monofixation syndrome
Also called MFS, microtropia, microstrabismus, monofixational phoria, Parks monofixation syndrome
Monofixation syndrome is a state of binocular vision in which one fovea is suppressed during binocular viewing while peripheral fusion, fusional vergence amplitudes and gross stereopsis are kept. The syndrome can exist with or without a measurable deviation of the eyes.1,2
A suppression scotoma about 2.5 to 3 degrees across removes the central image of one eye, and the periphery of the retina continues to fuse and holds the eyes nearly straight.1 The syndrome is often treated as a synonym for microtropia, but strictly it also includes patients with straight eyes and a foveal scotoma, so microtropia is its commonest form rather than its definition.1,2,3
Monofixation syndrome should be suspected when acuity in one eye is 20/25 to 20/40, stereoacuity is 30 to 80 seconds of arc and the cover test shows little or nothing.4 The 4 prism diopter base-out test confirms the central scotoma.4
More detail
Monofixation syndrome differs from bifoveal fusion, because fine stereopsis is absent.1 The alternate cover test often reveals more than the cover-uncover test.2 The syndrome is the usual best outcome after surgery for infantile esotropia and the reason the angle stays stable afterward.1
Sources (4)
- Yanoff and Duker, Ophthalmology (2023), ch. 11
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 16
- Kanski, Clinical Ophthalmology (2024), ch. 18
- Carlson and Kurtz, Clinical Procedures for Ocular Examination, ch. 4
Reviewed October 2026
Related terms
Nearby in the glossary
- medial rectus
- meridional amblyopia
- microtropia
- monofixation syndrome
- motor fusion (fusional reserves)
- myectomy