R 450
Anatomy and biomechanics of the zonular apparatus and its coupling to the lens
K. Ludwig
Introduction: Accommodation is brought about by the three-dimensional interplay of crystalline lens, zonular apparatus, ciliary muscle and its elastic suspension. The zonular apparatus, as a three-dimensional arrangement of elastic fibers, translates any accommodative distorsion and movement of the ciliary muscle into a corresponding change in the shape of the lens. The details of this interplay, however, are still a matter of ongoing scientific debate, not least because, under natural conditions, the essential components of the accommodative system are difficult to be observed.
Methods: In-vitro results from light- and electron microscopy and in-vivo results from Scheimpflug-photography and, more recently, from high-resolution ultrasound-biomicroscopy, allow a detailed description of the zonular structure and can add some new features to the understanding of accommodative dynamics.
Results: The longest section of zonular fibers extends, as a broad fiber carpet, between the ora serrata and an area characterized by tension fibers, first described by Rohen and Rentsch. The shorter anterior zonular section is grouped into periequatorial, to a smaller extent also equatorial bands, inserting under different angels at the peripheral lens capsule. The lens equator as the force resultant of the transmitted tensile forces is situated anterior to the lens center.
Discussion: The posterior zonular section between ora serrata and ciliary muscle apex may contribute an important component to the elastic forces acting on the inner ciliary muscle groups. The anterior zonular section yields a sophisticated, rotational symmetric transmission of tensile forces to the peripheral lens capsule. The position of the lens equator anterior to the lens center should lead to compression forces acting mainly on the anterior lens cortex. It has, therefore, a potential to explain the aspheric change of the anterior lens surface under near-accommodation.
Department of Ophthalmology, Ludwig-Maximilians-University Munich, Mathildenstr. 8, D 80336 München