pachymetry

Pachymetry is the measurement of the thickness of the cornea, the transparent front part of the eye. It is most commonly reported as central corneal thickness (CCT), the thickness at the cornea’s center, but thickness across the cornea can be mapped to produce a pachymetry map. Measurements are given in micrometers (µm).

There are contact and non-contact techniques. Ultrasound pachymetry uses a high-frequency probe placed on the cornea after topical anesthesia and directly measures the distance to the posterior corneal surface. Optical pachymetry employs non-contact imaging methods, including partial coherence interferometry, optical coherence tomography, and Scheimpflug tomography, to estimate thickness from light reflections and tomography.

Pachymetry plays a key role in several clinical contexts. CCT affects intraocular pressure readings and is a factor in glaucoma risk assessment and management. It is essential in planning refractive surgery (for example, LASIK) to ensure sufficient stromal tissue and to screen for corneal ectasia. Pachymetry maps aid in diagnosing corneal edema, keratoconus, and other corneal disorders, and are useful in contact lens fitting and postoperative follow-up.

Normal values and interpretation vary. In healthy adults, mean CCT is about 540 µm, with typical individual values ranging roughly from 500 to 600 µm. Variation exists with age, ethnicity, and measurement method; diurnal fluctuations and corneal surface conditions can also influence readings.

Limitations include dependence on device type, calibration, tear film quality, and operator technique. When comparing measurements, consistency in method and device is important for reliable assessment.