Researchers in Turkey recently realized traditional Scheimpflug tomography may not be an ideal measurement tool for tracking central corneal thickness (CCT) in keratoconic eyes that have undergone corneal collagen crosslinking (CXL). That’s because the measurements weren’t comparable with ultrasound pachymetry in these eyes.

The study included 50 eyes with keratoconus (further classified as mild or moderate), 50 eyes with progressive keratoconus that underwent CXL and 50 control eyes. The researchers measured each eye’s CCT using both the Pentacam Scheimpflug system and ultrasound pachymetry (UP).

Initially, the researchers noted the two devices were not comparable for the keratoconus and CXL groups compared with controls, with differences of −20.9±21.5μm and −10.6±20.3, respectively. However, when they analyzed the findings based on keratoconus severity, they found Scheimpflug and ultrasound pachymetry provided comparable measurements for eyes with mild keratoconus and controls. Eyes with moderate keratoconus, and any eyes that have undergone CXL exhibit different CCT measures depending on the device used, they noted in their paper on the study.

“Pachymetry measurements from Scheimpflug must be interpreted with extreme caution in crosslinked keratoconic eyes,” the researchers wrote in their paper. This is particularly true for eyes in need of an invasive procedure such as re-CXL or photorefractive keratectomy, they added. “It is recommended that UP should be recognized as the most reliable standard instrumentation for corneal thickness evaluation especially in keratoconus and [CXL] studies.”

Kosekahya P, Koc M, Yalcinsoy KO, et al. Comparative evaluation of central corneal thickness in cross-linked keratoconic eyes. Cornea. April 15, 2020. [Epub ahead of print].