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How do our eyes move?
Each
eyeball has 6 eye muscles around it, moving it as the brain directs it to go.
In the Figure above, you can see the eyeball
in a side view and front view. The lateral and medial recti (circled in the Figure) are the two eye muscles that control the
left-and-right eye movements of each eyeball
(it makes sense since they are placed on the left and right of the eyeball).
Imagine a pair of tight rubber bands that are fixed to a ball. When you pull
one rubber band and relax the other, the ball will turn to one side. This is
exactly what the brain directs the eye muscles to do to move your eyes.
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Can INS be cured? What
are the goals for nystagmus treatments?
Right
now Infantile Nystagmus [nĭ-STAG-muss] Syndrome (INS) cannot be cured but
can be helped. The current treatments for INS correct
head turns (if any) and improve visual function (you may see better, have a broader
good-vision field, and see faster).
Also nystagmus treatments may result in cosmetic improvement;
your eyes may wiggle less. The effects of treatments are different from
person to person. You first should have your
eye movements recorded, so that your doctor knows what type/types of nystagmus
you have, which surgery to perform, and how much improvement you should expect
from the surgery.
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What is a ÒNull
PointÓ?
A
Ònull pointÓ in INS means the visual angle where you see best. The null point
can be on the left, right, up or down side of your visual field. In order to
use your null point, you usually turn or tilt your head to one side to see an
object directly in front of you. Although most INS patients have a null point,
there are some who do not. Some may have a null point that changes with time.
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What does the Anderson-Kestenbaum
(AK) surgery do? Is the
improvement permanent?
The
Anderson-Kestenbaum (AK) surgery involves cutting and moving the eye muscles so
that you can make use of your null point when you look straight ahead. For
example, if your null point is on the right, the AK surgery will be done so
that both eyes will be moved to the left (the eyes will not look like they are squinted,
though). Once that is done, when you look straight ahead, your eyes will be in
your null point. This surgery may eliminate your head turn. Also, your
good-vision field may be broader, and you may see faster.
AK
is a simple, outpatient surgery. The key to a successful AK surgery is to find
out how much the eye muscles should be moved. Eye-movement recordings are necessary
for the doctors to find that information accurately. If the AK surgery is done properly, the
effects will last.
Base-left
or base-right prisms can be added to your glasses to help you make use of your
null point too. You might not get the Òbroadened, good-vision-fieldÓ effect though.
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Will strabismus be
corrected?
Strabismus
[stra-BIZZ-muss], or squint/lazy eye, often
happens together with INS. Strabismus can also be corrected along with the AK
surgery. The doctors need to make an adjustment to the amount of movement of
each eye muscle. Again, they can find that information in your eye-movement
recordings.
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What does the Bimedial
Recession (BMR) surgery do?
If you have a Òconvergence nullÓ, you see better when
you look at something near (as when you are reading a book). BMR (also called, Òartificial divergenceÓ) surgery
can help you in this case. This surgery moves your eye muscles so that your
eyes will be ÒconvergedÓ even when looking at a distant object. For example,
you may not have to hold the book close to see it well; you may see it as well
at a distance. Also, your good-vision field may be broader.
BMR is a simple, outpatient surgery. We usually
recommend that your eye doctor prescribe some base-out prisms before the
surgery. These prisms function the same as the surgery, and you can try it to
get a feel for how well you tolerate it and how much better you may see after
the surgery. Please note that you need to have good stereoscopic
vision (3-D vision) to be a candidate for this surgery. If you have
strabismus, BMR will not help your INS.
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What non-surgical
treatments have been reported to be effective?
Prisms
can be used as an alternative to the AK and BMR
surgeries, as mentioned before. Contact lenses may reduce your nystagmus
too, and they may give you a broader field of good vision.
Researchers
also have found several other non-traditional ways to improve the nystagmus:
blowing air to your forehead, vibrating your neck muscle, ear acupuncture and
so on. Unlike surgeries, these methods have temporary effects. As soon as you
stop them, your nystagmus will go back to the same as before.
Some
drugs (for example, Mamentine) have proven to be useful to improve the
nystagmus. The long-term effects of these drugs are unknown right now.