Tonometry: eye pressure
Pressure is measured by applanation, in which a small probe gently flattens the numbed cornea, or by rebound or air puff methods for screening. Normal is roughly 10 to 21 millimeters of mercury, but the range is wide and pressure varies through the day. A single reading is a snapshot; a pattern over visits, sometimes at different times of day, is what informs treatment. Pressure is the target of treatment but not the definition of the disease.
Pachymetry: corneal thickness
Tonometry assumes an average cornea. A thick cornea reads higher than the true pressure and a thin one reads lower, so thickness is measured once and used to interpret every pressure reading. Independently, thin corneas are associated with a higher risk of developing glaucoma.
Gonioscopy: the drainage angle
A mirrored lens on the eye lets the clinician see the angle between the iris and cornea where fluid drains. An open angle with impaired drainage is open-angle glaucoma; an angle narrowed or closed by the iris is angle-closure glaucoma, which is treated differently and can be an emergency. The angle is also inspected for pigment, scarring or abnormal vessels that point to secondary causes.
OCT: the structure of the nerve
Optical coherence tomography scans the retina with light and measures the thickness of the nerve fiber layer around the optic nerve and the ganglion cell layer at the macula to within a few microns. Thinning below the normal range for your age, particularly in the typical glaucoma pattern, is detectable years before the visual field changes. Repeated scans are compared over time to show whether loss is progressing.
Visual field testing: the function of the nerve
Automated perimetry maps your sensitivity to light across the visual field, one eye at a time, as you respond to flashes of varying brightness. Glaucoma produces characteristic patterns of loss (arcs and nasal steps) that correspond to the damaged nerve fibers. The test has a learning curve and some variability, so results are confirmed over two or three sessions before a change is accepted as real.
Optic nerve examination and photography
The nerve head is examined through a dilated pupil for the size of its central cup relative to its rim, for notching or thinning of the rim, and for small hemorrhages at its edge, which signal active damage. Photographs document its appearance for comparison over years.
Is this right for your eyes?
Nothing on this page is a diagnosis. Whether this is the right choice for you is decided by a full examination at one of our 4 offices: Pasadena, Huntington Beach, Woodland Hills and Beverly Hills.
About this content: This page was written with the assistance of AI tools and reviewed for medical accuracy by Dr. Bavand Youssefzadeh, DO. It is general information, not medical advice, and does not replace an eye examination. Individual results vary. Read our medical disclaimer.
