stereoacuity

立体視力

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/08/16 22:27:02」(JST)

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Stereoscopic acuity, also stereoacuity, is the smallest detectable depth difference that can be seen in binocular vision.

Specification and measurement

Howard-Dolman test.

Stereoacuity ^[1] is most simply explained by considering one of its earliest test, a two-peg device, named Howard-Dolman test after its inventors:^[2] The observer is shown a black peg at a distance of 6m (=20 feet). A second peg, below it, can be moved back and forth until it is just detectably nearer than the fixed one. Stereoacuity is this difference in the two positions, converted into an angle of binocular disparity, i.e., the difference in their binocular parallax.

Conversion to the angle of disparity dγ is performed by inserting the position difference dz in the formula

where a is the interocular separation of the observer and z the distance of the fixed peg from the eye. To transfer dγ into the usual unit of minutes of arc, a multiplicative constant c is inserted whose value is 3437.75 (1 radian in arcminutes). In the calculation a, dz and z must be in the same units, say, feet, inches, cm or meters. For the average interocular distance of 6.5 cm, a target distance of 6m and a typical stereoacuity of 0.5 minute of arc, the just detectable depth interval is 8 cm. As targets come closer, this interval gets smaller by the inverse square of the distance, so that an equivalent detectable depth interval at ¼ meter is 0.01 cm or the depth of impression of the head on a coin. These vary small values of normal stereoacuity, expressed in differences of either object distances, or angle of disparity, makes it a hyperacuity.

Tests of stereoacuity

Example of a Snellen-like depth test

Since the Howard-Dolman test described above is cumbersome, stereoacuity is usually measured using a stereogram in which separate panels are shown to each eye by superimposing them in a stereoscope using prisms or goggles with color or polarizing filters or alternating occlusion (for a review see [1]). A good procedure is a chart, analogous to the familiar Snellen visual acuity chart, in which one letter in each row differs in depth (front or behind) sequentially increasing in difficulty. For children the fly test is ideal: the image of a fly is transilluminated by polarized light; wearing polarizing glasses the wing appears at a different depth and allows stereopsis to be demonstrated by trying to pull on it.

Expected performance

There is no equivalent in stereoacuity of the normal 20/20 visual acuity standard. In every case, the numerical score, even if expressed in disparity angle, depends to some extent on the test being used. Superior observers under ideal conditions can achieve 0.1 arc min or even better.

The distinction between screening for the presence of stereopsis and a measurement of stereoacuity is valuable. To ascertain that depth can be seen in a binocular views, a test must be easily administered and not subject to deception. The random-dot stereogram is used widely for this purpose and has the advantage that for the uninitiated the object shape is unknown. It is made of random small pattern elements; depth can be created only in multiples of elements and therefore may not reach the small threshold disparity which is the purpose of stereoacuity measurements.

A population study revealed a surprisingly high incidence of good stereoacuity:.^[3] Out of 188 biology students, 97.3% could perform at 2.3 minutes of arc or better.

Factors influencing stereoacuity

Optimum stereoacuity requires that the following mitigating factors be avoided:

Low contrast ^[4]
Short duration exposures (less than 500 milliseconds) ^[5]
Fuzzy or closely spaced pattern elements.^[5]
Uncorrected or unequally corrected refractive errors (monovision)

Perceptual training in stereopsis

More than other such visual capabilities, the limits of stereopsis depend on the observer's familiarity with the situation. Stereo thresholds almost always improve, often several-fold, with training ^[6] and involve perceptual factors, differing in their particulars for each test.^[7] This is most vividly evident in the time it takes to "solve" a random-dot stereogram rapidly decreases between the first exposure and subsequent views ^[8]

References

^ Howard IP, Rogers BJ (2002) Seeing in Depth. Vol. 1I. Chapter 19 Porteous, Toronto
^ Howard HJ (1919) A test for the judgment of distance. Amer. J. Ophthalmol., 2, 656-675
^ Coutant BE(1993) Population distribution of stereoscopic ability. Ophthalmic Physiol Opt, 13, 3-7.
^ Westheimer G, Pettet MW (1990) Contrast and duration of exposure differentially affect vernier and stereoscopic acuity. Proc R Soc Lond B Biol Sci, 241, 42-6
^ The Ferrier Lecture (1994) Seeing depth with two eyes: stereopsis. Proc R Soc Lond B Biol Sci, 257, 205-14
^ Fendick M, Westheimer G. (1983) Effects of practice and the separation of test targets on foveal and peripheral stereoacuity. Vision Research, 23, 145-50
^ McKee SP, Taylor DG (2010) The precision of binocular and monocular depth judgments in natural settings. J. Vision, 10, 5
^ Harwerth RS, Rawlings SC (1977) Viewing time and stereoscopic threshold with random-dot stereograms. Am J Optom Physiol Opt, 54, 452-457.

External links

Review of 3D displays and stereo vision

English Journal

Diagnostic reliability and normative values of stereoacuity tests in preschool-aged children.

Afsari S, Rose KA, Pai AS, Gole GA, Leone JF, Burlutsky G, Mitchell P.SourceDepartment of Ophthalmology, Centre for Vision Research, University of Sydney, Westmead Hospital, Hawkesbury Road, Westmead, NSW 2145, Australia; paul.mitchell@sydney.edu.au.
The British journal of ophthalmology.Br J Ophthalmol.2013 Mar;97(3):308-13. doi: 10.1136/bjophthalmol-2012-302192. Epub 2013 Jan 3.
AIM: To establish the range of normal stereoacuity thresholds and evaluate the diagnostic reliability of stereoacuity tests in preschool-aged children.METHODS: 1606 children, aged 24-72 months, had detailed eye examinations and stereoacuity testing. Lang-Stereotest II (LangII) was attempted on all c
PMID 23292927

Screening for amblyopia among grade-1 students in primary school with uncorrected vision and stereopsis test in central China.

Fu J, Li SM, Li JL, Li SY, Liu LR, Wang Y, Li H, Zhu BD, Ji YZ, Yang Z, Li L, Chen W, Wang NL; g Childhood Eye Study Group.SourceBeijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University; Beijing Ophthalmology and Visual Science Key Laboratory, Beijing 100730, China.
Chinese medical journal.Chin Med J (Engl).2013 Mar;126(5):903-8.
BACKGROUND: Screening for amblyopia at earliest is important for early treatment and better prognosis. This study aimed to evaluate the validity of uncorrected distant and near visual acuity (VA) and stereoacuity for screening amblyopia in grade-1 students in primary school in central China.METHODS:
PMID 23489800

Effects of wearing yellow spectacles on visual skills, reading speed, and visual symptoms in children with reading difficulties.

Palomo-Álvarez C, Puell MC.SourceSchool of Optometry, Complutense University, Madrid, Spain, cpalomoa@fis.ucm.es.
Graefe's archive for clinical and experimental ophthalmology = Albrecht von Graefes Archiv für klinische und experimentelle Ophthalmologie.Graefes Arch Clin Exp Ophthalmol.2013 Mar;251(3):945-51. doi: 10.1007/s00417-012-2162-x. Epub 2012 Sep 26.
BACKGROUND: Possible beneficial effects of yellow-tinted spectacle lenses on binocular vision, accommodation, oculomotor scanning, reading speed and visual symptoms were assessed in children with reading difficulties.METHODS: A longitudinal prospective study was performed in 82 non-dyslexic children
PMID 23011002

Japanese Journal

間欠性外斜視患者における遠見・近見立体視と年齢および斜視角との関連 (第70回日本弱視斜視学会(3)) -- (ポスターセッション)

林麗如,林振民,山口真裕美 [他]
眼科臨床紀要 8(7), 496-499, 2015
NAID 40020536769

一般口演 3D・立体視遠見立体視の発達と加齢による変化 (第69回日本弱視斜視学会)

林麗如,林振民,鈴木利根 [他]
眼科臨床紀要 7(1), 37-42, 2014
NAID 40019947943

Effects of interpupillary distance on stereoacuity : the Frisby Davis distance stereotest versus a 3-dimensional distance stereotest

Eom Youngsub,Song Jong-Suk,Ahn Soh-Eun [他],KANG Su-Yeon,SUH Young-Woo,OH Jaeryung,KIM Seung-Hyun,KIM Hyo Myung
Japanese journal of ophthalmology 57(5), 486-492, 2013-09-01
NAID 10031201483