Three-Dimensional Mechanical Characterization of Normal, Subclinical, and Keratoconic Corneas Using Motion Tracking Brillouin Microscopy

Abstract

To characterize the 3-dimensional (3-D) mechanical differences between normal corneas and those with subclinical (SKC) or clinical keratoconus (KC) using motion-tacking (MT) Brillouin microscopy. Prospective cross-sectional study. There were 50 eyes from 50 patients evaluated, including 20 Control eyes from 20 patients, 20 SKC eyes from 20 patients, and 10 stage I or II KC eyes from 10 patients. All patients had Scheimpflug imaging for group classification and MT Brillouin microscopy using a custom-built device for mechanical evaluation. Mean and minimum MT Brillouin shift values were generated in anterior, middle, and posterior stromal regions. Receiver operating characteristic (ROC) curves were generated for MT Brillouin metrics to determine the area under the ROC curve (AUROC), sensitivity, and specificity for each variable at each location. There were no significant differences between groups for age, sex, or K Mean. There were significant differences between control, SKC, and KC groups for all MT Brillouin metrics, with greatest differences in Anterior Min (_ 43 to 57 MHz, p<0.001) and Mean (_ 34 to 37 MHz, p<0.001), Middle Min (_ 44 to 69 MHz, p<0.001) and Mean (_ 39 to 54 MHz, p<0.001), and least differences in Posterior Min (_ 15 to 22 MHz, p<0.001) and Mean (_ 20 to 32 MHz, p<0.001). Anterior Min values fully separated both SKC and KC groups from controls (AUC = 1.0 for each), while Anterior Mean (AUC = .98, 1.0), Middle Mean (AUC = .96, 1.0), and Middle Min (AUC = .94, 1.0) performed better than Posterior Mean (AUC = .81, .95) or Posterior Min (AUC = .78, .88). MT Brillouin microscopy identified 3-dimensional differences between controls eyes and those with subclinical or early-stage keratoconus. Differences were most pronounced in the anterior stroma and least pronounced in the posterior stroma, indicating relevant axial mechanical differences in eyes with subclinical keratoconus.