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A ring-shaped region surrounding the fovea, known as the [[parafovea]], is sometimes taken to represent an intermediate form of vision called paracentral vision.<ref name="Colman2009">{{cite book|last=Colman|first=Andrew M.|title=A Dictionary of Psychology|url=https://books.google.com/books?id=XxGbsjKjPZsC&pg=PA546|accessdate=30 November 2014|year=2009|publisher=Oxford University Press|isbn=978-0-19-953406-7|page=546}}</ref> The parafovea has an outer diameter of 2.5&nbsp;mm representing 8° of the visual field.<ref name="SwansonFish1995">{{cite journal|last1=Swanson|first1=William H.|last2=Fish|first2=Gary E.|title=Color matches in diseased eyes with good acuity: detection of deficits in cone optical density and in chromatic discrimination|journal=Journal of the Optical Society of America A |volume=12|issue=10|year=1995 |pages=2230|issn=1084-7529|doi=10.1364/JOSAA.12.002230}}</ref><ref name="Polyak">{{cite book | last1 = Polyak | first1 = S. L. | title = The Retina | year = 1941 | publisher = The University of Chicago Press | location = Chicago}}</ref>
A ring-shaped region surrounding the fovea, known as the [[parafovea]], is sometimes taken to represent an intermediate form of vision called paracentral vision.<ref name="Colman2009">{{cite book|last=Colman|first=Andrew M.|title=A Dictionary of Psychology|url=https://books.google.com/books?id=XxGbsjKjPZsC&pg=PA546|accessdate=30 November 2014|year=2009|publisher=Oxford University Press|isbn=978-0-19-953406-7|page=546}}</ref> The parafovea has an outer diameter of 2.5&nbsp;mm representing 8° of the visual field.<ref name="SwansonFish1995">{{cite journal|last1=Swanson|first1=William H.|last2=Fish|first2=Gary E.|title=Color matches in diseased eyes with good acuity: detection of deficits in cone optical density and in chromatic discrimination|journal=Journal of the Optical Society of America A |volume=12|issue=10|year=1995 |pages=2230|issn=1084-7529|doi=10.1364/JOSAA.12.002230}}</ref><ref name="Polyak">{{cite book | last1 = Polyak | first1 = S. L. | title = The Retina | year = 1941 | publisher = The University of Chicago Press | location = Chicago}}</ref>


The [[macula]], the next larger region of the retina, is defined as having at least two layers of [[ganglia]] (bundles of nerves and neurons) and is sometimes taken as defining the boundaries of central vs. peripheral vision<ref name="Morris1992">{{cite book|last=Morris|first=Christopher G.|title=Academic Press Dictionary of Science and Technology|url=https://books.google.com/books?id=nauWlPTBcjIC&pg=PA1610|accessdate=29 November 2014|year=1992|publisher=Gulf Professional Publishing|isbn=978-0-12-200400-1|page=1610}}</ref><ref name="M.D.1879">{{cite book|last=Landolt|first=Edmund|authorlink=Edmund Landolt|editor=Swan M.Burnett|title=A Manual of Examination of the Eyes|url=https://books.google.com/books?id=7JoqAAAAYAAJ&pg=PA201|accessdate=29 November 2014|year=1879|page=201}}</ref><ref name="Johnston1892">{{cite book|last=Johnston|first=J. Milton|title=Eye Studies; a Series of Lessons on Vision and Visual Tests|url=https://books.google.com/books?id=xqMqAAAAYAAJ&pg=PA56|accessdate=29 November 2014|year=1892|publisher=Johnston|page=56}}</ref> (but this is controversial<ref name="myths">{{cite journal | last1 = Strasburger | first1 = Hans | title = Seven myths on crowding and peripheral vision | journal = PeerJ Preprints| volume = 6:e27353 | year = 2019 | url = https://peerj.com/preprints/27353}}</ref>). Estimates of the macula’s size differ<ref>since there are no precise borders</ref>, its diameter estimated at 6° &ndash; 10°<ref name="Oyster">{{cite book |last= Oyster |first= Clyde W.|date= 1999|title= The Human Eye, Structure and Function | location= Sunderland, Mass.|publisher= Sinauer Associates |page= |isbn= 0-87893-645-9}}; sizes based on data of Polyak, Oesterberg, and Curcio.</ref> (corresponding to 1.7 &ndash; 2.9&nbsp;mm), up to 17° of the visual field (5.5&nbsp;mm<ref name="factor" />).<ref name="GuptaMazumdar2010">{{cite book |last1=Gupta |first1=AK.|last2=Mazumdar |first2=Shahana |last3=Choudhry|first3=Saurabh|title=Practical Approach to Ophthalmoscopic Retinal Diagnosis|url=https://books.google.com/books?id=OuK0cbytQWwC&pg=PA4|accessdate=30 November 2014|year=2010|publisher=Jaypee Brothers Publishers |isbn=978-81-8448-877-7|page=4}}</ref><ref name="Polyak" /> The term is familiar in the general public through the widespread [[macular degeneration]] (AMD) at older age, where central vision is lost.
The [[macula]], the next larger region of the retina, is defined as having at least two layers of [[ganglia]] (bundles of nerves and neurons) and is sometimes taken as defining the boundaries of central vs. peripheral vision<ref name="Morris1992">{{cite book|last=Morris|first=Christopher G.|title=Academic Press Dictionary of Science and Technology|url=https://books.google.com/books?id=nauWlPTBcjIC&pg=PA1610|accessdate=29 November 2014|year=1992|publisher=Gulf Professional Publishing|isbn=978-0-12-200400-1|page=1610}}</ref><ref name="M.D.1879">{{cite book|last=Landolt|first=Edmund|authorlink=Edmund Landolt|editor=Swan M.Burnett|title=A Manual of Examination of the Eyes|publisher=D.G. Brinton|url=https://archive.org/details/b21512619|accessdate=29 November 2014|year=1879|page=[https://archive.org/details/b21512619/page/201 201]}}</ref><ref name="Johnston1892">{{cite book|last=Johnston|first=J. Milton|title=Eye Studies; a Series of Lessons on Vision and Visual Tests|url=https://archive.org/details/eyestudiesaseri00johngoog|accessdate=29 November 2014|year=1892|publisher=Johnston|page=[https://archive.org/details/eyestudiesaseri00johngoog/page/n72 56]}}</ref> (but this is controversial<ref name="myths">{{cite journal | last1 = Strasburger | first1 = Hans | title = Seven myths on crowding and peripheral vision | journal = PeerJ Preprints| volume = 6:e27353 | year = 2019 | url = https://peerj.com/preprints/27353}}</ref>). Estimates of the macula’s size differ<ref>since there are no precise borders</ref>, its diameter estimated at 6° &ndash; 10°<ref name="Oyster">{{cite book |last= Oyster |first= Clyde W.|date= 1999|title= The Human Eye, Structure and Function | location= Sunderland, Mass.|publisher= Sinauer Associates |page= |isbn= 0-87893-645-9}}; sizes based on data of Polyak, Oesterberg, and Curcio.</ref> (corresponding to 1.7 &ndash; 2.9&nbsp;mm), up to 17° of the visual field (5.5&nbsp;mm<ref name="factor" />).<ref name="GuptaMazumdar2010">{{cite book |last1=Gupta |first1=AK.|last2=Mazumdar |first2=Shahana |last3=Choudhry|first3=Saurabh|title=Practical Approach to Ophthalmoscopic Retinal Diagnosis|url=https://books.google.com/books?id=OuK0cbytQWwC&pg=PA4|accessdate=30 November 2014|year=2010|publisher=Jaypee Brothers Publishers |isbn=978-81-8448-877-7|page=4}}</ref><ref name="Polyak" /> The term is familiar in the general public through the widespread [[macular degeneration]] (AMD) at older age, where central vision is lost.
When viewed from the pupil, as in an eye exam, only the central portion of the macula may be visible. Known to anatomists as the clinical macula (and in clinical setting as simply the macula) this inner region is thought to correspond to the anatomical fovea.<ref name="AlfaroKerrison2014">{{cite book|last1=Alfaro|first1=D. Virgil|last2=Kerrison|first2=John B.|title=Age-Related Macular Degeneration|url=https://books.google.com/books?id=HZhtBAAAQBAJ&pg=PT36|accessdate=30 November 2014|date=4 September 2014|publisher=Wolters Kluwer Health|isbn=978-1-4698-8964-1|pages=36–7}}</ref>
When viewed from the pupil, as in an eye exam, only the central portion of the macula may be visible. Known to anatomists as the clinical macula (and in clinical setting as simply the macula) this inner region is thought to correspond to the anatomical fovea.<ref name="AlfaroKerrison2014">{{cite book|last1=Alfaro|first1=D. Virgil|last2=Kerrison|first2=John B.|title=Age-Related Macular Degeneration|url=https://books.google.com/books?id=HZhtBAAAQBAJ&pg=PT36|accessdate=30 November 2014|date=4 September 2014|publisher=Wolters Kluwer Health|isbn=978-1-4698-8964-1|pages=36–7}}</ref>


A dividing line between near and mid peripheral vision at 30° radius can be based on several features of visual performance.
A dividing line between near and mid peripheral vision at 30° radius can be based on several features of visual performance.
[[Visual acuity]] declines systematically up to 30° eccentricity: At 2°, acuity is half the foveal value, at 4° one-third, at 6° one-fourth etc. At 30°, it is one-sixteenth the foveal value.<ref>The decline is according to ''E''<sub>2</sub>/(''E''<sub>2</sub>+''E''), where ''E'' is eccentricity in degrees visual angle, and ''E''<sub>2</sub> is a constant of approximately 2°. An ''E''<sub>2</sub> value of 2° results from Anstis’s (1974) Figure 1, with the foveal value assumed to be standard 20/20 acuity.</ref><ref name="StrasburgerRentschler2011" /> From thereon the decline is steeper.<ref name="Anstis">{{cite journal | last1 = Anstis | first1 = S. M. | title = A chart demonstrating variations in acuity with retinal position | journal = Vision Research | volume = 14 | pages = 589–592| year = 1974 | doi=10.1016/0042-6989(74)90049-2}}</ref><ref name="BesharseBok2011">{{cite book|last1=Besharse|first1=Joseph C. |last2=Bok |first2=Dean|title=The Retina and Its Disorders |url=https://books.google.com/books?id=xi9FyjeKQncC&pg=PA4 |year=2011|publisher=Academic Press|isbn=978-0-12-382198-0|page=4}}</ref> (Note that it would be wrong to say, the value were halved ''every'' 2°, as said in some textbooks or in previous versions of this article.) <ref name="myths" />
[[Visual acuity]] declines systematically up to 30° eccentricity: At 2°, acuity is half the foveal value, at 4° one-third, at 6° one-fourth etc. At 30°, it is one-sixteenth the foveal value.<ref>The decline is according to ''E''<sub>2</sub>/(''E''<sub>2</sub>+''E''), where ''E'' is eccentricity in degrees visual angle, and ''E''<sub>2</sub> is a constant of approximately 2°. An ''E''<sub>2</sub> value of 2° results from Anstis’s (1974) Figure 1, with the foveal value assumed to be standard 20/20 acuity.</ref><ref name="StrasburgerRentschler2011" /> From thereon the decline is steeper.<ref name="Anstis">{{cite journal | last1 = Anstis | first1 = S. M. | title = A chart demonstrating variations in acuity with retinal position | journal = Vision Research | volume = 14 | pages = 589–592| year = 1974 | doi=10.1016/0042-6989(74)90049-2}}</ref><ref name="BesharseBok2011">{{cite book|last1=Besharse|first1=Joseph C. |last2=Bok |first2=Dean|title=The Retina and Its Disorders |url=https://books.google.com/books?id=xi9FyjeKQncC&pg=PA4 |year=2011|publisher=Academic Press|isbn=978-0-12-382198-0|page=4}}</ref> (Note that it would be wrong to say, the value were halved ''every'' 2°, as said in some textbooks or in previous versions of this article.) <ref name="myths" />
Color perception is strong at 20° but weak at 40°.<ref name="AbramovGordon1991">{{cite journal|last1=Abramov|first1=Israel|last2=Gordon|first2=James|last3=Chan|first3=Hoover|title=Color appearance in the peripheral retina: effects of stimulus size|journal=Journal of the Optical Society of America A|volume=8 |issue=2 |year=1991 |pages=404 |issn=1084-7529 |doi=10.1364/JOSAA.8.000404}}</ref> 30° can thus be taken as the dividing line between adequate and poor color perception{{citation needed|date=November 2019}}. In dark-adapted vision, light sensitivity corresponds to rod density, which peaks just at 18°. From 18° towards the center, rod density declines rapidly. From 18° away from the center, rod density declines more gradually, in a curve with distinct inflection points resulting in two humps. The outer edge of the second hump is at about 30°, and corresponds to the outer edge of good night vision.<ref name="Sebag">{{cite book|last=Sebag|first=J.|title=Vitreous|url=https://books.google.com/books?id=CxusBAAAQBAJ&pg=PA484|accessdate=2 December 2014|publisher=Springer|isbn=978-1-4939-1086-1|page=484}}</ref><ref name="Zhaoping2014">{{cite book|author=Li Zhaoping|title=Understanding Vision: Theory, Models, and Data|url=https://books.google.com/books?id=AuHoAwAAQBAJ&pg=PA37|accessdate=2 December 2014|date=8 May 2014|publisher=OUP Oxford|isbn=978-0-19-100830-6|page=37}}</ref><ref name="McIlwain1996">{{cite book|last=McIlwain|first=James T.|title=An Introduction to the Biology of Vision|url=https://books.google.com/books?id=nvVFGm9CRXcC&pg=PA92|accessdate=2 December 2014|date=28 November 1996|publisher=Cambridge University Press|isbn=978-0-521-49890-6|page=92}}</ref>
Color perception is strong at 20° but weak at 40°.<ref name="AbramovGordon1991">{{cite journal|last1=Abramov|first1=Israel|last2=Gordon|first2=James|last3=Chan|first3=Hoover|title=Color appearance in the peripheral retina: effects of stimulus size|journal=Journal of the Optical Society of America A|volume=8 |issue=2 |year=1991 |pages=404 |issn=1084-7529 |doi=10.1364/JOSAA.8.000404}}</ref> 30° can thus be taken as the dividing line between adequate and poor color perception{{citation needed|date=November 2019}}. In dark-adapted vision, light sensitivity corresponds to rod density, which peaks just at 18°. From 18° towards the center, rod density declines rapidly. From 18° away from the center, rod density declines more gradually, in a curve with distinct inflection points resulting in two humps. The outer edge of the second hump is at about 30°, and corresponds to the outer edge of good night vision.<ref name="Sebag">{{cite book|last=Sebag|first=J.|title=Vitreous|url=https://books.google.com/books?id=CxusBAAAQBAJ&pg=PA484|accessdate=2 December 2014|publisher=Springer|isbn=978-1-4939-1086-1|page=484}}</ref><ref name="Zhaoping2014">{{cite book|author=Li Zhaoping|title=Understanding Vision: Theory, Models, and Data|url=https://books.google.com/books?id=AuHoAwAAQBAJ&pg=PA37|accessdate=2 December 2014|date=8 May 2014|publisher=OUP Oxford|isbn=978-0-19-100830-6|page=37}}</ref><ref name="McIlwain1996">{{cite book|last=McIlwain|first=James T.|title=An Introduction to the Biology of Vision|url=https://archive.org/details/introductiontobi0000mcil|url-access=registration|accessdate=2 December 2014|date=28 November 1996|publisher=Cambridge University Press|isbn=978-0-521-49890-6|page=[https://archive.org/details/introductiontobi0000mcil/page/92 92]}}</ref>


===Outer boundaries===
===Outer boundaries===


[[File:Traquair 1938 Fig 1 modified.png|thumb|Classical image of the shape and size of the visual field<ref name="Traquair" />]]The outer boundaries of peripheral vision correspond to the boundaries of the [[visual field]] as a whole. For a single eye, the extent of the visual field can be (roughly) defined in terms of four angles, each measured from the fixation point, i.e., the point at which one's gaze is directed. These angles, representing four cardinal directions, are 60° upwards, 60° nasally (towards the nose), 70–75° downwards, and 100–110° temporally (away from the nose and towards the temple).<ref name="Rönne">{{cite journal | last1 = Rönne | first1 = Henning | title = Zur Theorie und Technik der Bjerrrumschen Gesichtsfelduntersuchung | journal = Archiv für Augenheilkunde | volume = 78 | issue = 4 | pages = 284–301| year = 1915 }}</ref><ref name="Traquair">{{cite book |last= Traquair |first = Harry Moss |date= 1938 |title= An Introduction to Clinical Perimetry, Chpt. 1 |location= London|publisher= Henry Kimpton |pages = 4–5}}</ref><ref name="SavinoDanesh-Meyer2012">{{cite book|last1=Savino|first1=Peter J.|last2=Danesh-Meyer|first2=Helen V.|title=Color Atlas and Synopsis of Clinical Ophthalmology -- Wills Eye Institute -- Neuro-Ophthalmology|url=https://books.google.com/books?id=6RgSZGWQZGIC&pg=PA12|accessdate=9 November 2014|date=1 May 2012|publisher=Lippincott Williams & Wilkins|isbn=978-1-60913-266-8|page=12}}</ref><ref name="RyanSchachat2012">{{cite book|last1=Ryan|first1=Stephen J.|last2=Schachat|first2=Andrew P.|last3=Wilkinson|first3=Charles P. |author4=David R. Hinton |author5=SriniVas R. Sadda |author6=[[Peter Wiedemann]]|title=Retina|url=https://books.google.com/books?id=PdAsuzFRv5oC&pg=PT342|accessdate=9 November 2014|date=1 November 2012|publisher=Elsevier Health Sciences|isbn=978-1-4557-3780-2|page=342}}</ref><ref name="TrattlerKaiser2012">{{cite book|last1=Trattler|first1=William B.|last2=Kaiser|first2=Peter K.|last3=Friedman|first3=Neil J.|title=Review of Ophthalmology: Expert Consult - Online and Print|url=https://books.google.com/books?id=AazA_9TQnHYC&pg=PA255|accessdate=9 November 2014|date=5 January 2012|publisher=Elsevier Health Sciences|isbn=978-1-4557-3773-4|page=255}}</ref> For both eyes the combined visual field is 130–135° vertically<ref name="Dagnelie2011">{{cite book|last=Dagnelie|first=Gislin|title=Visual Prosthetics: Physiology, Bioengineering, Rehabilitation|url=https://books.google.com/books?id=GHoEWq6tcSgC&pg=PA398|accessdate=9 November 2014|date=21 February 2011|publisher=Springer Science & Business Media|isbn=978-1-4419-0754-7|page=398}}</ref><ref name="Dohse2007">{{cite book|last=Dohse|first=K.C.|title=Effects of Field of View and Stereo Graphics on Memory in Immersive Command and Control|url=https://books.google.com/books?id=p2pSW2D4s7gC&pg=PA6|accessdate=9 November 2014|year=2007|publisher=ProQuest|isbn=978-0-549-33503-0|page=6}}</ref> and 200–220° horizontally.<ref name="Traquair" /><ref name="name">{{Citation
[[File:Traquair 1938 Fig 1 modified.png|thumb|Classical image of the shape and size of the visual field<ref name="Traquair" />]]The outer boundaries of peripheral vision correspond to the boundaries of the [[visual field]] as a whole. For a single eye, the extent of the visual field can be (roughly) defined in terms of four angles, each measured from the fixation point, i.e., the point at which one's gaze is directed. These angles, representing four cardinal directions, are 60° upwards, 60° nasally (towards the nose), 70–75° downwards, and 100–110° temporally (away from the nose and towards the temple).<ref name="Rönne">{{cite journal | last1 = Rönne | first1 = Henning | title = Zur Theorie und Technik der Bjerrrumschen Gesichtsfelduntersuchung | journal = Archiv für Augenheilkunde | volume = 78 | issue = 4 | pages = 284–301| year = 1915 }}</ref><ref name="Traquair">{{cite book |last= Traquair |first = Harry Moss |date= 1938 |title= An Introduction to Clinical Perimetry, Chpt. 1 |location= London|publisher= Henry Kimpton |pages = 4–5}}</ref><ref name="SavinoDanesh-Meyer2012">{{cite book|last1=Savino|first1=Peter J.|last2=Danesh-Meyer|first2=Helen V.|title=Color Atlas and Synopsis of Clinical Ophthalmology -- Wills Eye Institute -- Neuro-Ophthalmology|url=https://books.google.com/books?id=6RgSZGWQZGIC&pg=PA12|accessdate=9 November 2014|date=1 May 2012|publisher=Lippincott Williams & Wilkins|isbn=978-1-60913-266-8|page=12}}</ref><ref name="RyanSchachat2012">{{cite book|last1=Ryan|first1=Stephen J.|last2=Schachat|first2=Andrew P.|last3=Wilkinson|first3=Charles P. |author4=David R. Hinton |author5=SriniVas R. Sadda |author6=[[Peter Wiedemann]]|title=Retina|url=https://books.google.com/books?id=PdAsuzFRv5oC&pg=PT342|accessdate=9 November 2014|date=1 November 2012|publisher=Elsevier Health Sciences|isbn=978-1-4557-3780-2|page=342}}</ref><ref name="TrattlerKaiser2012">{{cite book|last1=Trattler|first1=William B.|last2=Kaiser|first2=Peter K.|last3=Friedman|first3=Neil J.|title=Review of Ophthalmology: Expert Consult - Online and Print|url=https://books.google.com/books?id=AazA_9TQnHYC&pg=PA255|accessdate=9 November 2014|date=5 January 2012|publisher=Elsevier Health Sciences|isbn=978-1-4557-3773-4|page=255}}</ref> For both eyes the combined visual field is 130–135° vertically<ref name="Dagnelie2011">{{cite book|last=Dagnelie|first=Gislin|title=Visual Prosthetics: Physiology, Bioengineering, Rehabilitation|url=https://archive.org/details/Gislin_Dagnelie_Visual_Prosthetics|accessdate=9 November 2014|date=21 February 2011|publisher=Springer Science & Business Media|isbn=978-1-4419-0754-7|page=[https://archive.org/details/Gislin_Dagnelie_Visual_Prosthetics/page/n401 398]}}</ref><ref name="Dohse2007">{{cite book|last=Dohse|first=K.C.|title=Effects of Field of View and Stereo Graphics on Memory in Immersive Command and Control|url=https://books.google.com/books?id=p2pSW2D4s7gC&pg=PA6|accessdate=9 November 2014|year=2007|publisher=ProQuest|isbn=978-0-549-33503-0|page=6}}</ref> and 200–220° horizontally.<ref name="Traquair" /><ref name="name">{{Citation
| last = Szinte
| last = Szinte
| first = Martin
| first = Martin

Revision as of 05:41, 6 March 2020

For the Turnover album, see Peripheral Vision (album).
Peripheral vision of the human eye
Field of view of the human eye

Peripheral vision, or indirect vision, is vision as it occurs outside the point of fixation, i.e. away from the center of gaze. The vast majority of the area in the visual field is included in the notion of peripheral vision. "Far peripheral" vision refers to the area at the edges of the visual field, "mid-peripheral" vision refers to medium eccentricities, and "near-peripheral", sometimes referred to as "para-central" vision, exists adjacent to the center of gaze.[1]

Boundaries

Inner boundaries

The inner boundaries of peripheral vision can be defined in any of several ways depending on the context. In everyday language the term "peripheral vision" is often used to refer to what in technical usage would be called "far peripheral vision." This is vision outside of the range of stereoscopic vision. It can be conceived as bounded at the center by a circle 60° in radius or 120° in diameter, centered around the fixation point, i.e., the point at which one's gaze is directed.[2] However, in common usage, peripheral vision may also refer to the area outside a circle 30° in radius or 60° in diameter.[3][4] In vision-related fields such as physiology, ophthalmology, optometry, or vision science in general, the inner boundaries of peripheral vision are defined more narrowly in terms of one of several anatomical regions of the central retina, in particular the fovea and the macula.[1]

The fovea is a cone-shaped depression in the central retina measuring 1.5 mm in diameter, corresponding[5] to 5° of the visual field.[6] The outer boundaries of the fovea are visible under a microscope, or with microscopic imaging technology such as OCT or microscopic MRI. When viewed through the pupil, as in an eye exam (using an ophthalmoscope or retinal photography), only the central portion of the fovea may be visible. Anatomists refer to this as the clinical fovea, and say that it corresponds to the anatomical foveola, a structure with a diameter of 0.35 mm corresponding to 1 degree of the visual field. In clinical usage the central part of the fovea is typically referred to simply as the fovea.[7][8][9]

In terms of visual acuity, "foveal vision" may be defined as vision using the part of the retina in which a visual acuity of at least 20/20 (6/6 metric or 0.0 LogMAR; internationally 1.0) is attained. This corresponds to using the foveal avascular zone (FAZ) with a diameter of 0.5 mm representing 1.5° of the visual field. Although often idealized as perfect circles, the central structures of the retina tend to be irregular ovals. Thus, foveal vision may also be defined as the central 1.5–2° of the visual field. Vision within the fovea is generally called central vision, while vision outside of the fovea, or even outside the foveola, is called peripheral, or indirect vision.[1]

A ring-shaped region surrounding the fovea, known as the parafovea, is sometimes taken to represent an intermediate form of vision called paracentral vision.[10] The parafovea has an outer diameter of 2.5 mm representing 8° of the visual field.[11][12]

The macula, the next larger region of the retina, is defined as having at least two layers of ganglia (bundles of nerves and neurons) and is sometimes taken as defining the boundaries of central vs. peripheral vision[13][14][15] (but this is controversial[16]). Estimates of the macula’s size differ[17], its diameter estimated at 6° – 10°[18] (corresponding to 1.7 – 2.9 mm), up to 17° of the visual field (5.5 mm[5]).[19][12] The term is familiar in the general public through the widespread macular degeneration (AMD) at older age, where central vision is lost. When viewed from the pupil, as in an eye exam, only the central portion of the macula may be visible. Known to anatomists as the clinical macula (and in clinical setting as simply the macula) this inner region is thought to correspond to the anatomical fovea.[20]

A dividing line between near and mid peripheral vision at 30° radius can be based on several features of visual performance. Visual acuity declines systematically up to 30° eccentricity: At 2°, acuity is half the foveal value, at 4° one-third, at 6° one-fourth etc. At 30°, it is one-sixteenth the foveal value.[21][1] From thereon the decline is steeper.[22][23] (Note that it would be wrong to say, the value were halved every 2°, as said in some textbooks or in previous versions of this article.) [16] Color perception is strong at 20° but weak at 40°.[24] 30° can thus be taken as the dividing line between adequate and poor color perception[citation needed]. In dark-adapted vision, light sensitivity corresponds to rod density, which peaks just at 18°. From 18° towards the center, rod density declines rapidly. From 18° away from the center, rod density declines more gradually, in a curve with distinct inflection points resulting in two humps. The outer edge of the second hump is at about 30°, and corresponds to the outer edge of good night vision.[25][26][27]

Outer boundaries

Classical image of the shape and size of the visual field[28]

The outer boundaries of peripheral vision correspond to the boundaries of the visual field as a whole. For a single eye, the extent of the visual field can be (roughly) defined in terms of four angles, each measured from the fixation point, i.e., the point at which one's gaze is directed. These angles, representing four cardinal directions, are 60° upwards, 60° nasally (towards the nose), 70–75° downwards, and 100–110° temporally (away from the nose and towards the temple).[29][28][30][31][32] For both eyes the combined visual field is 130–135° vertically[33][34] and 200–220° horizontally.[28][35]

Characteristics

The loss of peripheral vision while retaining central vision is known as tunnel vision, and the loss of central vision while retaining peripheral vision is known as central scotoma.

Peripheral vision is weak in humans, especially at distinguishing detail, color, and shape. This is because the density of receptor and ganglion cells in the retina is greater at the center and lowest at the edges, and, moreover, the representation in the visual cortex is much smaller than that of the fovea[1] (see visual system for an explanation of these concepts). The distribution of receptor cells across the retina is different between the two main types, rod cells and cone cells. Rod cells are unable to distinguish color and peak in density in the near periphery (at 18° eccentricity), while cone cell density is highest in the very center, the fovea, and from there declines rapidly (by an inverse linear function).

Flicker fusion thresholds decline towards the periphery, but do that at a lower rate than other visual functions; so the periphery has a relative advantage at noticing flicker.[1] Peripheral vision is also relatively good at detecting motion (a feature of Magno cells).

Central vision is relatively weak in the dark (scotopic vision) since cone cells lack sensitivity at low light levels. Rod cells, which are concentrated further away from the fovea, operate better than cone cells in low light. This makes peripheral vision useful for detecting faint light sources at night (like faint stars). Because of this, pilots are taught to use peripheral vision to scan for aircraft at night. [citation needed]

Ovals A, B and C show which portions of the chess situation chess masters can reproduce correctly with their peripheral vision. Lines show path of foveal fixation during 5 seconds when the task is to memorize the situation as correctly as possible. Image from[36] based on data by[37]

The distinctions between foveal (sometimes also called central) and peripheral vision are reflected in subtle physiological and anatomical differences in the visual cortex. Different visual areas contribute to the processing of visual information coming from different parts of the visual field, and a complex of visual areas located along the banks of the interhemispheric fissure (a deep groove that separates the two brain hemispheres) has been linked to peripheral vision. It has been suggested that these areas are important for fast reactions to visual stimuli in the periphery, and monitoring body position relative to gravity.[38]

Functions

The main functions of peripheral vision are:[36]

  • recognition of well-known structures and forms with no need to focus by the foveal line of sight,
  • identification of similar forms and movements (Gestalt psychology laws),
  • delivery of sensations which form the background of detailed visual perception.

Extreme peripheral vision

Side-view of the human eye, viewed approximately 90° temporal, illustrating how the iris and pupil appear rotated towards the viewer due to the optical properties of the cornea and the aqueous humor.

When viewed at large angles, the iris and pupil appear to be rotated toward the viewer due to the optical refraction in the cornea. As a result, the pupil may still be visible at angles greater than 90°.[39][40][41]

Cone-rich rim of the retina

The rim of the retina contains a large concentration of cone cells. The retina extends farthest in the superior-nasal 45° quadrant (in the direction from the pupil to the bridge of the nose) with the greatest extent of the visual field in the opposite direction, the inferior temporal 45° quadrant (from the pupil of either eye towards the bottom of the nearest ear). Vision at this extreme part of the visual field is thought to be possibly concerned with threat detection, measuring optical flow, color constancy, or circadian rhythm.[42][43][44]

See also

References

  1. ^ a b c d e f Strasburger, Hans; Rentschler, Ingo; Jüttner, Martin (2011). "Peripheral vision and pattern recognition: A review". Journal of Vision. 11 (5): 13. doi:10.1167/11.5.13. ISSN 1534-7362. PMID 22207654.
  2. ^ Sardegna, Jill; Shelly, Susan; Rutzen, Allan Richard; Scott M Steidl (2002). The Encyclopedia of Blindness and Vision Impairment. Infobase Publishing. p. 253. ISBN 978-0-8160-6623-0. Retrieved 30 November 2014.
  3. ^ Grosvenor, Theodore; Grosvenor, Theodore P. (2007). Primary Care Optometry. Elsevier Health Sciences. p. 129. ISBN 978-0-7506-7575-8. Retrieved 29 November 2014.
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  5. ^ a b 1 mm = 3.436°
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  17. ^ since there are no precise borders
  18. ^ Oyster, Clyde W. (1999). The Human Eye, Structure and Function. Sunderland, Mass.: Sinauer Associates. ISBN 0-87893-645-9.; sizes based on data of Polyak, Oesterberg, and Curcio.
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  21. ^ The decline is according to E2/(E2+E), where E is eccentricity in degrees visual angle, and E2 is a constant of approximately 2°. An E2 value of 2° results from Anstis’s (1974) Figure 1, with the foveal value assumed to be standard 20/20 acuity.
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  29. ^ Rönne, Henning (1915). "Zur Theorie und Technik der Bjerrrumschen Gesichtsfelduntersuchung". Archiv für Augenheilkunde. 78 (4): 284–301.
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  35. ^ Szinte, Martin; Cavanagh, Patrick (15 October 2012), "Apparent Motion from Outside the Visual Field, Retinotopic Cortices May Register Extra-Retinal Positions", PLOS ONE, 7 (10): e47386, doi:10.1371/journal.pone.0047386, PMC 3471811, PMID 23077606, With our head and eyes steady, our normal binocular vision covers a visual field of about 200 to 220 degrees of visual angle.{{citation}}: CS1 maint: unflagged free DOI (link)
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  37. ^ DE GROOT, A. : Perception and memory in chess; an experimental study of the heuristics of the professional eye. Mimeograph; Psychologisch Laboratorium Universiteit van Amsterdam, Seminarium September 1969
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  43. ^ Williams, Robert W. (1991). "The human retina has a cone-enriched rim". Visual Neuroscience. 6 (4): 403–6. doi:10.1017/S0952523800006647. ISSN 0952-5238. PMID 1829378.
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