Traditionally, keratoconus is classified into four stages using the Amsler-Krumeich classifications. While useful, the system isn’t perfect. For one, it doesn’t account for patients who show signs from different stages, forcing clinicians to sometimes make a subjective judgement call. However, using placido disc-based videokeratography, which provides corneal topographic assessments, researchers are now saying they’ve been able to more accurately stage the condition using objective measurements.

A team of Spanish researchers used placido disc–based videokeratography to look at 70 healthy and 77 keratoconic eyes. They reviewed the patients’ mean values of coma, trefoil, tetrafoil, secondary astigmatism, spherical aberration and coma-like, third- and fourth-order root mean square (RMS) to calculate cutoff values, sensitivity and specificity to discriminate between normal and stage 1 keratoconus eyes and between each keratoconus stage after cross-validation analysis.

They concluded that anterior corneal high-order aberrations, specifically coma and third-order RMS, could assist in classification and that new cutoff values could improve staging. They note that all wavefront aberrations were significantly different between the healthy and keratoconus groups. The coma and third-order RMS values provided better sensitivity and specificity to distinguish keratoconus from healthy eyes than trefoil, tetrafoil, secondary astigmatism, spherical aberration and coma-like and fourth-order RMS values. However, the coma and third-order RMS values showed the highest specificity and great sensitivity to differentiate between stages 1 and 2 and good sensitivity and specificity to differentiate between stages 2 and 3.

Ortiz-Toquero S, Fernandez I, Martin R. Classification of keratoconus based on anterior corneal high-order aberrations: a cross-validation study. Optom Vis Sci. 2020;97(3):169-77.