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IOL Power Calculation in Post-LASIK/PRK Eyes: Challenges, Methods, and Accuracy

This article discusses the challenges faced in determining true corneal refractive power and the problems with current IOL formulas. It explores various IOL power calculation methods, including the use of historical data, and evaluates the accuracy of OCT-based formulas. The study also compares the accuracy of Galilei in IOL power calculation in eyes with prior myopic LASIK/PRK and RK.

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IOL Power Calculation in Post-LASIK/PRK Eyes: Challenges, Methods, and Accuracy

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  1. Financial Disclosure I have a financial interest with the following companies: Abbott Medical Optics Alcon Calhoun Vision NuLens Optimedica Optivue

  2. IOL power calculations in post-LASIK/PRK eyes Douglas D. Koch, M.D. Cullen Eye Institute, Baylor College of Medicine, Houston, TX

  3. Challenges Difficulties in determining true corneal refractive power Keratometric inaccuracy Invalid use of effective refractive index of cornea (1.3375) Problems in 3rd and 4th generation IOL formulas Inaccurate estimation of ELP Exception: Haigis formula

  4. So many formulas. . So we developed: http://www.ascrs.org/

  5. IOL power calculation

  6. Prior myopic-LASIK/PRK

  7. Double-K Holladay 1 and Haigis-L formulas 3 categories of formulas

  8. 3 categories • Traditionally “Gold” standard • KEY – accurate historical data • Data error 1:1 ratio • Use a fraction of ∆MR • Data error ↓ to 20 – 30% • Rely only on current data

  9. Pop-up windows explain methods used

  10. Prior hyperopic-LASIK/PRK

  11. Prior RK

  12. Monthly visits to the calculator in 2010

  13. Patients 2 study centers Consecutive cases of IOL implantation in eyes with prior myopic-LASIK SN60WF 72 eyes of 57 patients included Mean age: 58 ± 8 years (range 42 to 77 years) Myopic LASIK correction: 5.10 ± 2.55 D (range 0.98 to 11.21 D)

  14. Methods IOL prediction error = IOL implanted – IOL calculated Negative value  myopic results Consistency of prediction performance F-test for variances

  15. A S A 4.0 A A A A A A A A A 2.0 A 0.0 IOL prediction error (D) A A -2.0 A A -4.0 A A Masket Haigis-L Shammas Feiz-Mannis Clinical History Adjusted EffRP Corneal Bypass Modified-Masket Adjusted Atlas0-3 Average IOL power Wang-Koch-Maloney

  16. Variances of IOL prediction errors (SD2) - consistency of performance * * Significant differences (all P<0.05 with Bonferroni correction)

  17. Refractive prediction error Proposed UK NHS benchmark in normaleyes*: 85% ±1.0 D 55% ±0.5 D Met benchmark in normal eyes but well below latest standards *Significant lower % with historical methods (P<0.05). Gale RP, et al. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye. 2009;23:149-52

  18. Summary Using double-K Holladay 1 formula Greater prediction errors and variances with methods requiring Pre-LASIK Ks and ∆MR Use 100% of historical data Superior and essentially equivalent results with: Methods using a fraction of ∆MR and Methods using no prior data

  19. Optical coherence tomography (OCT) RTVue-CAM: an Fourier domain OCT system for both retinal and corneal imaging RTVue with CAM module

  20. Net Corneal Power (NCP):Combines anterior & posterior curvature measurements from OCT meridional scans 1.5mm 1.5mm n0 = 1 D n1 = 1.376 Ra Rp n2 = 1.336

  21. Evaluation of OCT-based formula IOL power calculation in post-LASIK eyes 12 eyes at Cullen Eye Institute 8 eyes at Doheny Eye Institute Refractive correction: -4.04 ± 3.60 D (range -0.88 to -9.81 D)

  22. OCT-based IOL power formula • ELP = 0.711 * (AL – ACD) – 0.25 * Pp + 0.623 * ALadj + pACD – 8.11 • Where • AL = axial eye length (mm) • ACD = Anterior chamber depth (mm) • Pp = posterior corneal power (D) • ALadj = sqrt(AL) if AL < 24.4mm • sqrt(AL+0.8*(AL-24.4)), if AL > 24.4mm • pACD = personalized ACD (ACD-constant) *Tang M, Li Y, Huang D. An Intraocular Lens Power Calculation Formula Based on Optical Coherence Tomography: a Pilot Study. J Refract Surg. 2010;26(6):430-437

  23. Refractive prediction error *P=0.65, n = 20 eyes of 15 subjects.

  24. Refractive prediction error • Within 0.5D: • Haigis-L: 11/20 • OCT: 10/20 • Within 1D: • Haigis-L: 15/20 • OCT: 19/20

  25. Summary Limitation: Small numbers Performance of OCT-based IOL formula was not compared to many methods on the ASCRS calculator Further studies desirable

  26. Recent study Accuracy of Galilei in IOL power calculation in eyes with prior myopic LASIK/PRK Consecutive cases of IOL implantation between April 08 to Feb. 11

  27. Patients 19 eyes of 16 patients had all historical data Myopic LASIK correction: 4.28 ± 2.61 D (range 0.88 to 8.50 D)

  28. Refractive MAE with all methods (n=19) 0.99 1.0 0.94 0.93 0.78 0.75 0.8 0.72 0.70 0.65   0.57 0.57 0.6   MAE (D) 0.52 0.47 0.44 0.42 0.4 0.2 0.0 Haigis-L Shammas Masket TCP-5mm TCP-4mm TCP-2mm TCP-3mm Feiz-Mannis Clinical History Adjusted EffRP Corneal Bypass Modified-Masket Adjusted Atlas0-3 Wang-Koch-Maloney 1.2 Galilei Significant greater MAE with methods using pre-LASIK Ks and ∆MR than those with  (all P<0.05)

  29. Refractive prediction error with all methods (n=19) 100 95 89 89 90 84 79 79 79 80 +/- 0.5 D 74 74 74 74 68 68 +/- 1.0D 70 63 58 58 58 60 53 53 47 % of eyes 50 42 40 32 32 32 32 32 26 30 21 20 10 0 Haigis-L Masket TCP-4mm TCP-5mm TCP-2mm TCP-3mm Shammas Feiz-Mannis Clinical History Adjusted EffRP Corneal Bypass Modified-Masket Adjusted Atlas0-3 Wang-Koch-Maloney UK NHS benchmark 85% ±1.0 D 55% ±0.5 D Galilei

  30. Accuracy of IOL power calculation in eyes with prior RK

  31. Purpose Because RK eyes have variable front and back curvatures, IOL calcs are especially challenging To evaluate the accuracy of 4 devices for calculating corneal power for IOL calculations in RK eyes undergoing cataract surgery IOLMaster, EyeSys, Atlas, Galilei

  32. Patients Consecutive cases of IOL implantation between April 08 to February 11 27 eyes of 18 patients, age 47 to 79 years

  33. Refractive mean absolute error (MAE) with different devices 0.8 0.67 0.7 0.66 0.65 0.58 0.6 0.5 MAE (D) 0.4 0.3 0.2 0.1 0.0 EyeSys EffRP IOLMasterK Atlaszone0-3 TCPannuli1-4 Galilei TCPannuli1-4 tended to produce smallest MAE (all P>0.05).

  34. Refractive prediction error +/- 0.50 D 90 85 85 85 +/- 1.0 D 78 80 70 59 60 52 50 % of eyes 40 33 30 30 20 10 0 EyeSys EffRP IOLMaster K Atlaszone0-3 TCPannuli1-4 UK NHS benchmark 85% ±1.0 D 55% ±0.5 D Proposed benchmark for normaleyes: Gale RP, et al. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye. 2009;23:149-52.

  35. Galilei Needs further work to improve IOL calculations after LASIK Helpful in eyes that have undergone radial keratotomy

  36. Thank you for your attention

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