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slanting or inclined in direction or course or position--neither parallel nor perpendicular nor right-angled; "the oblique rays of the winter sun"; "acute and obtuse angles are oblique angles"; "the axis of an oblique cone is not perpendicular to its base"
any grammatical case other than the nominative (同)oblique case

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傾いた,斜めの / 間接の,遠回しの / 〈C〉〈U〉斜線(/)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/08 18:18:13」(JST)

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Heterophoria is a type of eye condition in which the directions that the eyes are pointing at rest position, when not performing binocular fusion, are not consistent with each other. It is also known as 'latent squint' because tendency of the eyes to deviate is kept latent by fusion. A person with two normal eyes has single vision (usually) because of the combined use of the sensory and motor systems. The motor system acts to point both eyes at the target of interest; any offset is detected visually (and the motor system corrects it). Heterophoria only occurs during dissociation of the left eye and right eye, when fusion of the eyes is absent. If you cover one eye (e.g. with your hand) you remove the sensory information about the eye's position in the orbit. Without this, there is no stimulus to binocular fusion, and the eye will move to a position of "rest". The difference between this position, and where it would be were the eye uncovered, is the heterophoria.

In contrast, fixation disparity is a very small deviation of the pointing directions of the eyes that is present while performing binocular fusion.

Heterophoria is usually asymptomatic. This is when it is said to be "compensated". When fusional reserve is used to compensate for heterophoria, it is known as compensating vergence. In severe cases, when the heterophoria is not overcome by fusional vergence, sign and symptoms appear. This is called decompensated heterophoria. Heterophoria may lead to squint or also known as strabismus.

Cross-Cover test

The cross-cover test, or alternating cover test is usually employed to detect heterophoria. One eye is covered, and then the cover is moved immediately over to the other eye. With heterophoria, when the cover is moved to the other eye, the eye that has just been uncovered can be seen to move from a deviated point. The difference between heterotropia and heterophoria can be easily understood as follows. With heterotropia, a correcting movement of the eye can be detected already by the simple cover test; with heterophoria, such correcting movement only takes place in the cross-cover test. The reason is that subjects with heterophoria are able create and maintain binocular fusion through vergence, and the cross-cover test purposely breaks this fusion, making the latent misaligment visible.

Whereas the cross-cover test allows a qualitative assessment to be done, a quantitative assessment of latent eye position disorders can be done using the Lancaster red-green test.

Etiology of Heterophoria

In order to understand how heterophoria occurs, we must understand of how the eye can maintain proper fixation with non aligned visual axis. Heterophoria is actually the misalignment of the visual axis of both eyes. In other words, one or both eyes are not properly fixated to an object of interest. However, we must know that the eyes have a fusional vergence system which corrects this misalignment.

Manifestation of Heterophoria

When the fusional vergence system can no longer hold back heterophoria, the phoria manifests. In this condition, the eyes deviate from the fixating position.

External links

Ophthalmology: tropias versus phorias
Animation at mrcophth.com

http://eyes.cochrane.org/glossary

A small degree of axis deviation may be made manifest with powerful reading glasses causing difficulty in binocular vision when these are worn..

English Journal

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Frey UH1, Schnee C, Achilles M, Silvanus MT, Esser J, Peters J.
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Sharma A1, Foster RS2, Suh DW3, Smith D1, Kraft SP1, Ali A4.
American journal of ophthalmology.Am J Ophthalmol.2016 Jan;161:206-13. doi: 10.1016/j.ajo.2015.10.019. Epub 2015 Nov 14.
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Xiao Q1, Xu M2, Yu H2, Wang Y3, Yu X2.
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