Diagnosis
Screening for glaucoma is usually performed as part of a standard eye examination performed by optometrists, orthoptists and ophthalmologists. Testing for glaucoma should include measurements of the intraocular pressure via tonometry, changes in size or shape of the eye, anterior chamber angle examination or gonioscopy, and examination of the optic nerve to look for any visible damage to it, or change in the cup-to-disc ratio and also rim appearance and vascular change. A formal visual field test should be performed. The retinal nerve fiber layer can be assessed with imaging techniques such as optical coherence tomography, scanning laser polarimetry, and/or scanning laser ophthalmoscopy, also known as Heidelberg retina tomography.
Owing to the sensitivity of all methods of tonometry to corneal thickness, methods such as Goldmann tonometry should be augmented with pachymetry to measure central corneal thickness (CCT). A thicker-than-average cornea can result in a pressure reading higher than the 'true' pressure, whereas a thinner-than-average cornea can produce a pressure reading lower than the 'true' pressure.
Because pressure measurement error can be caused by more than just CCT (i.e., corneal hydration, elastic properties, etc.), it is impossible to 'adjust' pressure measurements based only on CCT measurements. The frequency doubling illusion can also be used to detect glaucoma with the use of a frequency doubling technology perimeter.
Examination for glaucoma also could be assessed with more attention given to sex, race, history of drug use, refraction, inheritance and family history.
| What Test Examines | How Examination is Accomplished | |
|---|---|---|
| Tonometry | Inner eye pressure | The eye is numbed via eye drops. The examiner then uses a tonometer to measure the inner pressure of the eye through pressure applied by a warm puff of air or a tiny tool. |
| Ophthalmoscopy (dilated eye exam) | Shape and color of the optic nerve | The pupil is dilated via the application of eye drops. Using a small magnification device with a light on the end, the examiner can examine the magnified optic nerve. |
| Perimetry (visual field test) | Complete field of vision | The patient looks straight ahead and is asked to indicate when light passes the patients peripheral field of vision. This allows the examiner to map the patient’s field of vision. |
| Gonioscopy | Angle in the eye where the iris meets the cornea | Eye drops are used to numb the eye. A hand-held contact lens with a mirror is placed gently on the eye to allow the examiner to see the angle between the cornea and the iris. |
| Pachymetry | Thickness of the cornea | The examiner places a pachymeter gently on the front of the eye to measure its thickness. |
| Nerve fiber analysis | Thickness of the nerve fiber layer | Using one of several techniques, the nerve fibers are examined. |
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