Reflection on refraction in multifocal intraocular lenses - Chapter 7: General discussion

Hele tekst

(1)CHAPTER 7 DISCUSSION.

(2)

(3) Discussion. DISCUSSION This thesis presents visual and refractive results of multifocal intraocular lens (IOL) implantation after previous refractive laser surgery in myopic and hyperopic eyes, including retreatments, and also identifies the best IOL power calculation formula to use in these specific patients. Multifocal IOL after corneal refractive laser surgery In the last few decades millions of treatments by corneal refractive laser surgery have been done. When these patients develop presbyopia or cataract a multifocal IOL can be considered to restore their independence of spectacle use. In time surgeons have developed experience with different types of multifocal IOL and good results in terms of refraction and visual acuity for distance and near can be achieved with high satisfaction rates.1 Known visual side-effects are halos and glare. Surgeons might be reluctant to implant multifocal IOLs in patients after refractive laser surgery because of the proposition that corneal laser surgery alters the cornea in such way that implanting a multifocal IOL might deteriorate visual acuity and visual quality. Also, accuracy problems in IOL power calculation complicate these cases. However, not many reports have been published about the use of multifocal IOLs in these specific patients2 and there are no clearly defined parameters regarding which eyes should be ruled out for multifocal IOLs. Muftuoglu et al3 described a cohort of 49 eyes of 38 patients with an Acrysof ReSTOR (Alcon Laboratories, Inc) IOL after previous myopic refractive laser and found a mean uncorrected distance visual acuity (UDVA) of 0.23 logarithm of minimum angle of resolution (LogMAR), 65% of eyes within ± 0.50 D of emmetropia and 84% of eyes within ± 1.00 D of emmetropia. In Chapter 2 of this thesis we describe a myopic cohort of 77 eyes of 43 patients with a mean UDVA of 0.14 ± 0.22 LogMAR and a slightly lower percentage (57%) of eyes within ± 0.50 D of emmetropia, and a comparable percentage (86%) of eyes within ± 1.00 D of emmetropia. We discovered that in eyes with myopia equal to or greater than 6.00 D the results were less predictable (absolute error of mean spherical equivalent of 1.00 D versus 0.54 D). Fernández-Vega et al4 compared the results of two types of multifocal IOL in a cohort of 22 (Acrysof ReSTOR (Alcon Laboratories, Inc)) and 26 eyes (Acri.Lisa (Acri. Tec)). The mean UDVA was 0.09 ± 0.12 and 0.04 ± 0.12 LogMAR respectively, and there was a much higher predictability of 86% and 85% within ± 0.50 D respectively; 100% within ± 1.00 D of emmetropia was described. However, the authors did not indicate whether these results were achieved before or after refractive enhancement and the cohorts are much smaller, which makes it difficult to compare these outcomes with our results in Chapter 2.. 91. 7.

(4) Chapter 7. In eyes after hyperopic laser surgery only one other study was published dealing with multifocal IOLs.5 In a cohort of 41 eyes of 23 patients a mean UDVA of 0.11 ± 0.10 LogMAR was described, with a predictability of 73% of eyes within ± 0.50 D and 100% within ± 1.25 D of emmetropia. In Chapter 3 we describe the results of a cohort of 40 eyes of 40 patients after hyperopic laser treatment. The mean UDVA was 0.16 ± 0.18 LogMAR and we found a predictability of 63% of eyes within ± 0.50 D and 88% of eyes within ± 1.00 D of emmetropia. These results are hard to compare with the results of Alfonso et al because these authors also did not indicate whether the results were achieved before or after refractive enhancement, the patient cohort was smaller than ours, and for some reason not the percentage of eyes within ± 1.00 D but those within ± 1.25 D was presented in the article. In the cohorts described in this thesis, patients were included for multifocal IOL implantation after examination of corneal topography. When irregularity was found on topography, especially a decentred ablation, patients were excluded. However, we realize that evaluation of other visual quality parameters, such as aberrometry and contrast sensitivity, were not included in these studies. Future research is needed to assess these aspects of visual quality in these specific patients. Residual refractive error Emmetropic outcome is important in multifocal IOL implantation. In eyes without previous laser surgery and multifocal IOLs corneal laser enhancements for residual refractive error are shown to be safe, effective and predictable.6 Enhancements are reported to be necessary in 11%7 to 35%8 of cases. There is scant information about refractive enhancements in patients with multifocal IOLs after previous refractive laser surgery. Muftuoglu et al3 reported a laser enhancement rate of 43%, with 10% of patients needing more than one enhancement to reach the desired refractive result. The most common complications of corneal laser enhancement after previous refractive laser surgery include infection, stromal haze formation, and epithelial ingrowth in cases where the LASIK flap was re-lifted.9, 10 In Chapter 4 we describe enhancements for residual refractive error in a cohort of 39 eyes with multifocal IOL implantation (Acrysof ReSTOR (Alcon Laboratories, Inc)) after previous corneal refractive laser surgery. We found that in 15% of cases more than one treatment was necessary to reach a satisfactory result. This percentage is slightly higher than the 10% in the study by Muftuoglu et al.3 More complications were seen with the LASIK flap lift procedures in comparison with surface ablation and we concluded that it might be safer to perform surface ablation instead of LASIK flap lift, which was in line with other studies in eyes with monofocal IOLs after refractive laser surgery.9, 10. 92.

(5) Discussion. IOL power calculation after refractive laser surgery To calculate the correct IOL power for an eye the axial length, the corneal power and the estimated lens position are needed. In eyes after refractive laser surgery inaccurate IOL power calculation will occur with the standard IOL power calculation formulas for three main reasons: the instrument error, the error in the index of refraction and the formula error11, 12 (see Chapter 1). In eyes with previous myopic laser surgery this will lead to a hyperopic refractive surprise. In eyes with previous hyperopic laser treatment the opposite will occur: a myopic outcome. Various IOL power calculation formulas for eyes after refractive laser surgery have been developed. However, no consensus has yet been reached as to which formula is best to use in these specific eyes. The American Society of Cataract and Refractive Surgery (ASCRS) developed an online IOL power calculator to facilitate comparison of different IOL power calculation formulas for eyes after refractive laser surgery (www.iolcalc.org). Over time less accurate formulas have been removed and newer formulas have been added. Wang and colleagues13 compared the optical coherence tomography (OCT)-based IOL power formula and the Barrett True-K formulas with other methods of the ASCRS calculator and found promising results for these newer formulas. Based on this study the OCT-based formula and Barrett True-K formulas were recently added to the ASCRS calculator. Currently, the ASCRS calculator incorporates 14 different methods for calculating the IOL power for eyes after myopic laser surgery and 9 methods for eyes after hyperopic laser surgery. In Chapters 5 and 6 a selection of 6 methods plus the average value of those methods was analysed and compared with each other. The three methods using historical data investigated in this thesis were the Masket formula14, the Modified Masket formula15 and the Barrett True-K formula16. The Masket Formula is a regression formula which modifies the predicted IOL power by using the patients’ post-laser K-readings by using the following formula: calculated IOL power post-laser + (refractive change after laser at the corneal plane * 0.326) + 0.101 = the adjusted IOL power to be implanted. The Modified Masket formula is a modification of the Masket formula to increase the accuracy, using the following formula: calculated IOL power post laser + (refractive change after laser at the corneal plane * 0.4385) + 0.0295 = the adjusted IOL power to be implanted. The Barrett True-K formula is a modification of the Barrett Universal II formula. It calculates a modified K-value based on the change in refraction and provides an internal double-Kbased solution. Details of the design of this formula have not been published. The three methods using no prior data investigated in this thesis were the Shammas formula,17 the Haigis-L formula18 and the Barrett True-K No History formula. The Shammas formula is a regression formula which estimates the post-laser corneal power through adjusting the measured post-laser K-readings by using the following formula in previously 93. 7.

(6) Chapter 7. treated myopic eyes: 1.14 * post-laser K-readings (average K) – 6.8 = post-laser corneal power. For eyes after hyperopic laser treatment the formula is as follows: 1.0457 * post-laser K-readings (average K) – 1.9538 = post-laser corneal power. The Haigis-L formula uses the corneal radius in mm to generate a corrected corneal radius which is then used by the regular Haigis formula to calculate IOL power. The corrected cornea radius is calculated as follows for myopic eyes: 331.5 / (-5.1625 * measured radius + 82.2603 – 0.35). For hyperopic eyes a comparable correction of the corneal radius is used.19 The Barrett True-K No History formula is the same formula as the Barrett True-K, with the difference that it does not use change in refraction, but employs an internal regression formula to calculate the mean K. Again, no details of the formula have been published. Several reports have been published about the performance of the formulas of the ASCRS calculator for eyes with previous myopic laser surgery and monofocal IOL implantation. The accuracy of the Haigis-L and Shammas formulas is reported variably, with the percentage of eyes given as within ± 0.50 D of target in 38% to 61% of cases.13, 16, 18, 20-27 The Masket formula also shows variable outcomes in predictability, with the percentage of eyes within 0.50 D of target as 55% to 73%.13, 16, 21-23, 25 For the Modified Masket formula the reported percentages are 53% to 67%.13, 16, 22, 23, 25 Small study populations could explain these differences. Few studies have been conducted about the performance of the newer Barrett True-K formulas. Without available historical data accuracy is reported as the percentage of eyes within ± 0.50 D from 57% to 67%.13, 16, 27 When historical refractive data is available, accuracy is reported as the percentage of eyes within ± 0.50 D of 67%.13, 16 All the previously mentioned reports are results with monofocal IOLs. In Chapter 5 we compared 6 methods of the ASCRS post-laser calculator, including the Barrett True-K formulas, in eyes after myopic laser treatment with multifocal IOL implantation. This is the first such a report in the literature. We found that the Shammas formula gave a statistically significant lower accuracy (median absolute prediction error 0.52 D, 50% of eyes within ± 0.50 D) compared with the other formulas (median absolute prediction error 0.28 to 0.45 D, 56% to 69% of eyes within ± 0.50 D). In eyes where no historical data were available we found that the Barrett True-K No History formula performed best. This is in line with the above mentioned literature with monofocal IOLs.13, 16, 27 There are not many studies reporting the accuracy of IOL power calculation formulas in eyes after hyperopic laser. Shammas et al28 show the results of 18 eyes and Hamill and colleagues29 show the results of 21 eyes after hyperopic laser treatment with monofocal IOL implantation. In Chapter 6 we describe the comparison of different IOL power calculation formulas for hyperopic eyes after laser surgery with multifocal IOL implantation in a large cohort of 65 eyes. We found a comparable accuracy in predicting IOL power for all formulas (median absolute prediction error 0.25 to 0.38 D, 64% to 73% of eyes within ± 94.

(7) Discussion. 0.50 D), except for the Modified Masket formula (median absolute prediction error 0.37 D, 59% eyes within ± 0.50 D), which performed less accurately than the Masket formula, the Barrett True-K formula and the mean value of all formulas. If we compare these results to the literature, we found comparable results for the tested formulas by Shammas et al28, except for the Haigis-L which performed better in our study. Compared to the results of Hamill et al,29 we found better predictability with a higher percentage of eyes within ± 0.50 D of target for all formulas. A possible explanation for this difference is the relatively small sample size in the other studies. The use of direct measurements of the anterior and posterior cornea by ray-tracing offers the advantage of not being subject to the established errors in calculation. Measurements can be performed over any corneal diameter, without having the problem of instrument error. Also, ray-tracing does not rely on a presumed index to calculate corneal power (refractive index error) and the effective lens position can be calculated instead of estimated on the basis of an incorrect measurement of the anterior corneal curvature (formula error). There are different techniques that incorporate direct measurements of the anterior and posterior cornea, namely Scheimpflug imaging, optical coherence tomography (OCT) and light emitting diode (LED) reflection technology, and several devices are on the market for obtaining these measurements. In Chapters 5 and 6 we did not include IOL power calculation formulas that use these direct measurements because we did not have access to these devices. Various studies show promising results with formulas incorporating these direct measurements.13, 30-32 However, more research is needed to compare these formulas with the other formulas of the ASCRS calculator using larger cohorts. Another relatively new method for IOL power prediction is intraoperative aberrometry. After the crystalline lens is removed, an aberrometer obtains intraoperatively an aphakic refraction which is then combined with biometrical data to calculate the IOL power. Accuracies are reported to be 67% to 74% of eyes within ± 0.50 D of target.20, 32 In conclusion, patients with previous corneal refractive laser surgery who wish to be independent of spectacle use could be offered a multifocal IOL. In this thesis we found good results in terms of refraction and visual acuity. In previously treated myopic eyes less predictable results were found with myopia of 6.00 D or more. Accuracy is lower compared with eyes that have not been treated with corneal refractive laser surgery.33, 34 This is the result of less accurate IOL power calculation in these eyes and patients should be aware of the possible need for retreatment(s) in the case of a residual refractive error, with the additional risks. The ASCRS online calculator is an easily accessible tool for surgeons to compare different IOL power calculation formulas to choose the best IOL power for these specific patients. In this thesis we found comparable results for the tested formulas in previously treated myopic eyes although the Shammas formula had lower accuracy, and when no 95. 7.

(8) Chapter 7. historical data is available, the Barrett True-K formula performed best. In previously treated hyperopic eyes we found comparable results in accuracy of the various tested formulas, except for the Modified Masket formula, which performed less accurately than the Masket formula, the Barrett True-K formula and the mean value of all formulas. Improvement in the accuracy of IOL power calculation in previously lasered eyes is still needed, and newer technology, including measurements of the posterior cornea by ray-tracing, offer promising developments.. 96.

(9) Discussion. REFERENCES 1. . Alió JL, Plaza-Puche AB, Fernández-Buenaga R, Pikkel J, Maldonado M. Multifocal intraocu lar lenses: An overview. Surv Ophthalmol. 2017;62(5):611-34. 2. Khor WB, Afshari NA. The role of presbyopia-correcting intraocular lenses after laser in situ keratomileusis. Curr Opin Ophthalmol. 2013;24(1):35-40. 3. Muftuoglu O, Dao L, Mootha VV, Verity SM, Bowman RW, Cavanagh HD, et al. Apodized diffractive intraocular lens implantation after laser in situ keratomileusis with or without subsequent excimer laser enhancement. J Cataract Refract Surg. 2010;36(11):1815-21. 4. Fernández-Vega L, Madrid-Costa D, Alfonso JF, Montés-Micó R, Poo-López A. Optical and visual performance of diffractive intraocular lens implantation after myopic laser in situ keratomileusis. J Cataract Refract Surg. 2009;35(5):825-32. 5. Alfonso JF, Fernández-Vega L, Baamonde B, Madrid-Costa D, Montés-Micó R. Refractive lens exchange with spherical diffractive intraocular lens implantation after hyperopic laser in situ keratomileusis. J Cataract Refract Surg. 2009;35(10):1744-50. 6. Schallhorn SC, Venter JA, Teenan D, Schallhorn JM, Hettinger KA, Hannan SJ, et al. Outcomes of excimer laser enhancements in pseudophakic patients with multifocal intra ocular lens. Clin Ophthalmol. 2016;10:765-76. 7. Gundersen KG, Makari S, Ostenstad S, Potvin R. Retreatments after multifocal intraocular lens implantation: an analysis. Clin Ophthalmol. 2016;10:365-71. 8. Muftuoglu O, Prasher P, Chu C, Mootha VV, Verity SM, Cavanagh HD, et al. Laser in situ keratomileusis for residual refractive errors after apodized diffractive multifocal intraocular lens implantation. J Cataract Refract Surg. 2009;35(6):1063-71. 9. Caster AI, Friess DW, Schwendeman FJ. Incidence of epithelial ingrowth in primary and retreatment laser in situ keratomileusis. J Cataract Refract Surg. 2010;36(1):97-101. 10. Friehmann A, Mimouni M, Nemet AY, Sela T, Munzer G, Kaiserman I. Risk Factors for Epithe lial Ingrowth Following Microkeratome-Assisted LASIK. J Refract Surg. 2018;34(2):100-5. 11. Hoffer KJ. Intraocular lens power calculation after previous laser refractive surgery. J Cata ract Refract Surg. 2009;35(4):759-65. 12. Koch DD, Wang L. Calculating IOL power in eyes that have had refractive surgery. J Cataract Refract Surg. 2003;29(11):2039-42. 13. Wang L, Tang M, Huang D, Weikert MP, Koch DD. Comparison of Newer Intraocular Lens Power Calculation Methods for Eyes after Corneal Refractive Surgery. Ophthalmology. 2015;122(12):2443-9. 14. Masket S, Masket SE. Simple regression formula for intraocular lens power adjustment in eyes requiring cataract surgery after excimer laser photoablation. J Cataract Refract Surg. 2006;32(3):430-4. 15. Hill W. IOL power calculations following keratorefractive surgery. Paper presented at: Cornea Day, American Society of Cataract and Refractive Surgery Annual Meeting; March 17-22, 2006; San Fransico, CA. 16. Abulafia A, Hill WE, Koch DD, Wang L, Barrett GD. Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia. J Cataract Refract Surg. 2016;42(3):363-9. 97. 7.

(10) Chapter 7 17. . 18. 19. . 20. . 21. . 22. . 23. . 24. . 25. . 26. . 27. . 28. 29. . 30. . 98. Shammas HJ, Shammas MC, Garabet A, Kim JH, Shammas A, LaBree L. Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis. Am J Ophthalmol. 2003;136(3):426-32. Haigis W. Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula. J Cataract Refract Surg. 2008;34(10):1658-63. Haigis W. Goes, JF. IOL calculation after refractive laser surgery for hyperopia. F.J. Goes (Ed), Lens Surgery After Previous Refractive Surgery, Jaypee Brothers, New Delhi, India (2011), pp. 55-59. Ianchulev T, Hoffer KJ, Yoo SH, Chang DF, Breen M, Padrick T, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology. 2014;121(1):56-60. McCarthy M, Gavanski GM, Paton KE, Holland SP. Intraocular lens power calculations after myopic laser refractive surgery: a comparison of methods in 173 eyes. Ophthalmology. 2011;118(5):940-4. Potvin R, Hill W. New algorithm for intraocular lens power calculations after myopic laser in situ keratomileusis based on rotating Scheimpflug camera data. J Cataract Refract Surg. 2015;41(2):339-47. Savini G, Barboni P, Carbonelli M, Ducoli P, Hoffer KJ. Intraocular lens power calculation after myopic excimer laser surgery: Selecting the best method using available clinical data. J Cataract Refract Surg. 2015;41(9):1880-8. Shammas HJ, Shammas MC. No-history method of intraocular lens power calculation for cataract surgery after myopic laser in situ keratomileusis. J Cataract Refract Surg. 2007;33(1):31-6. Wang L, Hill WE, Koch DD. Evaluation of intraocular lens power prediction methods using the American Society of Cataract and Refractive Surgeons Post-Keratorefractive Intraocular Lens Power Calculator. J Cataract Refract Surg. 2010;36(9):1466-73. Yang R, Yeh A, George MR, Rahman M, Boerman H, Wang M. Comparison of intraocular lens power calculation methods after myopic laser refractive surgery without previous refractive surgery data. J Cataract Refract Surg. 2013;39(9):1327-35. Cho K, Lim DH, Yang CM, Chung ES, Chung TY. Comparison of Intraocular Lens Power Calculation Methods Following Myopic Laser Refractive Surgery: New Options Using a Rotating Scheimpflug Camera. Korean J Ophthalmol. 2018;32(6):497-505. Shammas HJ, Shammas MC, Hill WE. Intraocular lens power calculation in eyes with previ ous hyperopic laser in situ keratomileusis. J Cataract Refract Surg. 2013;39(5):739-44. Hamill EB, Wang L, Chopra HK, Hill W, Koch DD. Intraocular lens power calculations in eyes with previous hyperopic laser in situ keratomileusis or photorefractive keratectomy. J Cata ract Refract Surg. 2017;43(2):189-94. Huang D, Tang M, Wang L, Zhang X, Armour RL, Gattey DM, et al. Optical coherence tomography-based corneal power measurement and intraocular lens power calculation following laser vision correction (an American Ophthalmological Society thesis). Trans Am Ophthalmol Soc. 2013;111:34-45..

(11) Discussion 31. . Tang M, Wang L, Koch DD, Li Y, Huang D. Intraocular lens power calculation after previous myopic laser vision correction based on corneal power measured by Fourier-domain optical coherence tomography. J Cataract Refract Surg. 2012;38(4):589-94. 32. Fram NR, Masket S, Wang L. Comparison of Intraoperative Aberrometry, OCT-Based IOL Formula, Haigis-L, and Masket Formulae for IOL Power Calculation after Laser Vision Correc tion. Ophthalmology. 2015;122(6):1096-101. 33. Melles RB, Holladay JT, Chang WJ. Accuracy of Intraocular Lens Calculation Formulas. Ophthalmology. 2018;125(2):169-78. 34. Reitblat O, Assia EI, Kleinmann G, Levy A, Barrett GD, Abulafia A. Accuracy of predicted refraction with multifocal intraocular lenses using two biometry measurement devices and multiple intraocular lens power calculation formulas. Clin Exp Ophthalmol. 2015;43(4):328-34.. 7. 99.

(12)

No results found