Pediatric emergency medicine trisk 0588 0588
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CHAPTER 28 ■ EYE: STRABISMUS
MICHAEL P. GOLDMAN, BRUCE M. SCHNALL
INTRODUCTION
Strabismus refers to any misalignment of the eyes such that they are not viewing
in the same direction. If the misalignment occurs using binocular vision (i.e., both
eyes are uncovered), it is termed a tropia (e.g., esotropia), or manifest strabismus.
If it occurs only when the two eyes are no longer looking at the same object, it is
termed a phoria (e.g., esophoria), or latent strabismus. Esotropia (or esophoria)
refers to eyes that are turned in (cross eyed). Exotropia (or exophoria) refers to
eyes that are turned out (wall eyed). The terms hypertropia and hypotropia refer
to a higher or lower eye, respectively.
All children with strabismus require an urgent formal evaluation by an
ophthalmologist for definitive diagnosis and management, but the emergency
physician should attempt to answer two questions: (1) “Is this strabismus an
emergency?” and, if so, (2) “What is the most likely cause?”
PATHOPHYSIOLOGY
Six muscles surround each eyeball ( Fig. 28.1 ). Understanding the action of these
muscles allows for the definition of diagnostic positions of gaze ( Table 28.1 ).
This can be helpful in pinpointing specific muscle dysfunction. For example, if a
muscle that primarily governs abduction (e.g., lateral rectus) is impaired, the eye
is unable to abduct and will usually lie in a position of adduction (esotropia).
Likewise, if a muscle that is involved with downward gaze (e.g., inferior rectus)
is impaired, the eye will have a tendency to remain in relative upward gaze
(ipsilateral hypertropia).
In broad terms, strabismus is categorized into misalignment as a result of
impaired muscle function or misalignment in the presence of normal muscle
function. In general, there are only two emergent reasons why the function of a
particular muscle might be impaired: neurogenic palsy or muscle restriction.
Nerve Palsies
Three cranial nerves are responsible for the innervation of the six extraocular
muscles ( Table 28.1 ). The sixth cranial nerve innervates the ipsilateral lateral
rectus muscle. This nerve exits the ventral pons and then travels on the wall of the
middle cranial fossa (clivus), reaching the sphenoid ridge, along which it travels
until entering the cavernous sinus. The course of this nerve allows it to be injured
