Welch Allyn 18200 Manual Del Usuario página 5

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Technique
1. The Operation of the Control Sleeve
of the Scope
The operator will note that the width of the
streak varies as the sleeve is raised and
lowered (see Figure 1). When the operating
sleeve is in the lowest position the light rays
emitted are slightly divergent. Here the
instrument acts with a plano mirror effect,
which reflects divergent rays that will never
come to a focus. As the sleeve is raised, the
streak focuses. With the sleeve all the way up,
the retinoscope acts with a concave mirror
effect, where the light rays cross and then
diverge. Because the rays cross, the eye's
reflex moves in opposite directions with the
concave mirror effect as compared to the
plano mirror effect.
Throughout this booklet, we will use the
plano mirror effect unless specified.
The rotary movement of the control sleeve
mechanism allows the streak to rotate 360°
to ascertain the axis of astigmatism (see
Figure 1).
2. Preliminary Steps
A) Set the sleeve in its lowest position
(plano-mirror effect).
Figure 1
3