Michael Goodman, Alexandra Paul and Andrew Hsu Effect of Corneal Curvature on Accuracy of IOL Power Calculations in Patients Having Standard and Premiums IOLs Ralph Falkenstein, MD Michael Goodman, Alexandra Paul and Andrew Hsu The authors have no financial interest in the subject matter of this e-poster

Introduction In the past, great attention has been played to the role of the axial length in creating lens power errors. Little information is available as to what role corneal curvature plays in lens power errors, especially since the onset of temporal topical surgery. This study reviews a series of over 189 cataracts surgery and attempts to analyze the role the cornea in lens power errors.

Methods After obtaining IRB approval for this study, the charts of 189 patients were examined retrospectively and selected in a sequential fashion, excluding all patients with any retinal or ophthalmic condition, to obtain the following information: sex age preoperative K1 reading preoperative K2 reading with axis axial length lens type with “A” constant chosen lens power postoperative prescription including sphere, cylinder and axis postoperative visual acuity ocular and medical history The IOL Master was used to create predicted postoperative refractive error for the chosen lens power through the use of three formulas: The Hoffer Q formula The Holladay formula The SRK/T formula

Calculations The results of these formulas were examined and used in the following manner, according to Hoffer: Patients that had axial lengths between 22 and 25, the convention of averaging these formulas was used to create a “predicted” postoperative refraction. Those patients with axial lengths less than 22 were compared using the Hoffer Q formula, while those patients with axial lengths between 25 and 26 used the Holladay formula. Patients with axial lengths greater than 26 mm used the SRK/T formula. The postoperative refraction was then made into its spherical equivalent. The predicted refraction was then subtracted from the actual refraction. The absolute value of this difference was created. The results were then segregated into groups based on axial length and average K values and the results of all patients with monofocal implants were graphed to observe trends. Similar calculations were made for patients with accommodative and multifocal lenses.

Spherical equivalent Error vs. Axial length There were no trends.

Spherical Equivalent Error vs. Grouped Average K Values The higher R2 value suggests that error occurs to a greater degree at higher K values.

Results in Table Form K value group aver error abs error 40 -0.250 41 -0.656 0.656 42 -0.358 0.460 43 -0.121 0.526 44 -0.368 0.574 45 -0.432 0.773 46 -0.675 0.675 47 -0.375 0.875

Comparison of Spherical equivalent Errors: Low K Values (<44 Comparison of Spherical equivalent Errors: Low K Values (<44.5) vs High K values (>44.5) Low Ks High Ks 0.532609 0.622283 ttest 0.047 The results suggest that steeper corneas behave different than flatter corneas

absolute average error standard deviation of average error Premium Lens Errors   average SE error absolute average error standard deviation of average error Restor 3 -0.3364 0.8711 0.8537 crystalens HD -0.2105 1.1842 0.9255 Crystalens 50 series -0.5042 1.0991 1.4625 These results were not statistically significant

Statistical Difference between High and Low K readings T test results comparing Restor with low K (<44.5) values vs. Restor with High K (>44.5) values show a p<.07 and for a comparison of the Values for Crystalens with low K value vs Crystalens with High K values showed a p < .03.

Wound Design and Steep corneas These types of refractive surprises in a population of Crystalens patients has been described previously and attributed to transient wound leaks which quickly reseal, but result in a forward positioning of the accommodating lens. Steeper corneas require the surgeon to tilt back his hand and proceed in a more anterior fashion which can lead to a surprised early entry into the cornea – thus decreasing the length of the self-dealing wound.

Lasting Thoughts This study suggest a value in further studying steeper K values and their effect on intraocular lens power calculations for all lenses, but especially accommodative lenses. In addition, the study supports the continued use of a suture in accomodative lenses, which was not done in any patient in this study.