Vision Problems
Vision Problems
Albinism
Albinism (from Latin albus, "white"; see extended etymology, also called achromia, achromasia, or achromatosis) is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair and eyes due to absence or defect of an enzyme involved in the production of melanin. Albinism results from inheritance of recessive gene alleles and is known to affect all vertebrates, including humans. The most common term used for an organism affected by albinism is "albino". Additional clinical adjectives sometimes used to refer to animals are "albinoid" and "albinic".
Albinism is associated with a number of vision defects, such as photophobia, nystagmus and astigmatism. Lack of skin pigmentation makes the organism more susceptible to sunburn and skin cancers.
Amblyopia
Amblyopia (say this: "am-blee-oh-pee-ah") is an eye problem that causes loss of or poor vision in one or both of a child’s eyes. Amblyopia usually affects only one of the eyes, but sometimes it can affect both. Amblyopia is the most common cause of vision problems in children.
What causes amblyopia?
Anything that happens to blur a child’s vision or cause the eyes to become crossed may cause amblyopia. For example, children who have strabismus(also called “crossed eyes”), cataracts, a droopy eyelid or who need glasses to see better may get amblyopia.
All babies are born with poor eyesight. As babies grow, their eyesight gets better. In order to develop good eyesight, both eyes needs to provide a clear, focused image that is the same in both eyes. If the image isn't clear in one eye or if the image isn't the same in both eyes, the child gets a different picture from each eye. The child’s brain naturally tries to fix this problem by blocking out the picture from the weaker eye. If the problem is not fixed when the child is young, the child’s brain will always ignore pictures from the weak eye, causing amblyopia.
How is amblyopia treated?
The treatment for amblyopia depends on what is causing it. After the cause of the amblyopia is found, the child will need to use the weaker eye most of the time, so it will get stronger. To make the child use the weaker eye, a patch can be put over the stronger eye. Sometimes, eye drops or special glasses are used to blur the vision in the stronger eye. This makes the weaker eye become stronger. Patches may be used all day or part of the day, depending on the child's age and vision.
Glasses or contact lenses fix some problems. Surgery may be needed for cataracts, droopy eyelids or crossed eyes.
Treatment usually lasts until vision is normal, or until vision stops getting better. For most children, this takes several weeks. A few children need to use eye patches until they are 8 years to 10 years of age.
Why is early treatment important?
The first few years of life are the most important for eyesight. After a child is 8 years to 10 years of age, the brain's vision system is complete. It can't develop anymore. If the amblyopia hasn't been treated by this age, the child will have poor vision for life. It won't be possible to fix it with glasses, patching or any other treatment.
There's a small chance that using an eye patch for too long can hurt the strong eye. For this reason, children who are wearing eye patches should see their doctor often during the treatment
Anophthalmia
Anophthalmia, is the congenital absence of one or both eyes.
True or primary anophthalmos is very rare. Only when there is complete absence of the ocular tissue within the orbit can the diagnosis of true anophthalmos be made. Extreme microphthalmos is seen more commonly. In this condition, a very small globe is present within the orbital soft tissue, which is not visible on initial examination.
There are three classifications for this condition:
§ Primary anophthalmia is a complete absence of eye tissue due to a failure of the part of the brain that forms the eye.
§ Secondary anophthalmia the eye starts to develop and for some reason stops, leaving the infant with only residual eye tissue or extremely small eyes which can only be seen under close examination.
§ Degenerative anophthalmia the eye started to form and, for some reason, degenerated. One reason for this occurring could be a lack of blood supply to the eye.
Causes
Anophthalmia and microphthalmia may occur secondary to the arrest of development of the eye at various stages of growth of the optic vesicle. It is important to recognize microphthalmia because the development of the orbital region, as well as the lids and fornices, is dependent upon the presence of a normal-sized eye in utero. Anophthalmia is sometimes a clinical characteristic of Trisomy 13 (Patau syndrome) which is a Gross Chromosomal Abnormality.
Treatments
Early treatment with various expanders or surgery, when necessary, will help decrease the orbital asymmetry and cosmetic deformities in these children.
Aniridia
Aniridia is the absence of the iris. This usually occurs in both eyes. It can be congenital or caused by a penetrant injury. Congenital aniridia is not just an isolated defect in iris development but is a panocular disorder with macular and optic nerve hypoplasia, cataract, andcorneal changes. Vision is severely compromised with the aniridia and the disorder is frequently associated with a number of complications with the eye: nystagmus, amblyopia, buphthalmos, and cataract.
Astigmatism
Astigmatism is a type of refractive error of the eye. Refractive errors cause blurred vision and are the most common reason why a person goes to see an eye professional.
Causes, incidence, and risk factors
People are able to see because the front part of the eye is able to bend (refract) light and point it to the back surface of the eye, called the retina.
Changes in the length of the eye, or the shape of either the lens or the cornea make it more difficult for the eyes to focus light. If the light rays are not clearly focused on the retina, the images you see may be blurry.
With astigmatism, the cornea (the clear tissue covering the front of the eye) is abnormally curved, causing vision to be out of focus.
The cause of astigmatism is unknown. It is usually present from birth, and often occurs together with nearsightedness or farsightedness.
Astigmatism is very common. It sometimes occurs after certain types of eye surgery, such as cataract surgery.
Symptoms
Astigmatism makes it difficult to see fine details, either close up or from a distance.
Signs and tests
Astigmatism is easily diagnosed by a standard eye exam with refraction test. Special tests are not usually required.
Children or others who cannot respond to a normal refraction test can have their refraction measured by a test that uses reflected light (retinoscopy).
Treatment
Mild astigmatism may not need to be corrected.
Glasses or contact lenses will correct astigmatism.
With refractive corneal surgery, lasers can change the shape of the cornea surface to correct astigmatism, along with nearsightedness or farsightedness.
Coloboma
A coloboma (from the Greek koloboma, meaning defect, and also part of the rare Cat eye syndrome) is a hole in one of the structures of the eye, such as the iris, retina, choroid or optic disc. The hole is present from birth and can be caused when a gap called the choroid fissure between two structures in the eye, which is present early in development in the uterus, fails to close up completely before a child is born. The classical description in medical literature is of a key-hole shaped defect. A coloboma can occur in one or both eyes.
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The effects a coloboma has on the vision can be mild or more severe depending on the size and location of the gap. If, for example, only a small part of the iris is missing, vision may be normal, whereas if a large part of the retina or optic nerve is missing, vision may be poor and a large part of the visual field may be missing. This is more likely to cause problems with mobility if the lower visual field is absent. Other conditions can be associated with a coloboma. Sometimes the eye may be reduced in size, a condition called microphthalmia, or there may be glaucoma, nystagmus, scotoma or strabismus.
Primary Congenital Glaucoma Overview
By definition, primary congenital glaucoma is present at birth. It is usually diagnosed at birth or shortly thereafter, and most cases are diagnosed during the first year of life. However, sometimes, its symptoms are not recognized until later in infancy or into early childhood.
Primary congenital glaucoma is characterized by the improper development of the eye's drainage channels (called trabecular meshwork). Because of this, the channels that normally drain the fluid (called aqueous humor) from inside the eye do not function properly. More fluid is continually being produced but cannot be drained because of the improperly functioning drainage channels. This leads to high pressure inside the eye, called intraocular pressure (IOP).
Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10-21 mm Hg. Elevated IOP is an eye pressure of greater than 21 mm Hg. An increase in IOP can damage the optic nerve and result in vision loss and even blindness.
In approximately 75% of cases, primary congenital glaucoma is bilateral, that is, it occurs in both eyes.
Primary congenital glaucoma occurs more often in boys than in girls, with boys accounting for approximately 65% of cases.
Primary congenital glaucoma is relatively rare. In the United States, it reportedly affects fewer than 0.05% of children. However, various studies suggest that from 2-15% of children in institutions for the blind have been diagnosed with primary congenital glaucoma.
Despite the rarity of primary congenital glaucoma, the impact on a child’s visual development can be extreme. Early recognition and appropriate therapy for the glaucoma by an ophthalmologist (a medical doctor who specializes in eye care and surgery) can significantly improve the child's visual future and prevent blindness.
Cortical Visual Impairment
Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. (The latter is sometimes termed "ocular visual impairment" when discussed in contrast to cortical visual impairment.) Some people have both CVI and a form of ocular visual impairment as well.
CVI is also sometimes known as Cortical Blindness, although most people with CVI are not totally blind. The term Neurological Visual Impairment (NVI) covers both CVI and total cortical blindness. Delayed Visual Maturation, another form of NVI, is similar to CVI, except the child's visual difficulties resolve in a few months. Though the vision of a person with CVI may change, it rarely if ever becomes totally normal.
The major causes of CVI are as follows: asphyxia, hypoxia (a lack of sufficient oxygen in the body’s blood cells), or ischemia (not enough blood supply to the brain), all of which may occur during the birth process; developmental brain defects; head injury; hydrocephalus (when the cerebrospinal fluid does not circulate properly around the brain, and collects in the head, putting pressure on the brain); a stroke involving the occipital lobe; and infections of the central nervous system, such as meningitis and encephalitis.
Symptoms of CVI usually include several (but not necessarily all) of the following:
§ The person with CVI exhibits variable vision. Visual ability can change from one day to the next but it can also fluctuate from minute to minute, especially when the person is tired. When undertaking critical activities, people with CVI should be prepared for their vision to fluctuate, by taking precautions such as always carrying a white cane even if they don't always use it to the full, or always having very large print available, just in case it's needed. (For example, consider the consequences of losing vision while giving a public speech). Managing fatigue can reduce fluctuations but does not eliminate them.
§ One eye may perform significantly worse than the other, and depth perception can be very limited (although not necessarily zero).
§ The field of view may be severely limited. The best vision might be in the centre (like tunnel vision) but more often it is at some other point, and it is difficult to tell what the person is really looking at. Note that if the person also has a common ocular visual impairment such as nystagmus then this can also affect which part(s) of the visual field are best. (Sometimes there exists a certain gaze direction which minimises the nystagmus, called a "null point.")
§ Even though the field of view may be very narrow indeed, it is often possible for the person to detect and track movement. Movement is handled by the 'V5' part of the visual cortex, which may have escaped the damage. Sometimes a moving object can be seen better than a stationary one; at other times the person can sense movement but cannot identify what is moving. (This can be annoying if the movement is prolonged, and to escape the annoyance the person may have to either gaze right at the movement or else obscure it.) Sometimes it is possible for a person with CVI to see things while moving their gaze around that they didn't detect when stationary. However, movement that is too fast can be hard to track; some people find that fast-moving objects "disappear." Materials with reflective properties, which can simulate movement, may be easier for a person with CVI to see. However, too many reflections can be confusing (see cognitive overload).
§ Some objects may be easier to see than others. For example, the person may have difficulty recognising faces or facial expressions but have fewer problems with written materials. This is presumably due to the different way that the brain processes different things.
§ Colour and contrast are important. The brain's colour processing is distributed in such a way that it is more difficult to damage, so people with CVI usually retain full perception of colour. This can be used to advantage by colour-coding objects that might be hard to identify otherwise. Sometimes yellow and red objects are easier to see, as long as this does not result in poor contrast between the object and the background.
§ People with CVI strongly prefer a simplified view. When dealing with text, for example, the person might prefer to see only a small amount of it at once. People with CVI frequently hold text close to their eyes, both to make the text appear larger and to minimise the amount they must look at. This also ensures that important things such as letters are not completely hidden behind any scotomas (small defects in parts of the functioning visual field), and reduces the chances of getting lost in the text. However, the simplification of the view should not be done in such a way that it requires too rapid a movement to navigate around a large document, since too much motion can cause other problems (see above).
§ In viewing an array of objects, a person with CVI can more easily see them if s/he only has to look at one or two at a time. People with CVI also see familiar objects more easily than new ones. Placing objects against a plain background also makes them easier for the person with CVI to see.
§ For the same reason (simplified view), the person may also dislike crowded rooms and other situations where their functioning is dependent on making sense of a lot of visual 'clutter'.
§ Visual processing can take a lot of effort. Often the person has to make a conscious choice about how to divide mental effort between making sense of visual data and performing other tasks. For some people, maintaining eye contact is difficult, which can create problems in Western culture (for example, bonding can be difficult for some parents who have an infant with CVI, and lack of contact in an older child can cause others to regard him or her with suspicion[1]).
§ It can also be difficult for some people with CVI to look at an object and reach for it at the same time. Looking and reaching are sometimes accomplished as two separate acts: look, then look away and reach.
§ People with CVI can sometimes benefit from a form of blindsight, which manifests itself as a kind of awareness of one's surroundings that cannot consciously be explained (for example, the person correctly guesses what they should do in order to avoid an obstacle but does not actually see that obstacle). However, this cannot be relied on to work all the time. In contrast, some people with CVI exhibit spatial difficulties and may have trouble moving about in their environment.
§ Approximately one third of people with CVI have some photophobia. It can take longer than usual to adjust to large changes in light level, and flash photography can be painful. On the other hand, CVI can also in some cases cause a desire to gaze compulsively at light sources, including such things as candle flames and fluorescent overhead lights. The use of good task lighting (especially low-temperature lamps which can be placed at very close range) is often beneficial.
§ Although people (with or without CVI) generally assume that they see things as they really are, in reality the brain may be doing a certain amount of guessing and "filling in", which is why people sometimes think they see things that turn out on closer inspection not to be what they seemed. This can occur more frequently when a person has CVI. Hence, a person with CVI can look at an optical illusion or abstract picture and perceive something that is significantly different from what a person without CVI will perceive.
The presence of CVI does not necessarily mean that the person's brain is damaged in any other way, but it can often be accompanied by other neurological problems, the most common being epilepsy.
Diagnosis
Diagnosing CVI is difficult. A diagnosis is usually made when visual performance is poor but it is not possible to explain this from an eye examination. Before CVI was widely known among professionals, some would conclude that the patient was faking their problems or had for some reason engaged in self-deception. However, there are now testing techniques that do not depend on the patient's words and actions, such as fMRI scanning, or the use of electrodes to detect responses to stimuli in both the retina and the brain. These can be used to verify that the problem is indeed due to a malfunction of the visual cortex and/or the posterior visual pathway.
Delayed Visual Maturation
Delayed Visual Maturation (DVM) is characterized by an otherwise normal eye exam in an infant that does not fix or follow or otherwise respond (e.g., blink to threatening object or bright flash of light) to a visual object. In an infant with DVM, the eyes, including the retinas and optic nerves, appear normal and the infant is otherwise neurologically normal. Infants with DVM do not have nystagmus and typically do not have "wondering" eye movements. Yet, the infant does not fixate on objects or track, even with jerking eye movements (saccades), objects that move across his/her visual field. By definition, however, at some point in time, usually by about 6 months of age, the infant will start to fix and follow and will then appear as a visually normal infant.
The typical infant with DVM is 2 to 4 months old and is otherwise healthy. The parents or grandparents become concerned because the infant does not appear to see things or track things like most infants their age. The parents end-up seeing an eye doctor and the eye exam is normal, except for the fact that the infant doesn't fix or follow objects placed in front of him/her. Depending on the situation, the eye doctor often will simply tell the parents that the child is delayed in vision abilities and that he/she will catch-up in a few months (and to come back and see the doctor in a few months). And sure enough, the infant will indeed start to fix and follow by about 6 months of age confirming the diagnosis of DVM.
In terms of vision development, some infants with DVM, parents report, act as though a switch in the brain has been turned-on and all of a sudden the infant starts to look at things and respond to objects in their visual space. Other infants with DVM start off slower and may first look at salient objects, periodically, and gradually start to fixate and tract objects. Very soon thereafter the infant with DVM appears normal in every respect and causes no further concern for the parents.
Nothing is harder for parents than waiting - waiting to see IF and WHEN their infant will start seeing. To alleviate fears and concerns, the eye doctor may have a Visual Evoked Response (VER, also called a Visual Evoked Potential, VEP) undertaken on the infant to ensure that the early visual pathways are intact and functioning. The VER to pattern stimulation is typically normal in infants with DVM. Often between the time that the VER is ordered and performed, say 2 weeks, the infant with DVM will start to respond to visual objects. If, however, the VER is abnormal or worse yet "flat" additional testing may be indicated. Additional testing might include the electroretinogram (ERG) to assess retinal function and CAT scan or MRI to evaluate brain structures.
What causes DVM? Nobody really knows what causes DVM. However, it is possible that DVM is the result of a delay in cortical maturation (or delay in myelination of cortical areas) - particularly the maturation of cortical areas responsible for "awareness" of visual objects. Recent research has shown that one particular cortical area called the Angular gyrus plays an important role in object awareness. For example, adults that have had damage to the Angular gyrus cannot identify an object by sight alone, but can identify the object if it makes a sound or has a familiar smell. For all practical purposes, people with damage to the Angular gyrus don't see - much like infants with DVM don't see. A big difference between adults with damage to the Angular gyrus and infants with DVM is that the later will eventually see.
What happens if the infant is older than 6 months and still doesn't fix or follow? If the infant is older than 6 months and still doesn't fix or follow then it may be necessary to undertake additional testing, including those discussed previously. Although rare, infants that do not fix or follow may have more serious vision problems including Leber's Congenital Amourosis or monochromatism. Usually, infants with more serious vision problems that are present at birth also exhibit other signs of vision loss such as nystagmus, or will exhibit self visual stimulating behavior like pushing the thumb, fingers or whole hand into the eye and rubbing vigorously.
Can anything speed-up the development of vision in an infant with DVM? Research is moot on this point. Nevertheless, experience suggests that infants that are continuously stimulated with visual objects including those that make sounds or/and that the infant can hold may facilitate vision development. Probably the most important stimuli for an infant with DVM are activities with the parents (feeding, talking, playing, holding) and, particularly,those undertaken by other older children or sibs.
Leber Congenital Amaurosis
Leber congenital amaurosis is an inherited retinal degenerative disorder that causes an infant to be born with severely impaired vision. It is inherited in an autosomal recessive manner, meaning that both parents must carry a defective gene for their child to be born with the disorder. Leber congenital amaurosis and early-onset retinitis pigmentosa are estimated to affect 3 in 100,000 newborns.
Symptoms
Infants born with Leber congenital amaurosis have severely impaired vision. They also are born with, or develop, roving or jerking involuntary eye movements (nystagmus). Children with the disorder may poke their eyes or press on them with their fists or fingers. This may lead to misshapen and thinned corneas (keratoconus), cataracts, and a sunken appearance of the eyes.
The appearance of the retinas may change with age but once childhood is past, vision usually remains stable. The individual with Leber congenital amaurosis may only have vision at the level of seeing light and dark or detecting hand motions.
Diagnosis
It may be difficult to differentiate Leber congenital amaurosis from early-onset retinitis pigmentosa or from syndromes that cause impaired vision. It is also hard to distinguish what is vision and what is behavior in an infant or very young child. Therefore, electroretinography (ERG) testing is important in measuring if the child can see, and how much. In Leber congenital amaurosis, the ERG usually detects little activity in the retinas.
Treatment
There is no specific treatment for Leber congenital amaurosis. Individuals with the disorder may benefit from the use of low-vision aids if they have enough vision.
Hyperopia
Farsightedness is greater difficulty seeing near objects than distant objects.
Causes, incidence, and risk factors
Farsightedness is the result of the visual image being focused behind the retina rather than directly on it. It may be caused by the eyeball being too small or the focusing power being too weak.
Farsightedness is often present from birth, but children have a very flexible eye lens, which helps make up for the problem. Most children outgrow the condition. As aging occurs, glasses or contact lenses may be required to correct the vision. If you have family members who are farsighted, you are also more likely to become farsighted.
Symptoms
· Blurred vision of close objects
· Crossed eyes (strabismus) in children
· Eye strain
· Headache while reading
Signs and tests
A general eye examination to diagnosis farsightedness may include the following tests:
· Eye movement testing
· Glaucoma testing
· Refraction test
· Retinal examination
Treatment
Farsightedness is easily corrected with glasses or contact lenses. Surgical techniques are available for correcting farsightedness and can be used for those who do not wish to wear glasses or contacts.
Ocular Motor Apraxia
What is Ocular Motor Apraxia?
'Fast' eye movements are called saccades. We use saccade eye movements to quickly change the direction that our eyes are looking. This helps us look at something that has suddenly moved near to us. This is so the eyes can focus sharply on an object. The eyes can then give clear signals to the brain to make clear vision. It also helps us quickly move our eyes across a page of writing while reading. Saccades are important in many other visual tasks. Ocular Motor Apraxia is a condition where a child has a breakdown (failure) in starting (initiating) fast eye movements.
Ocular Motor Apraxia has many different names. It is sometimes called Cogan's Ocular Motor Apraxia or Saccadic Initiation Failure (SIF). SIF is a useful name to help explain what the condition mainly is: a breakdown (failure) in starting (initiating) fast eye movements (saccades).
What is the cause of Ocular Motor Apraxia?
Many different parts of the brain control eye movements. If any part becomes damaged then ocular motor apraxia may develop.
A child may be born with these special eye movement control bits not working (congenital). Other children may develop it in childhood (acquired). There are many different reasons why a child might develop Ocular Motor Apraxia in childhood.
It is often not the only condition that the child may have. Children may also have:
- Learning difficulties
- Delayed language development
- Delayed sitting and walking skills
- Delay in toilet training
Very often no cause can be found. Doctors call this idiopathic.
A head scan can sometimes shows a certain part of the brain to be smaller than usual. This bit of the brain is called the vermis of the cerebellum. This part helps the eyes make exact and quick movements. It is not known why some children might have a small vermis.
How is Ocular Motor Apraxia diagnosed and how does it affect the way a child sees?
Ocular Motor Apraxia is often diagnosed by doctors asking parents questions about their child. Children often 'thrust' their head from side to side to change the direction they are looking. 'Head Thrusts' are a typical movement that helps a child overcome their difficulty in moving their eyes quickly. Children may also blink to start a fast eye movement. Parents will notice this. These children often tend to have difficulty reading. They may also dislike travelling in cars, as they will have difficulty seeing things passing by outside of the car.
During an examination of the child's eye movements an eye doctor can confirm the diagnosis. Sometimes other tests are also done. This may be to see if there is a cause for the condition. Often no cause is found. This is called idiopathic.
Does ocular motor apraxia get better?
The lack of eye movement in ocular motor apraxia is first seen during the first few weeks of life. The movements of the head develop later. During this early stage the baby may wrongly be thought to have poor vision because moving targets can't be followed by the eyes. Quick side to side head movements called head thrusts may then develop. Long term follow up has shown that these head movements decrease gradually over a number of years in many children. In addition eye movements can improve with time in some but not all children. It is not possible to predict which children will show improvement and which will not.
How can parents, family, friends and teachers make a difference?
Ocular motor apraxia may develop on its own. It is however more commonly seen along with other conditions. These conditions might cause slowing of some aspects of development. As far as vision is concerned there are a number of things to think about.
We use our vision to get around, learn new things and to meet other people and make friends. Most children with Ocular Motor Apraxia have few problems getting around. The way they act can give the impression that their vision is normal. It is important however to be aware of their own special problems with vision.
It can be difficult for the child to choose to look in a particular direction. This means that the child may not look at you. This does not mean that the child is not paying attention.
The child may find it difficult to follow moving objects, especially when they are small. Television programmes with fast movement, such as cartoons, may not be seen easily, and the child may choose to watch programmes in which there is less movement, like panel games. Children with ocular motor apraxia may choose to get close to the television. This does not cause any harm.
Some things, which are moving quickly, may not be spotted because the ability to locate and follow moving targets is reduced. It is important to teach how to cross roads safely. Ball sports can also be difficult. When a child is old enough it is worth practicing throwing and catching.
A child who chooses to use head thrusts should not be made to stop doing this. They are trying to improve their vision and are often doing it without knowing it.
Difficulties at school may be due to some of the reading books being hard to see. This often means it takes longer and more effort to do the work. If the size of print is increased most children find schoolwork easier. They may also benefit from using a computer software programme while reading. The programme only shows one word of a sentence at a time. It is in the middle of the computer screen. This reduces the need for fast saccadic eye movements. It can increase reading speed and reduce tiredness.
Even if a child has very poor vision many useful and practical things can be done to help.
Nystagmus
Nystagmus refers to rapid involuntary movements of the eyes that may be:
- Side to side (horizontal nystagmus)
- Up and down (vertical nystagmus)
- Rotary
Depending on the cause, these movements may be in both eyes or in just one eye. The term "dancing eyes" has been used in regional dialect to describe nystagmus.
Considerations
Uncontrollable eye movements are involuntary, rapid, and repetitive movement of the eyes.
The involuntary eye movements of nystagmus are caused by abnormal function in the areas of the brain that control eye movements. The part of the inner ear that senses movement and position (the labyrinth) helps control eye movements.
The exact nature of these disorders is poorly understood.
There are two forms of nystagmus:
- Congenital nystagmus is present at birth. This is the most common type.
- Acquired nystagmus develops later in life because of a disease or injury.
Causes
CONGENITAL NYSTAGMUS
Congenital nystagmus is usually mild, does not change in severity, and is not associated with any other disorder.
Affected people are not aware of the eye movements, although they may be noticed by a careful observer. If the movements are of large magnitude, visual acuity (sharpness of vision) may be less than 20/20. Surgery may improve visual acuity.
Rarely, nystagmus occurs as a result of congenital diseases of the eye that cause poor vision. Although this is rare, an ophthalmologist should evaluate any child with nystagmus to check for eye disease.