Abstract
Purpose :
Using Brillouin-scattering theory, the BOSS measures miniscule changes in the wavelength (‘frequency shift’) of laser light reflected back from an object, such as the cornea or crystalline lens. The measured frequency shift correlates with the material’s stiffness, that is, its “longitudinal elastic modulus”. In this study, BOSS measurements from water, plastic and porcine eyes were performed to investigate the data accuracy and repeatability.
Methods :
A polystyrene cube filled with water was placed on the chinrest. Ten Brillouin frequency-shift measurements were made at each of 5 different positions of the cube, producing 50 Brillouin images for both water and plastic. Five individual old (5 months) and young (8 weeks) porcine eyes were obtained and mounted on a custom setup. In the lens experiment, 3 replicate scans were performed per lens, from the anterior to posterior lens though a single point. Three cornea exams were also performed on each porcine eye, with depth scans at 7 locations around the entire cornea.
Results :
In the water and polystyrene experiment, the measured Brillouin frequency shifts were within 0.45% and 0.26%, respectively, of the formulated theoretical values and the coefficient of variation (CV) values were 0.4% and 0.3%, respectively, thus demonstrating exceptional accuracy and repeatability. In the porcine-eye lens experiment, the CV was 1.2% for the old eyes and 1.4% for the young eyes. The Brillouin stiffness of the old lenses (4.007±0.047 GPa) was significantly greater than that of the young lenses (3.699±0.051 GPa, P=0.0002). In the porcine cornea experiments, CV values of 1.0% and 1.4% were obtained for the old and young cornea samples, respectively.
Conclusions :
The BOSS measured the biomechanics of various materials, including corneas and lenses, with high precision and repeatability. Consistent with the fact that the crystalline lens becomes harder with aging, this study showed greater Brillouin stiffness in old porcine eyes than in young. Based on the proven measurement accuracy and repeatability, there are many possible applications for biomechanical properties: diagnosis of ophthalmic disorders, such as keratoconus; providing reference parameters for cataract or refractive surgeries; and functioning as a tool to prove the efficacy of newly developed medicines such as lens-softening drugs for presbyopia.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.