Relation between local acoustic parameters and protein distribution in human and porcine eye lenses

The purpose of this study is to characterize the eye lens (human, 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 microns. 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 23 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 literature. Additionally, Raman microspectroscopy was used to measure the local protein content of porcine lenses (n = 3). Profiles along the optical and equatorial axes were obtained. The relation between the protein content and the acoustic parameters was obtained qualitatively by comparison of the shape of the profiles and, where possible, quantitatively by calculating the Pearson correlation coefficients. Furthermore, the results have been related to a statistical metastudy found in literature in which the relation between collagen, protein and acoustic velocity in various biological tissues was investigated. The results show a gradual decrease of the magnitude of the acoustic parameters from the centre to the periphery of the porcine eye lens, which is clearly equivalent to the decrease in profiles of the protein content. 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 are found. It is concluded that protein concentration related phenomena can be investigated by measuring the acoustic parameters.