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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 most likely to be infantile (congenital) esotropia. It is called “infantile” rather than congenital because it is often not noticed until months after birth. Its pathogenesis is unknown. Although it is often an isolated abnormality, it can be associated with other brain and systemic dysgeneses. It represents a disturbance in the vergence system--the balance between convergence and divergence. The most important condition to rule out is sensory esotropia, wherein the misalignment is based on poor sight in one or both eyes. That diagnosis is unlikely here because the patient has apparently normal sight, a normal fundus exam, and no afferent pupil defect. The diagnosis is not likely to be a sixth nerve palsy because there is usually an abduction deficit (although it could be mild) and 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 not a good choice either. Why not? Because the refraction is plano yet the esotropia is present when the child views a distant target. (There is a form of accommodative esotropia associated with a plano refraction, but in those cases, the esotropia is present only when viewing a target at reading distance; such patients are believed to have a high accommodative convergence/accommodation ratio; they are treated with bifocal glasses.)

Of course, these conclusions depend on a skillful, thorough examination and reliable findings—not easy in such a young child. Be careful!

Before you go on to the next case, take a look at this video, which explains the significance of comitant and incomitant ocular misalignment.

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