Eyeworld

47 EW FEATURE January 2017 • All about IOL calculations References 1. Simon SS, et al. Achieving target refrac- tion after cataract surgery. Ophthalmology. 2014;121:440–444. 2. Kane JX, et al. Intraocular lens power formula accuracy: Comparison of 7 formulas. J Cataract Refract Surg. 2016;42:1490–1500. 3. Aristodemou P, et al. Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferom- etry. J Cataract Refract Surg. 2011;37:63–71. Editors' note: Dr. Holladay has fi- nancial interests with Abbott Medical Optics (Abbott Park, Illinois), AcuFocus (Irvine, California), Alcon (Fort Worth, Texas), ArcScan (Golden, Colorado), Carl Zeiss Meditec, Oculus (Arling- ton, Washington), and Visiometrics (Barcelona, Spain). Dr. Hoffer licenses the registered trademark name Hoffer to all biometer manufacturers to assure proper programming of the Hoffer Q and Hoffer H-5 formulas. Contact information Hoffer: KHofferMD@aol.com Holladay: holladay@docholladay.com most accurate over the whole axial length range. Of the 156 eyes in the study that had an axial length of 22 mm or less, the Holladay 1 formula had the lowest mean absolute prediction error (MAE), followed by the SRK/T, T2, Holladay 2, and Barrett Univer- sal II. The study authors reported the Haigis and Hoffer Q had the highest MAEs in this group, but noted that the differences between the formulas were not statistically significant. Of the 2,638 eyes between 22 mm and 24.5 mm in the study, the Barrett Universal II was found to be the most accurate with a statistically significant lower MAE compared to the other formulas. The Holladay 1 was found to be the next most accu- rate formula, but its difference was not statistically significant compared to the T2 or SRK/T formulas. The study authors wrote that the dif- ference was statistically significant when compared to the Holladay 2, Haigis, and Hoffer Q. The Barrett Universal II also had the lowest MAE in the medium-long eye group in this study (372 eyes), followed by the T2 and Holladay 1. The Barrett Universal II, SRK/T, T2, Haigis, Holladay 2, Holladay 1, and Hoffer Q, respectively, were found the most accurate in predicting IOL power for the 77 eyes that were 26 mm or greater. "[…] to our knowledge, [this] is the only study to assess 7 of the most commonly used IOL power for- mulas across the entire [axial length] range using a large enough patient cohort to detect differences between formulas," Kane et al. wrote of the study's significance. "[…] our study of 2,341 patients provides strong evidence that the Barrett Universal II formula is able to more accurately predict the post- operative refraction for eyes with a medium, medium-long, or long [axial length] compared with the 6 other IOL power formulas," Kane et al. concluded. "Although none of the formulas performed poorly, the marked difference between the Barrett Universal II formula and the other IOL power formulas for eyes with an [axial length] longer than 22.0 mm should prompt serious consideration of its use in these eyes by cataract surgeons worldwide." Commenting on this study, Dr. Hoffer said, "Their method of com- paring MAEs is inappropriate since absolute errors are not a normal Gaussian distribution. The authors should have compared the MedAE or performed the statistical boot- strapping technique on the data." He also noted, "The results in long and short eyes are exact- ly opposite of that found in the 8,108-eye U.K. study 3 using optical biometry, which showed the Hoffer Q to be statistically more accurate in short eyes and the SRK/T in very long eyes, as I first recommended in 1993." When it comes to preferred formulas, Dr. Hoffer said he would choose the Haigis formula with triple optimization, the Haigis-L for post-refractive eyes, and the new Hoffer H-5, especially in multi-racial groups. Dr. Holladay reiterated that he considers the Barrett Universal II, Olsen 2, and the Holladay 2 to be the best. EW AT A GLANCE • When doing calculations for a patient who has undergone previous refractive surgery, it's important to remember that the relationship between the front and back surface of the cornea has changed. • Different steps should be taken depending on the procedure the patient has had. • When choosing an IOL, it's important to account for induced spherical aberration. There may be a role for IOLs with extended depth of focus. by Ellen Stodola EyeWorld Senior Staff Writer Medicine, Houston; Samuel Masket, MD, Advanced Vision Care, Los An- geles, and clinical professor, David Geffen School of Medicine, UCLA; and Daniel Chang, MD, Empire Eye and Laser Center, Bakersfield, Cali- fornia, commented on how previous surgery could cause difficulties for surgeons, how these difficulties can Surgeons weigh in on how prior surgery might impact calculations C hoosing the correct IOL power can be challenging, and it can be even more so in patients who have undergone previous refrac- tive surgery. Douglas Koch, MD, professor and Allen, Mosbacher, and Law Chair in Ophthalmology, Cul- len Eye Institute at Baylor College of How previous refractive surgery affects IOL power choice Figure 1. A: Schematic conceptual relationship between the anterior and posterior corneal curvatures in the unoperated eye. B: Schematic conceptual corneal shape change after RK. C: Schematic conceptualized drawing of corneal shape after excimer photoablation for myopia. D: Schematic conceptualized drawing of corneal shape after hyperopic excimer photoablation. Source: Journal of Cataract & Refractive Surgery continued on page 50 be overcome, and which formulas and IOLs can be helpful. Calculations after refractive surgery There are at least three issues, Dr. Koch said. "One is that the anterior corneal surface is more irregular, Perfecting continued from page 46

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