Section 3
A-Scan Operation and Use
3
- 5
Figure 3-7 Manual Mode Screen Display
Touch the
[ TVEL# ]
key to edit the tissue
velocity for a particular gate area, enter the
appropriate value, and then touch the
[ ENTER ]
key. Verify that the tissue
velocity has changed, then press
[DONE]
.
3.
Immersion Option
. Ensure that the
immersion option is OFF as displayed on the
[IMMER
] selection key. The immersion
option may be toggled “ON” and “OFF” by
touching the
[ IMMER/(ON/OFF) ]
key.
4.
Scan Eye
. Instruct the patient to look
towards the red fixation light in the probe tip
and visually align the probe along the
patient's visual axis. Move the probe forward
until contact with the cornea is achieved.
Once contact is made, a live A-scan pattern
will be displayed and no further forward
movement should be made.
5.
Automatic Scan 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.
If necessary, the gain control may be
adjusted by rotating the
Gain Control
knob
located on the panel to the right side of the
instrument. The gain (in dB) is displayed on
the bottom center of the display. The default
gain is 40; however a gain of 65 to 75 has
been shown to give satisfactory results for
most eyes. The gain setting may not be
changed for any scan which has already
been frozen.
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
location of the key structures in the scan
waveform will be indicated by flashing gate
markers displayed above the waveform as
well as a blinking red dot at the threshold
level of each echo. The anterior chamber
depth and lens thickness will also be
displayed (except for Pseudophakic eye,
where a default lens thickness is used, or for
an Aphakic eye).
IMPORTANT
It is important to remember that the auto
modes are meant to facilitate the
examination procedure but not replace the
examiner's clinical judgment. All scans
should be thoroughly evaluated by the user
prior to being accepted and used for
calculating lens powers.
6.
Repeat
. The protocol can be repeated to
obtain up to five (5) scans. As the scans are
captured, the axial length for each is
displayed in the upper center of the Measure
Screen. Additionally, the axial length
average and standard deviation for the group
of scans will be displayed. Each scan pattern
may be reviewed by touching the
[SCAN#]
button to scroll through the captured scans.
Deleting Scans
. If a scan is captured which is no
longer desired, it may be deleted by scrolling to
the scan (as described above) and touching the
[ DEL SCAN ]
button. Deleting a scan will
remove the scan pattern and all associated data
from system memory, and will exclude the
associated axial length from the average and
standard deviation calculations. If
all
scans are
no longer desired, they may all be deleted by
touching the
[ CLR SCANS ]
button.
NOTE:
In the event that an echo is erroneously
selected by the auto mode, the user can
reposition the gate to the correct echo by first
pressing the [GATE] key repeatedly until the
desired gate marker is flashing. Once selected,
the gate can be repositioned using the joystick
located to the right of the display.
!
