Exams and Tests

An ophthalmologist performs tests to diagnose primary open-angle glaucoma and to distinguish it from either secondary causes of glaucoma or cases of ocular hypertension with only elevated intraocular pressure and no optic nerve damage. These tests are explained below.

• Your visual acuity, which refers to how well you can see an object, is initially assessed. Your ophthalmologist determines your visual acuity by having you read letters from across a room using an eye chart.
  
  
• The front of your eyes, including your cornea, anterior chamber, iris, and lens, are examined using a special microscope called a slit lamp.
  
  
• Tonometry is a method used to measure the pressure inside the eye. Because intraocular pressure varies from hour to hour in any individual, measurements may be taken at different times of day (eg, morning and night). A difference in pressure between the 2 eyes of 3 mm Hg or more may suggest glaucoma. Early primary open-angle glaucoma is very likely if the intraocular pressure is steadily increasing.
  
  
• 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.
    
    
  • Fundus photographs, which are pictures of your optic disc (the front surface of your optic nerve, located in the back of the eye), are taken for future reference and comparison.
  
  
• Pachymetry (or corneal thickness) is checked by an ultrasound probe to determine the accuracy of your intraocular pressure readings. A thinner cornea can give falsely low pressure readings, whereas a thick cornea can give falsely high pressure readings.
  
  
• 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 determine if the angles are open, narrowed, or closed and to rule out any other conditions that could cause elevated intraocular pressure.
  
  
• 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.
  
  
  • Visual field defects may not be apparent until over 40% of the optic nerve fiber layer has been lost.
    
    
  • Visual field testing may need to be repeated. 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.
    
    
  • If your visual field defects seem to progress in a manner that is uncharacteristic of glaucoma, then your ophthalmologist will perform additional tests to look for other causes of vision loss.
  
  
• If your ophthalmologist suspects that you have normal-tension or low-tension glaucoma, then additional tests may be needed to rule out other causes of optic nerve damage.