Binocular vision is vision in which both eyes are used together. In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain The word binocular comes from two Latin roots, bini for double, and oculus for eye. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. [1] Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a wider field of view. The field of view (also field of vision) is the angular extent of the observable world that is seen at any given moment For example, a human has a horizontal field of view of approximately 200 degrees with two eyes but only 160 degrees with one. [2]. Third, it gives binocular summation in which the ability to detect faint objects is enhanced. [3] Fourth it can give stereopsis in which parallax provided by the two eyes' different positions on the head give precise depth perception. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between Depth perception is the visual ability to perceive the world in three Dimensions Although any animal capable of moving around its environment must be able to [4] Such binocular vision is usually accompanied by singleness of vision or binocular fusion, in which a single image is seen despite each eye's having its own image of any object. [4] Other phenomena of binocular vision include utrocular discrimination, eye dominance, allelotropia, and binocular rivalry. Ocular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one Eye to the other Binocular rivalry is a phenomenon of Visual perception in which perception alternates between different images presented to each Eye.
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Field of view and eye movements
Some animals, usually prey animals, have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. The field of view (also field of vision) is the angular extent of the observable world that is seen at any given moment Examples include rabbits, buffalos, and antelopes. Rabbits are small Mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world Antelope are Ruminant hoofed Mammals of the family Bovidae in the order of Even-toed ungulates. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view.
Other animals, usually predatory animals, have their two eyes positioned on the front of their heads, thereby reducing field of view in favour of stereopsis. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Examples include eagles, cats, and snakes. Eagles are large birds of prey which are members of the Bird order Falconiformes and family Accipitridae, and belong to several genera WikipediaManual of Style (spelling, articles should conform to one overall spelling style of English typically the one most linked to the article topic (if it is geographic A snake is an elongate Reptile of the suborder Serpentes Like all reptiles snakes are covered in scales.
Some predator animals, such as sperm whales, have their two eyes positioned on opposite sides of their heads. The Sperm Whale ( Physeter macrocephalus or Physeter catodon) is the largest of all Toothed whales and largest living toothed animal Other animals that are not necessarily predators, such as fruit bats and some primates also have forward facing eyes. For other uses of the term "Flying fox" see Flying fox (disambiguation Megabats is the term used informally to refer to bats A primate is a member of the biological order Primates ( Latin: "prime first rank" the group that contains Lemurs the Aye-aye These are usually animals that need fine depth discrimination, for example, to pick fruit or to find a branch.
In animals with forward-facing eyes, the eyes usually move together.
When the eyes move laterally, in the same direction, this is called a version. A version is an Eye movement involving both Eyes moving synchronously and symmetrically in the same direction When the eyes move in opposite directions, to an object closer than where the eyes are pointing or farther than where the eyes are pointing, this is called a vergence. A vergence is the simultaneous movement of both Eyes in opposite directions to obtain or maintain single Binocular vision. When the eyes move in, it is a convergence eye movement; when the eyes move out, it is a divergence eye movement. In the absence of a more specific context convergence denotes the approach toward a definite value as time goes on or to a definite point a common view or opinion or In Vector calculus, the divergence is an Operator that measures the magnitude of a Vector field &rsquos source or sink at a given point the
Some animals (including some humans, notably exotropes) use both of the above strategies. A starling, for example, has laterally placed eyes to cover a wide field of view, but can also move them together to point to the front so their fields overlap giving stereopsis. Starlings are small to medium-sized Passerine Birds in the family Sturnidae. A remarkable example is the chameleon, whose eyes appear to be mounted on turrets, each moving independently of the other, up or down, left or right. Chameleons (family Chamaeleonidae) are squamates that belong to one of the best-known Lizard families A gun turret is a device that protects the crew or mechanism of a projectile firing weapon and at the same time lets the weapon be aimed and fired in many directions Nevertheless, the chameleon can bring both of its eyes to bear on a single object when it is hunting, showing vergence and stereopsis.
Binocular summation
Binocular summation means that the detection threshold for a stimulus is lower with two eyes than with one. In Physiology, a stimulus is a detectable change in the internal or external environment There are two forms. First, when trying to detect a faint signal, there is a statistical advantage of using two detectors over using one. Mathematically, the advantage is equal to the square root of 2, about 1. 41. Second, when some cells in the visual cortex receive input from both eyes simultaneously, they show binocular facilitation, a greater level of activity than the sum of the two activities evoked separately from each eye. The term visual cortex refers to the primary visual cortex (also known as striate cortex or Any advantage in using two eyes in detection task over 1. 41 is credited to this sort of mechanism, dubbed neural summation.
Binocular interaction
Apart from binocular summation, the two eyes can influence each other in at least three ways.
- Pupillary diameter. The pupil is the hole that is located in the center of the iris of the eye and that controls the amount of light that enters the Eye. Light falling in one eye affects the diameter of the pupils in both eyes. The pupil is the hole that is located in the center of the iris of the eye and that controls the amount of light that enters the Eye. One can easily see this by looking at a friend's eye while he or she closes the other: when the other eye is open, the pupil of the first eye is small; when the other eye is closed, the pupil of the first eye is large.
- Accommodation and vergence. Accommodation is the process by which the:eye increases Optical power to maintain a clear image ( focus) on an object as it draws near the eye A vergence is the simultaneous movement of both Eyes in opposite directions to obtain or maintain single Binocular vision. Accommodation is the state of focus of the eye. If one eye is open and the other closed, and one focuses on something close, the accommodation of the closed eye will become the same as that of the open eye. Moreover, the closed eye will tend to converge to point at the object. Accommodation and convergence are linked by a reflex, so that one evokes the other.
- Interocular transfer. The state of adaptation of one eye can have a small effect on the state of light adaptation of the other. An adaptation is a characteristic of an Organism that has been favored by Natural selection and Aftereffects induced through one eye can be measured through the other. Neural adaptation or sensory adaptation is a change over time in the responsiveness of the Sensory system to a constant stimulus.
Utrocular discrimination
Utrocular discrimination is the ability to tell, when both eyes are open, to which eye a monocular stimulus was shown. [5]
Singleness of vision
Once the fields of view overlap, there is a potential for confusion between the left and right eye's image of the same object. This can be dealt with in two ways: one image can be suppressed, so that only the other is seen, or the two images can be fused. If two images of a single object are seen, this is known as double vision or diplopia. Diplopia, commonly known as double vision, is the simultaneous Perception of two images of a single object Fusion of the images from the two eyes is considered to be separate from stereopsis for at least two reasons. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation First, some disorders of binocular vision, such as strabismus can spare fusion but abolish stereopsis. Strabismus (from Greek: στραβισμός strabismos, from στραβίζειν strabizein "to squint" from στραβός strabos Second, the depth of an object either much nearer to or farther from where the eyes are fixating can be accurately judged despite the images of the object appearing double.
Fusion of images occurs only in a small volume of visual space around where the eyes are fixating. Running through the fixation point in the horizontal plane is a curved line for which objects there fall on corresponding retinal points in the two eyes. This line is called the empirical horizontal horopter. In studies of Binocular vision the horopter is a volume centred on the fixation point that contains all points in space that yield single vision There is also an empirical vertical horopter, which is effectively tilted away from the eyes above the fixation point and towards the eyes below the fixation point. The horizontal and vertical horopters mark the centre of the volume of singleness of vision. Within this thin, curved volume, objects nearer and farther than the horopters are seen as single. The volume is known as Panum's fusional area (it's presumably called an area because it was measured by Panum only in the horizontal plane). Outside of Panum's fusional area (volume), double vision occurs.
Eye dominance
When each eye has its own image of objects, it becomes impossible to align images outside of Panum's fusional area with an image inside the area. This happens when one has to point to a distant object with one's finger. When one looks at one's fingertip, it is single but there are two images of the distant object. When one looks at the distant object it is single but there are two images of one's fingertip. To point successfully, one of the double images has to take precedence and one be ignored or suppressed (eye dominance). Ocular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one Eye to the other The eye of the image that takes precedence is called the dominant eye. Ocular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one Eye to the other
Stereopsis
Stereopsis is an ability to make fine depth discriminations from parallax provided by the two eye's different positions on the head. Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between There are two sorts: quantitative stereopsis, in which the depth seen is very similar to the actual depth of the object being judged, and qualitative stereopsis, in which the depth is correctly nearer or farther than the fixation point but the amount of depth does not grow with distance of the object from the fixation point. Quantitative stereopsis holds for small distances from the fixation plane (approximately within Panum's fusional area); qualitative stereopsis holds for larger distances from the fixation plane (outside of Panum's fusional area). Eventually an object can be moved so far from the fixation plane that there is no sense of depth of the double images--instead they appear to be on the fixation plane.
Allelotropia
Because the eyes are in different positions on the head, any object away from fixation and off the plane of the horopter has a different visual direction in each eye. Yet when the two monocular images of the object are fused, creating a Cyclopean image, the object has a new visual direction, essentially the average of the two monocular visual directions. Cyclopean image is a single mental Image of a scene created by the Brain by combining two images received from the two Eyes The mental process behind construction This is called allelotropia. The origin of the new visual direction is a point approximately between the two eyes, the so-called cyclopean eye. The position of the cyclopean eye is not usually exactly centred between the eyes, but tends to be closer to the dominant eye.
Binocular rivalry
When very different images are shown to the same retinal regions of the two eyes, perception settles on one for a few moments, then the other, then the first, and so on, for as long as one cares to look. This alternation of perception between the images of the two eyes is called binocular rivalry. Binocular rivalry is a phenomenon of Visual perception in which perception alternates between different images presented to each Eye.
Disorders of binocular vision
To maintain stereopsis and singleness of vision, the eyes need to be pointed accurately. The position of each eye in its orbit is controlled by six extraocular muscles. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The extraocular muscles are the six Muscles that control the movements of the (human eye. Slight differences in the length or 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. To do this test, look at a cooperative person's eyes. Cover one eye of that person with a card. Have the person look at your finger tip. Move the finger around; this is to break the reflex that normally holds a covered eye in the correct vergence position. Hold your finger steady and then uncover the person's eye. Look at the uncovered eye. You may see it flick quickly from being wall-eyed or cross-eyed to its correct position. If the uncovered eye moved from out to in, the person has exophoria. Exophoria is a form of Heterophoria in which there is a tendency of the Eyes to deviate outward If it moved from in to out, the person has esophoria. Esophoria is characterised by inward deviation of the eye usually due to Extra-ocular muscle imbalance If the eye did not move at all, the person has orthophoria. Most people have some amount of exophoria or esophoria; it is quite normal. If the uncovered eye also moved vertically, the person has hyperphoria (if the eye moved from up to down) or hypophoria (if the eye moved from down to up). Such vertical phorias are quite rare. It is also possible for the covered eye to rotate in its orbit. Such cyclophorias cannot be seen with the cover-uncover test; they are rarer than vertical phorias.
During the cover-uncover test, a person with some phoria will notice a brief episode of double vision or diplopia after uncovering the eye. Diplopia, commonly known as double vision, is the simultaneous Perception of two images of a single object This is a normal consequence of the eye's being briefly misaligned. If the diplopia is enduring, that is considered a disorder.
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 as he or she covers the second. If the eye moves from out to in, the person has exotropia. Exotropia is a form of Strabismus where the eyes are deviated outward If it moved from in to out, the person has esotropia. Esotropia is a form of Strabismus, or "squint" in which one or both Eyes turns inward People with exotropia or esotropia are wall-eyed or cross-eyed respectively. These are forms of strabismus with amblyopia. Strabismus (from Greek: στραβισμός strabismos, from στραβίζειν strabizein "to squint" from στραβός strabos Amblyopia, otherwise known as lazy eye, is a disorder of the Visual system that is characterized by poor or indistinct vision in an eye that 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. Hypertropia is a condition of misalignment of the Eyes ( Strabismus) whereby the Visual axis of one eye is higher than the fellow fixating eye Hypertropia is a condition of misalignment of the Eyes ( Strabismus) whereby the Visual axis of one eye is higher than the fellow fixating eye
See also
- Amblyopia
- Binocular rivalry
- Binocular summation
- Diplopia
- Eye dominance
- Eye movements
- Field of view
- Monocular vision
- Orthoptics
- Phoria
- Singleness of vision
- Stereoblindness
- Stereopsis
- Stereoscopy
- Strabismus
- Utrocular discrimination
- Vision
- Vision therapy
References
- ^ Harper, D. Amblyopia, otherwise known as lazy eye, is a disorder of the Visual system that is characterized by poor or indistinct vision in an eye that Binocular rivalry is a phenomenon of Visual perception in which perception alternates between different images presented to each Eye. Diplopia, commonly known as double vision, is the simultaneous Perception of two images of a single object Ocular dominance, sometimes called eye dominance or eyedness, is the tendency to prefer visual input from one Eye to the other The field of view (also field of vision) is the angular extent of the observable world that is seen at any given moment Monocular vision is vision in which each Eye is used separately Stereoblindness (also stereo blindness) is the inability to see in 3D using Stereo vision, resulting in inability to perceive stereoscopic depth Stereopsis (from stereo meaning solidity and opsis meaning vision or Sight) is the process in Visual perception leading to the sensation Stereoscopy, stereoscopic imaging or 3-D (three-dimensional imaging is any technique capable of recording three-dimensional visual Strabismus (from Greek: στραβισμός strabismos, from στραβίζειν strabizein "to squint" from στραβός strabos In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also Vision therapy, also known as visual training, vision training, or visual therapy, is a group of techniques attempting variously to correct or improve presumed (2001). Online etymological dictionary. Retrieved April 2, 2008, from http://http://www.etymonline.com/index.php?term=binocular
- ^ Stereoscopic Field of View of the Human Eyes at Roger Maddy
- ^ Blake, R. , & Fox, R. (1973). The psychophysical inquire into binocular summation. Perception & Psychophysics, 14, 161-185.
- ^ a b Wheatstone, C. (1838). Contributions to the physiology of vision. —Part the First. On some remarkable, and hitherto unobserved, phænomena of binocular vision. Philosophical Transactions of the Royal Society of London, 128, 371-394.
- ^ Blake, R. , & Cormack, R. H. (1979). On utrocular discrimination. Perception & Psychophysics, 26, 53-68.
Further reading
- Scott B. Steinman, Barbara A. Steinman and Ralph Philip Garzia. (2000). Foundations of Binocular Vision: A Clinical perspective. McGraw-Hill Medical. ISBN 0-8385-2670-5.
External links
- Livingstone MS, Conway BR (2004). "Was Rembrandt stereoblind?". N. Engl. J. Med. 351 (12): 1264-5. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15371590.
- Gaining Binocular Vision - No Longer Stereoblind - People Tell Their Stories
- VisionSimulations.com |Images and vision simulators of various diseases and conditions of the eye
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