In visual science, binocular vision focuses on visual perception with two eyes instead of one. Two main areas are directional vision and depth perception (stereopsis). Both eyes can positively or negatively influence each other's vision through binocular interaction.
In medical science, binocular vision refers to binocular vision disorders and tests and exercises to improve binocular vision. In biology, binocular vision refers to the placement of the eyes and its effects on the capabilities of depth perception and directional vision in animals. In society, binocular vision refers to applications for seeing stereoscopic images and aids for binocular vision.
Directional vision In the classical science of vision, directional vision describes; when a point of the retina is stimulated, this not only leads to a light sensation (image), but also a directional sensation; this is recorded by the brain in a combined image of both eyes, as a direction in which the observer is central (egocentric direction).
Depth vision
Depth perception focuses on how the brain uses the difference in perspective, between the two eyes; and how the brain uses it to recognize shapes and objects, see through camouflage and gather information about spatial relationships.
The main article on stereopsis discusses the qualities of depth perception, the area of space they cover, and how the observer controls the input through attention and eye movements.
Binocular interaction Binocular interaction is interaction between the vision received from the two eyes, which causes vision with both eyes to be different from vision with one eye alone. Vision can be better (binocular summation) or worse (binocular inhibition).
Binocular summation
In binocular summation, the signals from both eyes reinforce each other so that visual acuity, contrast sensitivity, flicker sensitivity, and brightness sensitivity improve.Foundations of binocular vision: a clinical perspective by Scott B. Steinman, Barbara A. Steinman, Ralph Philip Garzia 2000 pages 153-160 Maximum binocular summation occurs when the sensitivities of each eye are equal. Differences in sensitivity decrease the effect of binocular summation. The effect of binocular summation decreases with age."Functional Burden of StrabismusDecreased Binocular Summation and Binocular Inhibition" by Pineles SL, Velez FG, Isenberg SJ, Fenoglio Z, Birch E, Nusinowitz S, and Demer JL. JAMA Ophthalmol. 2013;131(11):1413-1419
Binocular inhibition In binocular inhibition, vision with both eyes is worse than with one eye. This can occur with strabismus or a lazy eye, because the weaker eye interferes with the stronger one. Eye dominance, where the image produced by one eye in the brain can suppress the other, is a form of binocular inhibition.
Perception systems Information processing for direction perception and depth perception takes place in two systems. One system specializes in color and fine detail and is concerned with discovering shapes and objects in a relatively static environment. The other system specializes in discovering spatial relationships in a rapidly changing environment. The first system contributes to the perception of fused images with fine depth information. The second system contributes to the perception of double images that quickly cover large distances in space and in which the coarse location is the most important information.
Disorders and tests Around 93% of adults under the age of 60 are estimated to have functional stereoscopic vision (stereopsis) - which means they can perceive depth. But not all can do so equally well. However, about 7% are stereoblind - which means they cannot perceive depth at all. Several tests can determine how well someone sees depth, and there are exercises to improve depth perception. If one eye does not function properly or is blind, this can cause stereoblindness, a complete lack of depth perception. There are other eye disorders that can affect binocular vision. For example, sometimes the eye muscles do not work properly, causing the images from both eyes to be misaligned. Another example is where one eye is dominant, so that the signals from the other eye do not come through in the binocular image, or so that the direction in which an object is seen changes. If eye dominance is noticed in time, an attempt can be made to reduce it through exercise, for example, by temporarily taping the dominant eye.
Prevalence Binocular vision abnormalities are among the most common visual disorders. They are usually accompanied by symptoms such as headache, eye strain, eye pain, blurred vision, and occasionally diplopia (double vision). Approximately 20% of patients who come to an optometry clinic have binocular vision defects. As the use of digital aids becomes more common, many children use them for a significant period of time. This can lead to various binocular vision defects, such as reduced accommodative amplitudes, accommodative powers, and positive fusional convergence, both near and far. The most effective way to diagnose visual defects is with the near point of convergence (NPC) test. During the NPC test, a target, such as a finger, is brought to the face until the examiner notices that one eye is turned outward and/or the person has experienced double vision. Binocular defects can be compensated for to some extent by adaptations of the visual system. However, if the deviations of binocular vision are too great (for example, if the visual system has to adapt to excessive horizontal, vertical, torsional or size (aniseikonic) deviations), the eyes tend to avoid binocular vision, which eventually causes or worsens squint.
Lazy eye
Lazy eye or amblyopia is a neurovisual developmental disorder. The condition is characterized by underdevelopment of several visual features and skills such as visual acuity, eye movements, eye teamwork and binocular depth perception.
Squint
Squint or strabismus is an eye condition in which the eyes do not look in the same direction.
It has long been known that full binocular vision, including stereopsis, is an important factor in stabilizing the postoperative outcome of strabismus corrections. Many people with a lack of stereopsis have (or had) visible strabismus, which has a potential socioeconomic impact on children and adults. Both wide-angle and narrow-angle strabismus, in particular, can negatively impact self-confidence because it disrupts normal eye contact, often leading to embarrassment, anger, and feelings of discomfortStrabismus, from All About Vision, Access Media Group LLC (see psychosocial effects of strabismus).
Aniseikonia
Aniseikonia is an ocular condition where there is a significant difference in the size of the retinal images of the two eyes caused by differences in refraction between the eyes.
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.Stereoacuity testing, ONE Network, American Academy of Phthalmology (downloaded September 2, 2014)
Random-dot stereo tests
Stereopsis ability can be tested with the Lang stereotest. It consists 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,Language stereotest in Farlex medical dictionary. Referring to: Millodot: Dictionary of Optometry and Visual Science, 7th edition. 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. There have been cases of spontaneous unexpected stereopsis improvements, e.g. by watching a 3D movie in the cinema, and by doing so, permanently enhancing the stereo perception for an individual.
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.