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Intraocular lens calculation for cataract after previous radial keratotomy
1Fyodorov Eye Institute, St Petersburg Branch, Russia. stakheev@mail.ru
Purpose:
The purpose of this study is to discuss the major reasons for the hyperopic shift after cataract surgery following radial keratotomy (RK) and to find potential methods to improve the prediction of intraocular lens power (IOLP).
Methods:
The results for 18 cataract surgery eyes that had undergone RK were analysed retrospectively. The IOLP was calculated using Haigis, Hoffer Q, and SRK/II formulae with different keratometric measurements. Theoretical IOLP miscalculation ((delta)IOLP(K)) was assessed in order to define the optimal combination of different keratometric parameters and intraocular lens prediction formula.
Results:
The research revealed a significant temporary hyperopic shift after cataract surgery, the maximum value of which was noted in the first week post-operatively. Standard keratometers and placido-topography systems overestimate comeal power after RK. Corneal power overestimation correlates significantly with the spherical equivalent change after RK. Theoretical formulae (Haigis, Hoffer Q) produced the lowest (delta)IOLP(K) using calculated corneal powers derived from spherical equivalent change.
Conclusions:
Standard autokeratometry significantly overestimates corneal power after RK performed for moderate and high myopia. The use of calculated corneal power and third-generation theoretical formulae seems to be the most appropriate for IOLP prediction.