Section 3 A-Scan Operation and Clinical Use
WATER IMMERSION TECHNIQUE
In addition to direct contact measurements, a
water immersion technique may be used with the
P
ACSCAN™ in order to completely eliminate
concerns over corneal compression skewing
results. The technique requires the use of a
Prager scleral shell set and is described below
using the automatic capture examination mode.
1. Examination Mode. Ensure the correct
examination mode is selected as indicated in
the upper right corner of the Measure
Screen. The examination mode may be
changed by touching the mode button until
the desired mode is shown. The following
automatic capture examination modes are
available:
¾ Cataract
¾ Dense Cataract
¾ Aphakic
¾ Pseudophakic
2. Tissue Velocity. Ensure the appropriate
tissue velocity is selected as indicated in the
upper right corner of the Measure Screen
(the system default tissue velocity is 1548
m/s).
The tissue velocity may be changed by first
touching the [ TVEL ] button to display the
Tissue Velocity Screen (see Figure 3-6).
Touch the [ TVEL ] button again to edit the
tissue velocity, enter the appropriate
number, and touch the [ ENTER ] button.
Verify that the tissue velocity has changed
when returned to the Measure Screen.
For Pseudophakic eye types use the
[ LENS ] button to select the proper lens
type and set the tissue velocity accordingly.
3. Immersion Option. Ensure that the
immersion option is ON as indicated in the
lower left corner of the Measure Screen. The
immersion option may be toggled between
ON and OFF by touching the [ IMMER ]
button.
4. Prepare Prager Scleral 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,
tighten the white nylon set screw to hold the
probe in place.
IMPORTANT
Proper measurement data will only be
obtained if the probe is properly placed in
the Prager 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
Prager Shell for proper use.
Fill a 5cc or 10cc syringe with saline or BSS
and connect to the catheter.
5. Applanating the Prager 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.
Doc # 0300-A-1901-3D 3 - 7
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