A key, or the pushbutton on the joystick, or
the button pictured above. This activates the axial length measurement, or ALM, mode.
Ask the patient to look directly at the small red fixation light and take all 20 measurements. Be
sure to use the Best Measurement
Technique and sample several areas within the
measurement reticule until the best axial length display is obtained.
Continue to take measurements from that area.
At
least four measurements should be within 0.02 mm, and show an Ideal Axial Length Display. Delete
those measurements that do not show an acceptable axial length
display. It should be remembered that the quality of the axial length display is
usually more important than the signal-to-noise ratio.
Use the
Space bar
to go to the next measurement mode.
With the IOL Master, you can accurately determine the axial
length of eyes ranging from 14.0 mm to 40.0 mm.
Note:
By selecting either the axial length icon, or the A key you can switch to taking axial length measurements from any other mode. The pushbutton on the joystick will activate the axial length mode only while in Overview Mode.
To measure aphakic eyes, Pseudophakic
Eyes, or eyes filled with Silicone
Oil,
select the corresponding mode from the AL Settings menu. The type of
axial length mode you have will be displayed in the video image field and
will be active until it is reset via the menu. The instrument will
automatically be reset to the "phakic" mode by changing the side (moving to
other eye), or by measuring a new patient.
Note:
While measuring Pseudophakic
Eyes, a falsely short axial length may be
displayed, or two peaks may simultaneously appear. Typically, the peak with
the shorter axial length is a reflection from the IOL, while the second peak
comes from the retinal pigment epithelium. In this case, manual correction
is necessary. See: Pseudophakic Eyes and
Evaluation of AL Measurement Results.
On activation of ALM mode, the instrument automatically changes the
magnification; a more magnified section of the eye becomes visible, with the
reflection of the alignment light (number 2 in graphic above)
and a vertical line (number 1 in graphic above).
Ask the patient to look at the red fixation light. On the
display, a cross hair (number 3 in graphic above) with a circle
in the middle appears.
Fine-align the instrument so that the reflection of the alignment
light
appears within the circle.
Start the measurement using the
pushbutton on the joystick or foot switch.
Note:
Before taking the measurement, tell the patient once more to fixate on
the red fixation light, which lights more intensively during the
measurement. If the patient's visual acuity is poor, ask if she/he can
see the fixation point at all.
If the patient is not able to fixate, the
measurement may not be to the center of the macula and there is the
possibility of having the IOL Master display an erroneous axial length.
In order to achieve the best axial length display, measurements may
also be taken around (but still within) the measurement reticule. See:
AL Measurement Technique for an explanation.
In the case of poor visual acuity/high ametropia (> ±6 diopters), it is advisable to measure both through the patients glasses and
without glasses. If taken conscientiously, such measurements can produce
excellent results.
Measurements through contact lenses will lead to measurement errors
and therefore should not be performed. It is also advisable to have
the patient remove soft contact lenses for at least two days prior to
keratometry and axial length measurements. Rigid, gas permeable contact
lenses should be removed for two weeks prior to keratometry and axial length
measurements.
Measurements of eyes with retinal detachment will lead to measurement
errors and therefore should not be performed.
In the status bar, a blue progress barbar will appear. The corresponding
display field in the video image will show the measured axial length. The
video image is overlaid with a graph similar to those found with A-scan
ultrasonography instruments. At the same time, the axial length and the
signal-to-noise ratio (SNR) of the measurement are displayed.
The signal-to-noise ratio (SNR) is one of two different ways to determine
the overall quality of each measurement. Measurements with an SNR between
1.6 and 1.9 appear with an exclamation mark after the measured value. At the
same time, the message "Borderline SNR" appears on the display.
See: Post-run Editing of AL Measurement for the assessment of SNR.
With more dense lens opacities, it may be advisable to defocus the
instrument. You may choose a reflection (number 2 in graphic
above) as large as the circle on the display. If even then measurements are impossible, refocus the instrument and shift the reflection to the bottom and/or top margin of the measurement reticule on the display by varying the vertical
adjustment (turning the joystick).
Note:
Defocusing and shifting the reflection within the circle will not
produce any problems. This is because axial length measurements by partial
coherence interferometry are distance-independent.
If a valid measurement is achieved, you may assume that the displayed result
is the correct axial length. Again, please review the Best Measurement
Technique for more detailed information.
It is possible to take up to 20 axial length measurements per eye in one
day. By pressing the pushbutton on the joystick the next measurement of this
eye will be made.
After the second measurement the average of the axial length measurements
will appear. This value will be recalculated, and updated, with each
additional measurement. If the result of one measurement differs by more
than 0.2 mm from the other(s), an "Evaluation" message will be displayed in
place of the average. This indicates that the measurement results must be
edited later. See: Post-run Editing of AL Measurements.
The last measured value is always highlighted by a blue background.
You can immediately delete the current value if it is obviously the
result of an erroneous measurement by pressing the Del key and
confirming the action with the Enter key on the keyboard.
The number of measurements of the respective eye taken on this day is consecutively counted in the Mode field of the status bar beside "ALM". If the count reaches 20, you cannot take further
measurements of this eye on this day. It is not possible to
reset the counter. Deleted measured values do not affect the
measurement count.
Note:
Only in ALM mode is the fixation light RED ;
otherwise it is always YELLOW
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fixation light and take all 20 measurements. Be
sure to use the 
With the IOL Master, you can accurately determine the axial
length of eyes ranging from 14.0 mm to 40.0 mm.
The signal-to-noise ratio (SNR) is one of two different ways to determine
the overall quality of each measurement. Measurements with an SNR between
1.6 and 1.9 appear with an exclamation mark after the measured value. At the
same time, the message "Borderline SNR" appears on the display.
See: 
