BIOMETRY & IOL SELECTION
Refraction failure after IOL implantation
With the increasing quantity of patients who deceide for refractive cataract surgery & lens surgery, the demands on the predictability of refraction result in the range <± 0.5 diopters increases.   The frequency of forecast error >±1.0 diopters is given in the literature as about 10%. Deviations of ±0.75 diopters are seen in about 40% of all cataract patients.
Aspheric aberration-correcting IOLs
The design of modern aspheric IOLs take into account the average asphericity of the cornea, thus minimizing the spherical aberration. Patients benefit from a better contrast and night vision. This can only be given in full when the postoperative defocus was minimized by the optimal IOL selection.
That is why for the modern IOLs the accurate IOL calculation and selection is crucial success factor.
Also the intraocular positioning of the monofocal aspheric intraocular lenses affects patient satisfaction. Holladay et al. calculated a critical amount of the decentering of 0.4mm and for the tilting of seven degrees. 
The same high expectations of predictability of refraktion results do exist concerning multifocal IOLs. A perfect centering and rhexis, minimal postoperative residual astigmatism and a final refraction <0.5 diopters create the best conditions for patient satisfaction.
Laser Interference Biometry
Although the problem of preoperative determination of the IOL to be implanted with the help of biometrics is considered solved, the literature indicates that the postoperative result deviates by more than 1 diopters of the target refraction in 10% of the cases.
The alternative to the gold standard IOLMaster (Zeiss), the Lenstar ® (Haag-Streit) also provides the precise measurement of anterior chamber depth and thickness of the natural lens additionally to the measurement of the axial length and corneal radius.
Prediction error of the IOL formulas
The prediction error of the IOL formulas of the third generation for a "average eye" consistently low. In eyes with (extremely) long and short axis lengths the error increases significantly. In particular the inclusion of the anterior chamber depth, lens thickness and the refraction values of the aphakic eye is useful. 
Intraoperative optical refractive biometry and raytracing
The optical refractive biometry, means the intraoperative refraction measurement of the aphakic eye, could promise a validation of preoperative biometry and IOL selection and thus a safety just before the IOL injection.  For the calculation of the IOL aphakic measurement by autorefractometer there are already some studies  , showing good reproducibility.
With the higher measurement accuracy of the wavefront analysis it could be possible to validate with minimal additional effort the preoperative biometry and IOL selection just before IOL implantation. For this purpose extensive studies are still needed.
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