Author reply

Abstract

We thank Drs Feiz and Mannis for their interest in our article and believe their nomogram represents a valuable method to calculate intraocular lens (IOL) power after myopic excimer laser surgery. Directly using the original regression formula (IOL power understimation = −0.231 + 0.595 × change in spherical equivalent) would probably represent an even better approach, as it is likely to provide higher accuracy than the nomogram itself. For this reason, we included such a formula in the spreadsheet we and Kenneth J. Hoffer, MD, developed (Hoffer KJ. Hoffer/Savini LASIK IOL Power Tool. Paper presented at: American Academy of Ophthalmology Annual Meeting, November 2006, Las Vegas, Nevada). We agree that a slightly myopic outcome after cataract surgery may represent a desiderable outcome and is obviously better than postoperative hyperopia; however, such a result is not likely fully to satisfy post-LASIK/photorefractive keratectomy patients, who were used to and expect to achieve emmetropia. The predictability of IOL calculation as determined by the Feiz–Mannis nomogram could be further lessened in previously highly myopic eyes, where the correlation reported by Sanders and Kraff (0.67 diopters [D] of myopic shift/1-D increase in IOL power) may no longer be valid, and based on the findings of our study, the IOL power overestimation is more evident (see our article’s Figure 5). In addition, given the large variability of IOL power calculation by the nomogram as compared with the benchmark for comparison, we recommend caution because refractive surprises cannot be ruled out, as demonstrated by the authors themselves in their 2005 publication.1Feiz V. Moshirfar M. Mannis M.J. et al.Nomogram-based intraocular lens power adjustment after myopic photorefractive keratectomy and LASIK A new approach.Ophthalmology. 2005; 112: 1381-1387Abstract Full Text Full Text PDF PubMed Scopus (46) Google Scholar Even using the latest version of the nomogram with 0.5-D steps would not lead to noteworthy improvements; we reanalyzed our data and found that a higher IOL power would have been calculated (mean IOL power overstimation, 0.84±0.72 D vs. 0.64±0.68 D). Finally, when considering our study it should be stressed that most formulas theoretically achieving more accurate results than the Feiz–Mannis nomogram require knowledge of the presurgical corneal power; when this is available, it is very likely that these methods (such as the double-K clinical history method and separate consideration of anterior and posterior corneal curvatures, as well as the Feiz–Mannis formula) represent the most appropriate choice. Conversely, the Feiz–Mannis nomogram needs only the surgically induced refractive change, and we feel that its application will play a major role when this is the only available information. As a consequence, its predictability should be compared mainly with the other methods requiring this information alone, such as the formulas by Latkany and Masket, or those based on an adjusted keratometric refractive index.2Latkany R.A. Chokshi A.R. Speaker M.G. et al.Intraocular lens calculations after refractive surgery.J Cataract Refract Surg. 2005; 31: 562-570Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar, 3Masket S. Masket S.E. Simple regression formula for intraocular lens power adjustment in eyes requiring cataract surgery after excimer laser photoablation.J Cataract Refract Surg. 2006; 32: 430-434Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar, 4Jarade E.F. Abi Nader F.C. Tabbara K.F. Intraocular lens power calculation following LASIK: determination of the new effective index of refraction.J Refract Surg. 2006; 22: 75-80PubMed Google Scholar, 5Savini G, Barboni P, Zanini M. Correlation between attempted correction and keratometric refractive index after myopic excimer laser surgery. J Refract Surg. In press.Google Scholar IOL CalculationsOphthalmologyVol. 114Issue 5PreviewWe read with interest the article by Savini et al in the August 2006 issue on the subject of intraocular lens (IOL) power calculation after refractive surgery.1 The authors compared the accuracy of several different methods including the formula and the nomogram developed at our center.2,3 Although we agree with many of the findings of this excellent study, we raise a few points regarding some of the conclusions. Full-Text PDF