Editing Dioptre (section)

==In vision correction==
The fact that optical powers are approximately [[wiktionary:additive|additive]] enables an [[eye care professional]] to prescribe [[corrective lens]]es as a simple correction to the [[eye|eye's]] optical power, rather than doing a detailed analysis of the entire optical system (the eye and the lens). Optical power can also be used to adjust a basic [[Eyeglass prescription|prescription]] for reading. Thus an eye care professional, having determined that a [[myopia|myopic]] (nearsighted) person requires a basic correction of, say, −2&nbsp;dioptres to restore normal distance vision, might then make a further prescription of 'add 1' for reading, to make up for lack of [[Accommodation (eye)|accommodation]] (ability to alter focus). This is the same as saying that −1&nbsp;dioptre lenses are prescribed for reading.

In humans, the total optical power of the relaxed eye is approximately 60 dioptres.<ref name=Najjar1>{{cite web |last=Najjar |first=Dany |url=http://www.eyeweb.org/optics.htm |title=Clinical optics and refraction |publisher=Eyeweb |access-date=2008-03-25 |url-status=dead |archive-url=https://web.archive.org/web/20080323035251/http://www.eyeweb.org/optics.htm |archive-date=2008-03-23 }}</ref><ref>{{cite web |url=https://www.aao.org/munnerlyn-laser-surgery-center/optical-properties-of-eye |title=Optical Properties of the Eye |publisher=American Academy of Ophthalmology |first=Daniel |last=Palanker |date=October 28, 2013 |access-date=2017-10-16}}</ref> The [[cornea]] accounts for approximately two-thirds of this refractive power (about 40 dioptres) and the [[lens (anatomy)|crystalline lens]] contributes the remaining one-third (about 20 dioptres).<ref name = Najjar1/> In focusing, the [[ciliary muscle]] contracts to reduce the [[Tension (mechanics)|tension]] or [[Stress (physics)|stress]] transferred to the lens by the [[Suspensory ligament of the lens|suspensory ligaments]]. This results in increased convexity of the lens which in turn increases the optical power of the eye. The [[amplitude of accommodation]] is about 11 to 16&nbsp;dioptres at age 15, decreasing to about 10&nbsp;dioptres at age 25, and to around 1&nbsp;dioptre above age 60.

[[Lens (optics)#Types of simple lenses|Convex lens]]es have positive dioptric value and are generally used to correct [[hyperopia]] (farsightedness) or to allow people with [[presbyopia]] (the limited accommodation of advancing age) to read at close range. [[over-the-counter drug|Over the counter]] [[eyeglasses|reading glasses]] are rated at +1.00 to +4.00&nbsp;dioptres. [[Lens (optics)#Types of simple lenses|Concave lens]]es have negative dioptric value and generally correct [[myopia]] (nearsightedness). Typical glasses for mild myopia have a power of −0.50 to −3.00&nbsp;dioptres. [[Optometrist]]s usually measure [[refractive error]] using lenses graded in steps of 0.25&nbsp;dioptres.