The monofixation syndrome (MFS) is a stable ocular alignment which often includes a small misalignment (strabismus) of the eyes (although straight eyes can also be less commonly seen), some amount of depth perception (stereopsis), and a unilateral mild decrease in vision (amblyopia). The disorder can be primary (occurring during normal development) or secondary (usually after extraocular muscle surgery to straighten misaligned eyes).
The primary form is often discovered on a routine eye examination as a child or during adulthood. The eyes are misaligned but not to a degree usually visible to the naked eye. The patient’s vision is typically mildly decreased in the non-dominant (non-fixating) eye and use of the two eyes together to achieve a high level of depth perception is not present. The patients are said to have peripheral rather than central fusion. The secondary form most commonly occurs after extraocular surgery for horizontal strabismus, when the patient has a resultant small angle residual misalignment. In fact, this is the desired result in many cases since it achieves a stable ocular alignment and excellent cosmesis.
No treatment for MFS is indicated unless there is a significant amount of amblyopia (and the patient is young enough for possible improvement) and/or the ocular alignment is unstable, noticeable or symptomatic (causing double vision). Treatment modalities include occlusion therapy, prisms and eye muscle surgery.