Three-dimensional ultrasound biomicroscopy, environmental and conventional scanning electron microscopy investigations of the human zonula ciliaris for numerical modelling of accommodation.
OBJECTIVE
Biomechanical modelling of the accommodation process is a useful tool for studying the mechanism of accommodation and presbyopia and can aid in the development of accommodative lens-replacing materials. Existing biomechanical models, however, use a very simplified zonula structure. The aim of this study was to use three-dimensional ultrasonic imaging and scanning electron microscopy to provide a more detailed, three-dimensional description of the structure of the human zonula to improve the modelling of accommodation.


METHODS
Five human eyes were examined without invasive manipulation using a custom-made three-dimensional ultrasonic imaging technique that allows scanning of features with a spatial resolution of 30 microm. Environmental and conventional scanning electron microscopy (SEM) provided information to complement the ultrasonic images for use in development of a more anatomically correct finite-element model of the zonula structures. These data along with the material properties of the ocular tissue structures were used to construct an advanced geometric model for finite-element simulation of the accommodation process.


RESULTS
Images were obtained through three-dimensional ultrabiomicroscopy (3D-UBM) of anatomical features heretofore not directly imagable in their native state. Ciliary processes and zonula structures were clearly separated by both the 3D-UBM and the SEM methods. It was found that fibres inserting on the anterior and posterior lens capsule emerge anteriorly at the ciliary body. Fibres emerging near the pars plana insert on the lens and the ciliary body. No X-shaped crossing fibres were found. Modelling of the accommodation process with both the simple and the more complex geometric models produced refractive power changes comparable with in vivo findings.


CONCLUSIONS
The 3D-UBM allowed examination of zonula structures in their native state with minimized preparation artefacts. While these data were incorporated into a complex and more anatomically correct finite-element simulation of intraocular features including lens, zonular system and ciliary body it was found that a simplified zonular model is sufficient for the numerical simulation of the accommodation process.
Stachs
Oliver
O
Eye Clinic, University of Rostock, Doberaner Strasse 140, 18055 Rostock, Germany. oliver.stachs@med.uni-rostock.de
Martin
Heiner
H
Behrend
Detlef
D
Schmitz
Klaus-Peter
KP
Guthoff
Rudolf
R
D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D000368:Aged; D000869:Anterior Eye Segment / Q000000981:diagnostic imaging; D002924:Ciliary Body / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008022:Ligaments / Q000000981:diagnostic imaging* / Q000648:ultrastructure*; D033401:Microscopy, Acoustic / Q000379:methods*; D008855:Microscopy, Electron, Scanning / Q000379:methods*; D008875:Middle Aged; D008954:Models, Biological