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Vision is an essential sensory input from infancy and throughout
childhood that allows for normal physical, cognitive, educational,
and social development and for adult occupational training. Vision
is present at birth at approximately a 20/200 level. Visual
acuity develops rapidly during the first year, with normal acuity reached
by 9 to 12 months of age. Blindness or visual impairment can be
assessed in terms of the level of visual function and by scoring
functional vision related to quality-of-life achievements. Assessment
of visual acuity is the most often used parameter for estimating
vision. The assessment of visual acuity in young children is imprecise.
Therefore, it is necessary to define ranges of visual loss. Also
test results may improve with advancing age and development. Levels
of visual function, ranging from normal to visually impaired, have
been categorized into five levels of performance (Table
584-1).
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Unsteady eye movements may be evidence of poor vision since birth
or with early onset before 2 years of age. When related to an ocular
etiology such as cataracts, retinal abnormalities, or optic nerve
defects, a pendular nystagmus is often present, which becomes a
characteristic jerk nystagmus in lateral gaze. A jerk nystagmus
demonstrates a slow-conjugate drift in one direction followed by
a rapid-corrective return to fixation. If the vision is very poor,
the abnormal eye movements are also conjugate but become more random
in many planes and are less sustained. This is sometimes referred
to as “wandering eye movements.” In the unique
case of neuroblastoma, children may have a very disorganized rapid
pattern of eye movements, often brought on by startle stimuli, known
as opsoclonus. Infantile sensory nystagmus may be seen with extreme
vision loss in only one eye, but in this setting is characteristically
only jerk in type. In addition to infantile sensory nystagmus, other
causes of nystagmus must be distinguished and include disturbances
of motor origin. Congenital motor nystagmus is usually idiopathic
but may also be seen as a hereditary disorder found in various Mendelian
patterns. It is important to recognize the significance of early
onset nystagmus as a key sign of vision loss since infancy. This
nystagmus may lessen with visual improvement or with aging.
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It has been estimated that there are 1.5 million blind children
worldwide and that 90% live in developing countries. Of
the estimated 500,000 children ...