Regular eye examinations by an ophthalmologist are important in detecting glaucoma in time, before damage to the optic nerves takes place. The National Eye Institute advises a comprehensive eye examination every two years for high-risk individuals (black people older than 40, anyone over 60). Earlier or more frequent examinations may be recommended for people with additional risk factors, such as other eye conditions or diabetes.

Screening and tests to detect glaucoma may include:

• Tonometry. This painless test measures pressure inside the eye (intraocular pressure, IOP). Variations include air puff tonometry, in which the eye is numbed with drops and a puff of air is blown at it to measure the amount of air deflected by the eye. During applanation tonometry, the eye is numbed and a slit lamp (device emitting powerful light) illuminates the eye so the physician can examine it.  A small pressure-sensitive tip measures IOP by touching the surface of the eye. There is also a hand-held, pen-like tonometer that measures IOP without touching the cornea. Eye pressure that exceeds 21 millimeters of mercury (mmHg) indicates a risk for glaucoma.
  
  
• Visual field test (perimetry). Various tests, some using computer screens, assess any loss of peripheral (side) vision, a sign of glaucoma.
  
  
• Visual acuity test. This eye chart test is used to measure the acuity of vision.
  
  
• Dilated pupil examination. Drops are put into the eyes to enlarge the pupils. The inside of the eye is then examined for damage to the retina or to the optic nerve, a sign of glaucoma. After the exam, vision remains blurred for a short time.
  
  
• Funduscopy (ophthalmoscopy). Examination of the back of the eye (fundus) for damage. A funduscope, ophthalmoscope or biomicroscope is used to look through the pupil to the back of the inner eye. Any abnormal “cupping” or depression in the optic nerve can be seen along the back wall of the eye. A laser light and computer tomograph can re-create a three-dimensional image of the optic nerve, revealing changes that may indicate glaucoma.
  
  
• Gonioscopy. A special lens with an angled mirror is placed on the eye to inspect the drainage angle. This procedure can predict the likelihood of a patient having an acute angle-closure attack.
  
  
• Pachymetry. Test to measure the thickness of the cornea (the clear covering over the front of the eye). The eyes are numbed and tested with an ultrasonic wave instrument to gauge the thickness of the cornea. People with thin corneas can have glaucoma even if the pressure in the eye is low.
  
  
• Polarimetry. Scanning lasers measure the retinal nerve fiber layer.
  
  
• Other tests. These may include computerized imaging and photographing the optic nerve while the eyes are dilated. The images are then studied and compared over time for changes in the eye.