Exams and Tests

IOP is an important risk factor for developing glaucomatous damage, but, alone, it is not sufficient for a diagnosis of glaucoma.

Some eyes undergo damage at IOP of less than 18 mm Hg, while others tolerate IOP of more than 30 mm Hg. In fact, as many as 50% of people with optic nerve damage or visual field changes due to glaucoma have IOP of less than 21 mm Hg on their initial evaluation.

During an eye examination, your ophthalmologist performs tests to measure IOP as well as to rule out early POAG or other possible causes of glaucoma. These tests are explained below.

• Tonometry is a method used to measure the pressure inside the eye.
  
  
  • Measurements are taken for both eyes on at least 2-3 occasions. Because IOP varies from hour to hour in any individual, measurements may be taken at different times of day (eg, morning and night). If you are a glaucoma suspect with normal IOP but a suspicious looking optic nerve, your IOP may be checked several times during a single day (called a diurnal assessment or diurnal curve).
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  • A difference in pressure between each eye of 3 mm Hg or more may suggest glaucoma. Early POAG is very likely if IOP is steadily increasing.
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  • In general and depending on your risk factors, IOP is checked every 3-12 months.
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• The front of your eyes, including your cornea, anterior chamber, iris, and lens, are examined using a special microscope called a slit lamp. During a slit lamp examination, the ophthalmologist looks for signs of other causes or risk factors of glaucoma.
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• Gonioscopy is performed to check the drainage angle of your eye; to do so, a special contact lens is placed on the eye.
  
  
  • This test is important to evaluate angle depth and to determine if the angles are open, narrowed, or closed. Narrow or closed angles reduce or stop the fluid flow from the eye, causing increased pressure.
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  • Gonioscopy is also used to rule out any other conditions that could elevate IOP.
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  • Gonioscopy is usually performed annually on all people who are glaucoma suspect.
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• Each optic nerve is examined for any damage or abnormalities; this may require dilation of the pupils to ensure an adequate examination of the optic nerves.
  
  
  • Different imaging studies may be conducted to document the status of your optic nerve and to detect changes over time.
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  • Fundus photographs, which are pictures of your optic disc (the front surface of your optic nerve), are taken for future reference and comparison in order to monitor any possible subtle progression.
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  • In certain people, ophthalmologists prefer to obtain this documentation yearly for detailed comparison.
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• The retina is examined for any defects. This may also require dilation of the pupils to ensure an adequate examination of the retina.
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• Visual field testing checks your peripheral (or side) vision, typically by using an automated visual field machine.
  
  
  • This test is done to rule out any visual field defects due to glaucoma. However, an absence of visual field defects does not ensure the absence of glaucoma. Visual field defects may not be apparent until as much as 50% of the optic nerve fiber layer has been lost.
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  • Visual field examinations are typically done every 6-12 months. If there is a low risk of glaucomatous damage, then the test may be performed only once a year. If there is a high risk of glaucomatous damage, then the test may be performed as frequently as every 2 months. Testing is repeated sooner if a defect is detected, usually within 1 month, to ensure that the defect is reproducible.