In vivo measurement of human lens stiffness using combined Optical Coherence Elastography and Brillouin microscopy

Abstract

Purpose : In vitro studies and computational modeling have linked age-related lens stiffness with presbyopia. Brillouin microscopy has been used in vivo to measure lens stiffness, but it needs to be calibrated to quantify Young’s modulus. This study aims to measure the elastic properties of the human lens using combined Optical Coherence Elastography (OCE) and Brillouin microscopy.

Methods : Lens elasticity was measured with a custom-built combined OCE+Brillouin system (Fig. 1). The OCE and Brillouin imaging systems share a single sample arm and delivery objective, mounted together on a slit-lamp table. For OCE, we used an 840nm phase-sensitive spectral domain OCT system to record shearwaves propagation on the lens surface generated by a 3.5 MHz acoustic radiation force (ARF) transducer, coupled with ultrasound gel to the eye. The Brillouin microscope uses a 780 nm diode laser and double-VIPA spectrometer design that enables high speed measurements. We carried out Brillouin then OCE measurements sequentially.
OCE and Brillouin measurements were acquired on the right eye of a 55-year-old subject following an IRB-approved protocol. For OCE, M-B-mode images were recorded to quantify the velocity of the shearwave produced by 3 cycles of ARF-induced deformation at 1 kHz with 50% duty cycle applied at the FDA-approved exposure limit. The OCE lens elasticity was calculated from shearwave velocity. We compared the central Brillouin shift plateau's width (mm) with nucleus thickness obtained from a custom-built swept-source OCT image.

Results : The central plateau of the Brillouin shift measures 3.46 mm, corresponding to 62% of the total Brillouin shift of 5.55 mm (Fig. 2b). The lens nucleus thickness was 2.96 mm (Fig. 2c), corresponding to 65% of the total lens thickness. The OCE shear wave group velocity was 4.87 m/s which corresponds to a Young’a\s modulus of 78 kPa.

Conclusions : This study demonstrates for the first time the feasibility of using combined OCE+Brillouin microscopy to measure the mechanical properties of the human lens in vivo. Our initial findings suggest that the central Brillouin shift plateau corresponds to the anatomical lens nucleus.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Fig1 - Human interface of the OCE-Brillouin microscopy