Computer model provides vital information about lens accommodation

During accommodation, changes in lens thickness are mainly caused by deformation of the nucleus. In older, non-accommodating lenses, the deformations occur predominantly in the equatorial region and do not affect the central curvatures of the lens, according to a report published online ahead of print by Acta Ophthalmologica.

Rob G. L. van der Heijde from Vrije Universiteit Medical Centre, Amsterdam and Henk Weeber from AMO, The Netherlands, created a computer-based mechanical model of accommodation using the finite element method. The lens geometry of the model was based on in vivo measurements of human lenses in the accommodated state. The mechanical properties of the lens were based on ex vivo measurements of the human lenses. To achieve a state of disaccommodation, the lens equator was stretched by 7%. The internal strains and displacements were calculated for a young accommodating lens, a lens of pre-presbyopic age and a lens of presbyopic age (20, 40 and 60 years old, respectively).

The model demonstrated that radial strain was maximal in the nucleus for the young accommodating lens and minimal in the nucleus for the oldest non-accommodating lens. In the young lens the deformations were concentrated in the equatorial region.