Pachymetrie

Pachymetrie, or pachymetry, is the measurement of the thickness of the cornea, typically the central corneal thickness (CCT). It is a fundamental parameter in ophthalmology, used to assess corneal structure, guide treatments, and monitor disease. Thickness is measured in micrometers (µm) and can be reported as central or peripheral pachymetry.

Measurements can be obtained with ultrasonic pachymetry, a contact method that uses a probe placed on the corneal surface after topical anesthesia. Optical methods do not require contact and include partial coherence interferometry, Scheimpflug tomography, and swept-source optical coherence tomography; these provide CCT and provide pachymetric maps of the cornea.

Clinical relevance includes several areas. In refractive surgery (LASIK, PRK), accurate pachymetry is essential to ensure a safe residual stromal bed and to assess ectasia risk. In glaucoma, CCT affects intraocular pressure readings and risk assessment, with thicker corneas potentially yielding higher IOP estimates and thinner corneas potentially masking true pressure. In corneal diseases, pachymetry helps diagnose and monitor conditions such as corneal edema (thickening) and keratoconus (thinning). It is also used to monitor corneal status after surgery or trauma and in pediatric populations, where thickness can vary with age.

Normal values for adult CCT are typically about 540–550 µm, with a normal range roughly 500–600 µm, though values vary by ethnicity and measurement technique. Limitations include variability between methods, tear film quality, surface irregularities, edema, and operator experience. See also intraocular pressure, corneal topography, keratoconus.