Improved detection of corneal deformation asymmetries in keratoconus patients using multi-meridian deformation imaging

Abstract

Purpose : To evaluate a recently developed multi-meridian air-puff deformation Optical Coherence Tomography (OCT) system (ImTopScanner) for improved early keratoconus (KC) detection in vivo. To investigate deformation asymmetries that are expected to occur due to biomechanical (bm) changes in KC corneas, on two meridians.

Methods : Multi-meridian air-puff OCT (Curatolo, BOE, 2020) was used to collect deformation images of three KC and two healthy corneas in vivo. The system allows deformation imaging along both, horizontal (H) and vertical (V) corneal meridian during a 20ms air-puff excitation. Custom image processing tools quantified (1) the deflection area (DeflArea) between undeformed and deformed cornea, (2) the Asymmetry in DeflArea (ADA), i.e. the difference between nasal/temporal and superior/inferior DeflArea. Eyes were also measured with a Pentacam®. Patient-specific finite element models were generated. In KC eyes, an algorithm detected the cone area and allocated it a separate material. Through an inverse analysis procedure and simulation of air-puff pressure, corneal material stiffness for second-order Ogden material model was estimated.

Results : KC eyes were classified into two mild and one moderate KC eyes, using the Pentacam Topographic Keratoconus Classification (Chen, JCRS, 2019). The mean DeflArea (H and V) at maximum deformation was 2.79±0.04 mm², 3.12±0.27 mm², and 2.88±0.17 mm², from the lowest to highest disease severity, respectively. In the same order, the absolute value of ADA at maximum deformation was 0.02±0.06 mm², 0.14±0.12 mm², 0.18±0.04 mm² (H), and 0.21±0.08 mm², 0.23±0.02 mm², and 0.3±0.02 mm² (V), revealing a lower ADA, but a more pronounced (up to a factor of 3) relative difference between H and V ADA for mild KC eyes. For healthy eyes, ADA remained <0.2 mm². Simulations estimated a 35.5% ±10.0% stiffness reduction in the cone area of KC eyes in comparison to outside the cone at 4% strain.

Conclusions : Initial results show that multi-meridian deformation imaging can aid in early detection of corneal bm changes taking place in KC. Differences in deformation asymmetries between orthogonal meridians may be more pronounced in early disease stages, where corneal geometry has not been significantly altered. Consideration of two meridians and identification of KC cone location are important for simulating realistic corneal material behavior in KC eyes.

This is a 2021 ARVO Annual Meeting abstract.