Corneal Biomechanical Strength May Be Keratoconus Biomarker

Among corneal biomechanical parameters assessed using Scheimpflug technology (ST), the stiffness parameter at first applanation (SPA1) has the best accuracy in distinguishing healthy thin corneas from those with keratoconus, according to research published in the Journal of Cataract and Refractive Surgery. The study shows the limits of other keratoconus screening parameters — such as Corvis Biomechanical Index (CBI) and Topographical/Biomechanical Index (TBI).

Researchers at a single center conducted a cross-sectional comparative study to compare the biomechanical parameters of corneas of keratoconus eyes with matched normal thin corneas.

The researchers examined 61 eyes with keratoconus corneas of 61 patients (mean age, 24.5±2.1 years; 50.8% women) and 61 matched-healthy thin corneas of 61 patients. (25.1±3.3 years; 59.0% women). They evaluated dynamic corneal response parameters using Corvis ST (corneal thinnest point <500 microns), and considered corneal thickness, biomechanically corrected intraocular pressure, and age as covariates. The study authors also used a receiver-operating characteristic curve analysis to determine the cut-off point with the highest sensitivity and specificity and the area under the curve (AUC) for each parameter.

The team found all biomechanical parameters were statistically significant between the keratoconus corneas and healthy thin corneas except for the first applanation length (2.0 vs 2.0 mm; P =.947), second applanation length (1.29 vs 1.34 mm; P =.582), first applanation velocity (0.15 vs 0.15 m/s; P =.783) and second applanation velocity (-0.37 vs -0.36 m/s; P =.301), and deformation amplitude in the highest concavity phase (1.18 vs 1.20 mm; P =.106). 

They observed the greatest mean difference between the keratoconus corneas and healthy thin corneas in the stiffness parameter at the first applanation (mean difference, 12.89±2.03 mm Hg/mm; mean SPA1, 70.77 vs 80.85 mmHg/mm, respectively; P <.001). 

Among the standard and combined biomechanical parameters, the researchers found the Corvis biomechanical index (CBI) and tomographic biomechanical index (TBI) had the highest detection ability based on the AUCs (0.912 and 0.959, respectively). Among keratoconus screening parameters, they found SPA1 yielded the highest discriminative ability with AUC of 0.793, sensitivity of 60.66%, and specificity of 90.16%.

“Despite the remarkable diagnostic ability of TBI and CBI based on their AUCs, optimal cut-off points close to the maximum value defined for these parameters limit their clinical use for differentiation purposes in these particular types of cases,” the researchers report.

Limitations of the study included lack of assessment of corneal stress-strain index and stiffness parameter at the highest concavity for comparison of healthy thin corneas with keratoconus eyes.

Disclosure: One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.