SPS-110 Post Refractive Surgery - IOL Calculations | ASCRS
2020 ASCRS Virtual Annual Meeting

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Papers in this Session
Expand each tab below to view the paper abstract for each paper within this session.
Astigmatism Reduction Following Implantation of Toric Intraocular Lens in Patients with Previous Radial Keratotomy
Authors
Meisha Raven, DO
Michael Shapiro, MD, MS
Patricia Sabb, MD
Sarah Nehls, MD

Purpose
To evaluate the effectiveness of astigmatism reduction following phacoemulsification with monofocal toric intraocular lens implantation in patients with previous radial keratotomy.

Methods
A retrospective chart review of data from patients with previous radial keratotomy (RK) who underwent routine cataract surgery with insertion of a monofocal toric IOL between January 2010 through September 2018 was performed. Fifty-one eyes of 35 patients were included in this study. This was a consecutive series of patients with a minimum 3-month postoperative follow up. No patients were excluded from the study. The outcome measurements included average keratometric K, pre- and postoperative best corrected visual acuity (BCVA), postoperative uncorrected visual acuity (UCVA), manifest refraction, keratometric astigmatism, and postoperative uncorrected visual acuity.

Results
Average autokeratometric mean was 39.33 D and average keratometric astigmatism was 3.34 D (1.26 - 14.73D). BCVA averaged 0.33 (Snellen equivalent of 20/42) ± 0.16 logMAR preoperatively and 0.08 (Snellen 20/24) ± 0.13 logMAR postoperatively. Fifty-five percent of the eyes achieved an UCVA of 20/30 or better and 73% with 20/40 or better. Mean UCVA postoperative vision was 0.24 (Snellen 20/34) +/- 0.17 logMAR. Residual refractive astigmatism of ≤1.00 D was achieved in 68% of eyes and <1.5 D in 80%. A Welch’s T-test showed a significant difference in the mean scores (µ = .06, SD=0.114) between post-operative BCVA logMAR for mean K ≤ 36 and (µ = .19, SD= 0.136) for mean K >36 (p-value of 0.023).

Conclusion
To our knowledge, this is the first study to report the outcomes of monofocal toric intraocular lens implantation in patients having phacoemulsification after previous RK surgery. Implantation of this lens in patients with previous RK surgery is a safe, effective method of reducing refractive astigmatism in cataract patients.
Outcome of Toric Intraocular Lens Implanted in Eyes with Previous LASIK/PRK
Authors
Li Wang, MD, PhD
Danmin Cao, MD
Douglas D. Koch, MD, ABO

Purpose
To evaluate the outcome of toric intraocular lens (IOL) implantation in eyes with previous LASIK/PRK.

Methods
Retrospectively, we reviewed consecutive cases that had previous myopic or hyperopic LASIK/PRK and had undergone cataract surgery with toric IOL implantation. We included eyes that had: 1) preoperative ocular biometry measurements with the Lenstar, 2) no intraoperative or postoperative complications, and 3) available postoperative manifest refraction at 3 weeks or longer with best-corrected visual acuity of 20/30 or better. Vector analysis was used to assess the preoperative corneal and postoperative refractive astigmatism.

Results
In 56 eyes with previous myopic LASIK/PRK and 19 eyes with previous hyperopic LASIK/PRK, respectively, the mean magnitudes of corneal astigmatism were 1.34 ± 0.62 D and 1.66 ± 0.80 D, 5% and 0% of eyes had anterior corneal astigmatism 0.5 D or less, and the centroid values were 0.31 D @ 19 degrees ± 1.45 D and 0.74 D @ 92 degrees ± 1.72 D preoperatively. Postoperatively, the mean magnitudes of refractive astigmatism were 0.36 ± 0.31 D and 0.34 ± 0.34 D, 80% and 84% of eyes had refractive astigmatism 0.5 D or less, and the centroid values were 0.12 D @ 152 degrees ± 0.46 D and 0.05 D @ 172 degrees ± 0.48 D (all P<0.05).

Conclusion
Toric IOLs are effective to correct preexisting corneal astigmatism in eyes with previous excimer laser corneal refractive surgery.
Accuracy of Astigmatism Correction with Toric Intraocular Lens Implantation in Eyes with Prior Radial Keratotomy
Authors
Ana Laura C. Canedo, MD
Douglas D. Koch, MD, ABO
Li Wang, MD, PhD

Purpose
To evaluate refractive outcomes of toric intraocular lens (IOL) implantation in eyes with previous radial keratotomy (RK).

Methods
Toric IOLs were implanted in 72 eyes. The same surgeon performed each operation. The Lenstar LS900 (Haag-Streit AG) was used in this study. Implanted IOLs were either the Alcon lenses (SN6ATx series, Fort Worth, TX, USA) or the Johnson & Johnson Vision lenses (ZCTxxx series, Santa Ana, CA, USA). Vector analysis was performed, and we compared preoperative corneal astigmatism to postoperative refractive astigmatism.

Results
Preoperatively, 1% and 8% of eyes had corneal astigmatism ≤0.5 D and ≤1.0 D, and postoperatively 69% and 83% of eyes had refractive astigmatism ≤0.5 D and ≤1.0 D, respectively (P<0.05). The centroid values were 0.93 D @ 1° ± 2.02 D preoperatively and 0.17 D @ 168° ± 0.68 D postoperatively (P<0.05).

Conclusion
Toric IOLs can be successfully used to treat corneal astigmatism in RK eyes.
Advanced IOL Calculations Using High-Resolution Scheimpflug and Spectral Domain OCT Imaging in Post-Myopic LASIK Cataract Eyes
Authors
Neeraj S. Chawla
Navaneet S. Borisuth, MD, PhD

Purpose
To compare the accuracy of a high-resolution Scheimpflug camera-based formula (Potvin-Hill) and a spectral-domain OCT based formula to the ASCRS calculator for previous myopic LASIK eyes undergoing phacoemulsification (PE) with standard (SV) and premium (P) IOLs.

Methods
This is a retrospective nonrandomized clinical cohort study of 170 post-myopic LASIK eyes that underwent PE with PCIOL implantation. Postoperative refractive data were used to compare back-calculated optimum IOL powers (BCO) and to derive the absolute prediction error (AE). We conducted further subanalyses of the relationship between axial length, optimum power IOL, and the Potvin-Hill and OCT formulas. Eyes with corneal pathologies including keratectasia, pterygium, and Fuch's endothelial dystrophy were excluded from the study as were retinal pathologies including epiretinal membranes, age-related macular degeneration, and active diabetic retinopathy.

Results
We implanted 72 SV PCIOLs and 98 P-IOLs (32 toric, 66 EDOF) in 170 post-myopic LASIK eyes undergoing PE. 81.6% and 91.1% of eyes fell within +/- 0.5D and +/-1.0D of target prediction refraction respectively. In descending order, BCO was most accurate for the Barrett True K formula(AE= 0.40), ASCRS Average (0.42), Masket (0.47), Modified Masket (0.53), Potvin-Hill (0.54), Haigis-L (0.54), OCT (0.62), and Shammas (0.67). When compared to the OCT and Shammas formulas, the Barrett True K, ASCRS Average, and Masket formulas demonstrated statistical significance (p<0.001).

Conclusion
The Barrett, ASCRS Average, and Masket formulas outperformed the Potvin-Hill and OCT power calculations although the difference was only statistically significant for the OCT power calculation comparison. The Potvin-Hill formula typically under-predicted optimum IOL power and performed best in eyes with a greater axial length.
Refractive Outcomes of a Light Adjustable Lens in Cataract Patients with a History of Radial Keratotomy and/or Astigmatic Keratotomy
Author
James D. Lehmann, MD

Purpose
To describe the results of phacoemulsification and implantation of a light adjustable lens in patients with a history of previous incisional refractive surgery such as RK and AK.

Methods
Retrospective case series of 11 patients (16 eyes) with cataract and a history of RK and/or AK who underwent phacoemulsification with implantation of a light adjustable lens. Two weeks after the second eye surgery, the patients underwent adjustment by ultraviolet (UV) light. Postoperatively, manifest refraction, astigmatism, and spherical equivalent were recorded for all patients. The mean absolute error (MAE) and percentage of eyes within 0.5 D from target were calculated. Follow-up time was between 2 and 4 months.

Results
The mean absolute error MAE after adjustment was 0.31 D, and the % of eyes within 0.5 D after adjustment was 94% (15/16 eyes). Prior to adjusting the IOL, the MAE was 0.97 D and the % of eyes within 0.5 D was only 50%.

Conclusion
The Light Adjustable Lens works well in eyes with previous RK surgery, with refractive results superior to current technology such as intraoperative aberrometry and IOL formulae. Limitations of these data include sample size and length of follow up.
Evaluation of IOL Power Calculation Formulas Using Different Keratometries in Post-Refractive Surgery Cases
Authors
Chad M. Serels
Helga P. Sandoval, MD, MSc
Richard Potvin, OD
Kerry D. Solomon, MD

Purpose
The purpose of this study is to provide information as to which keratometry measurements and which intraocular (IOL) power calculation formulas are best predictive for optimal outcomes in patients with previous corneal refractive surgery undergoing cataract surgery.

Methods
Retrospective chart review of all consecutive post refractive surgery patients undergoing cataract removal and implantation of a monofocal or monofocal toric IOL from January 2018 to July 2019. Eyes with postoperative refraction at least 3 weeks after surgery were included. IOL power was calculated with the ASCRS Online Post-Refractive IOL Calculator using anterior keratometry and recalculated using total corneal power (TK) measured with IOL Master 700. Intraoperative aberrometry data was also collected. Emmetropic IOL power will be back-calculated and the accuracy of treatment will be determined and compared between the different formulas, keratometry methods and intraoperative aberrometry.

Results
Data from 109 post myopic LASIK eyes, 46 of which had total corneal power available, were analyzed. Using TK, the Wang-Koch formula had the highest percentages of eyes with expected spherical equivalent refractive errors within 0.50D and 1.00D of plano (57% and 87% respectively). With anterior Ks the Barrett TrueK formula had the highest percentages within 0.50D and 1.00D of plano (64% and 92% respectively), but was not significantly better than Wang-Koch with TK within 0.50D and 1.00D (McNemar test, p > 0.2). Expected mean spherical equivalent results based on IA were not significantly different than for Barrett TrueK for within 0.50D or within 1.00D (McNemar test, p > 0.2).

Conclusion
Using measured total corneal power in existing post-LASIK formulas did not appear beneficial. The formulas themselves may have to be adjusted to account for TK. The best expected results were obtained with the Barrett TrueK formula and anterior keratometry. IA did not appear to materially improve sphere power determination.
Refractive Outcomes Using a Placido Optical Biometer & Barrett True K / True K Toric Formulae in Eyes with Prior Laser Refractive Surgery
Authors
Suzan Abouzeid, FRCS, MS
Mohammed Muhtaseb, FRCOphth, MBBS

Purpose
To report the accuracy of refractive outcomes after phakoemulsification when biometry was taken using a Placido-based optical biometer (Aladdin) and Barrett True K / True K toric formulae were used for IOL calculation in eyes that had prior corneal laser refractive surgery.

Methods
A retrospective review of refractive outcomes in 7 eyes that underwent phakoemulsification + IOL implantation between March & October 2019. Inclusion criteria were eyes that had previous corneal refractive surgery and either significant cataract or refractive error. Biometry was taken using the Aladdin Placido disc optical biometer, and IOL calculation was undertaken using the Barrett True K and True K Toric formulae (which are integrated into the Aladdin biometer). Surgeries were performed by a single surgeon using a 2.2mm corneal incision with IOL placement in the capsular bag. Final refraction was performed no earlier than 4 weeks post-operatively. Patients received a variety of IOL types

Results
Two eyes, that each received a multifocal IOL, were within +/- 0.25D of the pre-operative target. Unaided visual acuity was 20/16 for distance and J2 for near in each eye. One eye, that received a monofocal IOL, was within +/- 0.5D of the pre-operative target and unaided distance visual acuity was 20/20. Results from other eyes remain to be entered. Informal review of the IOL powers that would have been chosen if other formulae had been used showed that a lower level of refractive outcome accuracy would have been achieved.

Conclusion
Patients that had prior corneal laser refractive surgery often have high expectations for the visual result of cataract / RLE surgery, and frequently elect for premium IOLs Planning IOL implant surgery using the Aladdin biometer and Barrett True K / True K Toric formulae results in a high level of refractive outcome accuracy & patient satisfaction
Visual Outcomes in Post-Operative Adjustable Intraocular Lens after Cataract Surgery in Post-Refractive Patients
Authors
William F. Wiley, MD
Kathleen J Jee, MD
Shamik Bafna, MD
Kayla L. Karpuk, OD

Purpose
To evaluate the targeted refractive and visual outcomes after implantation of the Light Adjustable Lens (LAL, RxSight) after cataract surgery in patients with prior corneal refractive surgery.

Methods
In this single-center, consecutive, retrospective case series, patients with a history of prior corneal refractive surgery (LASIK or PRK) who underwent cataract extraction with implantation of the LAL were included. Primary outcome measures included best corrected acuity (BCVA), uncorrected visual acuity (UCVA), mean manifest refraction spherical equivalent (MRSE), and the number of patients within ±0.5 D and ±1.0 D of refractive target. Data was collected preoperatively and following final postoperative adjustment with the light delivery device (LDD).

Results
This study comprised 20 eyes of 18 patients (with plan to update with additional data prior to presentation). Following the final postoperative adjustment with the LDD, the mean MRSE was -0.23 D, with 75% of eyes within ±0.5 D and 100% within ±1.0 D of refractive target. 100% of eyes achieved UCVA of 20/40 or better, with 87% achieving 20/25 UCVA or better. Data will be updated prior to presentation at the ASCRS 2020 meeting.

Conclusion
The LAL provides excellent refractive and visual outcomes in patients with a history of corneal refractive surgery, who are known to have challenging intraocular lens power calculations. These results suggest the LAL is a favorable option in this patient cohort.
Accuracy of Intraoperative Aberrometry and Modern Preoperative Biometry for IOL Power Selection in Post-Refractive Surgery Patients
Authors
Allison J. Chen, MD
Christopher P. Long
Tianlun Lu, MS
Kevin Garff, MD
Chris W. Heichel, MD

Purpose
To assess the accuracy of intraoperative wavefront aberrometry (IWA) and modern intraocular lens (IOL) formulas including Hill-Radial Basis Function Version 2.0 (Hill-RBF), Barrett True K (BTK), Holladay 1 ± W-K adjustment, SRK/T, Haigis, and surgeon’s adjustment in post-refractive surgery patients undergoing cataract surgery.

Methods
Retrospective chart review. Thirty-four post-refractive eyes underwent cataract surgery with IWA from 05/2017 – 04/2019. Twenty-five eyes had prior myopic laser vision correction (LVC), 7 had hyperopic LVC, and 2 had radial keratotomy (RK). A capsular tension ring was placed in all eyes. Accuracy among ORA predictions and the above formulas for the chosen IOL was evaluated. Mean numerical error (MNE), mean absolute error (MAE), and percentages of prediction error within 0.25D, 0.50D, 0.75D, and 1.00D were calculated. Calculations were also performed for the percent of eyes with predicted hyperopic outcomes if the ORA-suggested versus the BTK-suggested IOL power were routinely selected.

Results
In post-myopic LVC eyes, MNE with ORA, BTK, Haigis, SRK/T, Hill-RBF, W-K adjusted Holladay 1, and surgeon’s adjustment were +0.172, -0.171, +0.212, +0.916, +0.792, +0.603, and +0.300 (F=8.49, p<0.001). MAE were 0.510, 0.503, 0.516, 1.00, 0.878, 0.668, and 0.611 (F=3.34, p<0.01), respectively. There was no difference in MNE (p=0.07) or MAE (p=0.95) between ORA-predicted and BTK in post-hoc analysis with Tukey HSD correction. If the ORA vs BTK-suggested IOL power were routinely selected, 28% and 16% of eyes would have projected hyperopic outcomes, respectively (p=0.31). In post-hyperopic LVC, MNE with ORA and BTK were -0.065 and 0.035 (p=0.83); MAE were 0.520 and 0.721 (p=0.53), respectively.

Conclusion
Our study suggests that in post-myopic and post-hyperopic LVC eyes undergoing cataract surgery with capsular tension rings, the accuracy of IWA and Barrett True K are comparable. BTK may yield fewer hyperopic surprises than ORA in post-myopic LVC eyes, though further studies with larger sample sizes are necessary.
Post Refractive IOL Outcomes Using Intraoperative Aberrometry and Cataract Refractive Suite
Author
V. Nicholas N Batra, MD

Purpose
This retrospective study reports on single site, single surgeon outcomes and compares the prediction error resulting from the calculated IOL to IOL recommended by intraoperative aberrometry. The investigator hopes to answer the question that all surgeons ask...is ORA better than formula for post-refractive cataract patients?

Methods
We compare the absolute prediction error of the ASCRS online calculator to the prediction error of intraoperative aberrometry on post-refractive eyes receiving IOLs during cataract surgery. Retrospective chart review including through EHR as well as manual review of data and ASCRS calculator. Post op MRSE will be used to back-calculate prediction error of the various formulas. Statistical Considerations: We should have approximated 150 patients in 3 subgroups: 10 RK, 30 post Hyperopic PRK/LASIK and 110 Post Myopic PRK/LASIK

Results
This represents interim data at post-op data is still being processed. A retrospective chart review of 156 patients undergoing cataract surgery who had had prior refractive surgery were analyzed from June 2013 to May of 2019. 54 Eyes had post-operative refractions available. Ora had a Mean (SD) 0.71(0.63) while the ASCRS calculator had a Mean 0.70(0.59) with a P-value 0.856. 51.9% of ORA patients were within 0.5D of predicted and 47.2% for the ASCRS calculator group with a p- value of 0.628. No subgroup was statistically significant.

Conclusion
At this point in the analysis, the data show similar outcomes between using ORA and the ASCRS calculator for post refractive cases with no statistically significant differences. The study however is limited due to small sample size and a lack of post-operative refractions. As additional data is input, we anticipate a more significant difference.
Compare and Contrast Visual Outcomes and Patient Satisfaction of Post LASIK Patients Receiving Multifocal, EDOF, and MonofocaI IOLs
Author
Frank A. Bucci Jr., MD

Purpose
Use a patient questionnaire and multivariate regression analysis to compare functional visual outcomes and patient satisfaction of post LASIK patients having received multifocal, EDOF, and monofocal intraocular lenses.

Methods
Three cohorts of 61 post LASIK eyes were analyzed: 35 multifocal IOLs (+3.25 ZLB00), 11 EDOF IOLs (Symf 9/Symf toric 2), and 15 monofocals IOLs (Tecnis asph 8/Akreos 7) were retrospectively evaluated. A 19 question pt questionnaire was administered to evaluate subjective pt responses with regard to halos, glare, starburst, UDVA, intermed, and near visual outcomes.31 objective metrics including preop sph eq, angle kappa, higher order aberrations, pupil size, UCVA, reading speed, reading accuracy, postop residual astig and sph eq, etc will also be evaluated. The 50 objective and subjective variables will be regressed against “overall pt satisfaction” to identify predictors of pt satisfaction.

Results
All pts were either very sat or sat, but a sig greater % were very sat in the MULTI & EDOF cohorts: (MULTI 28/4, EDOF 9/2, MONO 4/9). Regression revealed that near visual function variables explained greater pt sat in the MULTI (+3.25) vs EDOF & MONO cohorts including UCNVA p=.001, UCIVA p=.04, reading acuity p=.014, reading speed-WPM p=.05, glasses use-near p=.0014, reading newspaper p=.002. EDOF outperformed MONO for working on a computer p=.039. Contrast sens was sig less for MULTI vs both EDOF p=.05 and MONO p=.009. All 61 post LASIK eyes revealed sig greater HOAs vs a cohort of 350 nonpost LASIK presbyopic IOL eyes: RMS p=.009, coma p=.038, trefoil p=.049, and sph aberration p=.011.

Conclusion
1)Multifocal IOLs achieved high levels of pt satisfaction in post LASIK patients despite lower scores for contrast sens and HOAs 2) Regression revealed that numerous variables related to uncorrected near visual function explained the high levels of pt satisfaction 3) Halo, glare, and starburst did not contribute sig to scores for pt satisfaction
Comparison of Intraoperative Wavefront Aberrometry & Intraocular Lens Calculation Formulas for IOL Selection in Previous Refractive Surgery
Authors
Colin E. Brown, MD
Larissa Gouvea, MD
Kareem Sioufi, MD
Raphael C Penatti, MD
Walter Johnson Jr.
George O. Waring IV, MD, FACS
Karolinne M. Rocha, MD, PhD, ABO

Purpose
To compare accuracy of current intraocular lens (IOL) power calculation formulas with intraoperative wavefront aberrometry (ORA) in eyes with previous hyperopic and myopic advanced surface ablation surgery (LASIK/PRK)

Methods
Retrospective review of eyes with history of hyperopic or myopic ablation who underwent phacoemulsification between April 2015 and September 2019. All eyes underwent pre-operative optical biometry using the IOLMaster® and intraoperative biometry using ORA. IOL power was calculated using the Barrett-True K formula for post-hyperopic and post-myopic ablation. Comparison between ORA-recommended, Barrett-True K recommended, and IOL implanted was conducted. The error in the predicted refraction was calculated as the difference between the actual postoperative refractive outcome and the predicted refraction for each formula or method. A group of nonrefractive eyes was used as control.

Results
48 eyes with previous hyperopic ablation, 50 eyes with history of myopic ablation and 62 controls were included in this study. In the hyperopic group, the lowest mean prediction error (PE) was observed with the ORA-recommended IOL (0.030.57), compared to IOL implanted (0.1080.65), and Barrett-True K (0.3960.63; p=0.03). In the myopic group, the highest mean PE was observed with Barrett-True-K formula (0.460.79), followed by ORA-recommended (0.0610.48) and IOL implanted (0.060.48; p=0.001). In the control group, no statistically significant difference was seen in IOL calculations using Barrett Universal II (-0.010.66) and ORA (-0.060.77; p=0.69).

Conclusion
Intraoperative biometry may be an important tool to improve postoperative refractive outcomes in patients post-hyperopic or post-myopic advanced laser ablation, whereas in normal eyes, standard IOL calculation using Barrett Universal II yields good refractive outcomes.
Using Small Aperture Optics to Treat Post-Corneal Refractive Surgery Patients with Cataracts
Author
Roger Zaldivar, MD

Purpose
To evaluate visual performance and ease of use of a small aperture IOL in cataract patients with a history of corneal refractive surgery

Methods
Retrospective analysis of 10 patients presenting for cataract surgery with a history of prior corneal refractive surgery. Preoperative total high order aberrations were 0.5 um + 1.1 um. Prior corneal refractive surgery includes hyperopic and myopic laser vision correction (n=10). Patients were implanted either contralaterally with an IC-8 IOL (AcuFocus) in one eye and a monofocal IOL in their fellow eye. IC-8 IOL eyes were targeted for -0.75 D and their fellow monofocal eyes targeted for plano. Uncorrected visual acuity, total corneal higher order aberrations, and manifest refractive surgical equivalent (MRSE) were evaluated.

Results
Pre-op Sph Eq changed from -0,65 SD ±3,32 to -0,43 SD ± 0,50 after one month of the surgical procedure. The mean preop UCVA was 0,66 improving to 0,09 at 3 months. MEDIAN 0,71 (1day) 0,00 (3 months). 7 patients gained at least 1 line after 3 months of the surgery. MEAN preop BCVA was 0,22 improving to 0,05 at third month. SD preop 0,18 and 3 months postop 0,10. Preoperatively the mean near UCVA was 0,67 and improved to 0,15 three months after surgery. Patients increased their functional distances at near and intermediate. There was an improvement of night driving symptomatology.

Conclusion
The combination of a small aperture IOL and a monofocal IOL effectively compensated corneal higher order aberrations in patients with prior LASIK procedure. Patients increased their functional distances at near and intermediate. There was an improvement of night driving symptomatology. 7 patients gained at least 1 line after 3 months of the surgery
Comparison between Wavefront Aberrometry and Intraocular Lens Calculation Formulas for IOL Selection in Eyes with Previous Radial Keratotomy
Authors
Kareem Sioufi, MD
Colin E. Brown, MD
Larissa Gouvea, MD
Walter Johnson Jr.
George O. Waring IV, MD, FACS
Karolinne M. Rocha, MD, PhD, ABO

Purpose
To compare accuracy of current intraocular lens (IOL) power calculation formulas with intraoperative wavefront aberrometry in eyes with history of radial keratotomy (RK).

Methods
A retrospective comparative case-control series of 18 eyes with history of prior RK (study) and 36 age-matched nonrefractive eyes (control). All eyes underwent intraoperative biometry using the Optiwave Refractive Analysis (ORA) (Alcon, Fort Worth, TX, USA) and pre-op biometry using IOL Master (Carl Zeiss Meditec, Inc., Dublin CA, USA) between April 2015 and September 2019. IOL power was also calculated using the ASCRS post keratorefractive online calculator (http://iolcalc.ascrs.org). Comparison between ORA-recommended, ASCRS recommended, Barrett True K, and IOL implanted was conducted in the study group.

Results
There was no statistically significant difference between ORA recommended, ASCRS average, and Barrett True K (all p>0.182). Mean ORA-recommended was significantly higher than IOL implanted (22.13 vs. 22.83 diopters, p=0.013). In contrast, there was not statistically significant difference between mean IOL implanted and ASCRS average (p=0.501) or Barrett True K (p=0.792). Compared to the controls (study vs. control) there was no difference in ORA predicted error or post-operative SEQ (all p>194). The difference in ORA recommended (22.1 vs. 19.4 diopters, p<0.01) and difference between ORA recommended and IOL implanted (0.694 vs. 0.107, p=0.04) were statistically significant between groups.

Conclusion
Pre-op ASCRS post-refractive formula, Barrett True K, and ORA are helpful in determining IOL power in eyes with prior RK.

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