Sursa:
http://telemedicine.orbis.org/bins/content_page.asp?cid=1-2193-2348
[...] The term orthophoria is not a good one since, as mentioned above, orthophoria is the exception and heterophoria is the rule in normal binocular vision.1 The terms straight-appearing eyes or straight eyes, which all too often seem to escape editorial scrutiny in the contemporary American literature, are to be avoided. They lack precision in describing the functional state of the patient since they encompass a whole spectrum of conditions that includes orthotropia, heterophoria of varying degrees and clinical significance, and even microtropia and heterotropia with a small angle.
[...] Ideally, the fusion-free position of the eyes should be such that the visual lines are parallel in distance fixation and have the proper convergence in near vision. This ideal, termed orthophoria, is infrequently realized; it is only approached more or less closely. Whenever fusion is suspended by some means, there is usually a deviation of the visual axes even though it may be too small to be measured by ordinary clinical means.
Orthophoria therefore is not a normal condition in the majority of people free from ocular symptoms. Consequently, many clinicians consider a certain amount of heterophoria to be normal.
