Vergence Adaptation Maintains Heterophoria in Normal Binocular Vision

Vergence Adaptation in Subjects with Convergence Excess

“…Vergence adaptation can be illustrated by the process by which the eyes return to their habitual heterophoria or fixation disparity after a prism has been placed before one or both eyes. This ability to adapt to a prism, commonly called prism adaptation, has been shown by several researchers (Brautaset & Jennings, 2005a-c;Carter, 1963Carter, , 1965Henson & Daramshi, 1982;Henson & North, 1980;McCormack, 1985;Mitchell & Ellerbrock, 1955;North & Henson, 1981North et al, 1990North et al, , 1993Ogle et al, 1951;Ogle & Prangen, 1953). Similar adaptive response can be demonstrated in the accommodative system.…”

Near Heterophoria in Early Childhood

“…Given the consistency of the heterophoria position across age and moderate refractive error, it appears that this exophoria may be a robust state settled upon by the vergence system to serve binocular vision at near. 5,7,56,57 These data suggest that there is no qualitative difference between adults and young children, either in terms of the direction or range of values found. The apparent exophoria could perhaps be a position that the visual system even adapts to, given the range of interpupillary distances and refractive errors typically found with age.…”

Near visual function in young children. Part I: near point of convergence. Part II: amplitude of accommodation. Part III: near heterophoria

“…Many studies in the literature supported the view of readaptation to habitual phorias (Ellerbrock, 1950;Ogle and Prangen, 1953;Mitchell and Ellerbrock, 1955;Carter, 1957Carter, , 1958Carter, , 1963Carter, , 1965Ogle et al, 1967;Schor, 1979;North andHenson, 1981, 1985;Henson and Dharamshi, 1982;McCormack, 1985;North et al, 1986North et al, , 1989Sethi, 1986;Larson, 1990;Larson and Faubert, 1994). However, re-adaptation to the habitual heterophoria does not necessarily prove the action of heterophorisation because heterophoric subjects might have an abnormal or insucient adaptation response and the abnormal adaptation mechanism might tend to take the established heterophoria rather than orthophoria as its baseline (Dowley, 1987).…”