Essilor AKR 550, Maintenance Manual

Page: 5 / 62

4
3 Measurement Principle
1) Measurement of eye refraction
A measurement pattern for measurement of eye refraction is projected to an eyeground to
be measured.
The projected pattern changes its size depending on the eye’s refractive power. The reflect
light of this eyeground image is led to the sensor through the measurement system. The
detected data is stored in the frame memory and conducted pattern analysis by image
processing to calculate values of S, C and A.
Rough refractive power (temporary measurement) is calculated by the first measurement
and auto fogging operation and focusing operation of eyeground images are started based
on the data. Then, the actual measurement is started and the refractive power of the eye
to be measured is calculated and displayed.
2) Measurement of corneal curvature radius
A ring-shaped measurement pattern is projected onto a cornea of an eye to be measured.
The pattern projected on the cornea varies its size depending on the corneal curvature
radius. The projected light is led to the sensor through the cornea measurement system.
The detected data is stored in the frame memory and conducted pattern analysis by
image processing to calculate values of R1, R2 and A.
Subject’s eye
Cornea
Projected light
Corneal curvature
radius: small Corneal curvature
radius: large
Projected patterns on the sensor
Subject’s eye
Eyeground
Cornea
Projected light
Myopia
Hyperopia
Projected pattern on the sensor