Agreement Between Scheimpflug Imaging And The Swept-Source Optical Coherence Tomography Measurements In Keratometry, Pachymetry And Ectasia Risk Scores

To assess the agreement between corneal keratometry (K) and pachymetry measurements as well as the Belin/Ambrosio enhanced ectasia total deviation index (BAD-D) and the Screening Corneal Objective Risk of Ectasia (SCORE) values obtained by a swept-source optical coherence tomography (SS-OCT ANTERION®, Heidelberg Engineering, Heidelberg, Germany) and a Scheimpflug imaging device (Pentacam® HR), in healthy subjects submitted to refractive surgery.

Refractive Surgery Unit of the Ophthalmology Department of Unidade Local de Saúde de Santo António (ULSSA), a tertiary hospital in Oporto, Portugal.

Cross sectional study enrolling patients scheduled for refractive surgery between January 2023 and January 2024.  Ectasia display obtained with SS-OCT Anterion® and Pentacam®HR at pre-operative visit were analysed. The measurements evaluated included anterior steep and flat K, astigmatism and its axis and thinnest point corneal thickness. BAD-D and SCORE values were assessed and the percentage of BAD-D value above 1.6 and SCORE value above -0.5 was evaluated. To compare the mean values of the measurements, a paired t-test was used. The chi-square test was used to compare groups above and below cut-off values of ectasia scores.

Two-hundred and fifty-two eyes (126 patients), mean±SD age of 32.5±5.4 years, were enrolled. Significant differences among devices were found in flat K (42.4D vs 42.3D, p=0.03), corneal astigmatism (1.36D vs 1.45D, p<0.001) and axis (90.0 vs 74.4, p=0.01) and thinnest point thickness (553.9um vs 546.6um, p<0.001). BAD-D and SCORE values above the cut-off for normal corneas were found in 7.9% and 13.1% of eyes, respectively, with significant difference in the classification of abnormality between scores (p<0.001). We found strong correlations between steep k (ρ=0.96), flat k (ρ=0.97), astigmatism (ρ=0.93) and pachymetry on thinnest point (ρ=0.960), p<0.001.

Despite showing a strong correlation, there are significant differences in the keratometry and pachymetry values presented by Pentacam® HR and SS-OCT Anterion®, so these measurements should not be used interchangeably. We also demonstrated statistically significant differences between the two scores regarding the classification of eyes as 'normal' or 'borderline/suspect'. In the future incorporating a larger number of participants will be important to confirm these differences.