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The vision system in infants and children can be thought of as
a combination of the eye and extraocular orbital structures as well
as connections to the vision-related portions of the brain. A basic
understanding of the normal anatomy, embryology, developmental biology,
and physiology of these structures is necessary to comprehend the
abnormalities that result in disease and the appropriate means to
diagnose and treat them. The development of good visual function
requires an interaction of the cornea, lens, retina, optic nerve,
cranial nerves, and the autonomic nervous system, along with the
brain, to allow a properly focused, clear single image to fall on
the retina of each eye and then be converted into electrical signals
that are transmitted to the appropriate areas of the brain.
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Babies are not born with normal 20/20 visual acuity
or normal binocular vision, but must develop these by having a clear
focused image fall on the appropriate area of the retina of each
eye during the period from birth to 6 to 9 years of age, sometimes
called the “period of vision development.” Failure
of a focused image to fall on the retina during any part of this
critical period, due to uncorrected refractive error, eye misalignment
(strabismus), or ocular media opacity (eg, cataract, vitreous or
corneal opacity), can result in poor vision development, known as amblyopia.
For example, infants with bilateral congenital cataracts must have
their cataracts removed and appropriate optical correction applied
as early as possible in order to optimize visual outcome and prevent irreversible
deprivation amblyopia in 1 or both eyes. Infants with infantile
esotropia must be aligned before 2 years of age in order to demonstrate
at least some binocular vision. Therefore, it is mandatory that ocular
abnormalities in infants and children are diagnosed early and treated
in a timely fashion.
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Six of the 12 cranial nerves are involved in ocular physiology
and mechanics of vision. The second cranial nerve, the optic nerve,
allows afferent input for visual stimuli as well as pupillomotor
reactivity. Electrical impulses from the retina travel via the optic
nerve through the optic chiasm and the temporal and parietal lobes
of the brain, ultimately arriving at the occipital cortex to begin
the process of translation into vision. The third cranial nerve,
the oculomotor nerve, innervates the medial rectus (adduction),
superior rectus (elevation), inferior rectus (depression), and inferior
oblique (elevation, abduction, and extorsion) muscles, as well as
the levator palpebrae superioris muscle (elevation of the upper
eyelid). Additionally, the oculomotor nerve carries the parasympathetic
afferent input of the dilator muscle of the pupil. The fourth cranial
nerve, the trochlear nerve, innervates the superior oblique muscle
that depresses, abducts, and intorts the eyes. This is the most
likely nerve to be affected after trauma due to its long, unprotected
intracranial course over the dorsal aspect of the superior brainstem
to exit the cranial vault inferior to the brainstem. The fifth cranial
nerve, the trigeminal nerve, is responsible for ...