Acoustic characteristics of the eye lens

Abstract

The purpose of this study is to characterize the eye lens (human and porcine) by acoustic measurements and to investigate whether relations exist with the local protein content. The acoustic measurements were performed with a ‘scanning acoustic microscope’ (SAM), operating at a frequency of 20 MHz. At this frequency the lateral resolution in the acoustic images was 150 mm. A double-transmission pulse-echo technique was employed to obtain acoustic parameter images of a central, 1-mm thick slice of the lenses. The two-dimensional images were derived by ultrasonic spectroscopy displaying the ultrasound velocity, the attenuation at 20 MHz and the slope of the attenuation coefficient between 17 and 213 MHz. The images were summarized by profiles along the optical and equatorial axes of these parameters.

Acoustic parameters were obtained from human lenses (n = 13) and porcine lenses (n = 10). The protein contents of human lenses were obtained from the literature. Additionally, Raman microspectroscopy was used to measure the local protein content of porcine lenses (n = 3). The relation between the protein content and the acoustic parameters was investigated by comparing the axial and lateral profiles.

There was a gradual decrease of the magnitude of the acoustic parameters from the centre to the periphery of the porcine eye lens, which is clearly equal to the decrease in protein content profiles. For the human lenses the acoustic characteristics and the protein content exhibit the same profile, fairly constant in the lens nucleus and decreasing towards the periphery of the lens cortex. Strong positive correlation coefficients for acoustic parameters and protein content for the porcine lens were found.

It is concluded that protein concentration-related phenomena can be investigated by measuring the acoustic parameters.