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2. A 6 month old boy is sent to you because his parents have noticed that their child’s eyes have been “inwardly crossed” since birth. They had hoped for spontaneous improvement, but that has not happened. Your examination discloses that the child fixes and follows with each eye when either eye is occluded. You find a comitant esotropia when the child views distant and near targets. Ocular ductions are full and there is no nystagmus. The refractive error is plano, ophthalmoscopy is normal, and both pupils constrict normally to light without afferent pupil defect.
The likely cause of this abnormality is
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Correct!
If your observation is correct that ocular ductions are full and the esotropia is comitant (the misalignment is of the same amount in right and left gaze), the abnormality is not likely
to be a sixth nerve palsy. Why not? Because sixth nerve palsy should show an abduction deficit (although it could be mild) and produce an incomitant esotropia with greatest amount in
ipsilateral gaze. Yes, sixth nerve palsy can eventually develop full ductions and become a comitant esotropia, but that would be highly unusual in a 6 month old child. Accommodative
esotropia is ruled out by the plano refraction. Sensory esotropia, a diagnosis applied when the misalignment represents a breakdown of fusion owing to an underlying vision deficit, is an
unlikely choice because the examination shows apparently good vision in each eye, a normal fundus examination, and no afferent pupil defect. Of course, these conclusions depend on a
skillful, thorough examination and reliable findings—not easy in such a young child. Be careful!
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