Development and evaluation of virtual instrument to supplement ultrasonic echoscope system for ophthalmology

The aim of this paper was twofold: first, to present a virtual instrument for characterization of the cataract severity in the lens of the eye, based on the indirect measurements of ultrasound attenuation coefficient, second, to evaluate the instrument in vitro by assessment of measurement errors in case of the four different phantoms with a priory known characteristics (pure water, castor oil, soybean oil, plexiglass) and measurement conditions (distance to the lens or sample in phantoms). We demonstrated that such virtual instrument can be built by using standard PC, ultrasonic transducer for ophthalmology, the shelf digitizer (Picoscope ADC 212/100, Picotech Ltd.), laboratory generator and popular software package LabView (National Instruments Inc.). The instrument is able to process acquired data and assess the attenuation coefficient of the material or tissue in real time and would be able to provide the ophthalmologist with the timely feedback. Results of the in vitro experiments show that the random error (precision of measurements) of the attenuation coefficient estimates is proportional to the absolute value of the coefficients and can possibly limit the power of the method to characterize the lens state at advanced cataract stages. While the systematic error (accuracy of measurements), which is due to ultrasound beam diffraction, limits the possibilities to use the method for early detection of cataract. More sophisticated ultrasound signal processing methods must be developed in order to reduce attenuation coefficient estimation uncertainty.