The biomechanical properties of ocular tissues are critical for their function and can be significantly altered in various diseases such as keratoconus or cataract. The simultaneous assessment of cornea and crystalline lens stiffness can provide a comprehensive understanding of the biomechanical changes in these tissues in one assessment, reducing eye exposure and patient discomfort. This work demonstrates a completely contact-free characterization of the biomechanical properties of the lens and cornea simultaneously using an air-coupled ultrasonic (ACUS) transducer with optical coherence elastography (OCE). An unfocused 40 kHz ACUS transducer was used to induce elastic waves in the eye globe, which were imaged with a phase-sensitive OCT (PhS-OCT) system. OCE measurements were performed in ex vivo porcine eyes at various intraocular pressures (IOP), from 10 mmHg to 40 mmHg in 5 mmHg increments. The unfocused ACUS transducer generated mechanical waves at the limbus that traveled through the cornea and crystalline lens. The results showed differences in wave speed propagation in the cornea from 10 mmHg (3.16 m/s +/- 0.65 m/s) to 40 mmHg (12.12 m/s +/- 0.99 m/s) and the crystalline lens from 10 mmHg (2.75 m/s +/- 0.22 m/s) to 40 mmHg (6.33 m/s +/- 1.36 m/s). This method could be useful for a more comprehensive characterization of the mechanical properties of the major components of the ocular anterior segment in one measurement.

We present a technique for wide-field OCT imaging of the cornea using self-referenced interference of the anterior corneal surface with the underlying corneal structure. The method employs a custom objective lens that ensures that the probing beam remains nearly perpendicular to the anterior corneal surface, effectively utilizing it as a reference to generate interference. This approach allows for high-resolution, three-dimensional imaging of corneal layers over a 9mm optical zone. Tests on human subjects show the ability of the system to quantify the anterior corneal layer thickness.

Purpose:To evaluate the safety of acoustic radiation force (ARF) for in vivo lens biomechanics measurement in rabbits. Methods:Twelve New Zealand albino white rabbits were exposed to acoustic radiation force at intensities exceeding the US Food and Drug Administration (FDA)-recommended safety limits by 8 to 14 times. A spherically focused 3.5-MHz ARF transducer created deformations on the lens surface, which was imaged using a spectral-domain optical coherence tomography system during the ARF application. Intraocular pressure measurements and ocular health assessments using slit-lamp and OCT imaging were conducted pre- and postexposure over 3 weeks. Results:Hyperemia was observed in two rabbits immediately postexposure but resolved within 24 hours. No substantial changes in intraocular pressure were detected, and both slit-lamp examination and optical coherence tomography imaging showed normal ocular health across all groups after the follow-up period. Conclusions:ARF is a potentially safe technique for assessing the biomechanical properties of the lens in vivo. No eye damage was observed, even when ARF was applied at intensities well above FDA regulatory limits. Translational Relevance:This study is an important step toward the translation of the technology for ARF elastography of the crystalline lens, for studies on the mechanism of presbyopia, and to enable the assessment of new presbyopia treatments relying on lens softening.

Significance:Estimating biomechanical properties of the in vivo crystalline lens remains a challenge and is a barrier to evaluating novel lens softening therapies. There is a need to estimate quantitative biomechanical properties of the human anterior and mid segments of the eye in vivo for conditions such as presbyopia. Aim:We aim to develop a multimodal elastography device that enables high-performance sequential 3D imaging with both Brillouin microscopy and optical coherence elastography (OCE). Approach:We combined Brillouin spectroscopy and OCE on a modified slit lamp platform for human measurements. The multimodal system was first characterized and then tested on both a porcine eye and a human subject. Results:Both OCE and Brillouin microscopy were characterized at peak operating performance for clinical imaging. Successful measurements of an in situ porcine lens and a human in vivo lens are reported. Conclusion:We demonstrated the first successful multimodal OCE and Brillouin microscopy measurement in a human subject. This instrument offers the potential to characterize the biomechanical status of presbyopia with age.

This study investigates the relationship between photosensitizer concentration and singlet oxygen (O-1(2)) production, focusing on three xanthene-based dyes commonly used in photodynamic therapy (PDT): rose bengal (RB), erythrosin B (EB), and eosin Y (EY). O-1(2) measurements were performed using an optical dosimeter capable of detecting O-1(2) luminescence in the 1270-1280 nm infrared range in both ultra-pure water and saline (0.9 % NaCl) solutions for 10 concentrations ranging from 2.46 x 10(-5) to 1.97 x 10(-3) M. The results were fit with a model based on the Beer-Lambert law. Aggregation was quantified by analyzing the absorbance peak intensity ratios (measured using UV-vis spectroscopy). Our findings indicate that at lower concentrations (<2.46 x 10(-4) M), O-1(2) production increases with rising photosensitizer concentration until it reaches a peak and then decreases at higher concentrations, as predicted with the Beer-Lambert model. Additionally, an aggregation effect is detected at higher concentrations in ultra-pure water and more pronounced in saline solutions, where the hydrophobic nature of the photosensitizers leads to enhanced aggregation which also affects the O-1(2) generation. These results underscore the importance of optimizing photosensitizer concentration and solvent selection to maximize O-1(2) generated while minimizing aggregation. Understanding this balance is crucial for improving the efficacy of PDT in clinical use.

Purpose: Although the lens undoubtedly plays a major role in presbyopia, altered lens function could be in part secondary to age-related changes of the ciliary muscle. Ciliary muscle changes with accommodation have been quantified using optical coherence tomography, but so far these studies have been limited to quantifying changes in ciliary muscle thickness, mostly at static accommodative states. Quantifying ciliary muscle thickness changes does not effectively capture the dynamic anterior-centripetal movement of the ciliary muscle during accommodation. To address this issue, we present a method to quantify the movement of the ciliary muscle during accommodation using trans-scleral optical coherence tomography images obtained dynamically. Methods: An image processing framework including distortion correction, geometric transformation, and Procrustes analysis, was used to quantify the anterior-centripetal movement of the ciliary muscle apex and centroid during accommodation. The method was applied in a preliminary study to quantify ciliary muscle displacement and its relation to lens thickness change with accommodation on two young adults and two prepresbyopes. Results: The magnitude and the direction relative to the pupil plane of the apex/centroid displacement in response to a two diopters (2D) stimulus were 0.16/0.20 mm at 11.3 degrees/30.5 degrees and 0.26/0.34 mm at 6.6 degrees/33.2 degrees for the young adults and 0.20/0.20 mm at 29.7 degrees/40.6 degrees and 0.24/0.40 mm at 33.0 degrees/31.7 degrees for the prepresbyopes, respectively. Conclusions: This study demonstrates the feasibility of quantifying dynamic anterior-centripetal movement of the ciliary muscle during accommodation using optical coherence tomography. The method better captures the functional response of the muscle than the quantification of thickness changes. Translational Relevance: We provide a method that holds potential to better understand the age-related changes of the ciliary muscle on presbyopia.

Purpose: To assess the safety of acoustic radiation force optical coherence elastography in the crystalline lens in situ. Methods: Acoustic radiation force (ARF) produced by an immersion single-element ultrasound transducer (nominal frequency = 3.5 MHz) was characterized using a needle hydrophone and used for optical coherence elastography (OCE) of the crystalline lens. Preamplified signals at 50, 100, 250, 500, 750, 1000, and 1250 mV peak amplitude were tested on ex vivo porcine eyes (n = 21). Three-dimensional optical coherence tomography (OCT) and confocal microscopy images were acquired before and after ARF exposure to each signal amplitude to determine damage. Results: The acoustic intensity of the ultrasound transducer at 100-mV preamplified peak amplitude input demonstrated a signal-to-noise ratio high enough for tracking elastic wave propagation in the lens and spatial-peak pulse-average (SPPA) intensity of 24.1 W/cm(2) and mechanical index (MI) of 0.46. The SPPA intensity was lower than the U.S. Food and Drug Administration (FDA) safety limit (28 W/cm(2)), but the MI was twice the safety limit (0.23). OCT structural and confocal microscopy images showed damage only at levels exceeding 1150 W/cm(2) and 3.2 for SPPA intensity and MI, respectively. Conclusions: OCT and confocal microscopy showed that, even when the intensity exceeded FDA recommendations (>100 mV), no noticeable damage was observed. Although a further reduction in acoustic intensity is necessary to meet FDA safety limits, ARF-based elastography shows promise for safe clinical translation in quantitatively characterizing lenticular biomechanical properties. Translational Relevance: This work assessed the safety standards for acoustic radiation force to be used in human lens elastography according to the FDA safety limits.

Lens biomechanical properties are critical for our eyes to accommodate. While it is well understood that lens mechanical properties change with age, different experimental techniques have been used over the years, with varying results on how the lens modulus changes. In this study, we developed a spatial-varying elasticity model to characterize the overall elastic modulus of the lens and establish its effect on accommodation. First, to validate the model, ex vivo porcine lenses underwent compression testing using biopsy punches of different diameters to change the percentage of nucleus within samples. Importantly, we found that, indeed, changing nucleus/cortex spatial ratio produces dramatic (∼7-fold) increase in overall sample modulus. Comparing the model with human lens spatial ratios, we demonstrate how changing spatial mechanics are more influential than peak modulus changes on overall elastic modulus. Next, in vivo clinical measurements of the spatial-varying lens modulus were used to generate a simplified mechanical-optical model of accommodation. We defined an ellipsoid lens with patient-derived modulus and geometry measurements, and a statics simulation and ray tracing analysis were performed through the deformed and undeformed lens. The resulting accommodation estimates agree with general accommodation expectations.

Previous studies have shown that pharmaceutical agents such as lipoic acid have the ability to soften the lens, presenting a promising avenue for treating presbyopia. One obstacle encountered in the preclinical stage of such agents is the need for precise measurements of lens elasticity in experimental models. This study aimed to evaluate the effects of 25-hydroxycholesterol, lipoic acid, and obeticholic acid on the viscoelastic properties of mouse lenses using a custom-built elastometer system. Data were acquired on lenses from C57BL/6J female mice from two age groups: young (age: 8-10 weeks) and old (age: 32-43 weeks). OD lenses were used as the control and OS lenses were treated. Control lenses were immersed in Dulbecco's Modified Eagle Medium (DMEM) and treatment lenses were immersed in a compound solution containing 25-hydroxycholesterol (5 young and 5 old), lipoic acid at 2.35 mM (5 young and 5 old), lipoic acid at 0.66 mM (5 old), or obeticholic acid (5 old) at 37 degrees C for 18 h. After treatment, the mouse lenses were placed in a DMEM-filled chamber within a custom-built elastometer system that recorded the load and lens shape as the lens was compressed by 600 mu m at a speed of 50 mu m/s. The load was continuously recorded during compression and during stress-relaxation. The compression phase was fit with a linear function to quantify lens stiffness. The stress-relaxation phase was fit with a 3-term exponential relaxation model providing relaxation time constants (t1, t2, t3), and equilibrium load. The lens stiffness, time constants and equilibrium load were compared for the control and treated groups. Results revealed an increase in stiffness with age for the control group (young: 1.16 +/- 0.11 g/mm, old: 1.29 +/- 0.14 g/mm) and relaxation time constants decreased with age (young: t1 = 221.9 +/- 29.0 s, t2 = 24.7 +/- 3.8 s, t3 = 3.12 +/- 0.87 s, old: t1 = 183.0 +/- 22.0 s, t2 = 20.6 +/- 2.6 s and t3 = 2.24 +/- 0.43 s). Among the compounds tested, only 25-hydroxycholesterol produced statistically significant changes in the lens stiffness, relaxation time constants, and equilibrium load. In conclusion, older mouse lenses are stiffer and less viscous than young mouse lenses. Notably, no significant change in lens stiffness was observed following treatment with lipoic acid, contrary to previous findings.

Accommodation is the process by which the eye changes focus. These changes are the result of changes to the shape of the crystalline lens. Few prior studies have quantified the relation between lens shape and ocular accommodation, primarily at discrete static accommodation states. We present an instrument that enables measurements of the relation between changes in lens shape and changes in optical power continuously during accommodation. The system combines an autorefractor to measure ocular power, a visual fixation target to stimulate accommodation, and an optical coherence tomography (OCT) system to image the anterior segment and measure ocular distances. Measurements of ocular dimensions and refraction acquired dynamically on three human subjects are presented. The individual accommodative responses are analyzed to correlate the ocular power changes with changes in ocular dimensions.