Optic Nerve Hypoplasia and Nystagmus

ONH is present when the optic nerves fail to develop fully during early pregnancy (7-8 weeks gestation) for unknown reasons. The result is normal eyes and visual system of the brain at birth, but a shortage of nerve fibers to carry the information from the eyes to the brain. This results in field defects (blind spots) and/or reduced acuity (small details can’t be distinguished), and depth and color perception may also be reduced. The severity of these effects can range from negligible to perception of light and dark only. One or both eyes can be affected, and one may be worse than the other.

In rare cases, ONH can be part of a more complicated condition called septo-optic dysplasia (SOD), where the pituitary gland and midline of the brain are also affected. Growth deficiencies are generally the first sign that the pituitary is affected, so if growth is normal or close to it, there is a good chance the pituitary is fine. Hormone tests can identify deficiencies, and hormone levels can be maintained with drugs. An MRI can identify brain abnormalities.

There is no known cause for ONH, nor is there a cure, but it is also not progressive. Glasses do not help, although they are great for protecting the eyes if vision is bad enough to require it. Only enlarging or getting closer to things so that details can be seen, and moving things out of blind spots can allow a person with ONH to see better.

The visual system of the brain develops according to the visual input it receives in early childhood. Therefore, the brain adapts to the small optic nerves, and a child with ONH may have dramatically better vision at age 5 than they had at age 1. However, this also means that once a child reaches age 8 or so, even if new optic nerves could be generated by some miraculous procedure, their brain would not process visual input correctly for normal sight.

Nystagmus

Most very young kids that are diagnosed with ONH originally see their doctor because of nystagmus, which is involuntary occillations of the eyes. Perhaps the child looks like they are speed-reading all the time, or watching a ping pong ball bounce. Within the first year of birth, nystagmus begins to appear, and the parents take the child to the doctor, then the ophthalmologist, who dilates the child’s pupils, looks inside, and diagnoses ONH. The appearance of the optic nerve head inside the eye indicates ONH, but it cannot accurately predict the severity.

Nystagmus can accompany various retinal, optic nerve, vestibular, and brain conditions, and can also occur alone. Because nystagmus is such a generalized condition, with implications that vary with the accompanying condition (if there is one), my description concentrates on the form with which I am familiar. Please do not assume what I say here is complete. Please see the nystagmus links for more information.

Nystagmus also decreases acuity, especially at a distance, and can also reduce speed of perception and depth perception. As with ONH, glasses cannot correct for nystagmus, although there are some optical methods to dampen the nystagmus that may help in some cases. Enlarging or getting closer to objects are the most common methods of helping people with nystagmus to see better.

People with nystagmus often have a “null point”, a position at which the movement of the eye is most controlled. Kids learn to use their null point by trial and error, but it may change positions during early childhood. Sometimes the null point can be quite a bit off center, resulting in unusual postures and head turns. This should not be interfered with, as it allows the person the best vision that is possible for them. There is surgery that can move the null point closer to center if it causes severe muscle strain.

People with nystagmus often shake or nod their head unconsciously, especially when concentrating visually on something. It seems that it can be stopped with conscious effort, but some people feel that it helps them see better or that there must be some benefit. Friends, family, and coworkers can certainly get used to and hardly notice it.

Most people with nystagmus are not able to qualify for a driver’s license, although some can, depending on the qualifications required in their state or country.

Focusing on distant or fast moving objects is often difficult, and depth perception and balance can also be affected. Some people with nystagmus do not enjoy sports where these skills are required, but this varies greatly from person to person. I’ve heard of people with nystagmus participating in just about every sport I know of.

For people that developed nystagmus soon after birth, what they see does not normally jump around as their eyes move. Covering one eye, stress, and fatigue contribute to the severity of nystagmus, and when it is much worse than normal, the image may move around for them.

Some believe that vision therapy and cranial sacral therapy can help a person control nystagmus, there are many success stories out there. Neither is invasive or harmful, but they can be costly and may not be covered by insurance.

Visual Impairment

When ONH and nystagmus occur together, low vision rehabilitation is the best treatment.

Nearsightedness or farsightedness may accompany ONH and/or nystagmus. These can be corrrect by glasses. Although the person's vision will be better with the glasses, it will still be reduced due to the ONH and nystagmus.

People with a wide variety of vision problems often adjust slowly to lighting changes. Walking into a building after being in bright sunlight can leave them nearly blind for longer than you might expect. Paths that go in and out of the shade can be difficult to negotiate because their eyes are trying to constantly adjust and are not able to do so as quickly as the rest of us.

Although most fully-sighted people would have a difficult time getting along with reduced vision, those that have adapted to it can function normally and may even consider it to be no more than an annoyance. They may need to carry a cane or walking stick to handle steps when alone, use enlargers for reading small print (or Braille), monocular or binoculars for distant viewing, and may need to get very close to computer and TV screens or use speech adapters, but very few activities are beyond their capabilities. They do not need help unless they request if of you.

Above all, it is important to note that most people with any visual problems at all, including ONH and nystagmus, are not affected mentally or psychologically. You do not need to talk to them via their companion, or more loudly, or slowly. You should look at their face when you talk to them, just as you would anyone, even if they are not able to maintain eye contact as you normally see it.

Remember that your image probably does not jump around to them, even if their eyes move. Also remember that body language, waving from a distance, and other non-verbal cues may be missed, not because they are snobs or socially inept, but because they can’t see the cues. We use these cues more than we normally realize, but visually impaired people may rely on other cues that we normally miss, such as voice tone, body stance and posture.

Visually impaired people are as intelligent or as stupid as the rest of us, and as capable as well. It is not amazing or brave that they accomplish what the rest of us take for granted. They probably live a normal life, if any of our lives could be considered normal.

Our daughter, now in high school, has ONH and nystagmus. Most casual observers are unaware she has any visual problems because she has adapted so well, although she tests 20/200 with her contacts in. To envision what this is like, imagine a sign that you can barely read when it is 200 feet away from you. For her to barely read that same sign, with the same size letters, it must be 20 feet from her. 20/200 with all practical correction is "legally blind". (If glasses or contacts correct your vision to better than 20/200, you are not "legally blind".)

She does pull things very close to look at them, has trouble with uneven ground in places she doesn’t know, and wears contacts for severe nearsightedness. Her teachers say she asks for what she needs, which is half the battle won. She attends a regular public school and is doing very well. In fact, she attends a very competitive prep school. Her school district has implemented an IEP (Individual Education Plan), which requires a few minor accommodations and regular, brief meetings with a Visual Impairment Specialist to iron out any issues, and regular training with a Mobility Specialist, who has taught her essential skills to get around and function in a world that is mostly designed for people with good vision. She reads printed material without enlargement, although she holds books very close. She is on the swim team. She won't be able to drive, but rides her bicycle and the bus to get around.

Links

• SOD/ONH page: http://www.focusfamilies.org/
• Texas School of the Blind and Visually Impaired ONH Fact Sheet: http://www.tsbvi.edu/Outreach/seehear/spring99/opticnerve.htm
• American Nystagmus Network: http://www.nystagmus.org
• Nystagmus Network (U.K.): http://www.nystagmusnet.org/
• One Small Voice Foundation: http://www.onesmallvoicefoundation.org/

Disclaimer

This web page is intended for general educational purposes and is to the best of my knowledge accurate. However, most of the information contained comes from a variety of sources, including other web pages and public forums. Therefore information, procedures, or treatments should not be taken for granted. Please consult your ophthalmologist, neuro-ophthalmogist, optometrist, or medical physician to verify or answer any queries that you may have.


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