Keratron
™
Onda Installation and operating manual
OPTIKON 2000
Cod. 161401EN
10-25
2015-03-27
Rev.C
10.3.1 VERIFICATION
OF
ABERROMETRY
ACCURACY
USING
THE
CALIBRATION SPHERE
Insert the calibration sphere in the accessories hole on the chin-rest and orient it as
much as possible in the direction of the mires cone. Acquire the image of the sphere,
as it were the eye of a patient, with the Topo-Aberrometry function (section 7.6),
trying to avoid excessive flashes and retinal reflections.
Disable [Auto Rx] and set the defocus for a value ranging between the nominal
refraction of the sphere at 4 and that at 6 mm.
After the image is acquired, process it using the command [Process All]. For the
aberrometry, a rotationally symmetric map like the one in Figure 10-1 should appear.
In the panel shown in
Rx (vd=0)
, verify the sphere's refection by setting
pupil=4mm
as well as
pupil=6mm
, and compare it with the nominal data listed on the calibration
sphere itself.
The value of the sphere-equivalent [enclosed in square brackets] should not deviate
by more than ± 0.12 D from the nominal values. Even the residual astigmatism
(cylinder) should be less then 0.12 diopters. If the measurements should exceed
these limits, it is advisable to repeat the acquisition at least 3-4 times, trying to orient
or center the sphere differently, and calculate an average
The one in Fig. 10-1 is an example of a positive verification. In fact, the sphere
equivalent deviates by 0.05 - 0.06 D from the nominal values (-1.69 instead of -1.63,
and -103 instead of -0.98) and the residual astigmatism is only 0.03 D.
Figure 10-1: Verification of aberrometry accuracy using the calibration sphere
