Editing Visual system (section)

==Development==

===Infancy===
{{See also|Infant vision}}
Newborn infants have limited [[color perception]].<ref name="Lane2012">{{cite book|last=Lane|first=Kenneth A.|title=Visual Attention in Children: Theories and Activities|url=https://books.google.com/books?id=FdVDkAOK_WUC&pg=PA7|access-date=4 December 2014|year=2012|publisher=SLACK|isbn=978-1-55642-956-9|page=7}}</ref> One study found that 74% of newborns can distinguish red, 36% green, 25% yellow, and 14% blue. After one month, performance "improved somewhat."<ref name="AdamsCourage1994">{{cite journal|last1=Adams|first1=Russell J.|last2=Courage|first2=Mary L.|last3=Mercer|first3=Michele E.|title=Systematic measurement of human neonatal color vision|journal=Vision Research|volume=34|issue=13|year=1994|pages=1691–1701|issn=0042-6989|doi=10.1016/0042-6989(94)90127-9|pmid=7941376|s2cid=27842977}}</ref> Infant's eyes do not have the ability to [[accommodation (eye)|accommodate]]. Pediatricians are able to perform non-verbal testing to assess [[visual acuity]] of a newborn, detect [[nearsightedness]] and [[astigmatism]], and evaluate the eye teaming and alignment. Visual acuity improves from about 20/400 at birth to approximately 20/25 at 6 months of age. This happens because the nerve cells in the [[retina]] and brain that control vision are not fully developed.

===Childhood and adolescence===

[[Depth perception]], focus, tracking and other aspects of vision continue to develop throughout early and middle childhood. From recent studies in the [[United States]] and [[Australia]] there is some evidence that the amount of time school aged children spend outdoors, in natural light, may have some impact on whether they develop [[myopia]]. The condition tends to get somewhat worse through childhood and adolescence, but stabilizes in adulthood. More prominent myopia (nearsightedness) and astigmatism are thought to be inherited. Children with this condition may need to wear glasses.

===Adulthood===

Vision is often one of the first senses affected by aging. A number of changes occur with aging:
* Over time, the [[Lens (anatomy)|lens]] becomes yellowed and may eventually become brown, a condition known as brunescence or [[Brunescent cataract|brunescent]] [[cataract]]. Although many factors contribute to yellowing, lifetime exposure to [[ultraviolet light]] and [[ageing|aging]] are two main causes.
* The lens becomes less flexible, diminishing the ability to accommodate ([[presbyopia]]).
* While a healthy adult pupil typically has a size range of 2–8&nbsp;mm, with age the range gets smaller, trending towards a moderately small diameter.
* On average [[Tears|tear production]] declines with age. However, there are a number of age-related conditions that can cause excessive tearing.