Editing Pupil (section)

=== Evolution and adaptation ===
One explanation for the [[evolution]] of slit pupils is that they can exclude light more effectively than a circular pupil.{{citation needed|date=August 2017}} This would explain why slit pupils tend to be found in the eyes of animals with a [[crepuscular]] or [[nocturnal]] lifestyle that need to protect their eyes during daylight. Constriction of a circular pupil (by a ring-shaped muscle) is less complete than closure of a slit pupil, which uses two additional muscles that laterally compress the pupil.<ref name="Walls et al., (1942)">{{cite book |first=G.L. |last=Walls |title=The vertebrate eye and its adaptive radiation |publisher=Hafner |orig-year=1942 |year=1967 |oclc=10363617 |series=Cranbrook Institute of Science Bulletin |volume=19}}</ref>  For example, the cat's slit pupil can change the light intensity on the retina 135-fold compared to 10-fold in humans.<ref name="Hughes, (1977)">{{cite book |last=Hughes |first=A. |orig-year=1977 |chapter=The topography of vision in mammals of contrasting life style: comparative optics and retinal organisation |editor-first=F. |editor-last=Crescitelli |title=The Visual System in Vertebrates |chapter-url=https://books.google.com/books?id=qCDqCAAAQBAJ&pg=PA613 |date=2013 |publisher=Springer |isbn=978-3-642-66468-7 |pages=613–756 |series=Handbook of Sensory Physiology |volume=7/5}}</ref>  However, this explanation does not account for circular pupils that can be closed to a very small size (e.g., 0.5&nbsp;mm in the [[tarsier]]) and the rectangular pupils of many [[ungulate]]s which do not close to a narrow slit in bright light.<ref name="Land, (2006)">{{cite journal|doi=10.1016/j.cub.2006.02.046|pmid=16527734|author=Land, M.F.|title= Visual optics: the shapes of pupils|journal=Current Biology|volume=16|issue=5|pages=R167–8|year=2006|doi-access=free|bibcode=2006CBio...16.R167L }}</ref>  An alternative explanation is that a partially constricted circular pupil shades the peripheral zones of the lens which would lead to poorly focused images at relevant wavelengths. The vertical slit pupil allows for use of all wavelengths across the full diameter of the lens, even in bright light.<ref name="Malmstrom" />  It has also been suggested that in ambush predators such as some snakes, vertical slit pupils may aid in camouflage, [[Disruptive coloration|breaking up]] the circular outline of the eye.<ref name="Brischoux et al., (2010)">{{cite journal|doi=10.1111/j.1420-9101.2010.02046.x|pmid=20629855|author=Brischoux, F., Pizzatto, L. and Shine, R.|title=Insights into the adaptive significance of vertical pupil shape in snakes|journal=Journal of Evolutionary Biology|volume=23|issue=9|pages=1878–85|year=2010|doi-access=free}}</ref>