Diagnosing glaucoma can be quite difficult, especially for patients with early disease, but is generally established based on the evaluation of three parameters. The first approach is to measure IOP (intraocular pressure) with a tonometer, but a mid-range result may not be a definitive answer since IOP varies throughout the day. Another objective tool, the visual field machine, is used to detect gaps in vision, but these gaps don’t appear until the disease is in mid-course. Finally, the doctor can assess changes in the appearance of a patient’s optic nerve. While the assessment of the optic nerve was traditionally limited to a subjective review of optic nerve photographs, there are now computerized tools that lend more objectivity to the optic nerve assessment.
In June 2002, a research study co-sponsored by the National Eye Institute revealed that corneal thickness may have a significant impact on IOP measurements. For example, patients with thin corneas have less resistance when a tonometer is placed against their eyes, so their IOP readings may be lower. The reverse may be true for patients with thicker corneas, a condition relatively common among African-Americans. Since eye doctors treat glaucoma based in part on how each patient’s IOP measurements compare to ‘normal,’ this finding requires doctors to consider corneal thickness before determining a treatment plan.