Unexplained Visual Loss in Children

tisms, or other evidence of seizure activity coincident with the visual disturbance. Has there been recent head trauma to suggest the possibility of transient posttraumatic cerebral blindness or arterial dissection? Inquire about a personal or family history of thromboembolic events and look for nail bed splinter hemorrhages, which would suggest the rare possibility of antiphospholipid antibody syndrome or a protein S or C deficiency.79

2. Performing a complete neuro-ophthalmologic examination to look for papilledema, pseudopapilledema or other optic disc anomalies, optic disc pallor (possibly suggesting old optic neuritis), homonymous hemianopia, or other neurological deficits. If a child is examined during an episode of monocular visual loss, look for retinal vasospasm. Carefully examine the retina for detachments, tears, signs of vitreous traction (which are easily overlooked when they overlie the disc), and retinal whitening to suggest recent infarction. When transient visual disturbances are unilateral, look for an ipsilateral Horner’s syndrome, which would suggest carotid artery dissection.

3. Obtaining a pediatric examination to rule out clinical signs or symptoms of cardiac disease, collagen vascular disease, hypertensive encephalopathy, and other systemic disease.

Laboratory Evaluation of Transient Visual

Disturbances in Children

The laboratory investigations ordered depend on the examiner’s clinical impressions that are based on the history and physical findings (Fig. 5.6). If a clear-cut clinical picture of migraine is obtained, then no investigations are indicated. If the description of the visual disturbance is reminiscent of a seizure disorder or there are other abnormalities suggestive of a CNS disorder, MR imaging and EEG should be undertaken.

Children in whom the pathophysiology of the transient visual disturbance is not clearly migrainous or epileptic pose the greatest diagnostic dilemma. Cardiac disease is more frequently recognized as a cause of permanent neurologic impairment in children, now that advanced noninvasive cardiac imaging techniques, such as transesophageal echography, are available.332,441 Children with a history suggestive of intrinsic cardiac disease should be referred to a pediatric cardiologist for clinical and echocardiographic evaluation. A serum hemoglobin electrophoresis is indicated in black children to rule out sickle cell disease. A complete hemogram, erythrocyte sedimentation rate, platelet count, antinuclear antibody, and partial thromboplastin time (to screen for antiphospholipid antibodies) should be obtained when there are other systemic signs to suggest a vasculopathy. In the rare cases that are particularly suspicious for thromboembolic disease, anticardiolipin antibodies, antithrombin III, and protein C and S levels can be obtained to rule out a coagulopathy.

The diagnostic yield for these tests is low, but they are more likely to be abnormal when they are applied only in suspicious cases.

Unexplained Visual Loss in Children

Many children who have decreased vision are referred for neuro-ophthalmologic evaluation after ocular abnormalities have been ruled out. The subspecialist must be familiar with common as well as rare causes of unexplained visual loss in childhood so that the neuro-ophthalmologic examination and ancillary workup can be directed in an expedient fashion (Table 5.2). Underlying conditions can range from refractive errors to retinal or intracranial disorders that can reduce vision before visible signs of disease become evident.

Causes of Unexplained Visual Loss

in Childhood

Transient Amblyogenic Factors

Occasionally, a child is found consistently to have decreased vision in an eye that is otherwise normal. In such cases, it is assumed that transient amblyogenic factors must have led to amblyopia and subsequently resolved.407 Such factors may include neonatal lid swelling, early anisometropia, transient strabismus, macular hemorrhage, and vitreous hemorrhage. Monocular suppression on sensory testing (Bagolini striated lens, Worth 4-Four Dot) of an eye with no structural abnormality is suggestive of amblyopia.

There is a unique disorder that may present as a deficit of stereopsis, despite relatively normal monocular visual acuity in either eye. This disorder, labeled the monofixation syndrome, is characterized by the presence of a facultative central scotoma in one eye under binocular viewing conditions, which is absent under monocular conditions. As a result, central fusion and fine stereopsis are lacking, but peripheral fusion (which provides fusional vergence amplitudes and gross stereopsis) is retained. While the presence of strabismus is not a prerequisite for this condition, it is common for affected children to have an esotropia of 8–10 prism diopters or less on simultaneous prism cover testing and a larger esotropia (16–25 prism diopters) on alternate prism cover testing. The smaller deviation on simultaneous prism cover testing reflects the preservation of peripheral fusion. Children with monofixation syndrome may appear to have straight eyes and be found to have a surprisingly large deviation on prism alternate cover testing.

Children with monofixation syndrome often show some degree of superimposed amblyopia. The diagnosis is estab-