[Anisometropia and aniseikonia--unsolved problems of cataract surgery].
OBJECTIVE
Aniseikonia is one of the relevant unsolved problems of modern cataract surgery and may cause severe functional problems such as deteriorated binocular vision, diplopia or headaches. The aim of the present study is to assist the clinician as to how to estimate lateral magnification in a pseudophakic eye and how to reduce or eliminate aniseikonia.


METHODS
Based on the characterisation of a centred optical system in the paraxial space, the optical system eye is modelled with 2 x 2 matrices and the lateral magnification is extracted. This method is applied on the "thin lens model" as well as the "thick lens model" and illustrated in detail with 4 working examples. Additionally, we demonstrate how a predefined lateral magnification (e. g., from the contralateral eye) can be realised during cataract surgery by calculating an appropriate combination of an IOL and a spectacle correction. WORKING EXAMPLES: In example 1 the lateral magnification of the reference eye following cataract surgery is determined. In example 2 we estimate the lateral magnification behaviour that is expected after cataract surgery using the same IOL as in example 1. Example 3 gives an overview of how the magnification varies if the IOL position in the eye, the geometry of the lens or the central thickness is changed. Example 4 shows how to calculate an appropriate combination of an IOL and spectacle correction to realise an eikonic imaging of both eyes.


CONCLUSIONS
The present study should sensitise ophthalmic surgeons for the still unsolved problem of aniseikonia after cataract surgery and should give them a simple mathematical tool to help determine object-image magnification and show how to reduce or eliminate aniseikonia during cataract surgery.
Langenbucher
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Institut für Medizinische Physik, Universität Erlangen-Nürnberg. achim.langenbucher@imp.unierlangen.de
Szentmáry
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