A validated finite element model to reproduce Helmholtz’s theory of accommodation: a powerful tool to investigate presbyopia

Abstract

Accommodation is a dynamic change in the dioptric power of the eye that allows a change in focus from distant to near objects. This process is achieved by changing the shape of the lens, following contraction of the ciliary muscle, thereby releasing the zonular tension around the lens equator, according to the widely accepted accommodation theory of Helmholtz. 1 Numerous authors have confirmed this theory over time, including Fincham, 2 who demonstrated the ability of the elastic lens to round up after the release of zonular tension, and Glasser and Kaufmann, 3 who showed relaxation of the zonules due to ciliary muscle contraction along with other investigators. 4 The ciliary muscle is the engine that drives the accommodation process. It consists of three groups of muscle fibres (i.e., longitudinal, radial and circular), although their

A detailed methodology to model the Non Contact Tonometry: a Fluid Structure Interaction study

“…A 3D model of an eye ( Figure 1A ) is constructed based on averaged anatomic measures taken from literature ( Ariza-Gracia et al, 2018 ) ( Cabeza-Gil et al, 2021 ). It contains cornea, limbus, sclera, crystalline lens differentiated in cortex and nucleus, aqueous and vitreous humors separated by the vitreous membrane, and ciliary zonule modelled as a thin membrane.…”

A Novel Dual-wavelength, Dual-function Laser System for Presbyopia and Glaucoma Treatments

“…Therefore, lens is the prime component for the loss of accommodation with age. Accommodative lens thickening and the resting CM apex thickness explained accommodative amplitude slightly better than age alone [3][4][5][6][7]. Croft et al [5] also demonstrated that the vitreous zonules and its posterior insertion zone have a role in accommodation and presbyopia in the human eye.…”

“…The accommodative theory, postulated by Helmholtz, remains the most widely supported and cited [1,2]. Accommodation is the ability to focus on near objects through controlled changes in the shape and thickness of the crystalline lens and mediated by ciliary muscle (CM) contraction [3,4]. Optically, it is the lens shape change to increase the refractive power of the eye for accommodation occurs.…”

“…Croft et al [5] also demonstrated that the vitreous zonules and its posterior insertion zone have a role in accommodation and presbyopia in the human eye. During accommodation, the lens equator moves forward and inward, and this movement is reduced with age, possibly due to the agerelated loss in accommodative forward movement of the vitreous zonules posterior insertion zone [3,7].…”

“…The effectiveness of CM contraction for lens relaxation (or accommodation) may be influenced by the combined aging factors, including lens property changes (index, size, thickness and curvature), tissue elastic changes (in sclera and ciliary) and the zonular tension change [1,3]. Various options have been reported for presbyopia corrections include: bifocal or progressive spectacles, monofocal or multifocal contact lenses, scleral expansion band), scleral radial incision by knife, silicon expansion plugs, laser scleral ablation, conductive keratoplasty, diode laser thermal keratoplasty, LASIK -presbyopia and accommodative [1,2].…”