Abstract

DO.14.04

Performance of IOL loops under compression by shrinkage of the capsular bag

Roth E. H., Hoffmann C. G., Ludwig H. G. 
Institut für Physiologische Optik (IPO), Augenklinik Friedrichstadt, Düsseldorf

Objective: Capsular bag shrinkage after in-the-bag implantation may result in vertical displacement of the IOL due to compression of the IOL-loops that causes changes of focusing. There have been few approaches to average out the given capsular bag shrinkage by designing the IOL in a way, so that the compression is absorbed in the initial plane of the lens. Therefore a special measurement device was build to observe how the IOL-loops behave during the shrinkage of the capsular bag.
Methods: ISO 11979-3:2006 (ophthalmic implants part 3: mechanical properties and test methods) describes methods to observe changes of the IOL due to compression of IOL-loops down to diameter of 10 mm. These methods are suited for the measurement of forces and movements. But they give no information under the 10mm range. Also reciprocal effects between IOL-loops and capsular bag cannot be observed with this methods. To simulate how the IOL loops act in a capsular bag, while the bag shrinks from 12mm to 8mm, a new vacuum chamber technique was designed. As a model of the capsular bag a latex hose closed at one side was fitted in a cylindrical glass tube. The diameter of the bag was controlled by changing the pressure in the glass tube. The procedure applied to differently designed lenses was recorded by a video camera and the pictures evaluated by a computer program.
Results: Foldable three piece acrylat lenses with PMMA loops displace the optic of the IOL in the direction of the macula. In situ they will put on the backside of the capsular bag. During shrinkage one piece non foldable PMMA lenses rotate round the optical axis and do not displace the optic in direction of the optical axis. One piece foldable silicon and acrylat lenses with different designed loops displace the optic in direction to the iris along the optical axes.
Conclusions: Holes or other defects in the IOL-loops of one-piece-lenses seem to have a buffer effect at the beginning of the compression, but result mainly in the same structure as those do without them. Conventionally three-piece-lenses (PMMA or acrylat) have a very stable behavior compared to one-piece-Silicon-lenses.

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