accommodation
Accommodation is the increase in the eye's refractive power that lets a near object form a clear image on the retina. With accommodation relaxed, the anterior surface of the crystalline lens is comparatively flat and lens power is at its minimum, although the lens still supplies about one-third of the eye's power.1
The ciliary muscle works like a sphincter. When the ciliary muscle relaxes, the zonules pull outward on the lens equator and flatten the anterior lens surface. When the ciliary muscle contracts, zonular tension falls and the young lens takes its preferred rounded shape, which steepens the anterior surface and raises the lens's dioptric power.1 Blur from a minus lens and a proximal near target both stimulate accommodation. Accommodation is neurally coupled with convergence and pupil constriction, and the three responses together are called the near reflex or accommodative triad.2
The amplitude of accommodation is the most the eye can accommodate, and the amplitude falls steadily with age. A 10-year-old child may accommodate 12.00 D, while a 75-year-old adult has no ability to accommodate.1 Objective measurement shows a decline of about 2.5 D per decade, reaching zero at about 50 to 55 years of age.2 Presbyopia is the age-related loss of accommodative amplitude, usually noticed between ages 40 and 50 as near blur and asthenopia.1,2 Lens stiffness increases exponentially with age, and the ciliary muscle also loses mobility, so several tissues contribute to the loss.2
More detail
At rest the eye keeps a residual accommodation of about 0.5 to 1.5 D, called tonic accommodation or night myopia.2 Two-thirds of accommodative amplitude is gone by age 35 years, although most people do not notice the loss at that age. Subjective tests suggest that about 1 D remains after age 50, but that apparent response comes from depth of field rather than a change in lens power.2 Presbyopia is corrected by adding plus power to the distance correction, often as a bifocal add.1
Sources (5)
- Schwartz, Geometrical and Visual Optics, ch. 8
- Adler's Physiology of the Eye, ch. 3
- Charman, W.N. (2008) 'The eye in focus: accommodation and presbyopia', Clinical and Experimental Optometry, 91(3), pp. 207–225.
- Glasser, A. (2011) 'Accommodation', in Levin, L.A. et al. (eds) Adler's Physiology of the Eye. 11th edn. Edinburgh: Saunders/Elsevier, pp. 40–70.
- Kruger, P.B., Mathews, S., Aggarwala, K.R. and Sanchez, N. (1993) 'Chromatic aberration and ocular focus: Fincham revisited', Vision Research, 33(10), pp. 1397–1411.
Reviewed October 2026