Prevalence of Abnormal Ectasia Screening Indices and the Predictive Value of Anterior Keratometry in Refractive Surgery Candidates.
Purpose To determine the prevalence of abnormal ectasia screening indices among refractive surgery candidates and whether autorefraction-keratometry (ARK) can discriminate patients with abnormal Pentacam indices well enough to triage tomographic referral. Methods In this retrospective, cross-sectional study, 1,985 of 2,000 consecutive refractive surgery candidates with complete ARK and Pentacam data were analyzed. Screening-positivity was defined at the patient level as a Belin-Ambrósio Deviation (BAD-D) > 1.6 or Topographic Keratoconus Classification (TKC) ≥ 0.5 in either eye, and a clearly-abnormal category as BAD-D > 2.6 or TKC ≥ 1.0. Pre-specified ARK models were assessed for discrimination by the area under the receiver operating characteristic curve (AUC) with cross-validation, then translated into operating characteristics at fixed sensitivities. Results Screening-positivity was present in 25.0% of patients (95% CI, 23.1-26.9), whereas clearly-abnormal indices occurred in only 2.4% (1.8-3.1); positivity was driven mainly by the borderline BAD-D > 1.6 flag. ARK keratometry was significantly associated with screening-positivity (steep keratometry odds ratio, 1.48 per diopter; P < 0.001) but discriminated only modestly (AUC, 0.72; 95% CI, 0.69-0.74), with no improvement from additional ARK parameters. At a sensitivity of 95%, only 16.2% of patients could safely forgo tomography, and 100% sensitivity spared just 1.9%. Conclusions Abnormal ectasia screening indices were common but predominantly borderline, and anterior keratometry alone could not reliably triage which corneas require tomographic examination. They support routine tomographic evaluation where available and indicate that keratometry alone cannot replace it where it is not.