Editing Peripheral vision (section)

===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.<ref name="SardegnaShelly2002">{{cite book|last1=Sardegna|first1=Jill|last2=Shelly|first2=Susan|last3=Rutzen|first3=Allan Richard|author4=Scott M Steidl|title=The Encyclopedia of Blindness and Vision Impairment|url=https://books.google.com/books?id=l7UN5asLD0cC&pg=PA253|access-date=30 November 2014|year=2002|publisher=Infobase Publishing|isbn=978-0-8160-6623-0|page=253}}</ref> However, in common usage, peripheral vision may also refer to the area outside a circle 30° in radius or 60° in diameter.<ref name="GrosvenorGrosvenor2007">{{cite book|last1=Grosvenor|first1=Theodore|last2=Grosvenor|first2=Theodore P.|title=Primary Care Optometry|url=https://books.google.com/books?id=uEmQKPAOwccC&pg=PA129|access-date=29 November 2014|year=2007|publisher=Elsevier Health Sciences|isbn=978-0-7506-7575-8|page=129}}</ref><ref name="Bhise2011">{{cite book|last=Bhise|first=Vivek D.|title=Ergonomics in the Automotive Design Process|url=https://books.google.com/books?id=XgVHut1fVJQC&pg=PA68|access-date=30 November 2014|date=15 September 2011|publisher=CRC Press|isbn=978-1-4398-4210-2|page=68}}</ref> 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 centralis|fovea]] and the [[Macula of the retina|macula]].<ref name="StrasburgerRentschler2011">{{cite journal|last1=Strasburger|first1=Hans|last2=Rentschler|first2=Ingo|last3=Jüttner|first3=Martin|title=Peripheral vision and pattern recognition: A review|journal=Journal of Vision|volume=11|issue=5|year=2011|pages=13|url=http://jov.arvojournals.org/article.aspx?articleid=2191825|issn=1534-7362|doi=10.1167/11.5.13|pmid=22207654|doi-access=free|pmc=11073400}}</ref>

The fovea is a cone-shaped depression in the central retina measuring 1.5&nbsp;mm in diameter, corresponding<ref name="factor">1 mm = 3.436°</ref> to 5° of the visual field.<ref name="Millodot2014">{{cite book|last=Millodot|first=Michel|title=Dictionary of Optometry and Visual Science|url=https://books.google.com/books?id=3gygBAAAQBAJ&pg=PT250|access-date=30 November 2014|date=30 July 2014|publisher=Elsevier Health Sciences UK|isbn=978-0-7020-5188-3|page=250}}</ref> 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 [[Ophthalmoscopy|ophthalmoscope]] or [[Fundus photography|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&nbsp;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.<ref name="Small1994">{{cite book|last=Small|first=Robert G. |title=The Clinical Handbook of Ophthalmology|url=https://books.google.com/books?id=J0mO1sk6zj8C&pg=PA134|access-date=29 November 2014|date=15 August 1994|publisher=CRC Press|isbn=978-1-85070-584-0|page=134}}</ref><ref name="PeymanMeffert2000">{{cite book|last1=Peyman|first1=Gholam A.|author-link1=Gholam A. Peyman|last2=Meffert|first2=Stephen A.|last3=Chou|first3=Famin|author4=Mandi D. Conway|title=Vitreoretinal Surgical Techniques|url=https://books.google.com/books?id=gEaQ0wiM7JwC&pg=PA6|access-date=29 November 2014|date=27 November 2000|publisher=CRC Press|isbn=978-1-85317-585-5|pages=6–7}}</ref><ref name="Alfaro2006">{{cite book|last=Alfaro|first=D. Virgil|title=Age-related Macular Degeneration: A Comprehensive Textbook|url=https://books.google.com/books?id=npJ1tCXX-LAC&pg=PA3|access-date=29 November 2014|year=2006|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-3899-6|page=3}}</ref>

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&nbsp;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.<ref name="StrasburgerRentschler2011" />

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|access-date=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=2230–2236|issn=1084-7529|doi=10.1364/JOSAA.12.002230|pmid=7500203|bibcode=1995JOSAA..12.2230S }}</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|access-date=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|author-link=Edmund Landolt|editor=Swan M.Burnett|title=A Manual of Examination of the Eyes|publisher=D.G. Brinton|url=https://archive.org/details/b21512619|access-date=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|access-date=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 | last = Strasburger | first = Hans | title = Seven myths on crowding and peripheral vision | journal = i-Perception | volume = 11 | issue = 3 | date = May 19, 2020 | url = https://journals.sagepub.com/doi/10.1177/2041669520913052 | doi = 10.1177/2041669520913052 | doi-access = free | pmc = 7238452 }}</ref>). Estimates of the macula’s size differ,<ref>since there are no precise borders</ref> its diameter estimated at 6° – 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 |isbn= 0-87893-645-9}}; sizes based on data of Polyak, Oesterberg, and Curcio.</ref>  (corresponding to 1.7 – 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|access-date=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|access-date=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.
[[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 | issue = 7 | doi=10.1016/0042-6989(74)90049-2| pmid = 4419807 }}</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=404–414 |issn=1084-7529 |doi=10.1364/JOSAA.8.000404|pmid=2007915|bibcode=1991JOSAA...8..404A }}</ref> In dark-adapted vision, light sensitivity corresponds to rod density,{{cn|date=July 2021}} 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|date=October 2014|url=https://books.google.com/books?id=CxusBAAAQBAJ&pg=PA484|access-date=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|access-date=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|access-date=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>