peripheral fusion
Peripheral fusion is the fusion of images that fall on the peripheral retina of the two eyes, apart from the images on the foveae. Disparate targets placed in the retinal periphery can drive fusional movements on their own. A strong enough peripheral target can even break up central fusion while the observer attends closely to a central object.1
The periphery tolerates more disparity than the center. Panum's fusional area is about 6 to 10 minutes of arc wide near the fovea and grows to about 30 to 40 minutes of arc at 12 degrees from the fovea.2
Peripheral fusion can hold the eyes nearly straight when bifoveal fusion is missing. In microtropia, fusional impulses from peripheral vision hold the eyes at the small angle, and a form of pseudofusional reserve can be measured.3 Monofixation syndrome pairs peripheral fusion with reduced stereopsis in patients who cannot achieve bifoveal fusion.4
More detail
Peripheral fusion can blunt the cover test in microtropia. The examiner should hold the cover close to the eye to dissociate the eyes completely, because peripheral fusion can otherwise shrink the movement and hide the deviation.3
Sources (7)
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 4
- von Noorden and Campos, Binocular Vision and Ocular Motility, ch. 2
- Pickwell's Binocular Vision Anomalies, ch. 16
- Yanoff and Duker, Ophthalmology (2023), ch. 11
- Noorden, G.K. and Campos, E.C. 2002. Binocular vision and ocular motility: theory and management of strabismus. 6th ed. St. Louis: Mosby.
- Rutstein, R. and Daum, K. 1997. Anomalies of Binocular Vision: Diagnosis & Management. St. Louis: Mosby.
- Steinman, S.B., Steinman, B.A. and Garzia, R.P. 2000. Foundations of binocular vision: a clinical perspective. New York: McGraw-Hill. Webvision. 2005. The Perception of Space. [online] Available at: https://www.ncbi.nlm.nih.gov/books/NBK11512/ [Accessed 6 May 2024]. secondary
Reviewed October 2026