Huvitz CRK-1, Руководство по обслуживанию, Страница: 83 / 88

82 Auto Ref/Keratometer CRK-1 ------------------------------------------------------------------------------------------------
7. Technical Materials
(1) Fogging Method
It is recommended that the refractive power of eye is measured when it is in the hypero
pia-state. There happens some measurement error called mechanic myopia due to the ac
commodation of eye when it is measured by locating the internal eye-fixing target to the
position corresponding to the eyesight of examinee.
Foggy method is the method that the size of the target is modified to be greater than th
e eyesight of the examinee by +1D ~ +2D in order to reduce the error caused by this a
ccommodation. There is also another method called accommodation paralysis method. Me
chanic myopia occurs more easily in the case of the youth. Additionally, the accommodati
on of eye is one of the functions of the eye. It controls the thickness of crystalline lens
according to the movement of the ciliary body and changes the refractive power of crysta
lline lens.
(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, refracti
on power of correction lens is needed to be smaller, whereas, if VD is decreased, it is n
eeded to be larger than that of the standard VD as the following equation.
F
2
＝
F
1
1 +
d
F
1
1000