determine the thickness of your corneas. Central corneal thickness (CCT) is an important factor in diagnosing glaucoma. Thick corneas may increase eye-pressure readings in people who do not have glaucoma. However, people with thin corneas may have normal pressure readings but still have glaucoma. A thick CCT leads to an overestimation of the pressure, while a thin CCT leads to an underestimation of the pressure. The healthcare professional takes central corneal thickness into consideration when assessing risk factors.
  • Perimetry. This test, also called a visual field test, measures your side or peripheral vision. Today it is often done with computerized equipment. You place your chin on a stand in front of a computerized screen. You are asked to focus on a spot on the screen and push a button or indicate when you see a tiny flash of light. This gives your healthcare professional a map of your field of vision.
  • Ophthalmoscopy. In this test, your healthcare professional places drops in your eyes to widen (dilate) your pupils. Then the health professional looks through the pupil at the optic nerve using a special instrument (ophthalmoscope) or with a special lens that magnifies details at the back of the eye.

Continue Learning about Glaucoma Diagnosis

What is pachymetry?
Diana MeeksDiana Meeks
Pachymetry, or corneal pachymetry,  is a common test for glaucoma and usually part of the comprehens...
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What is a tonometer?
Dr. Jeanne Morrison, PhDDr. Jeanne Morrison, PhD
A tonometer is an instrument used to measure the intraocular pressure, or pressure within the eye. T...
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Is perimetry an effective screening test for glaucoma?
In perimetry, which is the measurement of visual fields, you respond to objects of varying brigh...
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How often should a person have a screening exam for glaucoma?
Louis B. Cantor, MDLouis B. Cantor, MD
It is important to monitor the eye pressure closely if it is elevated (normal is generally betwe...
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.