What is nystagmus
Nystagmus means the eyes make involuntary repetitive, rhythmic oscillations. It is
considered to be a fault in the mechanisms that hold the eyes or fixation steady, meaning
the neural systems involved in nystagmus include the cerebellovestibular, optokinetic, and
pursuit systems (which makes it real a challenge to research).
We have manifest, latent, and manifest-latent nystagmus for you. Manifest means it's there
all the time, latent means it's not there unless you occlude one eye, and manifest-latent
is an oxymoronic expression meaning it's there all the time but much worse when one eye is
Latent and Manifest-Latent Nystagmus
These two occur commonly in essential infantile esotropia, and are something else
entirely than manifest congenital nystgamus. Latent nystagmus appears only when one eye is
covered, then both eyes develop nystagmus with the slow phase toward the occluded eye and
the fast phase in the other direction (you don't see anything during a fast phase. Slow
phases give you some time to actually process the images flashing over your foveas).
Anywhere between a 10 and 52% percent incidence of (latent and manifest-latent) nystagmus
in those with congenital esotropia syndrome has been reported. Many turn their face such
that the preferred eye is turned inward a bit; in that position the nystagmus is absent or
much less. Latent nystagmus is a real bother during a standard visual acuity test - that
always involves the covering of one eye, and looking straight ahead too. That way, you'll
may never get any further than the big E on the Snellen chart, despite the fact that you
might very well see 20/20 when viewing binocularly.
Latent nystagmus is also a problem when using occlusion therapy (for the prevention of
amblyopia) in children; covering one eye results in nystagmus, and thus in decreased
vision, and an uncooperative child. Patching for a few hours each day is less effective
than patching for a long time, in those cases. If patching is continued for some time, the
Manifest nystagmus occurs equally commonly with congenital esotropia syndrome as latent
and manifest-latent nystagmus, as detemined with eye movement recordings. Based on
clinical examination alone, CN with a latent shift is likely to be classified as
manifest-latent nystagmus (which may be the reason some sources report that
latent-manifest nystagmus is more commonly found with congenital esotropia syndrome, than
is congenital nystagmus).
Often nystagmus is made less by converging the eyes or looking to one side; utilizing a
"null zone", positioning the eyes such the nystagmus is less. Nystgamus blockage
is when someone assumes an esotropic gaze posture while viewing at distance. It is
suspected to perhaps cause esotropia in those cases.
Manifest nystagmus can be caused by a vision impairment present at birth, like cataracts.
As the name implies, congenital nystagmus is present at birth; there is no known cause for
Most patients with congenital nystagmus have a relatively quiet or "null" zone
that can be eccentric to the primary position, and they will adjust a head turn to keep
this eccentric position straight ahead.
Some surgical techniques for nystagmus are based on this; shifting the positions of the
extra-ocular muscles such that the null zone is more or less straight ahead. Another
method is recessing all horizontal rectus muscles a whole lot (up to 10 mm) which dampens
the oscillations. Reportedly it doesn't have much effect on eye movements. Yet another
technique that only works if the nystagmus is dampened by convergence, is the
"artificial divergence" procedure, such that you have to 'converge' even when
looking straight ahead. Obviously, it is no use if there is no fusion present.
Biofeedback and acupuncture have also been tried.
A crude method to stabilize the image on the retina is using a high plus contact lens on
the eye and a high minus spectacle lens, but that probably has a bad effect on the quality
of the image.
Stimulating the 5th cranial nerve (trigeminal nerve; it handles facial sensation) by
simply massaging the forehead seems to decrease nystagmus, but it's not very practical.
This stimulation can also be provided by wearing a contact lens, in some cases it seems to
help a bit.
Experiments with several drugs and alcohol have been carried out too.
Nystagmus is increased by anxiety or "effort to see"; the more you try, the
worse it gets. So even if alcohol doesn't work to decrease nystagmus by influencing
neurochemistry, maybe a good glass of wine may help to relax. (Note: This last remark is
not intended to get y'all drinking like crazy!).