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Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in short eyes
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ARTICLE
Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in short eyes Shruti Sudhakar, MD, Darren C. Hill, MD, Tonya S. King, PhD, Ingrid U. Scott, MD, MPH, Gautam Mishra, MD, Brett B. Ernst, MD, Seth M. Pantanelli, MD, MS
Purpose: To compare the accuracy of preoperative biometrybased formulas to intraoperative aberrometry (IA) with respect to predicting refractive outcomes after cataract surgery in short eyes. Setting: Private practice and community-based ambulatory surgery center. Design: Retrospective consecutive case series. Methods: Eyes with an axial length (AL) shorter than 22.1 mm underwent cataract extraction and intraocular lens (IOL) implantation. The predicted residual refractive error was calculated preoperatively using Hoffer Q, Holladay 2, Haigis, Barrett Universal II, and Hill-RBF formulas and intraoperatively using IA. The postoperative spherical equivalent (SE) was compared with the predicted SE to evaluate the accuracy of each aforementioned method. Results: Fifty-one eyes from 38 patients met criteria to be included in the analysis. Without optimizing the formulas specifically
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hen planning for cataract surgery, calculating the appropriate intraocular lens (IOL) power is typically based upon preoperative biometry measurements. Although older formulas (ie, Holladay 1,1 SRK/T,2 and Hoffer Q3) rely only on axial length (AL) and keratometry measurements, newer ones (ie, Haigis,4 Holladay 2,A and Barrett Universal IIB) take advantage of additional parameters, such as directly measured anterior chamber depth, lens thickness, horizontal white-towhite, and preoperative refraction to improve accuracy. In normal eyes (AL Z 22.0 to 25.2 mm), refractive outcomes are reported to be within G0.5 diopter (D) in 55% to 75% of cases and within G1.0 D in 85% to 95% of cases.5–7 However, among eyes with an AL shorter
for short eyes, the mean numerical errors (MNEs) associated with Hoffer Q, Holladay 2, Haigis, Barrett Universal II, Hill-RBF, and IA were 0.08 (95% confidence interval [CI], 0.30 to 0.13), 0.14 (95% CI, 0.35 to 0.07), C0.26 (95% CI, 0.05 to 0.47), C0.11 (95% CI, 0.10 to 0.32), C0.07 (95% CI, 0.14 to 0.28), and C0.00 (95% CI, 0.21 to 0.21), respectively (P < .001). The proportion of eyes within G0.5 diopter (D) of the predicted SE were 49.0%, 43.1%, 52.9%, 52.9%, 60.8%, and 58.8%, respectively (P Z .06). The prediction outcomes from IA were statistically better than Haigis, but not other formulas. When formula and IA predictions differed by 0.5 D or more, IA’s ability to recommend a more emmetropic outcome was no better than chance (50%).
Conclusions: Intraoperative aberrometry is not significantly different from the best preoperative biometry-based methods available for IOL power selection in short eyes. J Cataract Refract Surg 2018; -:-–- Q 2018 ASCRS and ESCRS
than 22.0 mm, predictive accuracy is less precise. In these short eyes, accuracy to within G0.5 D ranged between 21% and 71% in a study by Aristodemou et al.7 and between 45% and 75% in a study by Roh et al.,8 depending on the formula used. Hoffer Q has traditionally been preferred for use in short eyes.9–13 More recent studies suggest that the Haigis and Barrett Universal II formulas might also be excellent choices for this population.8,9,13–21 Roh et al.8 reported that Haigis produced the smallest mean absolute error and had a higher proportion of outcomes within G1.0 D. Alternatively, in a study by Kane et al.,13 Barrett Universal II was the most accurate for all ALs, including short eyes. A new formula, Hill-RBF,C was introduced in 2016, and a
Submitted: July 17, 2018 | Final revision submitted: December 14, 2018 | Accepted: December 17, 2018 Penn State College of Medicine (Sudhakar), Hershey, Pennsylvania, the Department of Ophthalmology (Hill), University of Kentucky, Lexington, Kentucky, the Department of Public Health Sciences (King, Scott), Penn State College of Medicine, Hershey, the Department of Ophthalmology (Scott, Pantanelli), the Penn State College of Medicine, Hershey, and the Schein Ernst Mishra Eye (Mishra, Ernst), Harrisburg, Pennsylvania, USA. Presented in part at the annual meeting of the Association for Research in Vision and Ophthalmology, Seattle, Washington, USA, May 2016. Corresponding author: Seth M. Pantanelli, MD, MS, Penn State Eye Center, 500 University Drive, HU19, Hershey, PA 17033, USA. Email: spantanelli@pennstatehealth. psu.edu. Q 2018 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2018.12.016
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
recent study by G€ okce et al.20 reported a lower median numerical error with Hill-RBF than Hoffer Q in short eyes. Similarly, Roberts et al.21 also found that Hill-RBF yielded the lowest mean numerical error in long and short eyes. The many conflicting conclusions on this topic suggests that there is no consensus on which preoperative biometry-based formula is best for use in short eyes. The ORA System (Alcon Laboratories, Inc.) is an intraoperative wavefront aberrometer that uses preoperative biometry measurements and intraoperative Talbot-Moire interferometry to measure an aphakic eye’s refractive power for appropriate IOL selection.22,23 The technology seeks to overcome potential inaccuracies of clinic-based biometry by taking measurements in the aphakic state, which renders it uninfluenced by the cataractous lens. The intraoperative aberrometry (IA) device has already been shown to outperform conventional formulas for IOL power selection in patients with a history of refractive surgery (eg, laser in situ keratomileusis [LASIK] and photorefractive keratectomy).24–27 Fram et al.27 reported outcomes of 75% within G0.5 D and 97% within G1.0 D in eyes with previous laser vision correction.27 IA has also been validated as extremely accurate in eyes with axial myopia, with outcomes of 80% within G0.5 D and 98% within G1.0 D of target spherical equivalent (SE).28 In eyes with axial myopia, IA was shown to be equivalent or better than many biometry-based formulas (ie, Holladay 1, Holladay 2, Barrett Universal II, and Hill-RBF).28 To date, there is no published literature that evaluates IA specifically in short eyes. As such, the purpose of the current study was to compare the performance of IA (ORA System) to other conventional biometry-based formulas in short eyes.
PATIENTS AND METHODS A retrospective review was conducted of patients who underwent routine phacoemulsification cataract surgery with in-the-bag IOL implantation by one of two surgeons (B.B.E. or G.M.) between October 20, 2014 and September 11, 2017. All surgeries were performed at a private ambulatory surgery center (Capital Surgery and Laser Center, LLC, Harrisburg, PA). Eyes were excluded if they had a history of prior ocular surgery or trauma, ocular inflammatory conditions, vision-limiting retinal or optic nerve disease, complications during cataract surgery, a target postoperative refraction other than plano, lack of follow-up, or postoperative corrected distance visual acuity worse than 20/40. A total of 51 eyes from 38 patients were eligible for the inclusion in the study based on these criteria. Optical biometry was performed using partial coherence interferometry (IOLMaster, Carl Zeiss Meditec AG). The predicted refractive error was calculated using 6 different methods: (1) Hoffer Q, (2) Holladay 2, (3) Haigis, (4) Barrett Universal II, (5) Hill-RBF, and (6) IA (ORA System). It is not standard practice to optimize A-constants and surgeon factors specifically for short eyes; as such, the constants used for each formula and IOL were those recommended by the User Group for Laser Interference Biometry (ULIB) database.D For patients with no measured lens thickness, a standard lens thickness value of 5.0 mm was used for the Holladay 2 calculations.29 Calculations for the Barrett Universal II and Hill-RBF formulas were performed using online calculators from the Asia-Pacific Association of Cataract and Volume - Issue - - 2019
Refractive Surgeons and the expanded beta version of the HillRBF calculator, respectively.B,C Intraoperatively and after cortical clean-up, the eye was inflated to an intraocular pressure of 20 mm Hg using a balanced salt solution and a Barraquer tonometer for pressure measurement. IA was used to measure the eye in the aphakic state to estimate the predicted refractive error for the implanted IOL. If the IA system recommended an IOL that was different from that originally intended, the surgeon’s best judgement was used to implant the IOL most likely to result in emmetropia. The final refraction was performed at least 20 days and no more than 60 days after surgery. The primary outcome measures included the difference between predicted and actual postoperative SE (numerical error), and proportion of eyes within G0.5 D and G1.0 D of their target SE refraction. The mean and median numerical errors were calculated for each of the 6 methods, as were the proportion of eyes within G0.5 D and G1.0 D of predicted. In a separate analysis, the formulas were optimized specifically for the study population, and for the 35 eyes that received an Akreos AO60 IOL (Bausch & Lomb, Inc.), by adding the mean numerical error for each formula to the predicted SE for each eye, thereby driving the mean numerical error to zero. To evaluate the differences between formulas with regard to the mean numerical error and the median numerical error while accounting for the correlation within each patient, repeated-measures analysis of variance and repeated-measures rank analysis of variance tests were performed using SAS/STAT software (version 9.4, SAS Institute, Inc.) with a probability of less than 5% (P ! .05) representing statistical significance. Repeated-measures logistic regression and Cochran Q tests were performed to evaluate differences between formulas with regard to the proportion of eyes within G0.5 D and G1.0 D. A Bonferroni-adjusted pairwise analysis was used to identify statistically significant differences between the methods.
RESULTS The study comprised 51 eyes from 38 patients. Table 1 shows the demographics of the study population. Thirtyseven of the 51 eyes received a monofocal IOL (Akreos AO60 [Bausch & Lomb, Inc.], AF-1 FY-60AD [Hoya Surgical Optics, Inc.], or SA60AT [Alcon Laboratories, Inc.]); 9 received a toric IOL (Tecnis ZCT150, ZCT225, ZCT300, or ZCT400 [all Johnson & Johnson Vision Care, Inc.]); and 5 received a multifocal IOL (Tecnis ZKB00 or ZLB00 [Johnson & Johnson Vision Care, Inc.]). Table 2 shows a comparison of the outcomes of the 6 methods before optimizing for the study population. It is interesting to note that the Hoffer Q, Holladay 2, Barrett Universal II, Hill-RBF, and the IA system had mean numerical errors statistically equivalent to zero despite using lens constants and surgeon factors that were not specifically optimized for short eyes; this suggests that these particular methods might be well suited for a wide range of eyes and that the lens constants used for normal eyes are likely applicable to short eyes as well. Haigis was the only formula that had a mean numerical error statistically different from zero (P Z .02), with a tendency toward hyperopia. The IA also trended toward superior performance with respect to the proportion of eyes within G0.5 D and G1.0 D, although this superiority did not reach statistical significance. The Cochran Q test results were similar to those from the model-based approach shown in Table 2, with P values of
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
Table 1. Demographics of the study population. IOL Type Parameter IOL Power (D) Mean G SD Range AL (mm) Mean G SD Range
Monofocal
Toric
Multifocal
24.7 G 1.7 21.0, 28.5
29.1 G 4.0 22.5, 34.0
26.1 G 1.7 23.5, 28.0
21.69 G 0.33 20.41, 22.06
21.00 G 0.85 19.77, 21.92
21.70 G 0.25 21.32, 21.94
AL Z axial length; IOL Z intraocular lens
0.22 and 0.43 for the proportion of eyes within G0.5 D and G1.0 D, respectively. Because statistical significance was reached with respect to the mean numerical error, a Bonferroni-adjusted pairwise analysis was performed on this metric, the results of which are shown in Table 3. Hoffer Q, Holladay 2, and IA had the lowest mean numerical errors and were not significantly different from one another. All three of these formulas were superior to Haigis, which performed worst (P % .001). There was no statistically significant difference with regard to the proportion of eyes within G0.5 D and G1.0 D of the target SE. Table 4 shows a comparison of the outcomes of the 6 methods after optimizing for the study population. Because optimization cannot be done when a variety of IOLs are used, only eyes that received the monofocal Akreos AO60 IOL were included in this analysis. Although optimization did change the performance of many of the formulas with regard to the proportion of eyes within G0.5 D and G1.0 D of the target SE, these differences were small and not significant. IA remained one of the best performing methods, but its superiority was not statistically different from the other methods. The Barrett Universal II agreed with the aberrometer (within G0.5 D) 72.5% of the time. In instances in which there were disagreements greater than 0.5 D, the Barrett Universal II would have outperformed IA 13.7% of the time, and the IA would have outperformed the Barrett Universal II 13.6% of the time. Likewise, the Hill-RBF agreed with the IA (within G0.5 D) 88.2% of the time. In instances in which there were disagreements greater than 0.5 D, the Hill-RBF would have outperformed IA 5.9% of the time,
and the IA would have outperformed Hill-RBF 5.9% of the time. In other words, the probability that the IA improved outcomes when there was disagreement was no better than chance (50% of the time). The same trends were observed for all the other formulas (Hoffer Q, Holladay 2, and Haigis). DISCUSSION Previous studies have shown that IA performs well in eyes with a history of refractive surgery, such as LASIK.25–28 Similarly, Hill et al.19 demonstrated that IA (ORA) was equivalent to the most robust formulas in eyes with axial myopia. To the best of our knowledge, this is the first study to compare the Alcon ORA to preoperative biometry-based formulas in short eyes. We have shown that ORA performs at least as well as other commonly used formulas for this population. Users of IA might ascribe to the idea that improved outcomes come from the surgeon’s ability to change the chosen IOL power “on the fly.” For this to be true, it must first be shown that the IA’s predictions are better aligned with actual postoperative results than preoperative calculations. If this is not the case, it is impossible for the surgeon to know when to believe the IA calculations. As mentioned in the results above, the IA system’s ability to improve outcomes when its recommendation differed from Barrett Universal II and Hill-RBF by more than 0.5 D was no better than chance. This finding is supported in a previous study by Davison and Potvin,30 which found that when the preoperative and IA calculations differed by more than 0.5 D, the chance that the aberrometer’s recommendation was better was 56% and not statistically different from 50%. In
Table 2. Comparison of the 6 calculation methods before optimizing for the study population. Parameter 3
Hoffer Q Holladay 2A Haigis4 Barrett Universal IIB Hill-RBFC IA P value
MNE (95% CI) 0.08 ( 0.14 ( C0.26 C0.11 ( C0.07 ( C0.00 ( !.001
0.30, 0.13) 0.35, 0.07) (0.05, 0.47)* 0.10, 0.32) 0.14, 0.28) 0.21, 0.21)
MedNE
MAE
Within ±0.5 D (%)
Within ±1.0 D (%)
0.09 0.09 C0.19 C0.17 C0.11 0.02 !.001
0.54 0.53 0.60 0.51 0.49 0.48 0.47
49.0 43.1 52.9 52.9 60.8 58.8 0.06
86.3 88.2 80.4 86.3 90.2 88.2 0.31
CI Z confidence interval; IA Z intraoperative aberrometry; MAE Z mean absolute error; MedNE Z median numerical error; MNE Z mean numerical error *Statistically significant
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Table 3. Post hoc analysis of the mean numerical errors in the intraocular lens calculation methods. P Value Parameter Hoffer Q3 Holladay 2A Haigis4 Barrett Universal IIB Hill-RBFC IA
Hoffer Q
Holladay 2
Haigis
Barrett Universal II
Hill-RBF
IA
d d d d d d
.450 d d d d d
!.001* !.001* d d d d
.014 !.001* .047 d d d
.042 .006 .016 .665 d d
.259 .061 .001* .179 .360 d
IA Z intraoperative aberrometry *Statistically significant after Bonferroni correction
conclusion, we do not believe there is sufficient evidence to suggest that altering the IOL power implanted based on the aberrometer’s recommendations improves refractive outcomes for the short eye population. It is unfortunate that the performance of all methods, including IA, is so poor when compared with how well these methods fair in eyes with normal ALs. As has been described elsewhere, poor performance of biometry-based methods in short eyes is attributable to multiple factors. First, the variables determining effective lens position in this population might not be fully understood. Second, any miscalculation in the effective lens position will disproportionately translate to a larger prediction error in short eyes. Third, short eyes receive a disproportionately large number of high powered IOLs (eg, O25 D); the manufacturing tolerance for IOLs in this range is closer to 0.5 D to 1.0 D, as opposed to the 0.11 D to 0.3 D tolerance for lower-powered IOLs (Table 5).E As such, it is possible that the poorer outcomes in this population is partially attributable to the lens manufacturing processes. Last, because short eyes have a narrower depth of focus than normal and long eyes, any small error in IOL power selection will translate to disproportionately larger blur. Despite the fact that the IA system uses a completely different technology to predict residual refractive error and suggest IOL powers, it is unable to overcome the basic optical principles that drive poorer outcomes in this unique population. As illustrated above, performance of the tested methods was evaluated both before and after optimization for the study population; both provide important insights. The
analysis displayed before optimization (Table 2) is helpful because it is not practical or customary for surgeons to optimize their formulas specifically for short eyes. As a result, Table 2 shows the performance of the respective formulas with A-constants and surgeon factors that have been shown to work best for the spectrum of ALs that one typically encounters. These lens constants, which are available on the ULIB website,D are the most likely to be preprogrammed and used in biometers across the world. On the other hand, an analysis of the formulas after optimization (Table 4) is the truest test of each method’s performance in the study population. If it had been shown that optimization for short eyes resulted in a significant improvement in outcomes for even one formula, it would have provided evidence to suggest that surgeons should go through the effort of optimization for the sake of providing the best possible patient care. Nevertheless, it is unsurprising that optimization for the study population did not result in significantly improved outcomes in this population; similar data was recently published by G€ okce et al.20 There are several limitations of this study. First, the variety of IOL types implanted was large and included monofocal, toric, and multifocal IOLs. Although the results might have been more robust if a single IOL type had been included, one might also argue that the variety of IOLs used in this study is representative of the true assortment used in clinical practice. Therefore, the study provides realistic estimates of the performance these formulas will have in a setting that includes implantation of premium IOLs.
Table 4. Comparison of the 6 calculation methods after optimizing for the study population in the 35 eyes that received the monofocal Akreos AO60 intraocular lens (Bausch & Lomb, Inc.). Parameter*
MNE
MedNE
MAE
Within ±0.5 D (%)
Within ±1.0 D (%)
Hoffer Q Holladay 2 Haigis Barrett Universal II Hill-RBF IA P value
0.00 0.00 0.00 0.00 0.00 0.00 1.00
C0.04 0.02 0.13 C0.003 0.03 0.11 0.99
0.50 0.54 0.56 0.48 0.50 0.54 0.59
54.3 48.6 54.3 57.1 54.3 48.6 0.52
91.4 88.6 85.7 94.3 88.6 88.6 0.34
IA Z intraoperative aberrometry; MAE Z mean absolute error; MedNE Z median numerical error; MNE Z mean numerical error *Because of the optimization, the model-based mean and the 95% confidence interval is 0.00 and 0.311, 0.169, respectively, for each method
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Table 5. Minimum IOL manufacturing tolerance requirements as defined by the International Standards Organization (ISO 11979-2).E IOL Optic Power Range
5 to 34 with 0.5 D steps
P % 15 D 15 D ! P % 25 D 25 D ! P % 30 D 30 D ! P
G0.3 D G0.4 D G0.5 D G1.0 D
IOL Z intraocular lens; P Z intraocular lens power
Second, the results might have been more generalizable if data from multiple centers and surgeons (only two in the present study) were included in the retrospective analysis. Last, the Hill-RBF formula is not optimized for lens powers greater than C30.00 D, but the study included 4 eyes with IOL powers greater than 30.0 D; therefore, the performance of this method might be underestimated. To our knowledge, this is the first study to evaluate IA in a short eye population. We found that Hoffer Q, Holladay 2, and IA performed equally well, and that the Haigis formula had a tendency toward hyperopic outcomes. When the IA disagrees with the preoperative prediction by more than 0.5 D, the ability of the IA to suggest a more emmetropic outcome is no better than chance. Although the results suggest that IA can likely be relied on as another valid method for IOL selection in this challenging population, the study also underscores the importance of further work to improve outcomes in short eyes.
WHAT WAS KNOWN Refractive outcomes of cataract surgery in eyes with short axial lengths (ALs) are less accurate than in eyes with normal or long ALs. There is poor consensus on which preoperative biometrybased formulas are best in short eyes.
WHAT THIS PAPER ADDS Intraoperative aberrometry (IA) was equivalent to the best tested preoperative biometry-based methods of intraocular lens power prediction in short eyes. When IA disagreed with the preoperative prediction by more than 0.5 D, the ability of IA to suggest a more emmetropic outcome was no better than chance.
REFERENCES 1. Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988; 14:17–244 2. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990; 16:333–340; erratum, 528 3. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993; 19:700–712; errata, 1994; 20:677; 2007; 33:2–3 4. Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol 2000; 238:765–773
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5. Gale RP, Saldana M, Johnston RL, Zuberbuhler B, McKibbin M. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye (Lond) 2009; 23:149–152 €m C, Lundstro €m M. 6. Behndig A, Montan P, Stenevi U, Kugelberg M, Zetterstro Aiming for emmetropia after cataract surgery: Swedish National Cataract Register study. J Cataract Refract Surg 2012; 38:1181–1186 7. Aristodemou P, Knox Cartwright NE, Sparrow JM, Johnston RL. Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferometry. J Cataract Refract Surg 2011; 37:63–71 8. Roh YR, Lee SM, Han YK, Kim MK, Wee WR, Lee JH. Intraocular lens power calculation using IOLMaster and various formulas in short eyes. Korean J Ophthalmol 2011; 25:151–155 9. Hoffer KJ. Clinical results using the Holladay 2 intraocular lens power formula. J Cataract Refract Surg 2000; 26:1233–1237 10. Day AC, Foster PJ, Stevens JD. Accuracy of intraocular lens power calculations in eyes with axial length. Clin Experiment Ophthalmol 2012; 40:855– 862 11. Narvaez J, Zimmerman G, Stulting RD, Chang DH. Accuracy of intraocular lens power prediction using the Hoffer Q, Holladay 1, Holladay 2, and SRK/ T formulas. J Cataract Refract Surg 2006; 32:2050–2053 12. Gavin EA, Hammond CJ. Intraocular lens power calculation in short eyes. Eye (Lond) 2008; 22:935–938 13. Kane JX, Van Heerden A, Atik A, Petsoglou C. Intraocular lens power formula accuracy: Comparison of 7 formulas. J Cataract Refract Surg 2016; 42:1490–1500 14. Chatziralli I, Koutsandrea C, Moschos M. Intraocular lens power calculation in eyes with short axial length. Indian J Ophthalmol 2014; 62:692–694 15. Eom Y, Kang S-Y, Song JS, Kim YY, Kim HM. Comparison of Hoffer Q and Haigis formulae for intraocular lens power calculation according to the anterior chamber depth in short eyes. Am J Ophthalmol 2014; 157:818–824 16. MacLaren RE, Natkunarajah M, Riaz Y, Bourne RRA, Restori M, Allan BDS. Biometry and formula accuracy with intraocular lenses used for cataract surgery in extreme hyperopia. Am J Ophthalmol 2007; 143:920–931 17. Terzi E, Wang L, Kohnen T. Accuracy of modern intraocular lens power calculation formulas in refractive lens exchange for high myopia and high hyperopia. J Cataract Refract Surg 2009; 35:1181–1189 18. Carifi G, Aiello F, Zygoura V, Kopsachilis N, Maurino V. Accuracy of the refractive prediction determined by multiple currently available intraocular lens power calculation formulas in small eyes. Am J Ophthalmol 2015; 159:577–583 19. Cooke DL, Cooke TL. Comparison of 9 intraocular lens power calculation formulas. J Cataract Refract Surg 2016; 42:1157–1164 €kce SE, Zeiter JH, Weikert MP, Koch DD, Hill W, Wang L. Intraocular lens 20. Go power calculations in short eyes using 7 formulas. J Cataract Refract Surg 2017; 43:892–897 21. Roberts TV, Hodge C, Sutton G, Lawless M. contributors to the Vision Eye Institute IOL outcomes registry. Comparison of Hill-radial basis function, Barrett Universal and current third generation formulas for the calculation of intraocular lens power during cataract surgery. Clin Experiment Ophthalmol 2018; 46:240–246 ~o A, Hosking SL, Montes-Mico R, Bates K. Clinical ocular wavefront 22. Cervin analyzers. J Refract Surg 2007; 23:603–616 23. Huelle JO, Katz T, Druchkiv V, Pahlitzsch M, Steinberg J, Richard G, Linke SJ. First clinical results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol 2014; 98:1484–1491 24. Ianchulev T, Salz J, Hoffer K, Albini T, Hsu H, Labree L. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements. J Cataract Refract Surg 2005; 31:1530– 1536 25. Mackool RJ, Ko W, Mackool R. Intraocular lens power calculation after laser in situ keratomileusis: Aphakic refraction technique. J Cataract Refract Surg 2006; 32:435–437 26. Canto AP, Chhadva P, Cabot F, Galor A, Yoo SH, Vaddavalli PK, Culberton WW. Comparison of IOL power calculation methods and intraoperative wavefront aberrometer in eyes after refractive surgery. J Refract Surg 2013; 29:484–489 27. 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 correction. Ophthalmology 2015; 122:1096– 1101 28. Hill DC, Sudhakar S, Hill CS, King TS, Scott IU, Ernst BB, Pantanelli SM. Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in axial myopes. J Cataract Refract Surg 2017; 43:505–510 29. Srivannaboon S, Chirapapaisan C, Chirapapaisan N, Lertsuwanroj B, Chongchareon M. Accuracy of Holladay 2 formula using IOLMaster
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parameters in the absence of lens thickness value. Graefes Arch Clin Exp Ophthalmol 2013; 251:2563–2567 30. Davison JA, Potvin R. Preoperative measurement vs intraoperative aberrometry for the selection of intraocular lens sphere power in normal eyes. Clin Ophthalmol 2017; 11:923–929
OTHER CITED MATERIAL A. Holladay JT. Holladay IOL Consultant User’s Guide and Reference Manual. Houston, TX, Holladay Lasik Institute, 1999 B. Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs .org/barrett_universal2/. Accessed October 4, 2017 C. Hill WE. Hill-RBF method. Available at: http://rbfcalculator.com. Accessed October 4, 2017 D. User Group for Laser Interference Biometry. Available at: http://ocusoft .de/ulib. Accessed January 14, 2018 E. International Organization for Standardization. Ophthalmic Implants – Intraocular lenses – Part 2: Optical properties and test methods (ISO Standard
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No. 11979-2), 2014; Available at: from http://www.iso.org/standard/55682 .html. Accessed November 21, 2018
Disclosures: Dr. Pantanelli has participated in the past as an Advisory Board Member for Carl Zeiss Meditec AG. None of the other authors has a financial or proprietary interest in any material or method mentioned.
First author: Shruti Sudhakar, MD Penn State College of Medicine, Hershey, Pennsylvania, USA
ARTICLE
Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in short eyes Shruti Sudhakar, MD, Darren C. Hill, MD, Tonya S. King, PhD, Ingrid U. Scott, MD, MPH, Gautam Mishra, MD, Brett B. Ernst, MD, Seth M. Pantanelli, MD, MS
Purpose: To compare the accuracy of preoperative biometrybased formulas to intraoperative aberrometry (IA) with respect to predicting refractive outcomes after cataract surgery in short eyes. Setting: Private practice and community-based ambulatory surgery center. Design: Retrospective consecutive case series. Methods: Eyes with an axial length (AL) shorter than 22.1 mm underwent cataract extraction and intraocular lens (IOL) implantation. The predicted residual refractive error was calculated preoperatively using Hoffer Q, Holladay 2, Haigis, Barrett Universal II, and Hill-RBF formulas and intraoperatively using IA. The postoperative spherical equivalent (SE) was compared with the predicted SE to evaluate the accuracy of each aforementioned method. Results: Fifty-one eyes from 38 patients met criteria to be included in the analysis. Without optimizing the formulas specifically
W
hen planning for cataract surgery, calculating the appropriate intraocular lens (IOL) power is typically based upon preoperative biometry measurements. Although older formulas (ie, Holladay 1,1 SRK/T,2 and Hoffer Q3) rely only on axial length (AL) and keratometry measurements, newer ones (ie, Haigis,4 Holladay 2,A and Barrett Universal IIB) take advantage of additional parameters, such as directly measured anterior chamber depth, lens thickness, horizontal white-towhite, and preoperative refraction to improve accuracy. In normal eyes (AL Z 22.0 to 25.2 mm), refractive outcomes are reported to be within G0.5 diopter (D) in 55% to 75% of cases and within G1.0 D in 85% to 95% of cases.5–7 However, among eyes with an AL shorter
for short eyes, the mean numerical errors (MNEs) associated with Hoffer Q, Holladay 2, Haigis, Barrett Universal II, Hill-RBF, and IA were 0.08 (95% confidence interval [CI], 0.30 to 0.13), 0.14 (95% CI, 0.35 to 0.07), C0.26 (95% CI, 0.05 to 0.47), C0.11 (95% CI, 0.10 to 0.32), C0.07 (95% CI, 0.14 to 0.28), and C0.00 (95% CI, 0.21 to 0.21), respectively (P < .001). The proportion of eyes within G0.5 diopter (D) of the predicted SE were 49.0%, 43.1%, 52.9%, 52.9%, 60.8%, and 58.8%, respectively (P Z .06). The prediction outcomes from IA were statistically better than Haigis, but not other formulas. When formula and IA predictions differed by 0.5 D or more, IA’s ability to recommend a more emmetropic outcome was no better than chance (50%).
Conclusions: Intraoperative aberrometry is not significantly different from the best preoperative biometry-based methods available for IOL power selection in short eyes. J Cataract Refract Surg 2018; -:-–- Q 2018 ASCRS and ESCRS
than 22.0 mm, predictive accuracy is less precise. In these short eyes, accuracy to within G0.5 D ranged between 21% and 71% in a study by Aristodemou et al.7 and between 45% and 75% in a study by Roh et al.,8 depending on the formula used. Hoffer Q has traditionally been preferred for use in short eyes.9–13 More recent studies suggest that the Haigis and Barrett Universal II formulas might also be excellent choices for this population.8,9,13–21 Roh et al.8 reported that Haigis produced the smallest mean absolute error and had a higher proportion of outcomes within G1.0 D. Alternatively, in a study by Kane et al.,13 Barrett Universal II was the most accurate for all ALs, including short eyes. A new formula, Hill-RBF,C was introduced in 2016, and a
Submitted: July 17, 2018 | Final revision submitted: December 14, 2018 | Accepted: December 17, 2018 Penn State College of Medicine (Sudhakar), Hershey, Pennsylvania, the Department of Ophthalmology (Hill), University of Kentucky, Lexington, Kentucky, the Department of Public Health Sciences (King, Scott), Penn State College of Medicine, Hershey, the Department of Ophthalmology (Scott, Pantanelli), the Penn State College of Medicine, Hershey, and the Schein Ernst Mishra Eye (Mishra, Ernst), Harrisburg, Pennsylvania, USA. Presented in part at the annual meeting of the Association for Research in Vision and Ophthalmology, Seattle, Washington, USA, May 2016. Corresponding author: Seth M. Pantanelli, MD, MS, Penn State Eye Center, 500 University Drive, HU19, Hershey, PA 17033, USA. Email: spantanelli@pennstatehealth. psu.edu. Q 2018 ASCRS and ESCRS Published by Elsevier Inc.
0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2018.12.016
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
recent study by G€ okce et al.20 reported a lower median numerical error with Hill-RBF than Hoffer Q in short eyes. Similarly, Roberts et al.21 also found that Hill-RBF yielded the lowest mean numerical error in long and short eyes. The many conflicting conclusions on this topic suggests that there is no consensus on which preoperative biometry-based formula is best for use in short eyes. The ORA System (Alcon Laboratories, Inc.) is an intraoperative wavefront aberrometer that uses preoperative biometry measurements and intraoperative Talbot-Moire interferometry to measure an aphakic eye’s refractive power for appropriate IOL selection.22,23 The technology seeks to overcome potential inaccuracies of clinic-based biometry by taking measurements in the aphakic state, which renders it uninfluenced by the cataractous lens. The intraoperative aberrometry (IA) device has already been shown to outperform conventional formulas for IOL power selection in patients with a history of refractive surgery (eg, laser in situ keratomileusis [LASIK] and photorefractive keratectomy).24–27 Fram et al.27 reported outcomes of 75% within G0.5 D and 97% within G1.0 D in eyes with previous laser vision correction.27 IA has also been validated as extremely accurate in eyes with axial myopia, with outcomes of 80% within G0.5 D and 98% within G1.0 D of target spherical equivalent (SE).28 In eyes with axial myopia, IA was shown to be equivalent or better than many biometry-based formulas (ie, Holladay 1, Holladay 2, Barrett Universal II, and Hill-RBF).28 To date, there is no published literature that evaluates IA specifically in short eyes. As such, the purpose of the current study was to compare the performance of IA (ORA System) to other conventional biometry-based formulas in short eyes.
PATIENTS AND METHODS A retrospective review was conducted of patients who underwent routine phacoemulsification cataract surgery with in-the-bag IOL implantation by one of two surgeons (B.B.E. or G.M.) between October 20, 2014 and September 11, 2017. All surgeries were performed at a private ambulatory surgery center (Capital Surgery and Laser Center, LLC, Harrisburg, PA). Eyes were excluded if they had a history of prior ocular surgery or trauma, ocular inflammatory conditions, vision-limiting retinal or optic nerve disease, complications during cataract surgery, a target postoperative refraction other than plano, lack of follow-up, or postoperative corrected distance visual acuity worse than 20/40. A total of 51 eyes from 38 patients were eligible for the inclusion in the study based on these criteria. Optical biometry was performed using partial coherence interferometry (IOLMaster, Carl Zeiss Meditec AG). The predicted refractive error was calculated using 6 different methods: (1) Hoffer Q, (2) Holladay 2, (3) Haigis, (4) Barrett Universal II, (5) Hill-RBF, and (6) IA (ORA System). It is not standard practice to optimize A-constants and surgeon factors specifically for short eyes; as such, the constants used for each formula and IOL were those recommended by the User Group for Laser Interference Biometry (ULIB) database.D For patients with no measured lens thickness, a standard lens thickness value of 5.0 mm was used for the Holladay 2 calculations.29 Calculations for the Barrett Universal II and Hill-RBF formulas were performed using online calculators from the Asia-Pacific Association of Cataract and Volume - Issue - - 2019
Refractive Surgeons and the expanded beta version of the HillRBF calculator, respectively.B,C Intraoperatively and after cortical clean-up, the eye was inflated to an intraocular pressure of 20 mm Hg using a balanced salt solution and a Barraquer tonometer for pressure measurement. IA was used to measure the eye in the aphakic state to estimate the predicted refractive error for the implanted IOL. If the IA system recommended an IOL that was different from that originally intended, the surgeon’s best judgement was used to implant the IOL most likely to result in emmetropia. The final refraction was performed at least 20 days and no more than 60 days after surgery. The primary outcome measures included the difference between predicted and actual postoperative SE (numerical error), and proportion of eyes within G0.5 D and G1.0 D of their target SE refraction. The mean and median numerical errors were calculated for each of the 6 methods, as were the proportion of eyes within G0.5 D and G1.0 D of predicted. In a separate analysis, the formulas were optimized specifically for the study population, and for the 35 eyes that received an Akreos AO60 IOL (Bausch & Lomb, Inc.), by adding the mean numerical error for each formula to the predicted SE for each eye, thereby driving the mean numerical error to zero. To evaluate the differences between formulas with regard to the mean numerical error and the median numerical error while accounting for the correlation within each patient, repeated-measures analysis of variance and repeated-measures rank analysis of variance tests were performed using SAS/STAT software (version 9.4, SAS Institute, Inc.) with a probability of less than 5% (P ! .05) representing statistical significance. Repeated-measures logistic regression and Cochran Q tests were performed to evaluate differences between formulas with regard to the proportion of eyes within G0.5 D and G1.0 D. A Bonferroni-adjusted pairwise analysis was used to identify statistically significant differences between the methods.
RESULTS The study comprised 51 eyes from 38 patients. Table 1 shows the demographics of the study population. Thirtyseven of the 51 eyes received a monofocal IOL (Akreos AO60 [Bausch & Lomb, Inc.], AF-1 FY-60AD [Hoya Surgical Optics, Inc.], or SA60AT [Alcon Laboratories, Inc.]); 9 received a toric IOL (Tecnis ZCT150, ZCT225, ZCT300, or ZCT400 [all Johnson & Johnson Vision Care, Inc.]); and 5 received a multifocal IOL (Tecnis ZKB00 or ZLB00 [Johnson & Johnson Vision Care, Inc.]). Table 2 shows a comparison of the outcomes of the 6 methods before optimizing for the study population. It is interesting to note that the Hoffer Q, Holladay 2, Barrett Universal II, Hill-RBF, and the IA system had mean numerical errors statistically equivalent to zero despite using lens constants and surgeon factors that were not specifically optimized for short eyes; this suggests that these particular methods might be well suited for a wide range of eyes and that the lens constants used for normal eyes are likely applicable to short eyes as well. Haigis was the only formula that had a mean numerical error statistically different from zero (P Z .02), with a tendency toward hyperopia. The IA also trended toward superior performance with respect to the proportion of eyes within G0.5 D and G1.0 D, although this superiority did not reach statistical significance. The Cochran Q test results were similar to those from the model-based approach shown in Table 2, with P values of
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
Table 1. Demographics of the study population. IOL Type Parameter IOL Power (D) Mean G SD Range AL (mm) Mean G SD Range
Monofocal
Toric
Multifocal
24.7 G 1.7 21.0, 28.5
29.1 G 4.0 22.5, 34.0
26.1 G 1.7 23.5, 28.0
21.69 G 0.33 20.41, 22.06
21.00 G 0.85 19.77, 21.92
21.70 G 0.25 21.32, 21.94
AL Z axial length; IOL Z intraocular lens
0.22 and 0.43 for the proportion of eyes within G0.5 D and G1.0 D, respectively. Because statistical significance was reached with respect to the mean numerical error, a Bonferroni-adjusted pairwise analysis was performed on this metric, the results of which are shown in Table 3. Hoffer Q, Holladay 2, and IA had the lowest mean numerical errors and were not significantly different from one another. All three of these formulas were superior to Haigis, which performed worst (P % .001). There was no statistically significant difference with regard to the proportion of eyes within G0.5 D and G1.0 D of the target SE. Table 4 shows a comparison of the outcomes of the 6 methods after optimizing for the study population. Because optimization cannot be done when a variety of IOLs are used, only eyes that received the monofocal Akreos AO60 IOL were included in this analysis. Although optimization did change the performance of many of the formulas with regard to the proportion of eyes within G0.5 D and G1.0 D of the target SE, these differences were small and not significant. IA remained one of the best performing methods, but its superiority was not statistically different from the other methods. The Barrett Universal II agreed with the aberrometer (within G0.5 D) 72.5% of the time. In instances in which there were disagreements greater than 0.5 D, the Barrett Universal II would have outperformed IA 13.7% of the time, and the IA would have outperformed the Barrett Universal II 13.6% of the time. Likewise, the Hill-RBF agreed with the IA (within G0.5 D) 88.2% of the time. In instances in which there were disagreements greater than 0.5 D, the Hill-RBF would have outperformed IA 5.9% of the time,
and the IA would have outperformed Hill-RBF 5.9% of the time. In other words, the probability that the IA improved outcomes when there was disagreement was no better than chance (50% of the time). The same trends were observed for all the other formulas (Hoffer Q, Holladay 2, and Haigis). DISCUSSION Previous studies have shown that IA performs well in eyes with a history of refractive surgery, such as LASIK.25–28 Similarly, Hill et al.19 demonstrated that IA (ORA) was equivalent to the most robust formulas in eyes with axial myopia. To the best of our knowledge, this is the first study to compare the Alcon ORA to preoperative biometry-based formulas in short eyes. We have shown that ORA performs at least as well as other commonly used formulas for this population. Users of IA might ascribe to the idea that improved outcomes come from the surgeon’s ability to change the chosen IOL power “on the fly.” For this to be true, it must first be shown that the IA’s predictions are better aligned with actual postoperative results than preoperative calculations. If this is not the case, it is impossible for the surgeon to know when to believe the IA calculations. As mentioned in the results above, the IA system’s ability to improve outcomes when its recommendation differed from Barrett Universal II and Hill-RBF by more than 0.5 D was no better than chance. This finding is supported in a previous study by Davison and Potvin,30 which found that when the preoperative and IA calculations differed by more than 0.5 D, the chance that the aberrometer’s recommendation was better was 56% and not statistically different from 50%. In
Table 2. Comparison of the 6 calculation methods before optimizing for the study population. Parameter 3
Hoffer Q Holladay 2A Haigis4 Barrett Universal IIB Hill-RBFC IA P value
MNE (95% CI) 0.08 ( 0.14 ( C0.26 C0.11 ( C0.07 ( C0.00 ( !.001
0.30, 0.13) 0.35, 0.07) (0.05, 0.47)* 0.10, 0.32) 0.14, 0.28) 0.21, 0.21)
MedNE
MAE
Within ±0.5 D (%)
Within ±1.0 D (%)
0.09 0.09 C0.19 C0.17 C0.11 0.02 !.001
0.54 0.53 0.60 0.51 0.49 0.48 0.47
49.0 43.1 52.9 52.9 60.8 58.8 0.06
86.3 88.2 80.4 86.3 90.2 88.2 0.31
CI Z confidence interval; IA Z intraoperative aberrometry; MAE Z mean absolute error; MedNE Z median numerical error; MNE Z mean numerical error *Statistically significant
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
Table 3. Post hoc analysis of the mean numerical errors in the intraocular lens calculation methods. P Value Parameter Hoffer Q3 Holladay 2A Haigis4 Barrett Universal IIB Hill-RBFC IA
Hoffer Q
Holladay 2
Haigis
Barrett Universal II
Hill-RBF
IA
d d d d d d
.450 d d d d d
!.001* !.001* d d d d
.014 !.001* .047 d d d
.042 .006 .016 .665 d d
.259 .061 .001* .179 .360 d
IA Z intraoperative aberrometry *Statistically significant after Bonferroni correction
conclusion, we do not believe there is sufficient evidence to suggest that altering the IOL power implanted based on the aberrometer’s recommendations improves refractive outcomes for the short eye population. It is unfortunate that the performance of all methods, including IA, is so poor when compared with how well these methods fair in eyes with normal ALs. As has been described elsewhere, poor performance of biometry-based methods in short eyes is attributable to multiple factors. First, the variables determining effective lens position in this population might not be fully understood. Second, any miscalculation in the effective lens position will disproportionately translate to a larger prediction error in short eyes. Third, short eyes receive a disproportionately large number of high powered IOLs (eg, O25 D); the manufacturing tolerance for IOLs in this range is closer to 0.5 D to 1.0 D, as opposed to the 0.11 D to 0.3 D tolerance for lower-powered IOLs (Table 5).E As such, it is possible that the poorer outcomes in this population is partially attributable to the lens manufacturing processes. Last, because short eyes have a narrower depth of focus than normal and long eyes, any small error in IOL power selection will translate to disproportionately larger blur. Despite the fact that the IA system uses a completely different technology to predict residual refractive error and suggest IOL powers, it is unable to overcome the basic optical principles that drive poorer outcomes in this unique population. As illustrated above, performance of the tested methods was evaluated both before and after optimization for the study population; both provide important insights. The
analysis displayed before optimization (Table 2) is helpful because it is not practical or customary for surgeons to optimize their formulas specifically for short eyes. As a result, Table 2 shows the performance of the respective formulas with A-constants and surgeon factors that have been shown to work best for the spectrum of ALs that one typically encounters. These lens constants, which are available on the ULIB website,D are the most likely to be preprogrammed and used in biometers across the world. On the other hand, an analysis of the formulas after optimization (Table 4) is the truest test of each method’s performance in the study population. If it had been shown that optimization for short eyes resulted in a significant improvement in outcomes for even one formula, it would have provided evidence to suggest that surgeons should go through the effort of optimization for the sake of providing the best possible patient care. Nevertheless, it is unsurprising that optimization for the study population did not result in significantly improved outcomes in this population; similar data was recently published by G€ okce et al.20 There are several limitations of this study. First, the variety of IOL types implanted was large and included monofocal, toric, and multifocal IOLs. Although the results might have been more robust if a single IOL type had been included, one might also argue that the variety of IOLs used in this study is representative of the true assortment used in clinical practice. Therefore, the study provides realistic estimates of the performance these formulas will have in a setting that includes implantation of premium IOLs.
Table 4. Comparison of the 6 calculation methods after optimizing for the study population in the 35 eyes that received the monofocal Akreos AO60 intraocular lens (Bausch & Lomb, Inc.). Parameter*
MNE
MedNE
MAE
Within ±0.5 D (%)
Within ±1.0 D (%)
Hoffer Q Holladay 2 Haigis Barrett Universal II Hill-RBF IA P value
0.00 0.00 0.00 0.00 0.00 0.00 1.00
C0.04 0.02 0.13 C0.003 0.03 0.11 0.99
0.50 0.54 0.56 0.48 0.50 0.54 0.59
54.3 48.6 54.3 57.1 54.3 48.6 0.52
91.4 88.6 85.7 94.3 88.6 88.6 0.34
IA Z intraoperative aberrometry; MAE Z mean absolute error; MedNE Z median numerical error; MNE Z mean numerical error *Because of the optimization, the model-based mean and the 95% confidence interval is 0.00 and 0.311, 0.169, respectively, for each method
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INTRAOPERATIVE ABERROMETRY IN SHORT EYES
Table 5. Minimum IOL manufacturing tolerance requirements as defined by the International Standards Organization (ISO 11979-2).E IOL Optic Power Range
5 to 34 with 0.5 D steps
P % 15 D 15 D ! P % 25 D 25 D ! P % 30 D 30 D ! P
G0.3 D G0.4 D G0.5 D G1.0 D
IOL Z intraocular lens; P Z intraocular lens power
Second, the results might have been more generalizable if data from multiple centers and surgeons (only two in the present study) were included in the retrospective analysis. Last, the Hill-RBF formula is not optimized for lens powers greater than C30.00 D, but the study included 4 eyes with IOL powers greater than 30.0 D; therefore, the performance of this method might be underestimated. To our knowledge, this is the first study to evaluate IA in a short eye population. We found that Hoffer Q, Holladay 2, and IA performed equally well, and that the Haigis formula had a tendency toward hyperopic outcomes. When the IA disagrees with the preoperative prediction by more than 0.5 D, the ability of the IA to suggest a more emmetropic outcome is no better than chance. Although the results suggest that IA can likely be relied on as another valid method for IOL selection in this challenging population, the study also underscores the importance of further work to improve outcomes in short eyes.
WHAT WAS KNOWN Refractive outcomes of cataract surgery in eyes with short axial lengths (ALs) are less accurate than in eyes with normal or long ALs. There is poor consensus on which preoperative biometrybased formulas are best in short eyes.
WHAT THIS PAPER ADDS Intraoperative aberrometry (IA) was equivalent to the best tested preoperative biometry-based methods of intraocular lens power prediction in short eyes. When IA disagreed with the preoperative prediction by more than 0.5 D, the ability of IA to suggest a more emmetropic outcome was no better than chance.
REFERENCES 1. Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. A three-part system for refining intraocular lens power calculations. J Cataract Refract Surg 1988; 14:17–244 2. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990; 16:333–340; erratum, 528 3. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg 1993; 19:700–712; errata, 1994; 20:677; 2007; 33:2–3 4. Haigis W, Lege B, Miller N, Schneider B. Comparison of immersion ultrasound biometry and partial coherence interferometry for intraocular lens calculation according to Haigis. Graefes Arch Clin Exp Ophthalmol 2000; 238:765–773
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5. Gale RP, Saldana M, Johnston RL, Zuberbuhler B, McKibbin M. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye (Lond) 2009; 23:149–152 €m C, Lundstro €m M. 6. Behndig A, Montan P, Stenevi U, Kugelberg M, Zetterstro Aiming for emmetropia after cataract surgery: Swedish National Cataract Register study. J Cataract Refract Surg 2012; 38:1181–1186 7. Aristodemou P, Knox Cartwright NE, Sparrow JM, Johnston RL. Formula choice: Hoffer Q, Holladay 1, or SRK/T and refractive outcomes in 8108 eyes after cataract surgery with biometry by partial coherence interferometry. J Cataract Refract Surg 2011; 37:63–71 8. Roh YR, Lee SM, Han YK, Kim MK, Wee WR, Lee JH. Intraocular lens power calculation using IOLMaster and various formulas in short eyes. Korean J Ophthalmol 2011; 25:151–155 9. Hoffer KJ. Clinical results using the Holladay 2 intraocular lens power formula. J Cataract Refract Surg 2000; 26:1233–1237 10. Day AC, Foster PJ, Stevens JD. Accuracy of intraocular lens power calculations in eyes with axial length. Clin Experiment Ophthalmol 2012; 40:855– 862 11. Narvaez J, Zimmerman G, Stulting RD, Chang DH. Accuracy of intraocular lens power prediction using the Hoffer Q, Holladay 1, Holladay 2, and SRK/ T formulas. J Cataract Refract Surg 2006; 32:2050–2053 12. Gavin EA, Hammond CJ. Intraocular lens power calculation in short eyes. Eye (Lond) 2008; 22:935–938 13. Kane JX, Van Heerden A, Atik A, Petsoglou C. Intraocular lens power formula accuracy: Comparison of 7 formulas. J Cataract Refract Surg 2016; 42:1490–1500 14. Chatziralli I, Koutsandrea C, Moschos M. Intraocular lens power calculation in eyes with short axial length. Indian J Ophthalmol 2014; 62:692–694 15. Eom Y, Kang S-Y, Song JS, Kim YY, Kim HM. Comparison of Hoffer Q and Haigis formulae for intraocular lens power calculation according to the anterior chamber depth in short eyes. Am J Ophthalmol 2014; 157:818–824 16. MacLaren RE, Natkunarajah M, Riaz Y, Bourne RRA, Restori M, Allan BDS. Biometry and formula accuracy with intraocular lenses used for cataract surgery in extreme hyperopia. Am J Ophthalmol 2007; 143:920–931 17. Terzi E, Wang L, Kohnen T. Accuracy of modern intraocular lens power calculation formulas in refractive lens exchange for high myopia and high hyperopia. J Cataract Refract Surg 2009; 35:1181–1189 18. Carifi G, Aiello F, Zygoura V, Kopsachilis N, Maurino V. Accuracy of the refractive prediction determined by multiple currently available intraocular lens power calculation formulas in small eyes. Am J Ophthalmol 2015; 159:577–583 19. Cooke DL, Cooke TL. Comparison of 9 intraocular lens power calculation formulas. J Cataract Refract Surg 2016; 42:1157–1164 €kce SE, Zeiter JH, Weikert MP, Koch DD, Hill W, Wang L. Intraocular lens 20. Go power calculations in short eyes using 7 formulas. J Cataract Refract Surg 2017; 43:892–897 21. Roberts TV, Hodge C, Sutton G, Lawless M. contributors to the Vision Eye Institute IOL outcomes registry. Comparison of Hill-radial basis function, Barrett Universal and current third generation formulas for the calculation of intraocular lens power during cataract surgery. Clin Experiment Ophthalmol 2018; 46:240–246 ~o A, Hosking SL, Montes-Mico R, Bates K. Clinical ocular wavefront 22. Cervin analyzers. J Refract Surg 2007; 23:603–616 23. Huelle JO, Katz T, Druchkiv V, Pahlitzsch M, Steinberg J, Richard G, Linke SJ. First clinical results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol 2014; 98:1484–1491 24. Ianchulev T, Salz J, Hoffer K, Albini T, Hsu H, Labree L. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements. J Cataract Refract Surg 2005; 31:1530– 1536 25. Mackool RJ, Ko W, Mackool R. Intraocular lens power calculation after laser in situ keratomileusis: Aphakic refraction technique. J Cataract Refract Surg 2006; 32:435–437 26. Canto AP, Chhadva P, Cabot F, Galor A, Yoo SH, Vaddavalli PK, Culberton WW. Comparison of IOL power calculation methods and intraoperative wavefront aberrometer in eyes after refractive surgery. J Refract Surg 2013; 29:484–489 27. 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 correction. Ophthalmology 2015; 122:1096– 1101 28. Hill DC, Sudhakar S, Hill CS, King TS, Scott IU, Ernst BB, Pantanelli SM. Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in axial myopes. J Cataract Refract Surg 2017; 43:505–510 29. Srivannaboon S, Chirapapaisan C, Chirapapaisan N, Lertsuwanroj B, Chongchareon M. Accuracy of Holladay 2 formula using IOLMaster
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parameters in the absence of lens thickness value. Graefes Arch Clin Exp Ophthalmol 2013; 251:2563–2567 30. Davison JA, Potvin R. Preoperative measurement vs intraoperative aberrometry for the selection of intraocular lens sphere power in normal eyes. Clin Ophthalmol 2017; 11:923–929
OTHER CITED MATERIAL A. Holladay JT. Holladay IOL Consultant User’s Guide and Reference Manual. Houston, TX, Holladay Lasik Institute, 1999 B. Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs .org/barrett_universal2/. Accessed October 4, 2017 C. Hill WE. Hill-RBF method. Available at: http://rbfcalculator.com. Accessed October 4, 2017 D. User Group for Laser Interference Biometry. Available at: http://ocusoft .de/ulib. Accessed January 14, 2018 E. International Organization for Standardization. Ophthalmic Implants – Intraocular lenses – Part 2: Optical properties and test methods (ISO Standard
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No. 11979-2), 2014; Available at: from http://www.iso.org/standard/55682 .html. Accessed November 21, 2018
Disclosures: Dr. Pantanelli has participated in the past as an Advisory Board Member for Carl Zeiss Meditec AG. None of the other authors has a financial or proprietary interest in any material or method mentioned.
First author: Shruti Sudhakar, MD Penn State College of Medicine, Hershey, Pennsylvania, USA