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May consultation #5
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CONSULTATION SECTION
Refractive Surgeons post-keratorefractive intraocular lens power calculator. J Cataract Refract Surg 2010; 36:1466–1473
OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergone LASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2011 B. Solomon R, “A Study in the ORange Intraoperative Wavefront Aberrometer (WaveTec Vision Systems) to Make IOL Power Calculations in Eyes That Had Undergone Laser Vision Correction,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2001
- This was a PRK treatment before Food and Drug Administration approval in the United States, and it is unusual to have meaningful historical data from 20 years ago. Having this information is especially helpful because there appears to be an element of lens-induced myopia. There are 3 ways to perform this calculation. First, the IOL power can be estimated based on the preLASIK K values and the change in manifest refraction due to LASIK. These methods often result in overestimation of IOL power. Wang et al.1 have shown purely historical methods to be the least accurate. Second, the IOL power can be estimated using the change in manifest refraction due to LASIK and 1 of several topographic methods or small-zone autokeratometry using the IOLMaster or the Lenstar LS 900 (Haag-Streit AG) device. This approach has been shown to give the best overall results, with a G0.50 D accuracy range from 57% to 67%.1 Third, the IOL power can be estimated using only contemporary measurements with small-zone autokeratometry or the Atlas topographer combined with a modified theoretic formula, as described by Aramberri, or 1 that is not influenced by the artifact of iatrogenic central corneal flattening.2,3 Of these methods, the Haigis-L and Shammas have similar accuracy (approximately 60% at G0.50 D).1,3 These methods are especially helpful when no historical data are available. Methods using all 3 approaches are available on the ASCRS online post-keratorefractive calculator.A Of the calculation methods mentioned, the SRK/T formula without an Aramberri double-K method correction will typically underestimate IOL power, resulting in unanticipated postoperative hyperopia. The Haigis-L formula is a good option but will occasionally overcorrect by small amounts. Intraoperative aberrometry can be helpful in eliminating large refractive surprises but may not always be accurate because the intraoperative position of the IOL in a flaccid capsular bag may not correspond with its final position after capsular bag contraction. It is helpful to remember
that IOL power is relative to its distance from the principal plane of the cornea and is not an absolute value. After myopic LASIK, my experience has led me to look to the modified Masket, Haigis-L and Shammas methods and target mild myopia rather than hard plano.B The Haigis-L and Shammas methods recommend an Acrysof SN60WF IOL power of approximately C15.00 D for a postoperative target refraction of 0.25 D. The modified Masket method recommends less power. From this, I would estimate the correct IOL power to be between C14.50 D and C15.00 D. Looking to avoid postoperative hyperopia, I would select a C15.00 D Acrysof SN60WF IOL. Warren E. Hill, MD Mesa, Arizona, USA
REFERENCES 1. 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; 36:1466–1473 2. Aramberri J. Intraocular lens power calculation after corneal refractive surgery: double K method. J Cataract Refract Surg 2003; 29:2063–2068 3. Haigis W. Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula. J Cataract Refract Surg 2008; 34:1658–1663
OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergone LASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2012 B. Hill WE, “A Modification of the Masket Regression Formula,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California, USA, March 2006
- Accurate prediction of IOL power in eyes with previous corneal refractive surgery represents a challenging task that we are facing far more frequently. Because it has not been proven which proposed method works best in all eyes, surgeons should use as many methods as there are data available for and carefully evaluate the results. According to the PCI biometry results, the SRK/T formula recommended a 12.50 D IOL with a target postoperative refraction of 0.38 D. The Haigis-L formula recommended a 15.00 D IOL with a target refraction of 0.31 D. The Haigis-L formula is one of the most accurate in post-laser refractive cases. Because we have the preoperative K readings in this case, we can use the CHM to estimate the mean K after refractive surgery. Flattening of the corneal surface after laser ablation treatment reduces the ability of devices to measure
J CATARACT REFRACT SURG - VOL 38, MAY 2012
CONSULTATION SECTION
corneal power. In these cases, Hoffer1 proposes using the mean K before surgery and the refractive errors preoperatively and postoperatively (particularly the SE of them) to evaluate the new mean K (CHM). In our case, the patient had PRK for myopia 20 years ago. The patient's mean K reading before PRK was Kpreop Z ðK1 þ K2Þ=2 Z ð41:87 D þ 42:25 DÞ=2 Z 42:06 D The new mean K is Kafter Z Kpreop þ SEbefore SEafter Z 42:06 D þ ð3:75 DÞ ðþ1:125 DÞ Z 37:185 D In our case, the mean K value after PRK measured with Scheimpflug imaging (39.35 D) and PCI biometry (39.48 D) was overestimated. I used C0.75 C0.75 62 (error 6 months after surgery) and not 2.50 C0.50 15 (refraction at last examination) for the SE error after refractive surgery and before cataract formation. I speculate that the last refractive error is attributed to a myopic shift due to C2 nuclear sclerosis, not to regression of the refractive effect (because we do not have relevant data). The IOL power was calculated using the CHM new mean K (37.18 D) in conjunction with the Hoffer-Q formula and the SRK/T formula. The Hoffer-Q formula recommended a 16.00 D IOL with a target postoperative refraction of 0.10 D. The SRK/T formula recommended a 14.50 D IOL with a target postoperative refraction of 0.13 D. According to a recent study by McCarthy et al.,2 the optimum CHM combination was with the Hoffer-Q formula. The recommended IOL power concerns an Acrysof SN60WF IOL in all cases. To avoid a hyperopic surprise after cataract surgery, I would recommend a 16.50 D IOL with a target postoperative refraction of 0.50 D. Postoperative corneal topography shows no sign of ectasia and adequate corneal thickness for possible enhancement. Therefore, I would aim for a myopic refractive error postoperatively rather than a hyperopic error in case enhancement is required after cataract surgery. In any case, I would inform the patient about the problems associated with choosing the correct IOL power, the increased possibility of postoperative ametropia, and the options for further refractive surgery and lens exchange. George D. Kymionis, MD, PhD Heraklion, Crete, Greece REFERENCES 1. Hoffer KJ. Intraocular lens power calculation after previous laser refractive surgery. J Cataract Refract Surg 2009; 35:759–765
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2. 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; 118:940–944
- Intraocular lens calculation after corneal refractive surgery is one of the most difficult management issues for the cataract surgeon. In addition, IOL calculation is more difficult after RK than after PRK or LASIK. After RK, I first assess the visual fluctuation seen during the day and aim to give the patient slight myopia at the most hyperopic point due to the continued hyperopic progression in these patients. In this case, the mean K value was 39.45 D with Scheimpflug imaging and 39.47 D with the PCI biometry; the values are remarkably similar. In addition, the refraction SE started at 3.75 D; 6 months postoperatively, it was C1.12 D, a change of 4.87 D. This suggests that using the historical method, the true K should be the mean preoperative K value of 42.06 D 4.87 D, or 37.19 D if there were no progressive hyperopia. This suggests that the Scheimpflug imaging and PCI biometry K values were not accurate. In looking at the Scheimpflug central K color codes and not the K values, the flattest K approaches 36.00 D; however, the visual axis cannot be determined. For this reason I generally rely on Wavetec ORA intraoperative aberrometry for IOL calculations after corneal refractive surgery because the device incorporates the visual axis and provides real-time intraoperative information. New regression analysis software has significantly improved my results with these patients. I would likely repeat the biomechanical waveform analysis reading. If it were the same, I would add 0.50 to 1.00 D to the IOL to leave the patient slightly myopic. In conclusion, I would reenter the K values on the ASCRS IOL power calculatorA using a K value of approximately 36.50 D, which results in an IOL power of 12.50 D, and based on the intraoperative aberrometry, which predicted a 12.00 D IOL, I would implant the 12.50 D IOL. Eric D. Donnenfeld, MD New York, New York, USA OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergoneLASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2011
- My current algorithm for IOL calculation after myopic PRK or LASIK is to select an IOL based on the flat or central Pentacam value. In this case, if emmetropia
J CATARACT REFRACT SURG - VOL 38, MAY 2012
CONSULTATION SECTION
Refractive Surgeons post-keratorefractive intraocular lens power calculator. J Cataract Refract Surg 2010; 36:1466–1473
OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergone LASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2011 B. Solomon R, “A Study in the ORange Intraoperative Wavefront Aberrometer (WaveTec Vision Systems) to Make IOL Power Calculations in Eyes That Had Undergone Laser Vision Correction,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2001
- This was a PRK treatment before Food and Drug Administration approval in the United States, and it is unusual to have meaningful historical data from 20 years ago. Having this information is especially helpful because there appears to be an element of lens-induced myopia. There are 3 ways to perform this calculation. First, the IOL power can be estimated based on the preLASIK K values and the change in manifest refraction due to LASIK. These methods often result in overestimation of IOL power. Wang et al.1 have shown purely historical methods to be the least accurate. Second, the IOL power can be estimated using the change in manifest refraction due to LASIK and 1 of several topographic methods or small-zone autokeratometry using the IOLMaster or the Lenstar LS 900 (Haag-Streit AG) device. This approach has been shown to give the best overall results, with a G0.50 D accuracy range from 57% to 67%.1 Third, the IOL power can be estimated using only contemporary measurements with small-zone autokeratometry or the Atlas topographer combined with a modified theoretic formula, as described by Aramberri, or 1 that is not influenced by the artifact of iatrogenic central corneal flattening.2,3 Of these methods, the Haigis-L and Shammas have similar accuracy (approximately 60% at G0.50 D).1,3 These methods are especially helpful when no historical data are available. Methods using all 3 approaches are available on the ASCRS online post-keratorefractive calculator.A Of the calculation methods mentioned, the SRK/T formula without an Aramberri double-K method correction will typically underestimate IOL power, resulting in unanticipated postoperative hyperopia. The Haigis-L formula is a good option but will occasionally overcorrect by small amounts. Intraoperative aberrometry can be helpful in eliminating large refractive surprises but may not always be accurate because the intraoperative position of the IOL in a flaccid capsular bag may not correspond with its final position after capsular bag contraction. It is helpful to remember
that IOL power is relative to its distance from the principal plane of the cornea and is not an absolute value. After myopic LASIK, my experience has led me to look to the modified Masket, Haigis-L and Shammas methods and target mild myopia rather than hard plano.B The Haigis-L and Shammas methods recommend an Acrysof SN60WF IOL power of approximately C15.00 D for a postoperative target refraction of 0.25 D. The modified Masket method recommends less power. From this, I would estimate the correct IOL power to be between C14.50 D and C15.00 D. Looking to avoid postoperative hyperopia, I would select a C15.00 D Acrysof SN60WF IOL. Warren E. Hill, MD Mesa, Arizona, USA
REFERENCES 1. 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; 36:1466–1473 2. Aramberri J. Intraocular lens power calculation after corneal refractive surgery: double K method. J Cataract Refract Surg 2003; 29:2063–2068 3. Haigis W. Intraocular lens calculation after refractive surgery for myopia: Haigis-L formula. J Cataract Refract Surg 2008; 34:1658–1663
OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergone LASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2012 B. Hill WE, “A Modification of the Masket Regression Formula,” presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Francisco, California, USA, March 2006
- Accurate prediction of IOL power in eyes with previous corneal refractive surgery represents a challenging task that we are facing far more frequently. Because it has not been proven which proposed method works best in all eyes, surgeons should use as many methods as there are data available for and carefully evaluate the results. According to the PCI biometry results, the SRK/T formula recommended a 12.50 D IOL with a target postoperative refraction of 0.38 D. The Haigis-L formula recommended a 15.00 D IOL with a target refraction of 0.31 D. The Haigis-L formula is one of the most accurate in post-laser refractive cases. Because we have the preoperative K readings in this case, we can use the CHM to estimate the mean K after refractive surgery. Flattening of the corneal surface after laser ablation treatment reduces the ability of devices to measure
J CATARACT REFRACT SURG - VOL 38, MAY 2012
CONSULTATION SECTION
corneal power. In these cases, Hoffer1 proposes using the mean K before surgery and the refractive errors preoperatively and postoperatively (particularly the SE of them) to evaluate the new mean K (CHM). In our case, the patient had PRK for myopia 20 years ago. The patient's mean K reading before PRK was Kpreop Z ðK1 þ K2Þ=2 Z ð41:87 D þ 42:25 DÞ=2 Z 42:06 D The new mean K is Kafter Z Kpreop þ SEbefore SEafter Z 42:06 D þ ð3:75 DÞ ðþ1:125 DÞ Z 37:185 D In our case, the mean K value after PRK measured with Scheimpflug imaging (39.35 D) and PCI biometry (39.48 D) was overestimated. I used C0.75 C0.75 62 (error 6 months after surgery) and not 2.50 C0.50 15 (refraction at last examination) for the SE error after refractive surgery and before cataract formation. I speculate that the last refractive error is attributed to a myopic shift due to C2 nuclear sclerosis, not to regression of the refractive effect (because we do not have relevant data). The IOL power was calculated using the CHM new mean K (37.18 D) in conjunction with the Hoffer-Q formula and the SRK/T formula. The Hoffer-Q formula recommended a 16.00 D IOL with a target postoperative refraction of 0.10 D. The SRK/T formula recommended a 14.50 D IOL with a target postoperative refraction of 0.13 D. According to a recent study by McCarthy et al.,2 the optimum CHM combination was with the Hoffer-Q formula. The recommended IOL power concerns an Acrysof SN60WF IOL in all cases. To avoid a hyperopic surprise after cataract surgery, I would recommend a 16.50 D IOL with a target postoperative refraction of 0.50 D. Postoperative corneal topography shows no sign of ectasia and adequate corneal thickness for possible enhancement. Therefore, I would aim for a myopic refractive error postoperatively rather than a hyperopic error in case enhancement is required after cataract surgery. In any case, I would inform the patient about the problems associated with choosing the correct IOL power, the increased possibility of postoperative ametropia, and the options for further refractive surgery and lens exchange. George D. Kymionis, MD, PhD Heraklion, Crete, Greece REFERENCES 1. Hoffer KJ. Intraocular lens power calculation after previous laser refractive surgery. J Cataract Refract Surg 2009; 35:759–765
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2. 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; 118:940–944
- Intraocular lens calculation after corneal refractive surgery is one of the most difficult management issues for the cataract surgeon. In addition, IOL calculation is more difficult after RK than after PRK or LASIK. After RK, I first assess the visual fluctuation seen during the day and aim to give the patient slight myopia at the most hyperopic point due to the continued hyperopic progression in these patients. In this case, the mean K value was 39.45 D with Scheimpflug imaging and 39.47 D with the PCI biometry; the values are remarkably similar. In addition, the refraction SE started at 3.75 D; 6 months postoperatively, it was C1.12 D, a change of 4.87 D. This suggests that using the historical method, the true K should be the mean preoperative K value of 42.06 D 4.87 D, or 37.19 D if there were no progressive hyperopia. This suggests that the Scheimpflug imaging and PCI biometry K values were not accurate. In looking at the Scheimpflug central K color codes and not the K values, the flattest K approaches 36.00 D; however, the visual axis cannot be determined. For this reason I generally rely on Wavetec ORA intraoperative aberrometry for IOL calculations after corneal refractive surgery because the device incorporates the visual axis and provides real-time intraoperative information. New regression analysis software has significantly improved my results with these patients. I would likely repeat the biomechanical waveform analysis reading. If it were the same, I would add 0.50 to 1.00 D to the IOL to leave the patient slightly myopic. In conclusion, I would reenter the K values on the ASCRS IOL power calculatorA using a K value of approximately 36.50 D, which results in an IOL power of 12.50 D, and based on the intraoperative aberrometry, which predicted a 12.00 D IOL, I would implant the 12.50 D IOL. Eric D. Donnenfeld, MD New York, New York, USA OTHER CITED MATERIAL A. Hill W, Wang L, Koch DD. IOL calculator for eyes that have undergoneLASIK/PRK/RK. Available at: http://iolcalc.org/. Accessed March 2, 2011
- My current algorithm for IOL calculation after myopic PRK or LASIK is to select an IOL based on the flat or central Pentacam value. In this case, if emmetropia
J CATARACT REFRACT SURG - VOL 38, MAY 2012