الفهرس 
Principles of IOL Power CalculationOnly 14 pages are availabe for public view
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Abstract
Modern technology has significantly improved our ability to accurately measure ocular biometrical parameters. Hence, today, we are more confident fulfilling patient expectations. However, it is still very important to pay attention to, accurate biometry, and right IOL power formula selection. Eventually, the highest variable parameter is going to establish the outcome. In order to increase accuracy in ocular biometry practice, one must have sought the following realizations: properly calibrated instrument and an experienced operator, repeating measurements, using optical biometry rather than contact biometry, using last generation IOL formulae and tailoring the IOL constants accordingly, and evaluating refractive outcomes regularly. By following each step carefully understanding strengths and weaknesses during all these steps, successful outcomes are achievable. In our study, we used three different IOL power calculation formulae with the A scan guided biometry device and the IOL master device for biometry. Our findings indicated that Haggis a fourth generation formula would give the best refractive outcomes in high axial lengths. This is in contrast to the other two formulae which shows a tendency for hyperopic shift, that was smaller with Hoffer Q formula with mean PE of (+0.37± 0.41 D) than with the SRK -T formula with mean PE of (+0.51± 0.59 D). While, Calculation of IOL power in long eyes resulted in tendency for hyperopic shifts with the all three formulae, this hyperopic shift was minimal with Haggis formula (0.16 ± 0.58 D), followed by SRK -T (+0.34± 0.65 D), and Was largest with Hoffer Q formula (+0.84± 0.63 D). The Haggis formula, a fourth-generation formula, may have performed better than the others because of its inclusion of the IOL master-measured anterior chamber depth (ACD). Third-generation formulae such as the Hoffer Q, and SRK/T are 2-variable formulae that rely on AL and central corneal power to predict the postoperative IOL position. These formulae do not use actual measurements of the ACD; they assume that short eyes will have shallower ACDs and long eyes will have deeper ACDs, which are not always the case; this may be the reason why these formulae were less accurate in this study. Haigis formula in high myopic cataract patients is the best formula with minimal post-operative spherical equivalent errors as compared with SRK/T. We recommend the application of this formula in the high myopic cataract patients in calculation of IOL power and we hope to evaluate accuracy of Haigis formula in wide range group with variant refractions and axial lengths (emmetrope and hyperopic patients) and compare its results with different formulas to reach the answer of the old question what is the best formula? And also we recommend to compare our A scan guided biometry results with results of optical biometry partial coherence interferometry ( IOL master and lens star ) with all known formulas and not only our 3 selected formulas to evaluate the cost benefit of this new expensive instrument as compared with classic one.