Welch Allyn 18200 User manual

Streak Retinoscopy
Part Number 18200
La rétinoscopie à strie
No de référence :18200
Strichskiaskop
Teile-Nr. 18200
Retinoscopía de franja
No. de repuesto 18200
Retinoscopia a striscia
N. referenza 18200
English . . . . . . . .1
Français . . . . . .14
Deutsch . . . . . .28
Español . . . . . .42
Italiano . . . . . . .56
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Thank you for purchasing the Welch Allyn No. 18200
3.5v halogen streak retinoscope. This instrument
has been designed to meet the needs of today’s
practitioners and incorporates features not found
on any other retinoscope:
1. External Focusing Sleeve—unique planetary gear
system allows for easy adjustment no matter what size
hand or how instrument is held. Continuous 360°
rotation. Maintains the same plane of focus during
rotation.
2. Improved Light Output—brighter halogen lamp
provides 50 percent more intensity than previous lamps.
The reflex is now crisper and easier to see in all patient’s
eyes. Retinoscopy can be done faster and more accurately.
3. Dust-free Optics—new housings and glass cover on the
front keep the instrument cleaner longer.
4. Crossed Linear Polarizing Filter—dramatically
reduces glare from lenses. Allows retinoscopy to be
performed closer to the axis of the correcting lenses.
5. Fixation Cards—new cards that easily attach increase
the ease with which dynamic retinoscopy is performed.
6. Improved Optics—glare and shadows have been
eliminated for a clearer and more precise view.
7. Interchangeability—By simply changing the lamp,
the streak retinoscope can be converted to a spot
retinoscope.
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1
Introduction
Retinoscopy is a technique for objective refraction of the eye. There
are two basic types of retinoscopy. Static retinoscopy (described in
this booklet) is done with the patient fixating at a distance. Dynamic
retinoscopy is done with the patient fixating at a near target. These
techniques require diligence and expertise that can result in a
precise measurement of the refractive error of an eye.
There are two types of self-illuminated retinoscopes. The streak
retinoscope featured in this booklet is the most widely used
scope today and has largely supplanted the spot retinoscope. In
retinoscopy, a parallel or slightly divergent beam of light is directed
into the patient’s eye. This results in illumination of the retina, and
the reflected light from the retina causes reflexes observed by the
examiner in the patient’s pupil. The refractive status of the eye is
found by using correcting trial lenses to make the far point of the
ametropic eye conjugate to the pupil of the examiner’s eye. When this
is achieved, the movement of the reflex will be neutralized.
The material in the booklet is presented with the assumption that
the reader is familiar with retinoscopy in general. Two excellent
references for retinoscopic technique are:
Corboy, J.M.; The Retinoscopy Book, 3rd Edition, 1989, SLACK Incorporated.
or on videotape: Guyton, D.L.; Retinoscopy: Minus Cylinder Technique or
Retinoscopy: Plus Cylinder Technique, 1986, American Academy of
Ophthalmology—Continuing Ophthalmic Video Education.
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The streak retinoscope is found by most practitioners to be easy to
use, fast, accurate, and especially valuable in determining the axis of
astigmatism.
There are several features of the streak retinoscope that make
determining the refractive state of the eye easy and accurate. These
are:
1. Each meridian can be neutralized separately.
2. All errors can be neutralized using either “with” or “against”
motion or perhaps using both.
3. The axis of astigmatism is apparent.
4. Streak retinoscopy is easy because one watches a band of light
instead of a shadow.
5. Streak retinoscopy may easily be done with undilated pupils.
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3
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
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B) Position yourself 2/3 meter (26") from the patient. This
distance implies a working lens of +1.50D (computed as the
reciprocal of working distance in meters). Working distance
and lens may be varied to suit the practitioner’s needs. (In
this instruction book the 2/3 meter (26") working distance
is assumed. Different working distances can be used, but
remember to adjust for your working distance.)
C) With the refracting equipment in place, direct the patient’s
attention to a fixation spot at 15 feet or more from the eye
and align the streak vertically.
D) Observe the “reflex” which will appear as in Figure 2,
providing no oblique astigmatism is present. If oblique
astigmatism is present, the reflex will appear more like
Figure 3, where the reflex does not appear vertical.
E) Move the vertical streak horizontally across the pupil and
back again and observe whether the reflex moves in the same
direction as the streak or in the opposite direction.
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Figure 2 Figure 3
No oblique astigmatism Oblique astigmatism
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F) Rotate the control sleeve until the streak is horizontal
and move the streak vertically. The reflex will appear as in
Figures 4 or 5.
G) If the streak and the reflex move in the same direction with
no lens in the refractive apparatus, the refraction is one of
these:
1. Hyperopia;
2. Emmetropia;
3. Myopia of less than 1.50 diopters.
If the reflex moves in the opposite direction, the error is myopia
greater than 1.50 diopters.
3. Determining Refractive Error By Neutralization
Before starting, make sure the eye not being refracted has some
“against” motion using the plano mirror effect. This will blur vision
to prevent accommodation. If “with” or neutral motion is noticed
initially, place about a +1.00 sphere before the eye once neutral
motion is seen.
A) Neutralizing with spheres only:
1. Change sphere in the minus direction until the reflexes in
all axes have “with” motion.
2. Adjust in the plus direction until the reflex fills the pupil
in one meridian and all motion has stopped. This will be
one of the principal meridians if astigmatism is present.
That meridian is then said to be neutralized.
Figure 4 Figure 5
No oblique astigmatism Oblique astigmatism
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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).
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Figure 6
Figure 7 Figure 8
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4. Interpretation of Results
A) Hyperopia
1. Hyperopia exists when, at the 2/3 meter distance using the
plano mirror effect, “with” motion is neutralized using a
plus lens greater than +1.50 diopters and both meridians
neutralize with the same strength lens.
2. Total hyperopia is estimated by subtracting 1.50 diopters
from the total strength lens used. For example, if it takes a
+2.50 lens to neutralize motion at 2/3 meter, the total
hyperopic error is +1.00 diopter.
B) Myopia
1. Myopia exists under several circumstances.
a) When “with” motion, using the plano mirror effect at 2/3
meter, is neutralized with a plus lens of less than 1.50
diopter strength. (When motion is neutralized with
exactly a 1.50 diopter lens, the eye is emmetropic.)
b) When at 2/3 meter, using the plano mirror effect, no
motion appears at all. In other words, when the motion
is neutralized with no lens in the refracting apparatus.
The myopia is then exactly 1.50 diopters.
c) When the motion is “against” using the plano mirror
effect, and is neutralized with a minus lens.
C) Astigmatism
1. Astigmatism exists when the two principal meridians
neutralize with different strength lenses. It may be present
in many forms.
a) Simple hyperopic;
b) Simple myopic;
c) Compound hyperopic;
d) Compound myopic;
e) In the mixed form
(one meridian hyperopic and the opposite one myopic).
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2. Astigmatism can be measured in one of two ways:
a) Neutralize one principal meridian first. Then add the
appropriate plus or minus cylindrical lens until the
other principal meridian is neutralized.
b) Neutralization may also be done by continuing to add
spherical lenses until the second principal meridian
is neutralized. Then the astigmatic error is equal to
the difference in strength of lenses necessary to
neutralize the two meridians.
5. Special Considerations
A) Axis of astigmatism: Extreme care must be used in setting the
axis of the cylinder. If the correcting cylinder is of the proper
power, a 10° error in axis will produce a new astigmatism
of approximately one third of the strength of the original
astigmatism with its principal meridian at approximately 45°
to those of the original astigmatism. The technique for setting
the axis is referred to as “straddling”. When you have an
approximate correction of the refractive error and wish to
refine the axis setting, the following technique will be helpful.
Move up closer to the eye so that the edges of the reflex can
be seen, and compare the widths of the two reflexes as you
rotate the streak 45° to either side of the correcting cylinder
axis. Recede slowly while doing this. Compare the widths of
the two reflexes. If there is an axis error, the reflex will be
different widths in the two positions. If you are using plus
cylinders, rotate the axis toward the narrow band until the
reflex widths are equal. With minus cylinders, move the axis
away from the narrow band. When the reflex widths are
equal, the proper axis has been determined. It is important
that the spherical and cylindrical strength be checked again
after completion of this maneuver.
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