Welch Allyn 18200 Bedienungsanleitung Seite 8

3. Test for neutralization by one of these methods:
a) Move the sleeve all the way up (concave mirror
position); the reflex should also appear neutralized;
b) Move closer to the patient and "with" motion should
return; move away and "against" motion should
appear, or
c) Place an extra +0.25 sphere in the apparatus and
"against" motion should appear;
4. Repeat the neutralization in the meridian 90° away.
B) Locating the axis of astigmatism:
Two phenomena help in determining the axis of astigmatism:
break and width. Break is observed when the streak is not
aligned with a principal meridian of the astigmatism (Figures 3
and 5). The streak will be aligned with a principal meridian
when the break effect disappears and the width of the reflex is
narrowest (and it appears its brightest) (Figure 6).
Proceed with neutralization as before—neutralizing one principal
meridian first, then 90° away to neutralize the second principal
meridian (Figures 7 and 8).
Figure 7
Figure 6
6
Figure 8