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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.
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Revealing Regional Variations in Scleral Shear Modulus in a Rabbit Eye Model Using Multi-Meridian Ultrasound Optical Coherence Elastography
(RELX Group (Netherlands), 2023-01-01)
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Estimation of the Full Shape of the Crystalline Lens from OCT: Validation Using Stretched Donor Lenses
(Optica Publishing Group (formerly OSA), 2023-08-01)
Quantifying human crystalline lens geometry as a function of age and accommodation is important for improved cataract and presbyopia treatments. In previous works we presented eigenlenses as a basis of 3-D functions to represent the full shape of the crystalline lens ex vivo. Also, we presented the application of eigenlenses to estimate the full shape of the lens in vivo from 3-D optical coherence tomography (OCT) images, where only the central part of the lens -visible through the pupil- is available. The current work presents a validation of the use of eigenlenses to estimate in vivo the full shape of dis-accommodated lenses. We used 14 ex vivo crystalline lenses from donor eyes (11-54 y/o) mounted in a lens stretcher, and measured the geometry and the power of the lenses using a combined OCT and ray tracing aberrometry system. Ex vivo, the full extent of the lens is accessible from OCT because the incident light is not blocked by the iris. We measured in non-stretched (fully accommodated) and stretched (mimicking in vivo dis-accommodated lenses) conditions. Then, we simulated computationally in vivo conditions on the obtained ex vivo lenses geometry (assuming that just the portion of the lens within a given pupil is available), and estimated the full shape using eigenlenses. The mean absolute error (MAE) between estimated and measured lens' diameters and volumes were MAE= 0.26 ± 0.18 mm and MAE= 7.0 ± 4.5 mm3, respectively. Furthermore, we concluded that the estimation error between measured and estimated lenses did not depend on the accommodative state (change in power due to stretching), and thus eigenlenses are also useful for the full shape estimation of in vivo dis-accommodated lenses.
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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.
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