Background
Monofixation syndrome is a form of subnormal binocular vision without bifixation characterized by small-angle strabismus, unilateral absolute facultative central suppression scotoma of less than 3º, and peripheral fusion. While monofixation syndrome can be a primary disorder of binocular vision, it is more commonly a secondary sensory status due to various primary causes.
Pathophysiology
The main defect is a central suppression scotoma, which prevents bifixation.
The central retina has small receptive fields and is therefore more sensitive to image blur or image disparity than the peripheral retina. Conditions that cause a suppression scotoma in the central retina but allow for peripheral fusion cause monofixation syndrome. Studies in macaque monkeys have demonstrated that 2 adjacent neurons in the visual cortex could join receptive fields up to 5°, which correlates to the maximum deviation of 8 pd of monofixation syndrome. [1]
Some patients have an inherited inability to bifixate.
Epidemiology
Frequency
United States
The prevalence of monofixation syndrome in the general population is 1%.
Age
Monofixation syndrome is recognized mainly in children but is present at all ages.
Prognosis
Monofixation syndrome has been shown to remain stable over decades. Among patients who have been monitored for several years, sensory status has improved with higher-grade stereoacuity in a small percentage. A small percentage of patients may have decompensated motor loss over time. [2]
