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This 27-year-old man lost vision in his left eye at age 14 after developing a retinal detachment. In the last two years he was noted to have an esodeviation in the left eye of 60 prism diopters one day and of only 12 prism diopters on the next day. This has occurred in a repeating pattern for two years where he has a large ET on one day and a small ET on the next. Except for poor vision in the left eye the man is healthy. His refraction in the right eye is plano.

1.	This condition is called:
	d -- cyclic esotropia This is an example of cyclic esotropia.
2.	This condition is:
	b -- not well understood regarding its etiology The cause of this unusual condition is not fully understood.
3.	A reasonable treatment option is:
	e -- (a) and (d) Surgery for the angle of deviation on the esotropic day is appropriate for the strabismus.  The man should also wear safety glasses to protect his one good eye.

You can learn more about cyclic strabismus in:  Binocular Vision and Ocular Motility, vonNoorden and Campos in E-Resources, page 480.