Section 3
A-Scan Operation and Use
3
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4.
Prepare Immersion Shell (see instructions
provided with shell)
. Unscrew the probe
handle and pull it away from the probe tip.
Insert the probe tip into the shell, advancing
the probe until its tip is parallel with the line
scored in the shell barrel. Once the correct
position has been obtained, ensure that the
probe is secure.
IMPORTANT
Proper measurement data will only be
obtained if the probe is properly placed in
the Immersion shell. Proper positioning
must be confirmed by examining the
captured scan waveform.
Once the probe has been positioned within
the shell, attach a tubing set to the shell.
Consult the instructions supplied with the
particular Shell for proper use. Fill a 5cc or
10cc syringe with saline or BSS and connect
to the tubing set.
5.
Applying the Immersion Scleral Shell
. Rest
the syringe on the towel which has been
placed on the patient’s shoulder, and hold
onto the shell with probe in preparation for
insertion. Direct the patient to look
downward, toward the floor. Lift the
patient’s upper eyelid and insert the flared
rim underneath the lid (the upper portion of
the shell should make contact with the sclera
while the lower part should be held away
from the eye). Then direct the patient to look
straight ahead toward
the red fixation light
in the probe tip. Pull the patient’s lower
eyelid down and
gently pivot
the lower
portion of the shell into the lower fornix (i.e.
NOT
sitting atop a fold in the conjuctiva).
This pivotal motion avoids contact with the
cornea and ensures centering of the device
around the limbus.
6.
Scan Eye
. Press the footswitch and pick up
the syringe from its place on the patient’s
shoulder. Slowly inject the saline or BSS
into the shell. As soon as the liquid fills the
shell sufficiently to reach the tip of the probe
(about 2cc), the characteristic waveforms of
immersion biometry will be visible on the
display. Gently tap the side of the probe tip
to insure that no air bubbles have been
trapped on the tip of the probe.
7.
Automatic Image Capture
. If the scan meets
all the parameters of the selected
examination mode, it will immediately be
frozen, saved and a long audible tone will be
emitted signifying that the instrument has
accepted the measurement. The proper
location of the corneal echo should be
confirmed on the scan waveform (see Figure
3-8). The first spike seen on the waveform
is the probe “main bang” followed by the
corneal echo. The acceptable position for
the corneal echo is indicated by the corneal
echo window (horizontal bar) displayed
below the waveform. The echo from the
cornea must fall within this window for a
proper immersion scan. If the corneal echo
is outside of this window, the position of the
probe within the Scleral Shell should be
adjusted accordingly.
Figure 3-8 Immersion Mode Record Print
If necessary, the gain control may be
adjusted by rotating the
[ GAIN ]
knob
located to the right of the Measure Screen.
The resulting gain setting will be displayed
in the bottom center of the display.
Frequently a lower gain setting may be used
in Immersion scanning than typically used in
Direct Contact mode.
Once accepted, the scan pattern will be
displayed on the screen; the axial length will
be calculated and stored under “SCAN 1” in
the upper center of the Measure Screen. The
anterior chamber depth and lens thickness
will also be displayed. Gate markers will be
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