IngentaConnect Mechanism of Human Accommodation as Analyzed by Nonlinear Finite ...

Authors: Schachar Ronald A.; Bax Andrew J.

Source: Annals of Ophthalmology, Volume 33, Number 2, June 2001 , pp. 103-112(10)

Abstract:

Accommodation, the change in focus by the human eye, occurs because its deformable crystalline lens changes optical power.1 By observing the direction of movement of multiple reflections from the surface of the crystalline lens during human accommodation, it has been demonstrated that the central surface steepens while the peripheral surface of the crystalline lens flattens.2,3 Moreover, with increasing optical power during accommodation, the spherical aberration of the human crystalline lens decreases.1,4,5 Several theories have been proposed to explain the mechanism of accommodation of the human lens. The more widely accepted Helmholtz theory of accommodation assumes that the zonules supporting the crystalline lens are under maximal tension when the lens is at minimum optical power.6 The Helmholtz theory proposes that tension is exerted by the anterior and posterior zonules together or by all 3 sets of zonules simultaneously. This theory states that the optical power of the crystalline lens is increased by relaxation of the tension on these zonules, while an increase in zonular tension causes a decrease in optical power. This theory does not explain the peripheral surface flattening and the reduction in spherical aberration that have been reported to occur during accommodation. No working model lens based on the Helmholtz theory has been developed that can mimic the properties of the human crystalline lens during accommodation.

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Mechanism of Human Accommodation as Analyzed by Nonlinear Finite Element Analysis