This 19-year-old woman has had four prior surgeries for what was originally diagnosed as congenital esotropia.  Her eyes are aligned in the primary position, but she complains that when she is tired and at other times for simply no apparent reason her left eye drifts upward.  Her visual acuity is 20/20 in the right eye and 20/30 in the left.  Refractive error is low hypertropia.  She has no fusion and denies diplopia. The left hyperdeviation is apparent behind the translucent occluder.

1.	The most likely diagnosis in this case is:
	a -- This is clearly a case of dissociated vertical deviation greater in the left eye.  Inequality is frequently seen with this condition.
2.	The cause of this deviation is:
	b -- Dissociated vertical deviation (DVD) is seen in nearly every case of congenital esotropia.  It is seen slightly more often when patients have been treated surgically with alignment of the eyes.  It tends to occur about 18 months after alignment. Not every case of  DVD requires treatment.  It is treated only when the misalignment is noticeable and bothers the patient or the family.
3.	Surgical treatment of this hyperdeviation :
	b -- Since dissociated vertical deviation does not produce symptoms, it is treated on the basis of the misalignment being intolerable to the patient or the family.  Surgery in a case like this would usually entail recession of the left superior rectus.  In cases of unequal DVD, both eyes are treated surgically with the amount of surgery dosed to the deviation.  In many cases of DVD when just one eye is operated because the deviation is primarily in this eye, the other eye manifests a larger deviation and itself requires surgery.