We read with interest the article by Jarade and Tabara1 concerning a new formula to calculate intraocular lens (IOL) power after laser in situ keratomileusis (LASIK). We would like to congratulate them for their interesting research even if, as they state, there are several limitations to this study, among them that it was dependent on preoperative data. However, we would like to make some comments.
The authors stated that their formula was as accurate as the clinical history method. Unfortunately, several authors have shown that this method is not very accurate, whereas a new historical method, the double-K, seems to be more precise.2
We were surprised to read in the conclusion that a new method should be developed to allow simple prediction of K-readings after LASIK, and in the meantime, all the patients should have a card reporting their preoperative data and the stabilized refraction before lens opacity develops. The authors forgot to mention that at least 3 papers have shown a way to calculate the IOL power in these patients if the preoperative parameters and the amount of treatment are unknown. Among these, we were the first to publish a regression formula related to the axial eye length that should be used to calculate a correcting factor to be multiplied by the corneal radius to better measure the postoperative K-readings: y = 0.0276 × AL + 0.3635.3 With this formula, there is no need to know the preoperative parameters; the most important aspect of our regression formula is that it is axial eye length related. This should make the formula quite precise; most patients who have had refractive surgery should have an axial myopia, as patients with myopia due to changes in refractive index (ie, with a nuclear cataract) or with curvature myopia (ie, with keratoconus) should be excluded from the treatment. Moreover, if regression due to the change in corneal curvature is present, it should not make a great difference as we apply the correcting factor to the corneal radius that will change with the regression.
Nicola Rosa MD
Luigi Capasso MD
Michele Lanza MD
1. Jarade EF, Tabbara KF. New formula for calculating intraocular lens power after laser in situ keratomileusis. J Cataract Refract Surg 2004; 30:1711-1715
2. Aramberri J. Intraocular lens power calculation after corneal refractive surgery: double-K method. J Cataract Refract Surg 2003; 29:2063-2068
3. Rosa N, Capasso L, Romano A. A new method of calculating intraocular lens power after photorefractive keratectomy. J Refract Surg 2002; 18:720-724