The BOSS (Intelon Optics, Boston, MA, USA) is classified as an ANSI Z80.36 group 1 instrument for all single and combined light sources used in the instrument. The beam from the laser source of the BOSS is collimated to a diameter of 3.3 mm, undergoes divergence and convergence along the beam path, and is ultimately focused on the lens (with a focused beam diameter of approximately 5 µm). The light scattering produced by the Brillouin effect is imaged by BOSS and analyzed using an integrated high-resolution spectrometer to determine the spectral offset of the laser beam (
Fig. 1A). Longitudinal modulus of elasticity was calculated using the wavelength shift determined by the spectrometer based on established scientific relationships. Brillouin longitudinal modulus (M) was calculated from the Brillouin frequency shift (υB) according to the following relationship
18,21–25:
\begin{equation*}M = \frac{\rho \upsilon {B}^2\lambda^{2}}{4n^2sin^{2}\left( \theta/2\right)}\end{equation*}
where ρ is the mass density, λ (780 nm) is the optical wavelength in air, n the refractive index, and θ is the angle between incident and scattered light (180 degrees in our experimental condition). The ratio of ρ/n
2 was treated as a constant value of 0.5636 g/cm
3, consistent with the approach used by Besner et al.
18 for human lenses. The Brillouin frequency shift (υB) can be expressed as:
\begin{equation*}
\upsilon B = \frac{{2n}}{\lambda }V\cos \left(\frac{\theta }{2}\right)
\end{equation*}
where
V is the acoustic velocity. The laser power used in this experiment was 5 mW, which complies with the safety guidelines established by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for lens and cornea thermal hazards.
30 The same experienced physician examined the patient’s lenses using BOSS’s “Lens 1 pt” mode, ensuring that the measurement point was as close as possible to the center of the pupil, with no more than 1 mm deviation from the center of the pupil, in order to obtain data on the patient’s lenses (
Figs. 1B,
1C). The theoretical basis of this device for the detection of ocular longitudinal modulus and the delineation of the region of longitudinal modulus of the lens is derived from the study of Besner et al.
18 All participants were examined in a dark room at a temperature of 22 to 24°C. Participants were instructed to gaze at a fixed point generated by an LED light source, which was optically set at infinity to ensure relaxed accommodation during the measurement. Participants were asked to try to avoid intentional rapid blinking or excessive movement during the measurement, and the scanning process lasted approximately 50 seconds. Natural blinking was allowed throughout the test to maintain tear film stability and ocular comfort. Patient lenses were examined multiple times, and the average of the three scans with a Weighted Quality of “GOOD” and little fluctuation in pupil position was included in the subsequent statistical analyses. As shown in
Figure 1D, “little fluctuation” refers to a trajectory that approximates a horizontal line, indicating stable pupil positioning throughout the measurement. Scans with significant deviations or irregular patterns were excluded from the analysis.