AUTHOR AND EDITOR INFORMATION

Section 1 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

INTRODUCTION

Section 2 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

Background

Monofixation syndrome is essentially a form of subnormal binocular vision. It may also be considered a form of binocular single vision without bifixation due to an absolute scotoma of less than 3 degrees in one eye during binocular vision.  It can be a primary disorder of binocular vision, or it can be a secondary sensory status from a variety of primary causes.

Monofixation syndrome is a sensory adaptation that is characterized by small angle strabismus, unilateral facultative central suppression scotoma, and peripheral fusion.

Pathophysiology

The main defect is a central suppression scotoma.

The central retina has small receptive fields and is 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.

Some patients seem to have an inherited inability to bifixate.

Frequency

United States

The prevalence of monofixation syndrome in the general population is 1%.

Age

This condition is recognized mainly in children but can occur at all ages.

CLINICAL

Section 3 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

History

• Because monofixation syndrome is an asymptomatic condition, the diagnosis is often based on the physical examination.
• • Patients should be asked whether they have a history of muscle surgery, amblyopia, or retinal disease, as well as a family history of strabismus.
  • Adults with subnormal stereovision, mild anisometropia, and subtle asymmetry in best-corrected vision may have undiagnosed primary monofixation syndrome.

Physical

• Prism cover tests
• • Patients should display less than 8 prism diopters of heterotropia with a simultaneous prism cover test.
  • Alternate prism cover testing may result in 2-3 times greater measurement than simultaneous prism cover testing due to fusional vergence mechanisms.
  • Up to one third of patients have no deviation with alternate cover.
• Stereoacuity tests
• • Patients with monofixation syndrome have reduced stereopsis, ranging from 300 arc seconds to 67 arc seconds.
  • Stereopsis tends to be better at near than at distance.
• Central suppression scotoma tests
• Worth 4-dot test
• • At near (one-third meter), the standard flashlight tests peripheral fusion by subtending 6 degrees of the retina.
  • When performed at a distance of 6 meters, the patient with monofixation syndrome should only visualize from one eye because the target subtends only 1.25 degrees and slips into the suppression scotoma.
• 4 prism diopter base-out test
• • While having the patient read letters at 20 feet, a 4 prism diopter base-out is placed over one eye.
  • This is repeated on the other eye.
  • The test is positive when the eye that is suspected of having a suppression scotoma does not move after being covered with the prism.
  • This test has a high number of false negatives, especially if no manifest deviation is present.
• Bagolini lenses
• • Lenses are placed over the eyes, and the patient views a small handlight that is located one-third meter away in a normally lit room.
  • The eye with the suppression scotoma should have a line with a central interrupted portion.
• Binocular visual fields

Causes

• Corrected strabismus
• • Patients with corrected strabismus comprise the largest subgroup of patients with monofixation syndrome seen in clinical practice.
  • Patients who are surgically treated for esotropia more commonly develop monofixation syndrome than exotropia.
  • Of patients with congenital esotropia, 40-50% will develop monofixation syndrome if corrected to less than 8 prism diopters of deviation by age 2 years.
  • Late correction dramatically decreases the chances of developing monofixation syndrome.
  • Patients with congenital esotropia who develop monofixation syndrome are almost twice as likely to maintain long-term alignment.
• Anisometropia
• • Blurred image on one macula due to uncorrected refractive error leads to unilateral suppression scotoma and mild-to-moderate amblyopia.
  • Almost 50% of such patients show no manifest deviation.
• Primary monofixation syndrome
• • Most patients with primary monofixation syndrome are difficult to diagnose because of the lack of symptoms.
  • These patients have an inherent defect in central fusion, and most have mild amblyopia.
  • Prevalence of primary monofixation syndrome is 9% in families who have children with congenital esotropia.
  • Monofixation syndrome may represent the forme fruste of congenital esotropia.
• Macular lesion
• • Patients with organic macular lesions have a central scotoma.
  • They often maintain alignment because of peripheral fusion; they are the only group without a facultative scotoma.

DIFFERENTIALS

Section 4 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

Other Problems to Be Considered

Angle kappa
Pseudostrabismus

WORKUP

Section 5 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

Other Tests

• A variety of devices have been developed to detect microtropia based on the Bruckner reflex. These methods typically have a higher sensitivity in young children who lack subjective test cooperation.¹ 

TREATMENT

Section 6 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

Medical Care

• Monofixation syndrome may be the goal of strabismus surgery and is not an undesirable result.
• • If a manifest strabismus is present, it is cosmetically acceptable.
  • Patients who have undergone prior surgery for strabismus have a much greater likelihood of long-term alignment if they develop monofixation syndrome.
• Treatment is given for any associated amblyopia in accordance with standard ophthalmic principles.
• • Amblyopia in children should be treated with appropriate spectacle correction. A careful cycloplegic refraction should be performed to check for anisometropia.
  • Occlusive patching or optical penalization should be considered as the clinical situation warrants. The amount of occlusive patching is dependent upon many factors, including age, density of amblyopia, and underlying etiology. In cases of mild amblyopia secondary to anisometropia, part-time occlusion may be all that is needed.
  • Optical penalization is a method of amblyopia treatment. Optical penalization relies on optically blurring the image of the preferred eye. The most common method relies on using atropine 1% ophthalmic solution in the preferred eye.

Surgical Care

Heterotropia is cosmetically acceptable, so patients rarely need surgery. Monofixation syndrome tends to stabilize the alignment, thereby decreasing the need for further surgery.

FOLLOW-UP

Section 7 of 8  

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

Further Outpatient Care

• Patients with stable monofixation syndrome should have routine follow-up care.
• If patients have been treated for amblyopia, then the frequency of visits is determined by the intensity of their treatments.
• Monofixation syndrome may deteriorate, and patients may develop larger tropia, decreased stereovision, or diplopia.² Risk factors for deterioration include esotropia and amblyopia. Surgical treatment can often reduce the tropia and restore secondary monofixation syndrome.

Prognosis

• The prognosis for alignment and maintenance of subnormal binocularity is excellent.

REFERENCES

Section 8 of 8

• Authors and Editors
• Introduction
• Clinical
• DIFFERENTIALS
• WORKUP
• Treatment
• Follow-up
• References

1. Cibis GW. Video vision development assessment in diagnosis and documentation of microtropia. Binocul Vis Strabismus Q. 2005;20(3):151-8. [Medline].
2. Hunt MG, Keech RV. Characteristics and course of patients with deteriorated monofixation syndrome. J AAPOS. Dec 2005;9(6):533-6. [Medline].
3. Arthur BW, Smith JT, Scott WE. Long-term stability of alignment in the monofixation syndrome. J Pediatr Ophthalmol Strabismus. Sep-Oct 1989;26(5):224-31. [Medline].
4. Botet RV, Calhoun JH, Harley RD. Development of monofixation syndrome in congenital esotropia. J Pediatr Ophthalmol Strabismus. Mar-Apr 1981;18(2):49-51. [Medline].
5. Choi DG, Isenberg SJ. Vertical strabismus in monofixation syndrome. J AAPOS. Feb 2001;5(1):5-8. [Medline].
6. Parks MM. The monofixation syndrome. Trans Am Ophthalmol Soc. 1969;67:609-57. [Medline].
7. Scott MH, Noble AG, Raymond WR 4th, Parks MM. Prevalence of primary monofixation syndrome in parents of children with congenital esotropia. J Pediatr Ophthalmol Strabismus. Sep-Oct 1994;31(5):298-301; discussion 302. [Medline].
8. Tomac S. Monofixation syndrome and anisometropia. Ophthalmology. Jan 2002;109(1):3-4. [Medline].
9. Wright K. Visual development, amblyopia, and sensory adaptations. In: Pediatric Ophthalmology and Strabismus. St Louis, Mo: Mosby; 1995:119-138.

Article Last Updated: Sep 25, 2007