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This 29-year-old woman complains that her right eye sometimes goes down. At 18 years of age she had bimedial rectus recession for esotropia present since birth. At age 23 she underwent right superior rectus recession for a variable right hyper deviation diagnosed as dissociated vertical deviation. On motility examination the right hypotropia is variable and the eye moves up to the primary position and then downward periodically over a matter of minutes or else remains in the downward position approximately 10 to 15 prism diopters. Her visual acuity is OD 20/600 and OS 20/20. Refraction is OD +3.50 and OS +0.50. She does not wear glasses. The remainder of the eye examination is within normal limits.

1.	The main reason for reduced vision in the right eye is:
	b -- anisometropia This patient has two possible causes for her amblyopia. They are esotropia from early in life and anisometropia. An uncorrected hyperopic refractive error of +3.50 in one eye and a + 0.5 hyperopia is a powerful cause of anisometropic amblyopia. While the esotropia could definitely contribute to the amblyopia if she chose one eye for fixation instead of alternating, the anisometropia virtually assured her of left eye fixation and right eye amblyopia. It is important to correct anisometropia greater than +0.50 diopters in nearly every case, but definite parameters cannot be stated. Myopic anisometropia is not quite as likely to produce amblyopia because each eye will have a farpoint for potentially clear vision.
2.	This motility pattern is compatible with a diagnosis of:
	a -- Heimann-Bielschowksy phenomenon The history and clinical findings are compatible with a diagnosis of Heimann-Bielschowsky phenomenon. "Hypotropia in a poorly seeing eye which also ‘bobs’ up and down with nystagmoid movements is characteristic of the Heimann-Bielschowsky phenomenon. This patient could also demonstrate a DVD response with the right eye becoming hyperdeviated when the right eye is covered. Behavior of this sort can occur in a poorly seeing eye of long standing. I have seen similar behavior in more than a dozen such cases. The best treatment for this patient, in my experience, is recession of the inferior rectus of the hypotropic right eye. In cases like this that I have treated, there has been no exacerbation of the hyper response of the DVD." From: Surgical Management of Strabismus, ed. 5, page 358.
3.	A reasonable treatment would be:
	c -- right inferior rectus recession A reasonable surgical treatment for this case would be right inferior rectus recession. However, since this is a variable deviation and probably under supranuclear control, correction may not be precise and lasting so the patient must be informed ahead of time.