---------------------------------------------------------------------------------------------- Auto Ref/Keratometer HRK-8000A 63
(2) Vertex Distance (VD)
Vertex Distance is the distance between the backward vertex of the correcting lens (eye side)
and the vertex of cornea.
VD influences the refraction power of eyesight correction lens. If VD is increased, refraction
power of correction lens is needed to be smaller, whereas, if VD is decreased, it is needed to be
larger than that of the standard VD as the following equation.
(example)
F
1
＝
+ 1 0 D ,
d
＝
+ 3 m m : F
2
＝
+ 9 . 7 1 D
F
1
＝
+ 1 0 D ,
d
＝
- 3 m m : F
2
＝
+ 1 0 . 3 0 D
F
1
＝
- 1 0 D ,
d
＝
+ 2 m m : F
2
＝
- 9 . 8 0 D
F
1
＝
- 1 0 D ,
d
＝
- 2 m m : F
2
＝
- 1 0 . 2 0 D
The following four kinds of data can be chose according to examinee in
„User Setup Mode‟.
VD
＝
0 . 0 m m : h a r d c o n t a c t l e n s
VD
＝
1 2 . 0 m m : l e n s o f g l a s s e s ( o r ie n t a l p e o p le )
VD
＝
1 3 . 5 m m : l e n s o f g l a s s e s ( w e s t e r n p e o p le )
VD
＝
1 5 . 0 m m : l e n s o f g l a s s e s ( w e s t e r n p e o p le )
(3) Cylinder Form
There are three kinds of cylinder form.
－
:
A form displaying the data using minor meridian. Refraction power of the minor
meridian is displayed as SPH and the axis as AX. The difference between the major
and minor meridian is displayed as
–CYL.
＋
:
A form displaying the data using major meridian. Refraction power of the major
meridian is displayed as SPH and the axis as AX. The difference between the major
F
2
＝
F
1
1 +
d
F
1
1000
F
1
: Refraction Power with the standard VD in diopter
F
2
: Refraction Power with changed VD in diopter
d
: Difference between two VD in the unit of mm
