Combined corneal biomechanical and tomographical indices in subclinical and forme fruste keratoconus.

PURPOSE: Evaluation of combined corneal tomographic and biomechanical parameters in subclinical/forme fruste keratoconus (ScKC/FFKC).

DESIGN

Cross-sectional observational case-control study.

METHODS INCLUSION CRITERIA: Thirty-one eyes with ScKC (fellow eye of KC with any one sign: keratometry >47 diopters, cylinder >1.5 D, central corneal thickness <500 µm, with/without abnormal topography) or FFKC (fellow eye of KC with normal topography and slit lamp examination) >13 years (cases) and 44 eyes of age-matched 22 healthy subjects (controls).

EXCLUSION CRITERIA: Clinically diagnosed KC, presence of corneal scars, and prior ocular surgery eyes.

STUDY PARAMETERS: Sixteen Pentacam, 15 Corvis ST, and five Sirius parameters were analyzed using paired sample t -test, and a subsample found to be significantly different was used in receiver operating characteristic curve analysis. The Youden index was calculated, and Pearson's correlation analysis was done.

RESULTS

Five Pentacam, three Corvis ST, and two Sirius parameters had an area under curve (AUC) >0.75. Tomographic and biomechanical index (TBI) (cutoff 0.59, 95% specificity, 77% sensitivity), Belin Ambrosio enhanced ecstasia display (cutoff 1.8, 81% specificity, 80% sensitivity), and symmetry index of posterior corneal curvature (cutoff 0.16, 97% specificity, 67% sensitivity) best identified early KC. TBI strongly correlated with maximum Pentacam parameters in both cases and controls. Corvis biomechanical index strongly correlated only in cases, and SP-A1-SD weakly correlated in cases.

CONCLUSION

Upon combined analysis, the average sensitivity and specificity, respectively, of top three parameters (according to AUC) from Pentacam and Corvis ST were 74.1% and 95.4% for posterior elevation and TBI.

TRIAL REGISTRATION: The trial was registered in Clinical Trial Registry of India on January 28, 2022. The Trial Registration Number is REF/2022/01/050638.