Heartbeat-induced corneal axial displacements are larger in keratoconus patients

Abstract

Purpose : To measure and compare heartbeat-induced corneal axial displacements (CAD) in patients with keratoconus (KCN) and normal controls (NRL) using a high-frequency ultrasound elastography method (Kwok et al, TVST, 2020).

Methods : Twenty-nine eyes in 15 KCN patients (age: 20-66; 8 males, 7 females) and 40 eyes in 20 NRLs with no known ocular diseases (age: 22-67; 6 males, 14 females) were recruited. Topographic and tomographic evaulations were obtained with an Oculus Pentacam to confirm KCN diagnosis. Intraocular pressure (IOP) and ocular pulse amplitude (OPA) were measured using a PASCAL Dynamic Contour Tonometer. A 50-MHz ultrasound probe (FUJIFILM VisualSonics) was used to acquire 1000 cross-sectional scans of the central 5-mm cornea along the naso-temporal axis at 128 frames per second. A correlation-based speckle tracking algorithm (Tang & Liu, JBME, 2012) was used to compute corneal displacements between consecutive frames. CAD was obtained as the average trough-to-peak magnitude of three heartbeat-induced axial displacement cycles.

Results : IOP and OPA were not different between KCN and NRL (IOP: 16.1±3.5 vs 16.3±2.5 mmHg, p=0.85; OPA: 2.2±0.9 vs 2.6±0.8 mmHg, p=0.08; two-sample t-tests). The CAD in KCN was 52.5±20.8 μm, significantly larger than that (38.3±9.1 μm) in NRL (p<0.001, two-sample t-test; Fig. 1). In addition, a positive association between CAD and age was observed in KCN (r=0.42, 95% CI=0.063~0.68, p=0.02, n=29, Fig. 2), but no significant trend was observed in NRL (r=-0.10, 95% CI=-0.40~0.22, p=0.54, n=40).

Conclusions : High-frequency ultrasound elastography may offer a tool for clinical biomechanical evaluation of the cornea. Our results showed a larger heartbeat-induced CAD in KCN, suggesting that CAD may be a useful parameter for KCN diagnosis. The increased difference between KCN and NRL with age may indicate progressive corneal weakening in KCN. Future studies are needed to evaluate whether CAD is associated with KCN grade and KCN progression over time.

This is a 2021 ARVO Annual Meeting abstract.

 

Fig. 1: Distribution of CAD in KCN and NRL subjects showing significantly larger CAD in KCN eyes.

 

Fig. 2: CAD was positively associated with age in KCN, and no age-associated trend was observed in NRL. The difference between KCN and NRL increased with age.