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OPTOMETRY
OTHER MEASUREMENTS
Convergence and divergence Only in CV-5000
To measure convergence of a far point (5m), press the Prism [BO] switch to add prism for
"base out" to both eyes. When a vertical letter target of a visual acuity chart is seen double first
(where diplopia occurs first), record the value. This shows the convergence capacity of both
eyes.
With the rotary prism alone, the convergence of 40
Δ
(approx. 22°) can be measured.
To measure divergence, press the prism [BI] switch to add prism for "base in" to both eyes.
When diplopia occurs at the target first, record the value.
Vertical vergence
Only in CV-5000
To measure vertical vergence for a far point (5m), use the target of a horizontal letter line.
Press the prism [BU] or [BD] switch to add prism to both eyes. When a horizontal letter is seen
double first (where diplopia occurs first), record the value. This means the value of vertical ver-
gence.
POWER CONVERSION
Setting the measurement method by using the convex astigmatic lens
Since TOPCON designs instruments applied to the visual acuity measurement based on the
fogging method, this instrument contains the concave astigmatic lenses. If convex astigmatic
lenses are necessary, press [TRANSPOSE] of the controller. You can perform optometry by
using a convex astigmatic lens.
Power conversion
If the result of the visual acuity measurement based on the fogging method is hyperopic astig-
matism, perform power conversion because the astigmatic power of eyeglasses is displayed
as a plus value.
S (spherical power) C (astigmatic power) A (astigmatic axis)
→ S (spherical power + astigmatic power) C (astigmatic power × (-1)) A (astigmatic axis ±90)
This is the power conversion formula. That is,
S : Add the astigmatic lens power to the spherical lens power.
C : Change the symbols (+, -) of the astigmatic lens power.
A : Add 90° when the astigmatic axis is smaller than 90°.
Decrease 90° when the astigmatic axis is larger than 90°.
(Example) When "S" is +3.00D, "C" is -1.00D and "A" is 175°:
S : (+3.00) + (-1.00) = +2.00
C : – (-1.00) = +1.00
A : 175°– 90° = 85°
Therefore, "S" is +2.00D, "C" is +1.00D and A is 85°.