Corneal biomechanical parameters in healthy and early-stage keratoconus eyes from cross-meridian air-puff deformation OCT

Abstract

Purpose : The detection of localized biomechanical alterations in early keratoconus (KC) may open new pathways for diagnosis and customized treatment options. Cross-meridian air-puff deformation Optical Coherence Tomography (OCT) was applied to healthy and early KC subjects. Deformation parameters, cross-meridian symmetry and estimated corneal biomechanical properties were evaluated as potential biomarkers for KC detection.

Methods : Corneal air-puff deformation images from 8 eyes of 8 subclinical/early-stage KC patients (mean age 35yo), and 5 eyes from 3 control (C) subjects (mean age 28yo) were captured along the horizontal (H) and vertical (V) meridian using a novel OCT device (ImTOPScanner, Curatolo, 2020). Custom-built routines were used for image segmentation and quantification at maximum deformation for H and V: 1) Distance between the two peaks of deformed cornea (PD); 2) Asymmetry in Deformation Area (ADefA), i.e. difference between nasal/temporal and superior/inferior deformation area; 3) Deformation Amplitude (DA) Ratios (Vinciguerra, 2016) at distances n=1; 1.5; 2 mm from the corneal apex. Patient-specific eye models were generated using a second-order Ogden material model. Inverse analysis was performed to quantify biomechanical variations. For KC corneas, a custom-built algorithm detected the boundary of the region of pathology, to which distinct material parameters were allocated.

Results : KC corneas showed lower PD (mean PD_KC=4.70±0.03 mm) than C corneas (mean PD_C=5.13±0.02 mm). In KC corneas |ADefA_V-ADefA_H| was 0.12±0.15 mm², compared to 0.08±0.06 mm² in C corneas. The DA ratio was higher in KC than in C corneas for all n (mean increase 0.10±0.04 (H) and 0.14±0.06 (V) for n=1 mm; 0.28±1.11 (H) and 0.44±0.23 (V) for n=1.5 mm; 0.79±0.31 (H) and 1.71±1.17 (V) for n=2 mm). |DARatio_V-DARatio_H| was higher in KC than in C corneas (2.2, 2.7, and 6.6-fold for n=1; 1.5; 2 mm, respectively). Inverse analysis revealed a tangent modulus at 2% strain of 1.75±0.29 MPa for KC corneas; 1.20±0.37 MPa for KC areas of pathology and 1.43±0.18 MPa for C corneas.

Conclusions : Cross-meridian air-puff corneal deformation OCT reveals differences between healthy and early-stage KC patients. Parameters comparing different deformations in horizontal and vertical meridians seem a well-suited biomarker, independent of intraocular pressure. Results of inverse analysis complement these parameters.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.