Biometrics on the Eye Model

Measurement of sound travel times on an eye model as a typical biometric ultrasound application

The measurement of sound travel times on an eye model on an enlarged scale provides a typical biometric ultrasound application based on the A-image method (A-scan) in medical diagnostics in ophthalmology.

Keywords: Ultrasound echography, pulse-echo technique, sound transit time, sound velocity, reflection and transmission, reflection and transmission coefficient, A-scan, sonography of the eye, biometry

Ophthalmology is another medical field in which ultrasound is used. Here, ultrasound is particularly important for the biometric recording of the eye, i.e. the measurement of distances in the eye. For example, the distance between the cornea and the iris is very important for calculating the properties of an artificial lens, such as that implanted in patients with cataracts. Since the cornea or the lens are too cloudy for optical methods, the use of ultrasound methods is required here. Even though new methods using laser light or the ultrasound B-image method are used today, time-of-flight measurements of the ultrasound echoes of an A-scan of the eye offer a simple way of measuring the eye. When calculating the sound paths from the measured sound travel times, it must be taken into account that different sound speeds occur in the cornea, the lens, the vitreous humor or the other areas of the eye. In the eye model provided, the speed of sound in the lens is about 2500 m/s and in the vitreous humor about 1410 m/s.

Allocation of echo signal and origin

The figure shows a schematic representation of the eye model and an A-scan recorded with the measurement software. The individual ultrasound echoes are assigned to the locations where they originate in the eye model.

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