Accuracy
HD
Performance Anywhere You Go
Higher Definition = Higher Accuracy
High Definition Biometry significantly improves measurement errors
By sampling the ultrasonic reflections at a much higher rate than possible before, MMD has been able to increase the accuracy of its PalmScan A-Scan and Pachymeter devices. The discussion below explains why high definition sampling is so important to the accuracy of A-Scan and Pachymeter systems.
The Competition
High Definition Biometry has enabled us to achieve remarkable accuracy demonstrated by independent Studies (See PalmScan vs. IOL-Master Study) . The following text explains the reasons behind this improved accuracy.
Sampling is the acquisition of a continuous signal (the ultrasonic echo) at discrete time intervals and is a fundamental concept in real-time signal processing. Sampling error is a critical component of any digital biometry system. Since this error is not reduced by any type of averaging operation.
In what follows we give you an explanation of how sampling rate effects corneal thickness measurements. However, the same concepts apply equally well to Axial length measurements. The ultrasonic pulse travels at about 1640 m/s through the cornea; hence a pachymeter device that operates at 60 MHz sampling frequency has a sampling error of
In a 60MHz sampling rate system each sample corresponds to a time window of 16.7 nanoseconds. In other words, this system will integrate all the information within this time window into a single number and therefore is incapable of distinguishing between any information received within the 16.7 nanoseconds time window. Given that ultrasonic waves travel through the cornea at 1640 meters per second, we conclude that this system has an inherent sampling error of 27.3 microns.
In order to minimize this error, MMD’s High definition biometry systems utilize a sampling rate of upto 264MHz. This significant increase in sampling rate minimizes the PalmScan’s sampling error to 3.1 microns.
Not only is sampling speed important to the accuracy of the system, it also plays a key role in the reconstruction of the ultrasonic corneal waveform . Using a high frequency sampling system, we can reconstruct a very accurate representation of the ultrasonic echo.
Many device Manufacturers do not divulge the system’s sampling rate, but as an informed consumer be sure to ask for it.
