Rate of fractional change in corneal tomography parameters in keratoconus using a combination of predictive...

To compare the rate of fractional change for multiple corneal tomographic factors in progressive keratoconus (KC).

In this retrospective case series, 40 eyes (40 patients) with progressive KC (increase in central keratometry of 1.00 D or maximum keratometry of 1.50 D on two visits at least six months apart) were included. Cases with previous history of ocular surgery, poor scans, corneal scars, severe dry eyes, post-excimer ectasia, pellucid marginal degeneration were excluded. Medical records, corneal tomography and anterior corneal wavefront (8 mm) (Scheimpflug tomography, Pentacam, Oculus, Germany) were analyzed. Rate of fractional change (Rx = (x₁ - x₀)/(|x₀|t_m)); where, x₁ = value at follow-up, x₀ = value at initial visit and t_m = time in months, was measured.

The mean age of the patients was 30.0 ± 8.4 years. The mean follow-up duration was 8.9 ± 4.2 months. Coma (0.076 ± 1.4) had the largest rate of fractional change (P = 1.7 × 10^-14, Kruskal-Wallis test). The rate of fractional change was higher for aberrometric parameters (anterior corneal higher-order aberrations root mean square and anterior coma) compared to pachymetric and keratometric parameters (P values ranging from 1.4 × 10^-4 to 7.4 × 10^-10, Mann-Whitney test, effect size ranging from 0.4-0.7). The rate of fractional change was comparable between pachymetric and keratometric factors (P > 0.05 for all comparisons, Mann-Whitney test).

Anterior corneal wavefront, especially anterior coma, were noted to have higher rate of fractional change compared to single point keratometric and pachymetric indices in progressive KC. This information can be used for decision-making when monitoring patients with KC.