Abstract
Introduction
In general, there are two types of intraocular lens (IOL) calculation formulas: axial length vergence formulas and refractive vergence formulas.1 IOL formulas such as Hoffer Q,2 Holladay I,3 SRK/T,4 and SRK II5, 6 require the measurement of axial length, keratometry, and an IOL constant.
Alternately, refractive vergence formulas do not require axial length measurements, instead, they require the preoperative refraction and manufacturer's IOL constant to calculate IOL power. Refractive vergence formulas assume that the patient has clear media and that no power, e.g. lens, will be removed.1
Refractive vergence formulas are suitable for phakic IOLs, secondary IOLs for aphakia as in this study, and piggyback lenses for pseudophakia.
Refractive vergence formulas include Lanchulev,7 Holladay R,8 Khan,9 and Mackool.10
This study compares mean of the difference between predicted post operative refraction values and actual post operative refraction values of Axial length vergence formula versus refractive vergence formula.
References
- Holladay J.T. Intraocular lens power calculations for the refractive surgeon J Operat Tech Cataract Refract Surg.1998;1(3):105–117.
- Hoffer K.J. The Hoffer Q formula: a comparison of theoretic and regression formulas.J Cataract Refract Surg. 1993; 19(6):700–712. Erratum 1994; 20(6):677.
- Holladay J.T., Prager T.C., Chandler T.Y., Musgrove K.H., Lewis J.W., Ruiz R.S. A three-part system for refining intraocular lens power calculations.J Cataract Refract Surg. 1988;14(1):17–24.
- Retzlaff J., Sanders D.R., Kraff M.C. Development of the SRK/T intraocular lens implantation power calculation formula.J Cataract Refract Surg. 1990;16 (3):333–340. Erratum 1990; 16(4):528.
- Sander D.R., Retzlaff J., Kraff M.C. Comparison of the SRK II formula and other second generation formulas.J Cataract Refract Surg. 1988;14:36–41.
- Dang M.S., Raj P.P. SRK II formula in the calculation of intraocular lens power.Br J Ophthalmol. 1989;73:823–826.
- Ianchulev T., Salz J., Hoffer K., Albini T., Hsu H., Labree L. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements.J Cataract Refract Surg. 2005 Aug;31(8):1530–1536.
- Holladay J.T. Refractive power calculate-ons for intraocular lenses in the phakic eye.Am J Ophthalmol 1993;116(1):63–66.
- Khan A.O., AlGaeed A. Paediatric secondary intraocular lens estimation from the aphakic refraction alone: comparison with a standard biometric technique.Br J Ophthalmol. 2006 Dec;90(12):1458–1460. Epub 2006 Aug 17.
- Mackool R.J., Ko W., Mackool R. Intraocular lens power calculation after laser in situ keratomileusis: aphakic refraction technique.J Cataract Refract Surg. 2006 Mar;32(3):435–437.
- Abdel-Hafez G., Trivedi R.H., Wilson M.E., Bandyopadhyay D. Comparison of aphakic refraction formulas for secondary in-the-bag intraocular lens power estimation in children. J AAPOS. 2011;15(5):432–434.
Corresponding Author
Dr Anirudh Duhan
IOL fellow Sankara Eye Hospital, Anand, Gujarat
DOI: https://dx.doi.org/10.18535/jmscr/v6i10.221
