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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Binocular vision | 2/6 | https://en.wikipedia.org/wiki/Binocular_vision | reference | science, encyclopedia | 2026-05-05T15:53:38.467964+00:00 | kb-cron |
=== Stereopsis tests === In stereopsis testing (abbreviated to stereotesting), stereograms are used to measure the presence and sharpness of binocular depth perception (stereopsis). There are two types of common clinical tests: random-dot stereotesting and contour stereotesting. Random-dot stereotesting uses images of stereo figures embedded in a background of random dots. Contour stereo tests use images in which the targets presented to each eye are separated horizontally.
==== Random-dot stereo tests ====
Stereopsis ability can be tested with the Lang stereotest, consisting of a random-dot stereogram on which a series of parallel strips cylindrical lenses are printed in certain shapes, which represent the images which each eye sees in these areas, separate from each other. similar to a hologram. Without stereopsis, the image appears as a field of random dots, but the shapes become visible with increasing stereopsis and generally consist of a cat (indicating that a stereopsis of 1200 arc seconds of retinal disparity is possible), a star (600 arc seconds), and a car (550 arc seconds). To standardize the results, the image should be viewed at a distance of 40 cm from the eye and exactly in the frontoparallel plane. While most random-dot stereotests, such as the Random Dot "E" stereotest or the TNO stereotest, require special glasses (i.e., polarized or red-green lenses), the Lang stereotest works without special glasses, making it easier to use with young children.
==== Contour stereotests ==== Examples of contour stereotests include the Titmus stereotests, of which the Titmus fly stereotest is the best-known example, in which an image of a fly is shown with deviations at the edges. The patient uses 3D glasses to look at the image and determine whether a 3D figure can be seen. The degree of deviation in the images varies, for example, 400-100 arc seconds and 800-40 arc seconds.
=== Vision therapy ===
Vision therapy is a controversial treatment to improve stereopsis.
=== Other disorders === To maintain stereopsis and singleness of vision, the eyes need to be pointed accurately. The position of each eye is controlled by six extraocular muscles. Slight differences in length, insertion position, or strength of the same muscles in the two eyes can lead to a tendency for one eye to drift to a different position in its orbit from the other, especially when one is tired. This is known as phoria. One way to reveal it is with the cover-uncover test. In this test, one of a person's eyes is covered. With the uncovered eye, the person looks at a target such as a fingertip. The target is moved around to break the reflex that normally holds the covered eye in the correct vergence position. The target is held steady before the eye is uncovered. The eye may flick quickly from being wall-eyed or cross-eyed to its correct position. If the eye moved from out to in, the person has esophoria. If it moved from in to out, the person has exophoria. If the eye did not move at all, the person has orthophoria. Most people have some amount of exophoria or esophoria, which is normal. If the uncovered eye also moved vertically, the person has hyperphoria (if the eye moved from down to up) or hypophoria (if the eye moved from up to down). Such vertical phorias are quite rare. It is also possible for the covered eye to rotate in its orbit, known as cyclophoria, which is rarer than vertical phorias. The cover-uncover test may be used to determine the direction of deviation in cyclophorias. The cover-uncover test can also be used for more problematic disorders of binocular vision, the tropias. In the cover part of the test, the examiner looks at the first eye while covering the second. If the eye moves from in to out, the person has exotropia. If it moved from out to in, the person has esotropia. People with exotropia or esotropia are wall-eyed or cross-eyed, respectively. These are forms of strabismus that can be accompanied by amblyopia. There are numerous definitions of amblyopia. A definition that incorporates all of these defines amblyopia as a unilateral condition in which vision is worse than 20/20 in the absence of any obvious structural or pathologic anomalies, but with one or more of the following conditions occurring before the age of six: amblyogenic anisometropia, constant unilateral esotropia or exotropia, amblyogenic bilateral isometropia, amblyogenic unilateral or bilateral astigmatism, image degradation. When the covered eye is the non-amblyopic eye, the amblyopic eye suddenly becomes the person's only means of seeing. The strabismus is revealed by the movement of that eye to fixate on the examiner's finger. There are also vertical tropias (hypertropia and hypotropia) and cyclotropias. Binocular vision anomalies include diplopia, visual confusion (the perception of two different images superimposed onto the same space), suppression (where the brain ignores all or part of one eye's visual field), horror fusionis (an active avoidance of fusion by eye misalignment), and anomalous retinal correspondence (where the brain associates the fovea of one eye with an extrafoveal area of the other eye).
== In animals == Vision provides animals with the means to orient themselves in space, to recognize and manipulate objects, and to navigate. In The Ecology of Vision, James Gibson describes how these means have developed in an interactive interplay between observer and environment, and how the environment often contains much more practically useful information than we realize. For example, pilots, as well as fast-moving birds, rely solely on (monocular) motion vision to steer and avoid objects in a rapidly changing environment. In humans, this even leads to a (monocular) 3D sensation of stereopsis. Binocular depth perception (stereopsis) adds to this the notion that the 3D sensation is also available in situations where the observer is not moving quickly. This allows animals to wait for prey while stationary and strike when it is within reach.