Operation; Position Of Patient During Measurement; Fixation; Measured Variables - Haag-Streit LENSTAR LS 900 Mode D'emploi

 OPERATION

. Position of patient during measurement

The positioning of the device is done manually by the user. The pa-
tient must be positioned in such a way that the distance from the
measuring head to the eye is approx. 68 mm (Figure 52). A steady
head position is promoted by resting the patient's head well against
the chin rest and forehead band, and by the patient holding on to the
handles supplied. This can positively influence adjustment time and
measuring accuracy.

. Fixation

To obtain usable results, the patient must stare at the red fixation light
in the measuring lens during measurement. If the patient has difficu-
lty seeing the fixation light with the eye being measured, this can be
remedied by fixing the other eye on an opposed remote object.
To carry out peripheral measurement of corneal thickness, 32 green
fixation points are provided. These can be switched on or off by soft-
ware. The points are arranged in 2 rings. When the patient stares
at these points (Figure 53), a peripheral zone is measured with the
following distances (a) from the horizontal axis (standard eye R =
7.8 mm):
Outer distance: 2.7 mm
Inner distance: 2 mm
b: Fixation periphery
c: Eye
d: Fixation center (Measurement beam, red)

. Measured variables

.. A-Scan
Depending on the patient's gaze at the fixation light, the optical path
length of the visual axis is measured. (Figure 54)
CT: Corneal thickness
AD: Aqueous depth (back of cornea to front of lens)
LT: Lens thickness
AL: Eye length (front of cornea to retinal peak)
Note: Depending on the chosen software mode, eye length is in-
dicated to the inner limiting membrane (retinal pigment epithelium
– 0.2 mm).
.. Keratometry
Keratometry is calculated through the position of 32 projected light
reflections. Sixteen measuring points on each eye are arranged in two
rings with the following diameters (standard eye R = 7.8 mm):
Outer measuring points: 2.3 mm
Inner measuring points: 1.65 mm
For each measuring point, the equivalent of an ideal sphere is cal-
culated.
The values displayed (flat radius, steep radius) correspond to the
radii of an ellipsoid that fits into the assemblage of points. The axis
of its rotation is measured counter-clockwise from the horizontal to
the flat radius. (Figure 54)
e: Flat radius
f: Steep radius
g: Axis of its rotation
1500.7220055.04030
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