The purpose of this article is to help the pediatrician evaluate a child with visual difficulties. The pediatrician must decide whether the child needs referral for further neurologic or ophthalmologic evaluation. This article will discuss the examination of such a child and interpretation of the various signs and symptoms that point to neurologic diseases. Detailed lists of the various neuroophthalmic syndromes will not be given since they have been well described elsewhere.1 Nor will strabismus or amblyopia be discussed to any extent, since two other authors have treated those subjects in this issue.
The history, as related by the parent or the child, is very important; often providing important clues to the diagnosis. When someone notes that the child is bumping into objects only on one side, a visual-field defect should be suspected. If a child is having visual difficulties despite having recently received corrective lenses, this may indicate that there is underlying retinal, optic nerve, or chiasmal disease. The fact that a child holds an object close maybe of significance; however, it is not uncommon for normal young children to hold material very close to their eyes when they are learning to read. All these problems need ophthalmologic consultation.
Ocular Motor Function
Parents may bring their child to the pediatrician because his head tilts to one side. Head turns or tilts should always be considered to be ocular in origin until they are proven otherwise by a complete eye examination. Too many children have made unnecessary trips to orthopedic surgeons for nonexistent cervical spine disease or to a neurologist for torticollis. If the head tilt is secondary to an ocular muscle paresis, patching one ofthe child's eyes for 24 to 48 hours will eliminate or greatly reduce the tilt. Even young children who are unable to describe double vision will develop a head tilt to the opposite side of a palsied superior oblique muscle (Figure 1). By contrast, a child will develop a face turn to the ipsilateral side of a palsied lateral rectus muscle. In both instances the child is attempting to maintain binocular vision and avoid diplopia by the turn or tilt. Thus, inquiries about double vision are always appropriate if the child is old enough to describe it.
General Neurologic Symptoms
When any child has afferent visual problems* or ocular motor imbalance, inquiries should be made about headaches, balance problems, gait disturbances, nausea, and vomiting.
Medical History and Family History
History of previous visual difficulty should be sought. In addition, a drug history must be obtained. We have seen one child with papilledema and a sixth-nerve paresis secondary to nalidixic acid.
Family histories can be invaluable in identifying a variety of genetic abnormalities. Often, unless they are asked about it specifically, parents will fail to mention familial disease because they hope that it is not the same affliction they see in their child.
Using some fairly simple techniques, the pediatrician should be able to examine the child and recognize visual problems if they exist and require referral.
Figure 1. Fourteen-month-old child with a right superior oblique palsy.
We should divide the visual acuity and field examination of children into three categories, based on age:
* Category A: Infancy to one year of age.
* Category B: One to three years of age.
* Category C: Over three years of age.
Toys are indispensable in the examination of any child. It has often been said, "One toy, one look." Finger puppets (Figure 2), squiggle pictures (Figure 3), small noisemakers, small beads, and other small objects are all very useful. An optokinetic drum and tape (Figure 4), hand light, visual acuity charts using pictures, tumbling "E", and letters should be in the pediatrician's office.
Figure 2. Finger puppets for fixation and following.
Figure 3. Squiggle pictures are excellent fixation targets. When pictures are moved back and forth, animation results.
Objective measurements of visual acuity by optokinetic nystagmus* show that infants one to five days old have visual acuities of 20/670. By the time they have reached two weeks of age, their visual acuity is 20/400. At 3½ months, it is 20/200. Visual acuity remains at that level until children are between one and two years old, when it reaches 20/100. Most children have a visual acuity of 20/50 by the age of three.2 Recent studies have shown that if visual acuity is measured objectively by visually evoked potentials, an infant at six months has 20 20 vision, but it is not known whether he can sensorially process that information.3
Figure 4. An optokinetic drum and tape are used to elicit an optokinetic response.
Figure 5. Visually evoked response recorded over the occipital cortex produced by a rapidly reversing checkerboard pattern.
Category A: Infancy to One Year. The development of the fixation reflex* is first noted in infants shortly after birth.2 However, while pursuit movements are present in the normal infant shortly after birth, the eyes follow a fixation light poorly at this age. By between four and six weeks of age, good fixation patterns may be detected easily; by the time the infant is three months old, he is able to maintain fixation in all fields of gaze and reestablish fixation quickly after interruption. By noting the infant's ability to fixate binocularly and monocularly, and also observing his ability to follow a hand light, the pediatrician can reasonably assess whether or not there may be afferent visual problems.
A hand light or a small noisy toy can be used as a fixation device. If the infant objects to having his eye covered while viewing a fixation target, he should be evaluated for pathology in the uncovered eye.
If the infant fails to show a good fixation and following reflex, an optokinetic drum (Figure 4) should be used to see if this reflex can be elicited. The drum has red and white stripes, and when it is rotated in front of the child's eyes, they will automatically follow the moving stripes. If the pediatrician cannot demonstrate optokinetic nystagmus by the time the child is two or three months old, he may have a visual problem. Because of difficulties in assessing the optokinetic response in young infants, the pediatrician may assess the infant's response by rotating the child. If he fixates during such maneuvers, one observes both the vestibular and optokinetic nystagmus.
Any infant who fails to show appropriate visual responses during the first weeks of life should be referred for neuro-ophthalmic evaluation. The neuroophthalmologist, in addition to performing a complete eye evaluation, will do visually evoked response testing.
The visually evoked response is used to provide an objective method of identifying abnormalities of the afferent visual pathways. More than 30 years ago it was learned that when electroencephalograph leads were placed over the occipital cortex, minute variations in the EEG would appear in response to regularly repeated flashes of light before the eyes. These responses were so slight that it was difficult to measure them. But in the early 1960s, computer technology was developed to the point that the combined total of several evoked responses could be averaged and time-locked to the stimulus.
Thus, if a photostimulator or rapidly reversing checkerboard pattern is flashed 100 times before the eyes and the occipital EEG recorded by a computer-averager, the common time-locked evoked response is added together to produce a clear wave form while the random EEG noise is slowly approximated to zero. Therefore, the visually evoked response produced by repeated white light flashes or by a reversing checkerboard pattern may be used to objectively demonstrate intact afferent visual pathways.* In addition, visually evoked responses allow an objective measurement of visual acuity by varying the size of the checks in the checkerboard pattern ( Figure 5).4
Figure 6. Cover one eye, then the other, while having the child look at a fixation target. If he objects to having one eye covered, eye pathology can be suspected. The device is a squiggle picture attached to a ruler.
Category B: One to Three Years. The fixation-andfollowing reflex is still an important consideration in checking the eyesight of the child from one to three years of age. Again, the child who objects to having one eye covered while viewing a fixation target (Figure 6) should be evaluated for eye pathology. By the age of two, children can often pick out single beads or similar objects as a demonstration of visual acuity. By the age of three, many will be able to read a distance-picture acuity chart.
Figure 7. The TNO test for stereoscopic vision and the red-green glasses which accompany it.
Figure 9. A page from the TNO test booklet. Patients with binocular vision who are looking at the actual test pictures through red-green glasses will see a circle in each square with a wedge missing. By asking the child where the bear took the bite out of the pie, the examiner can often measure the child's level of stereoacuity.
The TNO* random-dot stereogram is another excellent test of afferent visual function that has recently become available for stereoscopic vision (Figure 7). Certain objects on each page ofthe TNO test can be seen monocularly or without the red-green glasses. In order to identify the rest of the objects on each page of the test correctly, it is necessary for the child to have binocular vision and wear the red-green glasses. Thus, the child who is using only one eye will give different responses than the binocular child.
By two to three years of age, the children are able to identify the balls or butterflies (Figure 8). By three years of age, some children can identify the later test pages.
These pages show a circle with a pie section missing (Figure 9). Often very good levels of stereoacuity can be achieved by asking the child where the bear took a bite out of this pie. The importance of this test is in identifying amblyopia or other visual dysfunction. Any child who identifies the first two test plates correctly very likely has no significant amblyopia or major afferent visual pathway lesion. Children who can achieve a stereoacuity of 240 seconds of arc or better can be considered to have very good binocular vision. Thus the TNO is an excellent screening test.5
Figure 8. Pages from the TNO stereoscopic vision test. A) Patients looking at the actual colored test pictures and wearing red-green glasses should see four balls. Children with amblyopia or monocular viewing will see only two balls. B) Children with binocular vision will see two butterflies, one with amblyopia or monocular viewing will see only one.
Figure 10. Checking the child's response to a visual threat is useful in establishing the integrity of visual fields in very young children.
Category C: Over Three Years. Children in this age group are usually able to do picture or "E" visualacuity charts. Fixation patterns should be checked, as with younger children. For this age group the TNO test for stereoscopic vision will be easier to perform.
Examination of visual fields depends on the age ofthe child. Visual threat response (Figure 10) in group A (up to one year of age) can be tested. In Group B (up to three years of age) the refixation reflex tested in various quadrants is very useful (Figure 1 1). Thus, animal targets are brought toward a child in each quadrant while he is attracted straight ahead with an interesting target. This method of testing is used until the age of four to six years, when finger-counting fields by double simultaneous stimulation may be used (Figure 12). (Remember to test the eyes monocularly and binocularly.) Children older than six years of age can often be tested by formal field testing in the ophthalmologist's office.
Figure 11. Refixation reflex to test visual fields. One finger puppet is used to attract attention straight ahead. A second puppet is brought into each quadrant in a surprise fashion. The child, if he sees the surprise puppet, will look at it, thus establishing the integrity of that field of gaze. Each of the four quadrants is tested, and each eye is tested individually.
Any widening of a palpebral fissure should arouse the suspicion of exophthalmus. One can confirm the fact that the eyeballs are protruding abnormally by looking at the eyes from the top of the head downward. Facial asymmetry should be noted; it may signify a seventhnerve paresis.
Pupils should also be examined and differences in pupil size recorded. Often anisocoria*of up to 1.5 mm may be considered normal.
The "swinging-flashlight test" ( Figure 1 3) is used to test pupillary direct and consensual light reflex. The child is asked to look at a distant target, and a flashlight is moved back and forth rhythmically from pupil to pupil. The normal response is pupillary constriction, followed by slight pupillary escape and minimal redilation.
If an optic nerve lesion is present, the affected eye will fail to constrict when illuminated but will slowly dilate. The explanation for this phenomenon resides in the fact that the consensual light response causes the contralateral pupil to constrict; but if an afferent visual pathway lesion exists in the contralateral optic nerve, that pupil will dilate when illuminated instead of constricting (Figure 14). This afferent pupillary defect is called a "Marcus Gunn" pupil and is commonly associated with optic nerve lesions. Common optic nerve lesions causing a Marcus Gunn pupil are optic neuritis, optic papillitis, and optic nerve tumors. Whenever a child has apparent visual loss, a Marcus Gunn pupil should be sought. Neither cataracts, refractive errors, nor amblyopia will cause a Marcus Gunn pupil. Thus, its presence is of great significance in identifying an optic nerve lesion.
Figure 12. Older children will often play the finger-counting game. By having the child look straight ahead and count the number of fingers presented simultaneously in various quadrants, one can obtain a reasonable idea of the integrity of the child's fields.
Figure 13. The swinging-flashlight test. The child is asked to look straight ahead while a lighted flashlight is moved rhythmically back and forth between the pupils.
Figure 14. The swinging-flashlight test is performed slowly and rhythmically, moving the light from pupil to pupil. If an optic nerve lesion exists, the pupil will dilate instead of constricting when illuminated.
Figure 15. A puppet or squiggle is brought to the child's nose, and pupil size is noted. The pupils normally should constrict with convergence.
Next, the near response is tested by having the patient look at a near target (Figure 15). The pupils should normally constrict with a near stimulus. When a child has a poor response to the light reflex but a good near response, tectal midbrain lesion* should be considered. This sign represents part of Parinaud's syndrome.
The most common ocular motor abnormality is seen in the child with strabismus. It should be kept in mind that the sudden onset of an esotropia, with poor abduction of one eye, may signal the presence of a sixth-nerve paresis.
Sixth-nerve paresis should also be suspected if the child suddenly starts complaining of double vision with distant objects but not with near objects. The child with accommodative esotropia will usually have a more gradual onset of symptoms and greater diplopia for near objects than for those at a distance.
The first observation regarding ocular motor function should be any head turn or tilt that may reflect a fourthor sixth-nerve paresis. Next, ocular fixation should be noted. While the child fixates on a toy, any abnormal eye movements, such as nystagmus, are noted. Then binocular rotations (versions) are performed with the child following a toy into all six positions of gaze (Figures 16 and 17). If one fails to show full excursion, ductions (monocular rotations) should be performed. These following eye movements, or pursuit movements, originate in the occipital lobe. Following movements are involuntary slow-phase movements that can be initiated only with following objects.
Next, saccades* are tested. This is done by having the child look from side to side and upanddown(Figure 18).
Difficulty with vertical upgaze saccades may be an early sign of lesion in the upper midbrain tectum. Lagging of a medial rectus on horizontal saccade testing may represent an internuclear ophthalmoplegia.
Finally, eyelid symmetry should be noted. Most ptosis seen in children will be congenital in origin, but occasionally a third-nerve palsy with ptosis and associated oculomotor dysfunction may be found. Also, when an acquired ptosis is noted, myasthenia gravis must be considered.
In a fundus examination, the presence of symmetrical red reflexes should be noted. Any obstruction in the vitreous or anterior segment will dull the red reflex. Next, the optic nerve, vessels, and macula should be observed.
Proper visualization of the fundus can be obtained by instilling phenylephrine, 2.5%, one drop in each eye twice, ten minutes apart.
In summary, the examination for neurologic disorders falls into six parts: visual acuity, visual fields, external examination, pupil examination, ocular motor examination, and fundus examination.
EYE MOVEMENT DISORDERS
In discussing eye movement disorders, we distinguish supranuclear lesions, such as nystagmus; nuclear and infranuclear disorders, such as cranial nerve palsies, and conditions simulating cranial nerve palsies, such as ocular myasthenia gravis, Duane's syndrome, and Brown's tendon sheath syndrome.
Figure 16. Checking ocular motor function. Child is asked to follow finger puppet through nine cardinal positions of gaze as examiner looks for signs of muscle paresis.
Supranuclear Lesions. Supranuclear disorders are eye movement abnormalities that are caused by lesions above the final common pathways (ie, the third, fourth, or sixth cranial nerve nuclei or the brain-stem gaze centers).6
Congenital strabismus, although not commonly considered a supranuclear problem, is the most common supranuclear disorder. Unfortunately, we know very little about the sites or defects involved in strabismus.
Nystagmus is a rhythmic oscillation of the eyes. Jerk nystagmus is characterized by an initial slow phase, followed by a corrective fast phase in the opposite direction. Pendular nystagmus exhibits eye movements of equal velocity in both directions.
The physician must ask two simple questions when he first sees a patient with nystagmus: how long has the condition been present and what drugs is the patient taking?
Many children with congenital nystagmus are not referred for neuro-ophthalmic evaluation until they are two or three years old. The parents may note the abnormal eye movements at birth, but they fail to seek medical advice at that time. Since many drugs (ie, phénobarbital, phenytoin, etc.) may cause nystagmus, it is important to know all drugs the child is taking.
Nystagmus can be divided into physiologic, sensory deprivation, and motor imbalance nystagmus.
Physiologic Nystagmus. There are two types, endpoint nystagmus and optokinetic nystagmus.
* End -point nystagmus is a normal phenomenon that is seen fairly often; it occurs at the extremes of gaze as a fine jerk nystagmus, with the fast phase in the direction of gaze.
* Optokinetic nystagmus is a jerk nystagmus elicited by moving repetitive visual stimuli through the visual field (Figure 19) and may be elicited in neonates. The absence of optokinetic nystagmus by the time the infant is two months old should raise suspicion concerning the integrity of the afferent visual pathways. Also, if optokinetic nystagmus is asymmetric - more pronounced in one direction than the other- the examiner should wonder about a visual-field defect or supranuclear eyemovement disorder.
Figure 17. The finger puppet is used as a visual target for Figure 16.
Sensory Deprivation Nystagmus results from an afferent visual defect and can be due to the loss of central vision. Sensory deprivation nystagmus is often pendular in the primary position but frequently becomes a jerk nystagmus on gaze to either side. When there has been profound visual loss, the oscillations are so coarse and irregular that a pendular quality may be difficult to identify.7
Figure 18. Saccades are tested by having the child look rapidly at the puppet from side to side, then up and down.
Blindness or severe bilateral visual sensory deprivation that is present at birth usually results in nystagmus by three to four months of age. This is in contrast to congenital motor imbalance nystagmus, which starts at birth. Indeed, binocular loss of vision developing before age two always results in nystagmus. Between the ages of two and six, the development of nystagmus with visual loss is variable. Binocular visual loss after age six never results in nystagmus.6
Monocular nystagmus may be seen in an eye with severe visual sensory deprivation starting at birth. For example, an eye with a congenital monocular cataract will often develop a fine pendular nystagmus.
Ocular Albinism is a partial albinism inherited in a Xlinked recessive manner. Light skin and hair may be associated with the lack of ocular pigmentation. Decreased visual acuity and photophobia are often accompanied by the development of large-amplitude pendular nystagmus, which commences around three to four months of age. A family history of albinism, a very blond fundus with a poor macular reflex (due to macular hypoplasia or aplasia), and translucent irides should help establish albinism as a cause of pendular nystagmus.6
Achromatopsia is inherited as a recessive trait and is associated with low visual acuity, complete lack of color discrimination, normal or near-normal fundi, photophobia, and pendular horizontal nystagmus. The photophobia produces a characteristic picture of habitual blepharospasm and head held low to avoid bright lights.
Figure 19. The optokinetic drum is used to test for optokinetic nystagmus. If an asymmetric response is produced, the possibility of a visual-field defect or supranuclear lesion should be considered. Here optokinetic nystagmus is tested horizontally in both directions.
Latent Oculomotor Nystagmus is a congenital fixation nystagmus that appears or is increased when one eye is covered. It is often associated with strabismus.8 Because the latent nystagmus may reduce visual acuity under monocular testing, the pediatrician should think of this when binocular visual acuity is much better than monocular acuity.
Motor Imbalance Nystagmus. Motor imbalance nystagmus appears to result from a defect in the efferent motor system controlling eye movements and results in a jerk nystagmus that may be pendular in appearance.
Congenital Nystagmus starts at birth. The defect can be transmitted as an X-linked recessive or, occasionally, as a dominant trait. It is often a pendular nystagmus but may be a jerk nystagmus in different gaze positions. Characteristically, the nystagmus slows or stops in one position of gaze; this is called the neutral or null point. The child will turn or tilt his head to maintain this neutral position. An important characteristic of congenital nystagmus is that it usually continues to beat horizontally in all fields of gaze. Nystagmus caused by acquired brainstem lesion is often upbeating on upgaze or may be downbeating on downgaze.
Visual acuity may be good to poor, depending on the amount of movement at the neutral position. Interestingly enough, convergence usually eliminates or slows the nystagmus. These children may have poor distance vision but are able to read without difficulty. As the children grow older, the nystagmus usually slows.
Spasmus Nutans is a syndrome of infants and young children. The syndrome consists of ocular nystagmus, head nodding, and torticollis or head turning. Spasmus nutans develops between the second and 1 2th months of life and clears in most cases from one to four years after onset. The nystagmus tends to be fine and rapid (six to eight cycles per second) and to be monocular or predominately monocular in at least one position of gaze.9 Not all children develop head nodding, and fewer develop torticollis. Generally, no serious ocular or central nervous system problemscan be found. Thus an extensive neurologic evaluation is not justified unless other problems are evident.
Convergence-Retraction Nystagmus is not a true nystagmus but, rather, a contraction of all the extraocular muscles, with convergence resulting from the superior power of the medial recti.10 Convergence-retraction nystagmus in conjunction with other midbrain signs constitutes Parinaud's Syndrome.
Children with this syndrome often have great difficulty in making voluntary upward eye movements. Following eye movements are often performed more easily. Voluntary upward eye movements produce the convergence-retraction nystagmus. It is best elicited by having the child observe an optokinetic tape or drum moving down (Figure 20). Each upward saccade to observe the next stripe elicits the convergence-retraction nystagmus.11
In addition to the nystagmus, these children have pupils that respond poorly to light but better for accommodative responses. They may have diplopia, lid retraction, or skew deviation.* All these phenomena result from a lesion in the upper midbrain tectum - in children, most often a pinealoma.
Lid retraction in a baby with beginning internal hydrocephalus and a deficiency in upward eye movements has been named the "setting-sun sign." Dilation of the posterior portion of the third ventricle or cerebral aqueduct, with resulting pressure on the upper midbrain, may be responsible for this sign.
Internuclear Ophthalmoplegia (MLF syndrome) results from a lesion of the medial longitudinal fasciculus in the brain stem. When looking laterally away from the side of the MLF lesion, children with internuclear ophthalmoplegia develop monocular nystagmus in the abducting eye. With rapid horizontal saccade testing, the eye on the side of the MLF lesion will tend to lag on adduction with apparent medial rectus weakness. The most common cause of MLF syndrome in children is probably a brain-stem neoplasm, 12 but myasthenia gravis should be considered.13 In adults demyelinating or vascular disease would be the most common cause, depending on the patient's age.
Figure 20. Optokinetic nystagmus is tested vertically both up and down. Convergence-retraction nystagmus is best elicited by having the child observe the drum moving down.
Pathologic Vestibular Nystagmus may be caused by lesions in the brain stem or in the peripheral labyrinthine pathways. This nystagmus is a jerk nystagmus, usually greater to one side or the other. Rotary nystagmus is always due to a vestibular lesion, either peripheral or central.
Drug-induced Nystagmus is the most common cause of co-existing horizontal and vertical nystagmus. The common offending agents are sedative drugs, such as barbiturates and antihistamines, as well as anticonvulsants.
Vertical nystagmus is highly indicative of a brain-stem lesion (unless drug-induced) and should be investigated.
Other Abnormal Eye Movements
Opsoclonus is a sequence of rapid, voluntary eye movements that are predominantly horizontal. These movements are extremely rapid - often the eyes are in continuous conjugate, chaotic motion - and represent saccades. Neuroblastoma has been associated with opsoclonus in younger children. When the condition is seen in older children and adults, it is accompanied by ataxia and other cerebellar signs, often the result of a post-infectious encephalopathy.14
Congenital Oculomotor Apraxia isa syndrome that develops in the first months of life. These children show impairment of voluntary saccadic eye movements, most often horizontally. When these children want to look from side to side, they thrust their head in a characteristic fashion. By the teenage years, the head thrust usually disappears. Because of the difficulty with voluntary eye movements, these children may have difficulty reading. This syndrome is usually benign, and these children should not have an extensive neurologic workup unless it is warranted for other reasons.15
Nuclear or Intranuclear Eye Movement Disorders.
Nuclear or infranuclear disorders are secondary to lesions of the third, fourth, or sixth cranial nerves, their nuclei, or the muscles they innervate. In talking about these disorders, we must again state that any child with a head tilt or turn has an ocular motor imbalance until proven otherwise. The child maintains this head position to avoid diplopia and maintain fusion. Patching one eye for 24 to 48 hours will usually cause the head tilt to disappear, revealing ocular imbalance as the cause ofthe tilt. Thus, a child with such a turn or tilt deserves a complete ophthalmologic evaluation before any other evaluation.
Cranial Nerve Palsies. Third-nerve palsies are uncommon in children. These children present with unilateral ptosis, a larger pupil on the affected side, and an eye that is exotropic with poorability to elevate. When third-nerve palsies do occur without a history of trauma. one must consider ophthalmoplegic migraine, aneurysm, or tumor.16 This deserves immediate referral and evaluation.
Patients with sixth-nerve palsies present with a face turn toward the side ofthe paretic lateral rectus muscle. If the child shows no signs of increased intracranial pressure, otitis media, or other neurologic abnormalities, he can be followed initially without an extensive neurologic evaluation (since many of these conditions are postviral in origin).1 Brain-stem neoplasms must be kept in mind, however, so the child should be followed closely. The pediatrician should be sure he is not dealing with Duane's syndrome in a child who appears to have a sixthnerve palsy.
The most common origin of fourth-nerve palsies in children, excluding trauma, is congenital. Usually, the child develops a head tilt after the first month of life, with the head tilting to the side opposite the palsied superior oblique muscle (Figure 2 1). Patching one eye will stop the tilt, revealing its ocular origin. When ductions (monocular rotations) and versions (binocular rotations) are performed, underaction of the palsied superior oblique muscle will be noted, with overaction of the ipsilateral inferior oblique muscle (Figure 22). This abnormality needs to be corrected by eye muscle surgery before permanent neck contractures form.
Figure 21. Fourteen-month-old child with a right superior oblique palsy. Note characteristic left head tilt and face turn to the side opposite the palsied right superior oblique.
Figure 22. A) Gaze to the right is normal. B) Gaze to the left shows underaction of the palsied right superior oblique and overaction of the right inferior oblique.
Conditions Simulating Cranial Nerve Palsies.
Three conditions simulating cranial nerve palsies are ocular myasthenia gravis, Duane's syndrome, and superior oblique tendon sheath syndrome.
Ocular Myasthenia Gravis must always be considered in any child who develops ptosis or an atypical ocular muscle imbalance.
Duane's Congenital Retraction Syndrome is a congenital syndrome frequently confused with a sixthnerve palsy by those not familiar with the entity. It consists of a congenital deficiency of abduction, usually with retraction of the eye on adduction (Figure 23). The syndrome is often seen in otherwise normal individuals.1 Electromyographic findings would tend to support the theory that in some Duane's syndrome patients the lateral rectus is innervated by an anomalous third nerve with little if any sixth-nerve innervation. This accounts for the loss of abduction and retraction on adduction.18
Superior Oblique Tendon Sheath Syndrome (Brown's Syndrome) is another congenital syndrome in which there is severe limitation of elevation of the involved eye in adduction (Figure 24). Those not familiar with the syndrome will believe the problem is due to an inferior oblique palsy. However, the eye cannot be elevated with a forceps in adduction - revealing the true nature of the problem, which is a congenitally tight superior oblique tendon.17 Thus, a positive traction test makes the diagnosis, and further neurologic evaluation, unnecessary.
LESIONS OF THE AFFERENT VISUAL PATHWAYS
Strabismus and Marcus Gunn Pupil. The pediatrician must know that any child who develops strabismus needs a thorough ophthalmologic evaluation. The child may simply be developing an accommodative esotropia, requiring proper refractive correction. However, he may have a lesion of the afferent visual pathway - a cataract, retinal lesion, or tumor of the chiasm or optic nerve.
The presence of an afferent visual pathway lesion results in visual sensory deprivation, with resulting esotropia in younger children and exotropia in older children. The Marcus Gunn pupil becomes an important clinical sign. The Marcus Gunn pupil will never be present in children with cataracts, amblyoia, or small retinal lesions. Thus a positive Marcus Gunn pupil signifies a potentially more ominous problem, such as a large retinal lesion, optic nerve tumor, optic neuritis, or a tumor pressing on the optic nerve.
Fundus findings. The pediatrician must know that all swollen optic nerve heads are not papilledema. The term papilledema should be reserved for swollen optic disks secondary to increased intracranial pressure. Papilledema is usually bilateral, although it may be asymmetric. Vision and fields are normal, and there is no Marcus Gunn pupil.
Papillitis is unilateral and secondary to some local inflammatory condition of the optic nerve head. Ophthalmoscopically, it may look identical to papilledema. However, it is differentiated from papilledema because it is unilateral; vision is usually rather rapidly and severely reduced; and a Marcus Gunn pupil is present. When there is the rather sudden onset of unilateral visual loss with a Marcus Gunn pupil and normal optic nerve head, the condition is called retrobulbar neuritis. The cause of these conditions is unclear. Most investigators feel these are viral diseases and on some occasions may herald the onset of a demyelinative process.1 The vision usually recovers spontaneously in both of these conditions after several weeks.
Drusen of the optic nerve represent a congenital condition with an irregularly dominant mode of inheritance.20 Drusen are hyaline bodies situated in front of the lamina cribrosa, which frequently becomes replaced with calcium deposits. They are the most common cause of pseudopapilledema in children (Figure 25).
Figure 23. A) Patient with Duane's syndrome of the right eye. B) Gaze to the right shows marked limitation of abduction of the right eye, with widening of the palpebral fissure. C) Gaze to the left with adduction shows retraction of the right eye and narrowing of the right palpebral fissure because of the eye retraction.
Figure 24. A) Patient with Brown's syndrome (superior oblique tendon sheath syndrome). B) Gaze up to the right shows limitation of left eye secondary to tight left superior oblique tendon. C) Gaze up to the left is normal.
Drusen produce blurred, elevated disk margins in childhood. In adults, they erupt on the surface of the disk margin and can be seen as refractile bodies with the ophthalmoscope, making the diagnosis simple. The anomalous configuration of the retinal arterioles, along with the irregular dominant inheritance pattern, may help identify drusen as the cause of blurred disk margins.
Recent reports in the ophthalmic literature have noted optic nerve drusen with hemorrhages in both teenagers and adults. These hemorrhages have been located superficially on the optic disk or deep in the peripapillary retina. The distinction between early papilledema and drusen of the optic disk may be made more difficult by the presence of hemorrhages, but if one keeps the distinguishing feature of drusen of the optic disk in mind (Figure 25, bottom), the diagnosis should be easier.
The parents' fundus should be observed before papilledema is diagnosed in an otherwise healthy child. If the pediatrician sees elevated disk as an incidental finding in an otherwise asymptomatic child, he should obtain on ophthalmologic consultation before proceeding with a neurosurgical evaluation. The ophthalmologist should be able to help make the diagnosis of drusen. Ultrasound testing of the orbit shows the drusen very well in the optic nerve head. Many patients have been subjected to neurosurgical diagnostic and surgical procedures for this relatively benign ophthalmologic condition.
Optic Atrophy may be very difficult to diagnose in a young child. This will usually require the help of the ophthalmologist, who can examine the optic nerves with the indirect ophthalmoscope.
Children malingering about visual complaints are not uncommon. However, the reasons children give for malingering are different from those of adults. Children often use this method to express unhappiness with their environment. They hope to receive attention or recognition when more conventional methods have failed. These children are often from broken or unhappy homes. Also, poor school performance may precipitate malingering visual complaints as an explanation to parents for poor academic performance.
Malingering children present an unusual challenge to the ophthalmologist and pediatrician. Usually, by talking with parents, one can identify the source of the problem and arrive at a solution. The child is given assurance that his eyes will soon be better. The parents should attempt to correct the precipitating problem. Punitive action is the wrong approach and will only sublimate the problem and produce a different somatic complaint.
The pediatrician needs to develop some skills in evaluating afferent visual functions and ocular motor abnormalities. He must know some fundamental neuroophthalmologic facts to prevent his patients from undergoing unnecessary diagnostic and surgical procedures. In addition, he needs to understand the fundamentals of strabismus and amblyopia, which are briefly considered in this article.
Figure 25. A) and B) Differentiating papilledema and C) and D) drusen. A) Patient with papilledema shows obscuration of the blood vessels at the disk margin and edema in the nerve fiber layer. B) Note total obscuration of the blood vessels, with exudates on the disk. In two patients with drusen of the optic nerve head C) and D), note presence of retractile calcium bodies, aberrant vessels on the disk and the i rregular disk border, and the absence of vessel obscuration and of edema in the nerve fiber layer. The retractile calcium bodies do not show up until the second decade of life. These features should help distinguish between drusen of the optic nerve and papilledema.
First, the most common type of nystagmus in children is congenital nystagmus. These children often have a head turn or tilt. Also, it should be remembered that numerous drugs may cause nystagmus.
Second, any child with a head turn or tilt must be considered to have some ocular motor abnormality until a complete ophthalmologic evaluation has eliminated this possibility. In addition, before a child is considered to have an isolated sixth-nerve palsy, the child should be examined for Duane's retraction syndrome. Also, before an inferior oblique palsy is diagnosed, a Brown's tendon sheath syndrome should be considered. Thus, any ocular muscle abnormality deserves an ophthalmologic evaluation.
Third, when bilateral swollen optic nerves are noted as an incidental finding, drusen of the optic nerve head should be suspected. A unilateral swollen disk with decreased visual acuity and a Marcus Gunn pupil should bring to mind a papillitis, which is a local inflammatory condition of the optic nerve head. Remember, papilledema is a bilateral condition secondary to increased intracranial pressure with normal vision. Children with papilledema usually have other signs of increased intracranial pressure.
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