Visual acuity ( VA ) usually refers to clarity of vision. Visual acuity depends on the optical and nerve factors, namely, (i) the sharpness of the retinal focus in the eye, (ii) the health and retinal function, and (iii) the sensitivity of the interpretive faculty of the brain.
Common causes of low visual visibility are a bias error (ametropia), or an error in how light is refracted in the eyeball. The causes of refractive errors include irregularities in the form of eyeballs, corneal shape, and reduced lens flexibility. An overly high or too low bias error (in relation to the length of the eyeball) is the cause of farsightedness (myopia) or farsightedness (hyperopia) (normal refractive status referred to as emmetropia). Other causes of optics are astigmatism or more complex corneal aberrations. These anomalies can mostly be corrected by optical means (such as glasses, contact lenses, laser surgery, etc.).
The nerve factor that limits sharpness lies in the retina or brain (or path leading to it). Examples for the former are the detached retina and macular degeneration, to name just two. Other generalized damage, amblyopia, is caused by a poorly developed visual brain in early childhood. In some cases, low visual acuity is caused by brain damage, such as from a traumatic brain injury or stroke. When optical factors are corrected, sharpness can be considered a good measure of neural function.
Visual acuity is usually measured when fixed, ie as a measure of central (or foveal) vision, for that reason is the highest there. However, the sharpness in peripheral vision can be just as important (or sometimes higher) in everyday life. Sharpness decreases toward peripherals in inverse-linear force (ie decreases following hyperbola).
Video Visual acuity
Definisi
Visual acuity is a measure of the spatial resolution of a visual processing system. The VA, as sometimes referred to by optical professionals, is tested by requiring people whose visions are being tested to identify what are called optotypes - stylized letters, Landolt rings, pediatric symbols, symbols for illiterate and standardized Cyrillic letters in Golovin. Table -Sivtsev, or other patterns - on the print chart (or some other way) from the specified viewing distance. Optotypes are represented as black symbols with a white background (ie at maximum contrast). The distance between the person's eye and the test graph is arranged in such a way as to approach "optical infinity" in the way the lens tries to focus (sharpness away), or at a specified reading distance (near sharpness).
The above reference value that visual acuity is considered normal is called 6/6 vision, the equivalent of USC which is 20/20 vision: At 6 meters or 20 feet, a human eye with a performance capable of separating contours that are approximately 1.75 mm apart. Vision 6/12 corresponds to a low, 6/3 vision for better performance. The normal individual has a sharpness of 6/4 or better (depending on age and other factors).
In the 6/x expression vision, the numerator (6) is the distance in meters between the subject and the graph and the denominator (x) the distance at which a person with 6/6 sharpness will see the same optotype. Thus, 6/12 means that a person with 6/6 vision will distinguish the same optotype from 12 meters (ie at a distance of twice the distance). This is equivalent to saying that with 6/12 vision, the person has half the spatial resolution and takes twice the size to distinguish optotype.
A simple and efficient way to express sharpness is to complete a fraction to a decimal number. 6/6 then according to the sharpness (or Visus) 1.0 (see Expression below). 6/3 corresponds to 2.0, which is often achieved by healthy young subjects and corrected with binocular vision. Stating the sharpness as a decimal number is a standard in European countries, as required by European norms (EN ISO 8596, formerly DIN 58220).
The exact distance at which measured sharpness is not important as long as it is far enough and the size of the optotype on the retina is the same. The size is defined as the visual angle, which is the angle, in the eye, where the optotype appears. For 6/6 = 1.0 sharpness, the font size on Snellen chart or Landolt C map is the visual angle of 5 minute arc (1 minute arc = 1/60 degree). With a typical optotype type design (like Snellen E or Landolt C), the critical gap to be solved is 1/5 of this value, that is, 1 minute of arc. The latter is the value used in the definition of international visual acuity:
Sharpness = 1 / the gap size [arc min]
Sharpness is a measure of visual performance and is not related to prescription glasses needed to correct vision. Instead, an eye exam tries to find a recipe that will provide the best visual performance that can be improved. The resulting sharpness may be larger or smaller than 6/6 = 1.0. Indeed, subjects diagnosed to have 6/6 vision will often actually have higher visual acuity because, once this standard is achieved, subjects are considered to have normal (undisturbed) vision and smaller optotypes not tested. Emmetropic subjects with 6/6 or "better" vision (20/15, 20/10, etc.), may still benefit from corrective eyewear for other problems associated with the visual system, such as astigmatism, ocular injury, or presbyopia.
Maps Visual acuity
Measurement
Visual acuity is measured by psychophysical procedures and thus links the physical characteristics of the stimulus to the subject's perception and the responses it produces. Measurements can be made using the eye charts invented by Ferdinand Monoyer, with optical instruments, or by computer tests such as Fract.
Care must be taken to ensure that the display conditions meet the standards, such as the correct lighting of the room and the eye chart, the correct visibility, enough time to respond, allowance errors, and so on. In European countries, this condition is standardized by European norms (EN ISO 8596, formerly DIN 58220).
History
Physiology
Day vision (ie photopic vision) is subsidized by cone-receptor cells that have high spatial density (in the central fovea) and allow high sharpness of 6/6 or better. In low light (ie, scotopic) vision, the cone lacks sufficient sensitivity and the vision is supported by the rod. Spatial resolution is much lower. This is due to the spatial addition of the stem, ie a number of rods joining into bipolar cells, in turn connecting to the ganglion cell, and the resulting unit for great resolution, and small acuity. Note that there is no rod in the center of the visual field (foveola), and the highest performance in low light is achieved in close edge vision
The maximum angular resolution of the human eye at a distance of 1 km is usually 30 to 60 cm. It provides a resolution angle between 0.02 and 0.03 degrees, which is approximately 1.2-1.8 minutes arc per line pair, which means a pixel distance of 0.6-0.9 minutes arc. 6/6 vision is defined as the ability to complete two points of light separated by the visual angle of one minute arc, or about 320-386 pixels per inch for display on devices that have 25 to 30 cm from the eye.
Thus, visual acuity, or strength of completion (in daylight, central vision), is the property of a cone. To complete the detail, the optical eye system must project images focused on the fovea, the region within the macula that has the highest photoreceptor cone density (the only type of photoreceptor present in the center of the fovea which is very 300 m in diameter), thus having the highest resolution and vision the best colors. Sharpness and color vision, though mediated by the same cells, are distinct physiological functions that are not related except by position. Sharpness and color vision can be independently affected.
Photographic mosaic grains have limited breaking strength as a "grain" of the retinal mosaic. To view details, two sets of receptors must be intervened by the middle set. The maximum resolution is 30 arcsecond, corresponding to the foveal cone diameter or the angle deposited at the nodal point of the eye. To obtain the reception of each cone, as if the vision is on a mosaic basis, a "local sign" must be obtained from a cone through a bipolar chain, ganglion, and geniculate lateral cells respectively. However, the key factor of obtaining a detailed vision is inhibition. It is mediated by neurons like amacrin and horizontal cells, which functionally make the spread or convergence of signals inactive. The tendency for this one-to-one signal is supported by central and surrounding enlightenment, which triggers the inhibition of one-to-one cable. This scenario, however, is rare, because cones can connect to both midget and flat bipolar (diffuse), and amacrine and horizontal cells can incorporate messages as easily as they inhibit them.
Light moves from the fixation object to the fovea through an imaginary path called the visual axis. The network and the structure of the eye on the visual axis (as well as the adjacent tissue) affects the image quality. These structures are: tear film, cornea, anterior chamber, pupils, lens, vitreous, and finally the retina. The posterior part of the retina, called retinal pigment epithelium (RPE) is responsible for, among many other things, absorbs light across the retina so it can not bounce off to other parts of the retina. Interestingly, in many vertebrates, like cats, where high visual acuity is not a priority, there is a reflecting tapetum layer that gives the photoreceptor a "second chance" to absorb light, thus enhancing the ability to see in the dark. This is what causes the animal's eyes to shine in the dark when light shines on them. RPE also has an important function to recycle chemicals used by rods and cones in photon detection. If the RPE is damaged and does not purge it, blindness "shed" can occur.
As with photography lenses, visual acuity is influenced by the size of the pupil. Eye optical aberrations that reduce visual acuity are maximized when the largest pupil (about 8 mm), which occurs in low light conditions. When the pupil is small (1-2 mm), the sharpness of the image may be limited by the diffraction of light by the pupil (see the diffraction limit). Among these extremes is the pupil diameter that is generally best for visual acuity in normal and healthy eyes; this tends to be about 3 or 4 mm.
If the optical eye is otherwise perfectly, theoretically, the sharpness will be limited by the diffraction of the pupil, which will be a finite diffraction sharpness of 0.4 minute arc (minarc) or 6/2.6 sharpness. The smallest cone cell in the fovea has a size corresponding to 0.4 minarc of the visual field, which also places the lower limit on sharpness. The optimum sharpness of 0.4 minarc or 6/2.6 can be demonstrated by using a laser interferometer that passes through any defect in the optical eye and projecting a straight dark and light pattern on the retina. Laser interferometers are now used routinely in patients with optical problems, such as cataracts, to assess the health of the retina before subjecting them to surgery.
The visual cortex is part of the cerebral cortex in the posterior part of the brain responsible for processing visual stimuli, called the occipital lobes. The middle 10 Â ° field (approximately the extension of the macula) is represented by at least 60% of the visual cortex. Many of these neurons are believed to be directly involved in processing visual acuity.
Development of normal visual acuity depends on humans or animals who have normal visual input when they are very young. Any visual plunder, that is, anything that interferes with the input over a long period of time, such as cataracts, heavy eye shifts or strabismus, anisometropia (unequal refractive errors between the two eyes), or covering or patching the eye during medical treatment, will usually resulting in a sharp decline in visual acuity and pattern recognition of affected eyes if not treated early in life, a condition known as amblyopia. Decreased acuity is reflected in various abnormalities in cell properties in the visual cortex. These changes include a clear decrease in the number of cells connected to the affected eye as well as the cells connected to both eyes in the cortical region V1, resulting in a loss of stereopsis, the perception of depth by binocular vision (colloquial: "3D vision"). The period of time in which animals are so sensitive to visual plunder as it is called a critical period.
The eye is connected to the visual cortex by the optic nerve coming out of the back of the eye. Two optic nerves come together behind the eye on optical chiasms, in which about half of the fibers of each eye cross over to the opposite side and join the fibers of the other eye representing the corresponding visual plane, the combined nerve fibers of both eyes form optical channels. This ultimately forms the physiological basis of binocular vision. The tractate projectes to a relay station in the midbrain called the geniculate lateral nucleus, part of the thalamus, and then to the visual cortex along a collection of nerve fibers called optical radiation.
Any pathological process in the visual system, even in older humans beyond the critical period, will often lead to a decrease in visual acuity. So measuring visual acuity is a simple test in accessing eye health, visual brain, or pathway to the brain. Any sudden drop in visual acuity is always a concern. Common causes of decline in visual acuity are cataract and corneal scarring, affecting optical pathways, diseases affecting the retina, such as macular degeneration and diabetes, diseases affecting optical pathways to the brain such as tumors and multiple sclerosis, and diseases affecting the visual cortex such as tumors and stroke.
Although the strength of the settlement depends on the size and density of photoreceptor packing, the nervous system must interpret receptor information. As determined from single cell experiments in cats and primates, different ganglion cells in the retina are tuned to different spatial frequencies, so that some ganglion cells in each location have better acuity than others. Finally, however, it appears that the size of the cortical network patch in the visual area V1 that processes a particular location in the visual field (a concept known as cortical enlargement) is equally important in determining visual acuity. In particular, it is the largest in the center of the fovea, and decreases with increasing distance from there.
Optical aspects
In addition to the neural connections of the receptor, the optical system is the same key player in the retinal resolution. In the ideal eye, diffraction grating images can mix 0.5 micrometers on the retina. This of course does not happen, and further pupils can cause diffraction of light. Thus, the black lines on the grille will mix with the white lines of the intervening to make the display gray. Damaged optical problems (such as uncorrected myopia) may worsen, but appropriate lenses may be helpful. Images (such as grilles) can be sharpened with lateral inhibition, that is, the more vibrant cells inhibit less-vibrant cells. A similar reaction in the case of chromatic aberrations, where the color around the black and white objects is inhibited the same.
Expression
Visual acuity is often measured by the size of the letters seen on Snellen charts or other symbol sizes, such as Landolt Cs or E Chart.
In some countries, sharpness is expressed as a vulgar fraction, and some of it as a decimal number.
Using a meter as a unit of measurement, visual acuity (fractional) is expressed relative to 6/6. If not, using the foot, visual acuity is declared relative to 20/20. For all practical purposes, the 20/20 vision equals 6/6. In the decimal system, sharpness is defined as the reciprocal value of the gap size (measured in arc minutes) of the smallest Landolt C, a reliably identifiable orientation. A value of 1.0 equals 6/6.
LogMAR is another commonly used scale, expressed as logarithm (decadent) from a minimum angle of resolution (MAR). The LogMAR scale converts the geometric sequence from the traditional graph to a linear scale. This measures the loss of visual acuity: positive values ​​indicate vision loss, whereas negative values ​​indicate normal or better visual acuity. This scale is rarely used clinically; this is more often used in statistical calculations because it provides more scientific equivalents for traditional clinical statements of "missing lines" or "line obtained", which only applies when all the steps between lines are the same, which is usually not the case.
Visual acuity 6/6 is often described as meaning that a person can see the detail of 6 meters (20 feet) the same as a person with a "normal" vision will see from 6 meters. If a person has visual acuity of 6/12, he is said to see details of 6 meters (20 feet) equal to a person with a "normal" vision will see it from 12 meters (39 feet).
A healthy young observer may have higher binoculars than 6/6; the uneven human eye sharpness limit is about 6/3-6/2.4 (20/10-20/8), although 6/3 is the highest score recorded in the study of some US professional athletes. Some birds of prey, such as eagles, are believed to have a sharpness of about 20/2; in this case, their vision is much better than human vision.
When visual acuity is below the largest optotype on the graph, the reading distance is reduced until the patient can read it. After the patient can read the chart, the font size and test distance are recorded. If the patient can not read the graph at any distance, it will be tested as follows:
Legal definition
Different countries have established legal restrictions for poor visual acuity that qualify as defective. For example, in Australia, the Social Security Act defines blindness as:
A person meets the criteria for permanent blindness under section 95 of the Social Security Act if the corrected visual acuity is less than 6/60 on the Snellen Scale in either eye or there is a combination of visual defects that result in the same permanent visual level. loss.
In the US, relevant federal laws define the following blindness:
[T] he calls "blindness" means central 20/200 or lower visual acuity in the eyes better with the use of correction lenses. An eye accompanied by limits in the field of vision such that the widest diameter of the visual field of angle subtends of not more than 20 degrees should be considered for purposes in this paragraph as having central visual acuity of 20/200 or less.
The visual acuity of a person is documented as follows: whether the test is for near or near vision, the eye is evaluated and whether the corrective lens (ie glasses or contact lenses) is used:
- The distance from the graph
- D (remote) for evaluation is done at 20 feet (6.1 m).
- N (close) for evaluation performed at 15.7 inches (40 cm).
- The eye is evaluated
- OD (Latin oculus dexter ) for the right eye.
- OS (Latin oculus sinister ) for the left eye.
- OU (Latin oculi uterque ) for both eyes.
- The use of glasses during the test
- cc (Latin cum correctore ) with the corrector.
- sc: (Latin sinus correctore ) without the corrector.
- Needle pinhole
- The PH abbreviation is followed by visual acuity measured by pinhole occlusion, which temporarily corrects bias errors such as myopia or astigmatism.
So, the visual acuity away from 6/10 and 6/8 with the pinhole in the right eye would be: DscOD 6/20 PH 6/8. Visual acuity away from the calculated and 6/17 fingers with the pinhole on the left eye would be: DscOS CF PH 16/17. Close visual acuity 6/8 with pinhole remaining in 6/8 on both eyes with glasses will be: NccOU 6/8 PH 6/8.
"Dynamic visual acuity" defines the ability of the eye to visually distinguish fine detail in moving objects.
Measurement considerations
Visual acuity measurements involve more than being able to see optotypes. Patients should be cooperative, understand optotypes, be able to communicate with doctors, and many other factors. If any of these factors are lost, then the measurement will not represent the patient's real visual acuity.
Visual acuity is a subjective test which means that if the patient is unwilling or unable to work together, a test can not be performed. A patient who is sleepy, drunk, or has a disease that can change their consciousness or mental status, may not achieve maximum possible sharpness.
Illiterate patients who can not read letters and/or numbers listed have very low visual acuity if this is unknown. Some patients will not tell testers that they do not know optotypes, unless asked directly about it. Brain damage can cause the patient to not recognize the letters, or can not spell it.
Motor inability can make a person wrongly respond to the displayed optotype and negatively affect the measurement of visual acuity.
Variables such as pupil size, background adaptation lighting, presentation duration, the type of optotype used, the interaction effect of adjacent visual contours (or "crowding") can all affect the measurement of visual acuity.
Testing on children
The visual acuity of newborns is about 6/133, progressing to 6/6 after six months of age in most children, according to a study published in 2009.
Visual acuity measurements in infants, pre-verbal children and special populations (eg, disabled individuals) are not always possible with a letter chart. For this population, special testing is required. As a basic examination step, one must check whether visual stimuli can be glued, centered and followed.
More formalized tests using preferential techniques use the sharpened Teller card (presented by a technician from behind a window on the wall) to check whether the child is more visually concerned with random presentation of vertical or horizontal grids on one side than on a page empty on the other - the bars become ever more subtle or closer together, and the end point is noted when the child in the lap of the adult guard equally prefers both sides.
Another popular technique is electro-physiological testing using cortical visual potential (VEP or VECPs), which can be used to estimate visual acuity in dubious cases and the expected severe loss of vision such as congenital amaurosis Leber.
The VEP test of sharpness is somewhat similar to preferential in using a series of black and white lines (sinus grating wave) or checkerboard pattern (which results in a larger response than the lines). No behavioral response is required and brain waves created by the presentation of patterns are recorded instead. Patterns become finer and smoother until the brain waves are removed simply, which is considered the ultimate measure of visual acuity. In adults and older, verbal children who are able to pay attention and follow instructions, the end point provided by VEP fits very well with the psychophysical measure of standard measurement (ie the perceptual endpoint determined by asking the subject when they can no longer see the pattern). There is a presumption that this correspondence also applies to children and babies who are much younger, although this should not be the case. Studies do show brain waves that arouse, as well as sharpness that comes from, very mature-as at the age of one year.
For reasons that are not fully understood, until a child is several years old, the visual acuity of the preferential behavioral technique that usually lags behind that is determined using VEP, the direct physiological size of the initial visual processing in the brain. It may take longer for more complex behavioral and attention responses, involving areas of the brain that are not directly involved in vision processing, to adulthood. Thus the visual brain can detect a smoother pattern (reflected in brainwaves generated), but a child's "behavioral brains" may not feel sufficiently prominent to pay special attention.
A simple but less used technique is to check the oculomotor response with the optokinetic nystagmus drum, where the subject is placed in the drum and surrounded by black and white spinning lines. This creates unintentional sudden eye movements (nystagmus) when the brain tries to trace the moving lines. There is a good correspondence between the optokinetic eye sharpness and the usual in adults. A potentially serious problem with this technique is that the process is reflexive and mediated in the lower brain stem, not in the visual cortex. Thus one can have a normal optokinetic response and not yet become blind cortically without a conscious visual sensation.
"Normal visual acuity
Visual acuity depends on how accurately the light is focused on the retina, the integrity of the eye neural elements, and the interpretive faculty of the brain. The "normal" visual acuity (at the center, the foveal vision) is often regarded as what Herman Snellen defined as the ability to recognize the optotype when it subtended 5 minute arcs, ie Snellen chart 6/6 meters, 20/20 feet, 1.00 decimal or 0.0 logMAR. In young humans, the average visual acuity of healthy eyes and emmetropic (or ametropic eyes with correction) is about 6/5 to 6/4, so it is inaccurate to refer to 6/6 visual acuity as "perfect" vision . 6/6 is the visual acuity required to distinguish two contours separated by 1 minute arc - 1.75 mm at 6 meters. This is because letter 6/6, E for example, has three limbs and two spaces between them, giving 5 different detailed fields. The ability to complete this because it takes 1/5 of the total font size, which in this case will be 1 minute (visual angle). The importance of the 6/6 standard can be regarded as a normal lower limit or as a screening pruning. When used as a screening test, subjects reaching this level need not be investigated further, although the average visual acuity with a healthy visual system is usually better.
Some people may suffer from other visual problems, such as color blindness, reduced contrast, mild amblyopia, visual impairment of the brain, inability to trace fast-moving objects, or one of many other visual disorders and still have "normal" visual acuity. Thus, normal "visual acuity" does not imply normal vision. The reason the visual acuity is so widely used is that it is easy to measure, the reduction (after correction) often indicates some disruption, and that it often corresponds to normal daily activities that a person can handle, and evaluates the disorder to do so (though there is heavy debate about the relationship).
Other sizes
Usually, visual acuity refers to the ability to complete two separate points or lines, but there is another measure of the visual system's ability to distinguish spatial differences.
Vernier sharpness measures the ability to align two line segments. Humans can do this with remarkable accuracy. This success is sometimes regarded as hyperacuity . Under optimal conditions of good illumination, high contrast, and long line segments, the limit for vernier sharpness is about 8 arcsec or 0.13 minute arc, compared to about 0.6 minutes arc (6/4) for normal visual acuity or 0 , 4 minutes arc diameter foveal cone. Because the vernier sharpness limit is far below that imposed on the usual visual acuity by "retina grains" or foveal cone size, it is considered the visual cortex process rather than the retina. In support of this idea, vernier sharpness seems to be very closely related (and may have the same basic mechanism) that allows one to distinguish very little difference in the orientation of two lines, in which orientation is known to be processed in the visual cortex.
The smallest detectable visual angle produced by a fine dark line against a uniformly lit background is also much smaller than the foveal cone size or regular visual acuity. In this case, under optimal conditions, the limit is about 0.5 arcsecond or only about 2% of the foveal cone diameter. This produces approximately 1% contrast with the surrounding cone lighting. The detection mechanism is the ability to detect small differences in contrast or illumination, and does not depend on the width of the bar angle, which can not be seen. So when the line becomes smoother, it seems dimmer but not getting thinner.
Stereoscopic acuity is the ability to detect depth differences with both eyes. For more complex targets, stereoacuity is similar to normal monocular visual acuity, or about 0.6-1.0 minute arcs, but for simpler targets, such as vertical bars, may be as low as 2 arcseconds. Although stereoacuity is usually associated very well with monocular acuity, it may be very bad, or absent, even on subjects with normal monocular sharpness. Such people usually have abnormal visual development when they are very young, such as alternating strabismus, or eye rotation, where both eyes rarely, or never, point in the same direction and therefore do not work together.
Motion acuity
Eyes have sharpness limits for motion detection. The forward motion is limited by limited angle velocity detection threshold (SAVT), and the sharpness of horizontal and vertical movement is limited by the lateral threshold of motion. The lateral motion boundary is generally below the limits of the looming motion, and for objects of a certain size, lateral movement becomes more apparent from both, as the observer moves quite far from the journey path. Below this threshold subjective constancy is experienced in accordance with Stevens law and Weber-Fechner laws.
Lower angle speed detection threshold (SAVT)
Ada is hitting the Kailanan spyphist dalam to mendetear gerakan menjaring objek yang mendekat. Ini dianggap sebagai ambang batas deteksi kecepatur sudut tersudut (SAVT) dari ketajaman visual. Ini memiliki nilai practiced 0,0275 rad/s. Untuk seseorang dengan batas SAVT , gerakan yang menjulang dari objek yang mendekati ukuran S , bergerak denotes kecepat < var> v , tidak dapat dihapus sampai jaraknya D adalah
where the term S 2 /4 is omitted for small objects relative to the distance with a small-angle approach.
Untuk melebihi SVAT, objek dengan ukuran S bergerak sebagai kecepat v harus lebih decat daripada D ; di luar jarak itu, keteguhan subjektif dialami. SVAT gives a long look at the address of the word Yang menjulang pertama kali terdeteksi:
where the term S 2 is ignored for small objects relative to the distance with a small-angle approach.
SAVT has the same type of interest for driving safety and sports as a static limit. This formula is derived from taking derivatives from a visual angle with respect to distance, and then multiplying with speed to obtain the visual expansion time level ( d ? /d t = d < var>? /d x Ã, Â · d x /d t ).
Lateral movement
Ada batas ketajaman ( ) dari gerakan horisontal dan vertikal juga. Mereka dapat is a long time in the end of Didefinisica oleh deteksi ambang pergerakan suatu objek yang berjalan pada jarak D dan kecepatan v orthogonal terhadap arah pandangan, dari jarak set-back B dengan rumus
Since the tangent of the substituted angle is the ratio of the orthogonal distance to the set-back distance, the angular time rate (rad/s) of the lateral motion is simply the derivative of the inverse tangent multiplied by the velocity ( d /d < var> t = d ? /d x Ã, Â · d x /d t ). In this app means orthogonal travel objects will not be seen as moving until it reaches distance
di mana untuk gerakan lateral umumnya> = 0.0087 rad/s dengan ketergantungan yang mungkin pada penyimpangan dari fovia dan orientasi gerakan, kecepatan adalah dalam hal unit jarak, dan I'm not sure I'm going to stop. Jarak objek yang jauh, jarak dekat yang decat, dan checepha rendah biasanya menurunkan arti gerakan lateral. Detoxify denotes set-back decades ago, but does not say that it would be possible to have a problem in Peru.
Gerakan radial
R harus melebihi :
Radial motion is found in clinical and research environments, in the dome theater, and in a virtual reality headset.
See also
- Dioptre
- Eye check
- Fovea centralis
- Hyperacuity (scientific term)
- The Landolt Ring
- Optical resolution
- Pediatric ophthalmology
- Psychophysics
- Bias error
- The retinal sum
- Strabismus
- Troxler fades
- Golovin-Sivtsev table - Golovin-Sivtsev table to test visual acuity
References
Further reading
- Duane Clinical Ophthalmology . Lippincott Williams & amp; Wilkins. 2004. V.1 C.5, V.1 C.33, V.2 C.2, V.2 C.4, V.5 C.49, V.5 C.51, V.8 C.17.
- Golovin SS, Sivtsev DA (1927). ??????? ??? ???????????? ??????? ?????? [ Table to learn visual acuity ] (in Russian) (3rd ed.). < span>
- Carlson, Kurtz (2004). Clinical Procedure for Ocular Examination (3rd ed.). McGraw Hill. ISBN: 0071370781.
External links
- How Visual Acuity Is Measured to Prevent Blindness
- Visual Acuity Measurement Standard, International Council of Ophthalmology, 1984
- Visual Acuity of the Human Eye
- Visual Reference chapter of Webvision reference, University of Utah
- Freiburg Visual Frequency (Fract) Test
Source of the article : Wikipedia
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