Your doctor thinks that you have had an episode of
optic neuritis. This is the most common cause of sudden visual loss
in a young patient. It is often associated with discomfort in or
around the eye, particularly with eye movement.
Anatomy
We do not see with our eyes. Our eyes send a message via the optic
nerves to the back part of the brain (occipital lobes) where the
information is interpreted as an image.
The optic nerve fibers are coated with myelin to help
them conduct the electrical signals back to your brain.
Physiology
In the most common form of optic neuritis, the optic nerve has been
attacked by the body's overactive immune system. The immune system
is very important to our well being. It is responsible for fighting
off bacteria and viruses that can cause infection. In optic neuritis
and other autoimmune diseases, the body's immune system has decided
that otherwise normal tissues are foreign and therefore have attacked
it. In the case of optic neuritis, the myelin coating the optic
nerve has been targeted as foreign material. A viral infection that
may have occurred years, or even decades, earlier may have set the
stage for an acute episode of optic neuritis. What triggers the
sudden loss of vision and optic nerve dysfunction at this time is
unknown but probably occurs in individuals with a certain type of
immune system. The inflammation associated with optic neuritis can
result in discomfort (particularly with movement of the eye). In
some cases of optic neuritis there may be more extensive involvement
including the other optic nerve, the chiasm (where the two optic
nerves come together), or other tissues in the brain.
Symptoms
The most common symptom of optic neuritis is sudden decrease in
vision. Patients may describe this as blurred vision, dark vision,
dim vision or simply loss of vision in the center or part or all
of the visual field. In mild cases, it may look like "the contrast
is turned down" or that colors appear "washed out."
This may vary and, not infrequently, will progress from the time
it is first noticed. The second most common symptom associated with
optic neuritis is discomfort in or around the eye often made worse
by movement of the eye.
Signs
Optic neuritis may be difficult to diagnose, as your eye looks perfectly
normal. Often the inside of your eye also looks normal. A few patients
with optic neuritis have swelling of the optic disc (the beginning
of the optic nerve) at the back of the eye. This is referred to
as papillitis. One sign usually detected by your eye doctor is the
presence of an afferent pupillary defect. This indicates that there
is less light being sensed by the affected eye than the opposite
eye. This is found by swinging a bright light back and forth between
your two eyes while observing how your pupil reacts.
Prognosis
The pain will go away, usually in a few days. The vision problems
will improve in the majority (92%) of patients. There are rare patients
who have continued progressive loss of vision. Even in the 92% that
improve, often they do not return completely to normal. Patients
may be left with blurred, dark, dim, or distorted vision. Frequently
colors look different or "washed out." Visual recovery
usually takes place over a period of weeks to months, although both
earlier and later improvement is possible.
Late variations in vision are common, often associated with exercise
or taking a hot shower or bath. This is known as Uhthoff's phenomena
and is probably related to damage to the myelin coating. Patients
who notice this problem are not more likely to get worse.
Optic neuritis can recur involving the same eye, the other eye or
other parts of the central nervous system (brain and spinal cord).
This may result in recurrent episodes of decreased or loss of vision
or problems with weakness, numbness or other signs of brain involvement.
An MRI scan can give us to give a rough guess as to the likelihood
of recurrence.
It will not completely exclude the possibility of
future episodes or guarantee that they will happen.
Other testing techniques are sometimes used to confirm the suspicion
of optic neuritis. These may include visual evoked potentials (a
test where you are shown a checkerboard of light and signals are
recorded from electrodes on your scalp) that can show a delay in
conduction due to the damage to the myelin.
Treatment
A study (the Optic Neuritis Treatment Trial (ONTT)) suggested that
the likelihood of recovery at 6 months was equal whether they were
treated with steroids or sugar pills. Patients treated with oral
(pills) steroids seemed to have a higher chance of recurrent episodes.
Therefore, steroid pills are not recommended as treatment. Patients
who were treated with intravenous (given by needle) steroids did
have a slightly more rapid recovery of their vision, although the
final visual outcome was not better than in those who were not treated.
Thus, IV steroids can be recommended for patients with severe involvement
or involvement of both eyes. The ONTT also suggested that IV steroids
in those patients at high risk (as determined by their MRI scan)
could have a reduction in the chances of a second episode over the
next three years. Recent studies have suggested that the chance
of developing a recurrent episode may be reduced by starting other
medications after IV steroids in those patients at high risk. MRI
is important in suggesting the chance of recurrence or progression.
Your doctor can address questions about possible treatment with
you.
Frequently asked questions
What caused this to happen? We don't have a complete understanding of optic neuritis at
this time. It is likely that it represents a combination of a particular
form of immune system combined with a previous stimulation possibly
a virus.
What's going to happen to my vision? In the vast majority of patients, your vision will improve.
It may not improve to normal, but it is likely that there will be
a substantial improvement whether or not you are treated.
Can treatment with steroids make this better?
Treatment with IV steroids has been demonstrated to accelerate recovery
but it will not change the ultimate level of recovery on average.
We have no way to guarantee that vision will recover and in some
patients it will not.
Do I have MS?
Multiple sclerosis (MS) is a disease process where the body's immune
system attacks multiple areas in multiple episodes. An episode of
optic neuritis may be the first indication of multiple sclerosis.
With a single episode, without other evidence of involvement, we
usually cannot make the diagnosis at that time. An MRI scan may
be helpful in dividing those patients into high and low risks. Finding
evidence of other areas of inflammation on MRI scanning suggests
you may be at higher risk for recurrent episodes and thus MS. Your
doctor may suggest consultation with a neurologist to discuss treatments
that might reduce the risk of recurrent disease. Even a normal scan
does not guarantee that episodes may not recur over years. Whether
or not this turns out to be MS in the future, the prognosis in terms
of visual recovery is still good for this particular episode.
Can I prevent MS? The ONTT demonstrated that the use of high dose
intravenous steroids in patients at high risk (2 or more spots on
MRI scan) may delay the onset of MS. Recent data suggests that some
of the newer medications may also decrease the chance of having
another neurologic event. Thus it may be important to recognize
those patients at higher risk to start earlier treatment. This is
best determined by MRI. There is no treatment that will absolutely
prevent the development of multiple sclerosis.
