DAROFF-DELLÕOSSO OCULAR MOTILITY
LABORATORY (DD_OMLAB)
LOUIS STOKES CLEVELAND DEPARTMENT OF VETERANS AFFAIRS MEDICAL CENTER
CASE
School of Medicine
10701 East Boulevard
Mail Code #151W
Cleveland,
OH 44106, USA
Phone: (216) 421-3224
Fax: (216) 231-3461
Website: http://www.omlab.org
Note: Information
from this page contains no medical advice.
You should always consult your doctor about INS treatments.
This document was created by Z. I. Wang
and edited by Dr. L.F. DellÕOsso, 12/2007.
Note: In this document, we have presented
very complex scientific information in laymenÕs terms.
DD_OMLAB
Patient Information Series:
5. MISCELLANEOUS QUESTIONS ON INFANTILE NYSTAGMUS
v
In some cases, even
if Infantile Nystagmus Syndrome (INS) is reduced to a very small amount, people
will still not see 20/20. Why?
Remember,
while the nystagmus [nĭ-STAG-muss] waveforms can affect the visual acuity,
any other visual deficits accompanying INS can also reduce visual acuity. For
example, a retinal underdevelopment can reduce the visual acuity from 20/20 to
20/80, and the nystagmus further reduces it to 20/100. In this case, even if we
could get rid of all the nystagmus (which is not achievable), the highest
possible visual acuity would still be 20/80, not 20/20. We canÕt easily treat
the sensory defects in the visual system, because they are located in the
brain; all the growth and development of the visual system occurred when you
were an infant, while the nervous system was still developing.
v
What can you do to
minimize the effects of INS during a driverÕs license vision test?
Nystagmus
tends to really get worse when you are nervous. If you are on the borderline of
qualifying on the vision test, being nervous might make your nystagmus worse
and make your acuity worse, although you can see much better when you are not
stressed. So do your best to relax!
There
are some other things you can do to ensure you get an optimal result. (We are
not suggesting here that you should be ÒsneakyÓ and attempt to fool the DMV
staff; we are offering some suggestions that can make your vision test results
closer to how well you actually can see in your daily life. You should always
know your limits when it comes to driving.)
Try
to use both eyes to look at the chart. If the staff insists on covering one eye
and testing each eye individually, explain to them that covering one eye might
make your nystagmus worse. This is because you probably have a preferred eye
with a better acuity. The non-preferred eye, more than likely, will have a
worse acuity. When you are walking or driving, you are using the preferred eye
and the better acuity. A poor test result in the non-preferred eye should not
be the reason to deny your driverÕs license. Also, the latent component in INS,
if you have it, will generally be larger if one eye is covered than with both
eyes open.
Ask
for a regular eye chart if you feel uncomfortable with the testing machine that
has small scopes to look into. Having a larger field of view might help you get
one more line. Also, if you have a ÒnullÓ point to the side, you cannot use it
if you are looking into the machine.
v
Why do some people
with INS feel more sensitive to light? Why canÕt some people see 3D movie
effects?
Some
INS patients have varying degrees of symptoms of Òocular albinismÓ. It means
that light can come through the pupil, iris and the white part of the eyeball.
In people without Òocular albinismÓ, light only comes through the pupil and the
pupil can adjust its size according to the strength of the light. In ocular
albinism, although the pupil might still work on changing its size, it does not
help much, because light is coming in from everywhere! What you need in bright
sunlight are large wrap-around sunglasses to reduce the total amount of light coming
in.
ÒStereovisionÓ
enables you to see 3D movies. It is developed very early in infancy. It relies
on two eyes well lined up and working together. About half INS patients do have
3D vision. However, others do not because of their strabismus [stra-BIZZ-muss] (their eyes are not aligned). Even
if you have them aligned later in life, you still probably canÕt get much
better 3D vision, because you have missed a critical stage in visual system
development. Stereovision and nystagmus are two separate things. Nystagmus by
itself does not cause the loss of stereovision. Loss
of 3D vision does not mean you canÕt identify whatÕs close and whatÕs far away.
You can still use visual cues: for example, you know a pigeon in the sky as
small as a black dot is actually not a black dot, it is small because it is far
away. When you go to the 3D movies, however, the images are manipulated to have
a 3D effect, so you probably wonÕt see it if you donÕt have stereovision.
v
WhatÕs the difference
between a nystagmus surgery and a strabismus surgery? Are they performed
separately?
In
a nystagmus surgery, the ÒgoodÓ eye (viewing eye) is what determines the
operation, that is, moving the eye muscles so that the null point is in a
straight-ahead position. Tenotomy & reattachment (T&R)
operates on 4 muscles (2 per eye) of both eyes to achieve both damping and
broadening effects. In T&R, no muscles are moved, so it does not change the
alignment. In a strabismus surgery, the ÒbadÓ eye (non-viewing eye) is the
biggest concern, since every effort is made to correct its misalignment. In the
case of nystagmus plus strabismus surgery, the ophthalmologist must be sure
that the viewing eye is moved to wherever the nystagmus has the best waveform,
and then correct the strabismus by aligning the other eye with the viewing eye.
All these are performed in one outpatient surgery. Testing should be done to
decide if you need a strabismus correction, and how that could be combined with
the nystagmus surgery.
T&R
is a nystagmus surgery, not a strabismus surgery, because it does not move the
muscles. Some doctors do not yet believe in or fully understand the beneficial
effects of tenotomy because they say, it does not ÒmoveÓ any muscles. It is not
meant to. T&R was not designed to correct strabismus, but to reduce the
nystagmus, which is a more important, functional result, once the 3D development critical period is
past.