Quiz: 40 Prism Diopter Esotropia

A 4-year-old male presents with a 40 prism diopter (PD) esotropia, present for the past few months. He is otherwise healthy and normal. At near fixation, the esotropia measures 55 PD. There is a fixation preference for the right eye but uncorrected visual acuities are normal at 20/20 in either eye and ocular motility is normal with the exception of mild inferior oblique overaction in each eye as seen in this photo collage. What could be happening?

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