168
Accutome A-Scan Plus User’s Guide
How to Adjust
Gates/
Threshold
The Accutome A-Scan Plus takes measurements by
sending a signal through the eye via the ultrasonic
probe. The various parts of the eye have different
velocities. The signal passes through each part of the
eye at different speeds depending upon the acoustic
velocity of the eyes’ components. (If there is already an
IOL in the eye the signal will travel at a different speed
than it would through a natural lens.)
Each time the signal encounters a change in velocity,
due to the difference in material, the signal echoes off
that part of the eye and is transmitted through the probe
as a vertical spike in waveform. The vertical spikes in
the waveforms are events, or the point in time when the
signal encountered the different material. The Accutome
A-Scan Plus measures the distances between these
spikes and calculates the AXL value by summing all
pieces of the waveform.
The events the Accutome A-Scan Plus seeks when
scanning are:
Cornea
Anterior Lens (if eye is not Aphakic)
Posterior Lens (if lens thickness is
measurable)
Retina
There is also unnecessary information captured in a
waveform. There is a threshold for echoes to meet to be
included as part of the measurement.
Accuracy depends upon the location of the gates and
threshold along the waveform. The purpose of the
gates/threshold is to delimit events. The gates/threshold
tell the Accutome A-Scan Plus when to start looking for
the different events in the waveform. Events will be
detected to the right of the gate and above the threshold.
The location of detected events are displayed in the
scale below the waveform as indicated by solid black
triangles.
If an event is not detected or is associated with an
anomalous echo the user must reposition the gates/
threshold to properly measure the waveform.
To Next Page
Loading...
