15
DEUTSCH
ENGLISH
FRANÇAIS
ITALIANO
ESPAÑOL
NEDERLANDS
PORTUGUÊS
SVENSKA
DEUTSCH
ENGLISH
FRANÇAIS
ITALIANO
ESPAÑOL
NEDERLANDS
PORTUGUÊS
SVENSKA
© HAAG‑STREIT AG, 3098 Koeniz, Switzerland ‑ HS‑Doc. no. 1500.7220055‑04150 – 2022 – 09
5.5 Measured variables
5.5.1 A-Scan
Depending on the patient’s gaze at the fixation light,
the optical path length of the visual axis is meas-
ured (34).
CCT: Central corneal thickness
AD: Aqueous depth (back of cornea to front of
lens).
LT: Lens thickness
AL: Axial eye length (front of cornea to the inner
limiting membrane).
NOTE!
Since the device measures up to the retinal pigmented epithelium, the
reading displayed is adjusted to the internal limiting membrane, either
automatically, as a function of axial length, or manually, according to the
mode selected. (Manual correction is not available in the USA)
5.5.2 Keratometry
Keratometry is calculated through the position of 32 projected light reflections. Two
rings, with sixteen measuring points on each eye are arranged in two rings with the
following diameters:
(standard eye R=7.8 mm)
Outer measuring points:
Inner measuring points:
2.3 mm
1.65 mm
For each measuring point, the equivalent of an ideal sphere is calculated.
The values displayed (flat radius, steep radius) corres-
pond to the radii of an ellipsoid that fits into the array
of points. The axis of its rotation is measured counter-
clockwise from the horizontal to the flat radius (35).
• a: Flat radius
• b: Steep radius
• c: Axis of rotation
5.5.3 White-to-white distance
The white-to-white distance (WTW) is determined using the image of the iris and the
eye radii obtained from keratometry. The value displayed corresponds to the diamet-
er of an ideal circle (36).
5.5.4 Pupillometry & visual axis
Pupil diameter (Ø) corresponds to the diameter of an ideal circle, with the smallest
error perpendicular to the established pupil border. At the same time, the shift of
visual axis towards the centre of the pupil is provided. The calculated dimensions
are located on the theoretically derived level of the iris. The image enlargement
achieved by the refraction of the eye is disregarded (37).
