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J Cataract Refract Surg. 2010 Jan;36(1):87-96. doi: 10.1016/j.jcrs.2009.07.011.

Intraocular lens power calculation after laser refractive surgery: corrective algorithm for corneal power estimation.

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  • 1Guangdong Eye Institute, Guangdong Academy of Medical Sciences, Guangzhou, China.

Abstract

PURPOSE:

To evaluate an algorithm for corneal power estimation in intraocular lens (IOL) power calculation after myopic laser refractive surgery using direct corneal measurements.

SETTING:

International Vision Correction Research Centre, University of Heidelberg, Heidelberg, Germany.

METHODS:

Corneal parameters in normal eyes and eyes of refractive surgery cases were evaluated by rotating Scheimpflug imaging. Corneal optical power (K(optical)) calculated by a Gaussian optics formula was simplified as K(optical) = K(anterior) + K(2) (K(anterior) = anterior corneal power; K(posterior) = posterior corneal power; K(2) = K(posterior)--K(anterior) x K(posterior) x corneal thickness/1.376). The variation and change in K(2) induced by refractive surgery were analyzed. A corrective algorithm to calculate K(optical) using mean K(2) (-6.10 diopters [D]), K(corrective) = 1.114 x measured K - 6.10, was derived based on statistical analysis, which was in accordance with the modified Maloney method. The IOL power after refractive surgery was calculated using K(corrective).

RESULTS:

The mean K(2) of normal and post-refractive corneas was -6.10 +/- 0.23 D and -6.16 +/- 0.17 D, respectively (P = .17). The mean refractive surgery-induced change in K(2) was -0.06 +/- 0.10 D. The variations in K(2) were small (95% confident interval, -6.55 to -5.65 [normal cornea]; -6.48 to -5.70 [pre-refractive]; - 6.49 to -5.83 [post-refractive)]. Using K(corrective) for IOL power calculation in post-refractive cases yielded mean absolute prediction errors of 0.58 +/- 0.52 D (Haigis), 0.59 +/- 0.49 D (double-K Hoffer Q), and 0.58 +/- 0.47 D (double-K SRK/T).

CONCLUSION:

The algorithm that induced low error in corneal power estimation was relatively reliable in IOL calculation after myopic laser refractive surgery.

FINANCIAL DISCLOSURE:

No author has a financial or proprietary interest in any material or method mentioned.

Copyright 2010 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

PMID:
20117710
[PubMed - indexed for MEDLINE]
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