Biomechanical modelling of the human eye 24. September Zoltán Bocskai Imre Bojtár 18th Inter-Institute Seminar for Young Researchers Medical partner: Dr. Andrea Kerek Honvéd Hospital - Department of Opthamology, 1134 Budapest - Róbert Károly körút 44.

Content - Subjects of the research - Physiology of the human eye - Geometry of the eye - Material properties - Refractive eye surgeries - The FE model for analyses 2 18th Inter-Institute Seminar - Z. Bocskai !

Subjects of the Research The process of the accommodation (Helmholtz, Schachar) The reasons of presbyopia* (changes of geometry and material parameters): causes, symptoms and treatment? The effect of refractive eye-surgery (diminish of the cornea) *presbyopia: Presbyopia usually begins around the age of 40, when people experience blurred near vision during reading, sewing or working at the computer. 3 18th Inter-Institute Seminar - Z. Bocskai

4 Anatomy of the human eye The human eye is an organ which reacts to light for several purposes. RodRod and cone cells in the retina could conscious light perception and vision including color differentiation and the perception of depth.coneretina 18th Inter-Institute Seminar - Z. Bocskai

5 Accommodation of the eye The diameter of the eye: mm. The cornea, the aqueous humor, and the vitreous body have 42 D refractivity The lens refractivity is changeable: D The sum of the four refractive parts: ≈66 D The light-ray goes through four refractive parts: cornea, aqueous humor, lens, vitreous body. But only the lens is able to change its refractivity. ! 18th Inter-Institute Seminar - Z. Bocskai

6 Accommodation of the eye Helmholtz (1909) Schachar (1993) The lens is held in a state of radial tension by the zonular fibres that connect the ciliary body to the lens equator. During accommodation, contraction of the ciliary muscle causes the tension in the zonular fibres to reduce and, as a consequence, the lens changes its shape. This change in shape causes the optical power of the lens to increase. The ciliary body causes tension just several parts of the zonular fibers. In few fibers arise compression. ! 18th Inter-Institute Seminar - Z. Bocskai

The geometrical parameters 7 The lens: The lens size is age-related. 18th Inter-Institute Seminar - Z. Bocskai

8 The material properties of the human eye The material properties are age-related: with age the elasticity will be more rigid. 18th Inter-Institute Seminar - Z. Bocskai

Refractive eye-surgeries 18th Inter-Institute Seminar - Z. Bocskai 9 - PRK (Photorefractive keratectomy) - LASIK (Laser-Assisted in-Situ Keratomileusis) - IntraLASIK !

Anathomy ANSYS 3D continuum model 1018th Inter-Institute Seminar - Z. Bocskai FEM model

Some details from the complex model The geometry of my model Ciliary body Sclera Cornea Iris Lens cortex Capsule Lens nucleus Aqueous humor Zonula fibers Vitreous body 18th Inter-Institute Seminar - Z. Bocskai

The geometry of the model with fat and muscles 12 18th Inter-Institute Seminar - Z. Bocskai

13 Frictional connection: - Aqueous humor contacts - Vitreous body contacts - Between lens nucleus and cortex - Between lens capsule and cortex Material properties: - Linear elastic, isotropic  except cornea and sclera (Uchio 1999) Constructed model Geometry section 18th Inter-Institute Seminar - Z. Bocskai

14 Three-dimensional model - 3D solid meshing The muscles are not axi-symmetric. Fat Eyeball Lens & zonulas Muscles 18th Inter-Institute Seminar - Z. Bocskai

First result of the complex model Load: self-weight Total deformation Normal stress – X direction Equivalent stress Further results are in progress! 15 18th Inter-Institute Seminar - Z. Bocskai

16 First result of the complex model Lens equivalent elastic strain Eyeball - Normal stress – X direction Sclera - shear stress - XY direction Further results are in progress!

Thank you for your attention! 1718th Inter-Institute Seminar - Z. Bocskai