Corneal Surface Wave Propagation Associated with Intraocular Pressures: OCT Elastography Assessment in a Simplified Eye Model

Abstract

Assessing corneal biomechanics in vivo has long been a challenge in the field of ophthalmology. Despite recent advances in optical coherence tomography (OCT)-based elastography (OCE) methods, controversy remains regarding the effect of intraocular pressure (IOP) on mechanical wave propagation speed in the cornea. This could be attributed to the complexity of corneal biomechanics and the difficulties associated with conducting in vivo corneal shear-wave OCE measurements. We constructed a simplified artificial eye model with a silicone cornea and controllable IOPs and performed surface wave OCE measurements in radial directions (54–324°) of the silicone cornea at different IOP levels (10–40 mmHg). The results demonstrated increases in wave propagation speeds (mean ± STD) from 6.55 ± 0.09 m/s (10 mmHg) to 9.82 ± 0.19 m/s (40 mmHg), leading to an estimate of Young’s modulus, which increased from 145.23 ± 4.43 kPa to 326.44 ± 13.30 kPa. Our implementation of an artificial eye model highlighted that the impact of IOP on Young’s modulus (ΔE = 165.59 kPa, IOP: 10–40 mmHg) was more significant than the effect of stretching of the silicone cornea (ΔE = 15.79 kPa, relative elongation: 0.98–6.49%). Our study sheds light on the potential advantages of using an artificial eye model to represent the response of the human cornea during OCE measurement and provides valuable insights into the impact of IOP on wave-based OCE measurement for future in vivo corneal biomechanics studies.

Dual-channel air-pulse optical coherence elastography for frequency-response analysis

“…We developed a dual-channel air-pulse OCE system based on the previously reported OCE system [ 34 ], which enabled simultaneous measurement of the air-pulse profiles and the induced sample’s dynamic response at the same data acquisition frequency of 70 kHz. This system comprises an air-pulse sub-system and a synchronized phase-sensitive spectral domain OCT sub-system, as illustrated in Fig.…”

“…The rise in the IOP from 5 mmHg to 40 mmHg coincided with changes in the silicone cornea's geometry. OCT measurements revealed a decrease in the anterior radius of curvature from 7.57 mm to 6.89 mm, as indicated by the linear fitting equation , accompanied by a 0.50 mm increase in the center height ( ) [ 34 ].…”

“…To accomplish this, we intentionally stimulated the sample with a range of pulse parameters (pressure: 200 Pa, duration: 3–35 ms) to create a diverse range of excitation spectra, spanning from broad to narrow, as well as a diverse set of sample response spectra, from clean to noisy. The air pulse was delivered at the center of the sample, and radial-scan OCT measurements [ 34 ] were performed in the 45°–315° directions (18° increments). Each radial direction had 17 sampling points, covering a distance of 0.93–2.80 mm.…”