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Item type:Publication, Revealing regional variations in scleral shear modulus in a rabbit eye model using multi-directional ultrasound optical coherence elastography(Nature Research, 2024-12-01)The mechanical properties of the sclera play a critical role in supporting the ocular structure and maintaining its shape. However, non-invasive measurements to quantify scleral biomechanics remain challenging. Recently introduced multi-directional optical coherence elastography (OCE) combined with an air-coupled ultrasound transducer for excitation of elastic surface waves was used to estimate phase speed and shear modulus in ex vivo rabbit globes (n = 7). The scleral phase speed (12.1 ± 3.2 m/s) was directional-dependent and higher than for corneal tissue (5.9 ± 1.4 m/s). In the tested locations, the sclera proved to be more anisotropic than the cornea by a factor of 11 in the maximum of modified planar anisotropy coefficient. The scleral shear moduli, estimated using a modified Rayleigh-Lamb wave model, showed significantly higher values in the circumferential direction (65.4 ± 31.9 kPa) than in meridional (22.5 ± 7.2 kPa); and in the anterior zone (27.3 ± 9.3 kPa) than in the posterior zone (17.8 ± 7.4 kPa). The multi-directional scanning approach allowed both quantification and radial mapping of estimated parameters within a single measurement. The results indicate that multi-directional OCE provides a valuable non-invasive assessment of scleral tissue properties that may be useful in the development of improved ocular models, the evaluation of potential myopia treatment strategies, and disease characterization and monitoring. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Air-Coupled Ultrasonic Optical Coherence Elastography Reveals Protocol-Dependent Corneal Stiffening in Epi-On and Epi-Off Riboflavin Crosslinking(Association for Research in Vision and Ophthalmology, 2026-07-10)Purpose: To evaluate the biomechanical impact of corneal crosslinking (CXL) when combining three different ultraviolet A (UV-A) riboflavin (RB) photosensitizers and protocols (Dresden protocol [DP] and accelerated protocol [AP]) using air-coupled ultrasonic optical coherence elastography in ex vivo rabbit corneas. Methods: An air-coupled ultrasound excitation optical coherence elastography system was used to excite the corneal apex and generate Lamb wave propagation along 16 corneal cross-sectional meridians. Measurements were conducted on ex vivo rabbit eyes (n = 45) during three treatment phases: Virgin, after 30 minutes of RB soaking, and after UV-A irradiation. The protocols used include the DP (3 mW/cm2, 30 minutes) and two accelerated protocols (AP-1: 9 mW/cm2, 10 minutes; and AP-2: 30 mW/cm2, 3 minutes). Each protocol was tested with three photosensitizers: epithelium-on (TE), and epithelium-off with hyperosmolar (M) and hypo-osmolar solutions (D). Lamb wave speed and average corneal thickness were calculated for each meridian to estimate meridian-dependent corneal shear modulus. Differences were statistically analyzed using linear mixed-effects regression. Results: The DP-D produced the strongest significant corneal stiffness increase (480.5 kPa; P < 0.001) during the UV irradiation phase, and the most pronounced corneal thinning (186 µm; P < 0.001). DP-TE achieved the next strongest stiffening (309.5 kPa) during UV irradiation, with no significant thickness change. All other protocol-photosensitizer combinations did not achieve significant corneal stiffening except for AP-1-D and AP-2-D during the RB soaking phase. Conclusions: Accelerated protocols did not produce significant corneal stiffening for any RB photosensitizer except when using dextran-based D. DP-D and DP-TE produced the greatest balance between shear modulus increase and corneal thickness decrease, suggesting DP-TE as a potential compromise between biomechanical impact, corneal integrity, and faster postoperative recovery. Translational Relevance: This work quantified the impact of clinically used crosslinking photosensitizers and protocols on corneal stiffening using an air-coupled ultrasound excitation optical coherence elastography, which holds promise for clinical assessments in patients.