The measurement of intra-ocular pressure (pressure within the eye) is an important element in the detection of glaucoma. Historically doctors have accepted eye pressure values directly. It is now understood that when intra-ocular pressure is measured the validity of the pressure test is directly influenced by the thickness of the cornea, the outer clear window of the eye. Since the thickness of the cornea varies meaningfully from eye to eye, it becomes a factor in the determination of the actual eye pressure.

Pachymetry is a simple, painless ultrasonic measurement to determine the thickness of the cornea. If this test demonstrates a thicker than usual cornea the actual intra-ocular pressures are in reality lower that what the glaucoma pressure test alone records. In patients with thinner corneas, the pressures are actually higher, and as a result, demonstrate a greater pressure risk in regard to glaucoma. Pachymetry findings are applied to a calculation scale and eye pressure readings are adjusted accordingly to the corneal thickness. Pachymetry measurement is now considered a routine standard of care in the diagnosis and treatment of glaucoma.

In addition, pachymetry is utilized when corneal swelling (edema) is suspected. Swelling of the cornea may result in reduced transparency causing cloudy vision. Pachymetry is also used to determine candidacy for refractive surgery since a thinner cornea may not have enough thickness to correct the refractive error fully.