Keratoconus Grading System Demonstrates High Specificity and Sensitivity

Macro close up eye.
Researchers examine the specificity and sensitivity of the ABCD keratoconus progression display to determine whether it can allow for more rapid referrals and better visual outcomes.

A keratoconus (KC) progression display can assess KC progression with high sensitivity and specificity, according to research published in Eye.

Researchers enrolled 30 patients (eyes, 30; 76% men; mean age, 24.8±4.8 years) with KC who underwent corneal crosslinking in the retroscopic analysis. Patients underwent Scheimpflug imaging over 2 visits spaced 6 months apart and maximum keratometry (Kmax), K1, K2, and corneal thickness at the thinnest point measurements were obtained.  

The ABCD algorithm generated 3 parameters for each exam based on a 3.0 mm optical zone which centered on the thinnest point. The algorithm included the anterior radius of curvature at the thinnest corneal point (A), the posterior radius of curvature at the thinnest corneal point (B), the thinnest corneal thickness (C), and corrected distance visual acuity (D). Sensitivity and specificity were calculated for the ABCD progression display. 

KC progression was determined by a change in 2 ABCD parameters above 80% confidence interval (CI) (criterion 1) or a change in 1 ABCD parameter above 95% CI (criterion 2). 

Criterion 1 classification resulted in a sensitivity of 61.9% and specificity of 88.9%, while criterion 2 classification resulted in higher sensitivity (80.9%) and specificity (100%). 

Pairwise comparisons of the receiver operating characteristic (ROC) curves show that the area under the curve (AUC) achieved by criterion 2 was significantly higher compared with criterion 1 (0.905 vs 0.754; P =.0332). Evaluating all ABCD combinations with a significant change of 80% or 95% CI failed to show superiority over criterion 1 or 2 regarding progression detection, according to the report. The D parameter had a very low AUC (0.5–0.556).

“The ABCD progression display has a graphical outcome through which progression can be easily detected during regular Pentacam acquisition,” according to the researchers. “This clear display allows for a rapid interpretation of disease severity by the technician performing the imaging. It may, in turn, lead to a more rapid referral pattern to a cornea consultant, reduced waiting interval for treatment, and eventually to better visual outcome.”

Study limitations include its retroscopic nature, small sample size, and short duration. 


Achiron A, Yavnieli R, Tiosano A, et al. ABCD progression display for keratoconus progression: a sensitivity-specificity study. Eye (Lond). Published online July 22, 2022. doi:10.1038/s41433-022-02183-3