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The basic streak reflexes
As you move the streak across the pupil, there are four basic types of
reflexes that will be seen:
- "with"-motion
- "against"-motion
- a "neutral" reflex
- an undetermined reflex
The basic reflexes are illustrated below. An undermined reflex is a
reflex that cannot be recognized as one of the other three. It may be a
scissors type reflex, a reflex too dim to make out, or any reflex
that is confusing to you as a retinoscopist.
Our patient is positioned behind the phoropter. We are using the widest
possible streak, as discussed in Section 1. This is the sleeve-up
position. The streak is oriented vertically and we are sweeping across the
180 degree meridian. This is called "streaking 180". The
streak really looks like a bar of light, but in these illustrations the
center of the streak is clear so that you can see better what is behind
it. As the streak strikes the pupil, a reflex is seen as described
below.
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With-motion: As the streak moves
across the pupil, the reflex moves across the pupil in the same
direction as the streak. |
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Against-motion: As the streak moves across the
pupil, the reflex moves in the opposite direction as the streak. |
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Neutral reflex: Once the streak touches the
pupil, the pupil lights up and remains constant as the streak
moves across the pupil |
When performing retinoscopy, it is your task to convert with-motion or
against-motion to a neutral reflex. This is accomplished by adding lens
power with the phoropter. It is much easier to approach neutrality and to
determine neutrality from the with-motion direction. Therefore, a
basic technique we will use will be to convert against-motion to with-motion
before beginning the neutralization process.
Procedure for neutralizing spherical refractive errors
Fortunately for us as technicians, most eyes are not optically
spherical. Most eyes have some degree of astigmatism. I say
fortunately because if every eye were spherical, then patients could
refract themselves and our skills would be less
valuable in the job market. Although you may not know before hand whether
or not an eye is optically spherical, the procedure for
neutralizing a spherical correction serves to demonstrate the basics of
neutralization by retinoscopy.
- The patient is set up as is discussed in the previous
section. Begin
by streaking the patient's right eye with your right eye. Of
course, the retinoscope is in the sleeve-up position.
- Scope the four primary retinoscopy meridians (90, 180, 135, and 45
degrees) by moving the streak back and forth along each of these
meridians. Although the meridian of any astigmatism present may not
fall exactly on one of the primary meridians, we will be able to
detect any astigmatism present by streaking these primary meridians. In the illustrations above the 180 degree meridian is being
streaked. Notice the motion of the reflex.
- There are four possible situations that will arise with a spherical eye:
A. You may see against-motion in each of the primary
meridians. In this case you must convert the against-motion to with-motion. You do this by adding minus spherical power. In other
words, you turn the sphere wheel in the minus direction.
You began your retinoscopy at plano (no lens power), so change the
sphere power to -1.00. Streak the primary meridians again. If
you do not see with-motion in every meridian, add another -1.00 D
sphere power (you are now at -2.00) and streak the primary meridians
again. Continue adding minus sphere power and streaking all the
primary meridians until you see with-motion in all the meridians. Go
to step 4.
B. You may see a neutral reflex in each of the primary
meridians. In this case you will need to confirm that it is indeed a
neutral reflex. This is done by converting the reflex to with-motion. As with
against-motion, you will add minus sphere power
1 diopter at a time while you streak the primary meridians. Once you
see with-motion in all the meridians, stop adding minus power and go
to step 4.
C. You may see an unrecognized reflex in each of the primary
meridians. In this case try to convert the reflex to with-motion by
adding minus sphere power as discussed above. If the reflex cannot be
converted to with-motion after adding several diopters of minus sphere
power, you may be dealing with a very high refractive error, or
a distorted reflex.
Try to recognize a high refractive error by changing the sphere power
-3.00 diopters at a time while streaking the primary meridians. If you
cannot convert to with-motion by going in the minus direction, rule
out a high plus refractive error by returning to plano and adding plus
sphere power 3 diopters at a time while streaking the primary meridians.
If nothing seems to work, you may be dealing with a reflex
distorted by a cataract, an edematous cornea, an opaque
posterior capsule, or some other optical distortion. You can
usually confirm this by examining the eye with the slit lamp
microscope. In this situation you can use the keratometer to try to
measure any astigmatism and use this information to begin refractometry.
D. You may see with-motion in each of the primary meridians.
In this case, go to step 4.
As stated earlier, it is best to neutralize using with-motion. If you do not have with-motion in every meridian, you
add minus sphere power until you get it. Now that you have a with-reflex in every meridian, you will begin the neurtalization process.
To neutralize, start adding plus sphere
power, 1/2 diopter at
a time, while streaking each of the primary meridians after each
addition of plus sphere power. If you
are a long way from neutrality, the with-reflex will be wide and
"slow". As you approach neutrality, the streak reflex
will narrow somewhat and appear to speed up. As you reach neutrality, the
reflex will quickly widen and fill the pupil with the "neutral
reflex". If the eye is spherical, each of the primary
meridians will neutralize at the same time. If the eye is
astigmatic, then one of the meridians will neutralize before the
others do.
The final step is to adjust for your working distance.
This must
be done because you are working at a distance from the eye (arm's length)
that is closer than infinity. For most people the adjustment will be
-1.50 D sphere power. If you work a little farther away, the
adjustment will be about -1.00. If you work a little closer, the
adjustment will be about -2.00 D. This amount is subtracted (six
clicks on the sphere wheel for -1.50) from your neutrality reading to arrive at your
final estimate of the refractive error.
This working distance adjustment assumes that you are emmetropic when you
are performing the retinoscopy. In other words, you are using
any distance correction that you might need. If not, you will
also need to adjust for your refractive error. As you gain experience,
the easy way to make these adjustments is to note how far you are off in
your retinoscopy (on a consistent basis) and make an appropriate
adjustment.
Example
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We begin streaking with the phoropter
sphere setting on zero and notice that there is a reflex that shows
against-motion in all meridians. In this example we are streaking
the 135 degree meridian. See the animation above for an example of
against motion. |
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If we do not see with-motion in all
meridians, the rule is that we add minus sphere power until we do
see with-motion in all meridians. So we change the sphere power to
-1.00 and streak all of the primary meridians again. We still
detect against-motion but the streak has become wider. In this
illustration we are streaking the 180 degree meridian. |
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As pictured above, we are still seeing
against-motion, so we add another -1.00 D sphere power to make the total
sphere power -2.00 now. This change gives us what appears to be a
neutral reflex, as pictured to the left. |
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Given the neutral reflex as seen
above, it is still not with-motion, so we add another -1.00
D sphere power to make the total sphere power -3.00. Now we are
seeing a steak reflex that has with-motion in all meridians, as
pictured to the left. Here we are streaking the 90 degree
meridian. |
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We now begin the neurtalization process by
adding +0.50 D sphere power and again streaking all of the primary
meridians. The total sphere power is now -2.50 and we notice that
the streak is widening but there is still with-motion. |
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Another +0.50 is added to the sphere
power, making the total -2.00 now. The pupil seems to be filling
with light but there is still a little with-motion. We add another
+.25 D sphere power and the pupil illuminates and the with-motion is
gone. We check all of the primary meridians to confirm
neutrality. The sphere power is now at -1.75 D. It would
have been OK to stop at -2.00 D also, with a small amount of with-motion
remaining. |
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| We are not finished
yet. We have to subtract our working distance. We
change the sphere wheel -1.50 D, giving us a final value of
-3.25. This is our refractive error estimate and our starting
point for refractometry. Seeing against-motion at the beginning of
the retinoscopy gave us a clue that we were dealing with a myope. |
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Streak
reflex width and streak speed
In general, the width of
the streak reflex and the apparent speed of the streak reflex as it moves across the pupil
give an indication of how far you are from neutrality. Young eyes that are
not diseased and have not had surgery give the most defined reflexes.
Corneal diseases, cataracts, IOLs, hazy posterior capsules, and cloudiness in
the vitreous distort the reflexes and change the "rules" of
appearance. Sometimes width and speed do not give reliable clues and you
must just rely on apparent with-motion to arrive at the best retinoscopic
estimate.
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A very wide (almost filling the
pupil), slow moving streak reflex indicates that you are a long way from
neutrality. For instance, the with-reflex you would see at
plano when streaking a +5.00 hyperope. |
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As we add plus sphere
power the streak tends to narrow and speed up in its apparent
motion. |
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As we continue adding plus
sphere power and approach neutrality, the streak widens again and
speeds up even more. |
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At neutrality the streak reflex
widens more to completely fill the pupil. |
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Go to: Section 3
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