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Nystagmus is defined as involuntary eye
movements, commonly called "dancing eyes", "jerking eyes" or
"back-and-forth" eyes. Congenital means present at birth or very shortly
thereafter. Thus, congenital nystagmus means involuntary eye movements
present at birth or within the first month or two of life. However,
detection of the nystagmus varies significantly and may not be observed
until 5 or 6 months of age. Congenital nystagmus has also been referred
to as "congenital motor nystagmus", "idiopathic infantile nystagmus" and
"infantile nystagmus" among others.
Strictly speaking, congenital nystagmus
should be limited to patients who do not have an obvious cause or reason
for the nystagmus such as a retinal disease, optic nerve disease or
brain tumor. As a consequence, before the diagnosis of congenital
nystagmus is made, the patient may need to undergo a series of
diagnostic tests to rule-out such diseases or causes. Typically,
patients with retinal disease/degeneration will develop nystagmus
between 2 and 4 months of age. However, it is often difficult to know
exactly when the nystagmus started given that young infants sleep most
of the time and when the eyes are open they are open only temporarily.
Congenital nystagmus typically involves
horizontal eye movements, although vertical and rotary eye movements
have also been reported. When the nystagmus is horizontal, it may be
pendular (i.e., as if the patient is watching a pendulum swing
back-and-forth) or may be more jerk-like (i.e., the eyes appear to move
slowly in one direction and than snap back in the opposite direction and
start over). In general, as the patient gets older the size or amplitude
of the nystagmus decreases and the frequency of the nystagmus increases,
particularly when the patient tries to fixate or look directly at an
object. The nystagmus will worsen and increase in size and frequency
when the patient is tired, sick or fatigued.
Many patients with congenital nystagmus
will find that their nystagmus may decrease or even stop in certain
directions of gaze (e.g., looking right). Also, the nystagmus may
decrease in size when the patient looks at close objects (i.e., with
convergence). The eye doctor will refer to a "null point" when the
nystagmus stops with a certain gaze direction. A "semi null point"
occurs when the nystagmus decreases but does not totally stop in the
certain direction of gaze.
Patients with congenital nystagmus may
also experience head nodding or head shaking. Some believe that the head
nodding and/or head shaking are compensatory head movements; to
compensate for the involuntary eye movements and to improve vision.
Although such compensatory head movements may occur in some patients,
when investigators simultaneously record eye and head movements in such
patients, there is not a high degree of compensation evident. In other
words, in many patients that have nystagmus and head nodding or shaking
the two may be independent or simply a symptom of the same disorder.
Usually, over time, the head nodding and head shaking disappear.
Clinical Features and Symptoms
1. There are certain clinical features
of patients with congenital nystagmus. These clinical features include:
2. Both eyes have horizontal nystagmus
and it is symmetrical ( same in both eyes).
3. The nystagmus typically decreases
with convergence.
4. Esotropia (crossed-eyes) is present
(about 50% of patients).
5. At some time/age the patient
demonstrates head shaking or nodding.
6. No movement of the visual world
(oscillopsia) is experienced.
7. The nystagmus is not present during
sleep and decreases when the eyes are closed.
8. There is a preferred direction of
gaze (null point or semi null point)
9. Demonstrates an opposite OKN effect
(2/3 of patients).
10. Life long condition.
11. There are no other significant eye
(media, retina, optic nerve) problems.
Causes of Congenital Nystagmus
The cause of congenital nystagmus is
not known. In terms of genetics, there appears to be different
hereditary types of congenital nystagmus including, X-linked, dominant
and recessive. In the X-linked type, the unaffected females (mothers)
are carriers of the defective gene and they have a 50% probability of
passing it along to a male child who will be born with the congenital
nystagmus. The affected mothers also have a 50% probability of passing
the defective gene to a female child. The female child will be a carrier
and not affected. A gene associated with X-linked congenital nystagmus
has been reported on the short arm of the X chromosome (Xp11.4 – p11.3).
In the dominant form of congenital
nystagmus, 50% of all family members have a possibility of receiving the
defective gene and having congenital nystagmus. Every generation is
affected and, thus, either the mother or father of an affected patient
must also have the nystagmus. A patient with the dominant form of
congenital nystagmus will have a 50 % probability of having a child with
congenital nystagmus. If an offspring does not have the congenital
nystagmus then their offspring will not be affected. A dominant
congenital nystagmus gene has been linked to chromosome 6p12.
In the recessive form of the disease,
neither the mother nor father is typically affected and there is
typically no family history of such a condition. When a child is born
with the recessive form of congenital nystagmus, there is a 25% chance
that other children by the same mother and father will have a chance of
having the nystagmus. The patient with congenital nystagmus has a very
low possibility of having children with the nystagmus.
Visual acuity in Congenital Nystagmus
Patients with congenital nystagmus
typically have some loss of visual acuity, which cannot be corrected
with glasses. In general, visual acuity ranges from 20/30 (best) to
20/200 (legal blindness). On average, patients with congenital nystagmus
have a visual acuity of 20/60 or better, good enough to drive a car. An
important determinant of visual acuity is whether the patient has a null
point or semi-null point; that is, if the patient can voluntarily stop
or slow down the frequency and size of the nystagmus by looking a
certain way. Visual acuity is better in patients with a null point than
in patients that do not have a null point.
Another important fact for patients
that do have a null point is that when the patient gets older s/he may
be able to have eye muscle surgery to move the eyes such that the null
point is in straight ahead gaze (primary gaze). For example, suppose the
patient has a null point when s/he looks to the right. In such patients,
in order to look straight ahead s/he would have to turn the head to the
left so that s/he is looking straight ahead without the nystagmus. An
ophthalmologist could move the eye muscles attached to each eye so that
the null point could be in the primary position, when the patient looks
straight ahead. Now if the patient looks to the right s/he would have
the nystagmus. In a sense, following the eye muscle surgery the brain
"thinks" that the eyes are turned to the right but are really straight
ahead (and without nystagmus). Such eye muscle surgery could result in
some improved vision in straight a-head gaze. In addition, a patient
with a head turn could develop skeletal muscle problems from always
turning the head to the right, for example. As a consequence, eye muscle
surgery may be advised in some patients.
Patients with congenital nystagmus can
usually read normal print if they’re allowed to hold the text and
position their head to maximize vision. Under no circumstances should a
teacher or parent force the child to hold the text a certain way or have
the head, say, straight ahead. Leave the child determine the best
position for reading and school work.
Unusual Findings in Congenital
Nystagmus
There are several unusual or
interesting findings in patients with congenital nystagmus. For example,
about 2/3 of patients with congenital nystagmus will demonstrate an
opposite OKN effect. Optokinetic Nystagmus (OKN) is elicited by having
the patient look at a series of moving vertical black and white stripes,
typically on a drum. When the stripes move, say, left to right, the OKN
will be observed as a series of slow and fast eye movements with the
slow eye movements in the direction of the moving stripes (rightward)
and the fast eye movements in the opposite direction (left). A patient
with congenital nystagmus may demonstrate just the opposite – when s/he
is presented with a series of stripes moving left to right s/he’ll
elicit fast movements to the right and slow eye movements to the left.
Some patients with congenital nystagmus
will demonstrate a condition called "paradoxical pupillary constriction"
to darkness. In normal patients, darkness will cause the pupil of the
eye to expand and get bigger and lightness will cause the pupil of the
eye to constrict or get smaller. In some patients with a diagnosis of
congenital nystagmus, darkness causes the pupil to get temporarily
smaller and after some time the pupil will slowly get bigger. Strictly
speaking, we do not believe that the diagnosis of congenital nystagmus
is appropriate for patients who demonstrate the paradoxical pupillary
constriction. Such an effect strongly suggests the presence of a retinal
disease or degeneration, or possible optic nerve disease as a cause of
the nystagmus. As a consequence, the nystagmus is probably secondary to
or caused by the retinal or optic nerve disease.
Congenital Nystagmus vs Spasmus nutans
Spasmus nutans is defined as a triad of
symptoms including asymmetric nystagmus, abnormal head posture and the
presence of head shaking or nodding. As such, Spasmus nutans can
sometimes be confused with congenital nystagmus. However, close
observation can differentiate the two. For example, note the in Spasmus
nutans the nystagmus is not symmetrical in the two eyes. In deed,
sometimes there is nystagmus only in one eye. In congenital nystagmus
the two eyes move in a similar fashion. In Spasmus nutans the head
nodding or head shaking occurs BEFORE the nystagmus, usually by 1 or 2
months. Head nodding and head shaking always occurs after the nystagmus
occurs in congenital nystagmus. While the nystagmus eventually
disappears in patients with Spasmus nutans, usually by 4 years of age,
the nystagmus is always present in patients with congenital nystagmus
(although it may get so small in amplitude to make it difficult to see).
As a cautionary note, remember that patients are individuals and not all
symptoms are seen in all patients. As a consequence, sometimes a correct
diagnosis is made only after years of observation and when symptoms
appear or/and disappear.
Misc.
1. Patients with congenital nystagmus
may be able to drive a car in most states.
2. Pure congenital nystagmus may be
confused with nystagmus in patients with incomplete congenital
stationary night blindness.
3. About 10% of patients diagnosed with
congenital nystagmus may have congenital periodic alternating nystagmus
4. Patients diagnosed with congenital
nystagmus may have ocular albinism (and vise versa)
5. About 10% of blind and visually
impaired children have a diagnosis of congenital nystagmus.
6. About 1 in every 1,500 live births
have congenital nystagmus
7. The frequency of the eye movements
in congenital nystagmus average about 2.8 Hz under binocular viewing and
4.6 Hz under monocular viewing.
8. About a third of patients may have a
color vision deficiency (deuteranomaly).
9. 30% of patients with congenital
nystagmus may have or develop amblyopia. |
