OPTIKON KERATRON ONDA, Инструкция по установке и эксплуатации

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Keratron
™
Onda Installation and operating manual
OPTIKON 2000
Cod. 161401EN 5-4
2015-03-27
Rev.C
distance, for maximum peripheral coverage, and the distance that is 3 mm farther
away, to reduce invasiveness. This choice can be made during the topographic or
topo-aberrometric acquisition using the
touch-screen (for example buttons 3 and 4 in
Figure 7-23).
The cone is backlit by an LED matrix with two wavelengths: Near infrared (
λ=750nm)
for aberrometric recordings under scotopic conditions, and yellow-amber (
λ=590nm)
to capture the topographic images and the pupil contraction in daylight. A video
camera monitors and captures images of the eye in the two phases.
The operator thus can only take images, by pressing the pushbutton on the joystick
only when the patient eye is at a preset distance, which is the same distance at
which the instrument was formerly calibrated on a sphere having a known curvature
radius.
After the image has been acquired, specific algorithms reconstruct the shape of the
cornea by analyzing more than 7000 points located on the intersection between the
28 mires edges from black to white and from white to black and the 256 radials or
“meridians" .
The curvature values are represented on the screen in the form of chromatic maps.
The center of the rings is the corneal vertex , that is the point of the cornea which is
closer to the observing TV-camera, and that is an important reference point for all
corneal maps. The
entrance pupil is also detected.
5.1.3 ABERROMETRY
The projection of an emission band with a small cross-section, produced by a
superluminescent diode (SLD), , inside the eye for the purpose of generating a point
of light on the fovea, causes a wave front emerging from the eye itself. This front,
which is commonly called “retinal reflection,” is “distorted” on the return path by the
eye’s aberrations.
By means of the analysis of the wave front, it is possible to accurately quantify these
aberrations.
In the Keratron
™ Onda a measurement method is used in the image space
(modified Hartmann-Shack mtype sensor) in which the emerging band is projected in
turn on a lenslet array (Figure 5-4).