Descemet membrane endothelial keratoplasty (DMEK) is quickly becoming the procedure of choice for the treatment of corneal endothelial diseases such as Fuchs endothelial dystrophy.1,2 Because cataract formation is common at the time patients are being considered for DMEK, particularly in older patients,3 DMEK combined with cataract surgery (DMEK triple) is an attractive option that reduces the need for and associated risks of a second surgery. A large retrospective case series showed that DMEK triple was as safe and effective as DMEK alone, with no increased rates of graft failure, rebubbling, endothelial cell loss, cystoid macular edema, or other complications.4 Compared to Descemet stripping automated endothelial keratoplasty (DSAEK), DMEK offers more rapid visual rehabilitation and superior final visual outcomes, including fewer higher order aberrations.5–8
With DMEK achieving excellent visual acuity results, refractive success in DMEK triple procedures is a growing focus. After DSAEK, a hyperopic shift of 0.82 to 1.13 diopters (D) has been reported in several studies,9–11 which stabilizes approximately 3 to 6 months postoperatively. Similarly after DMEK, a hyperopic shift is known to occur, with prior studies reporting means of 0.32 to 0.49 D of hyperopic shift.12,13 There is currently no widely accepted consensus on predictive factors for eyes with refractive surprise after DMEK triple, nor on the optimal method to adjust for expected refractive shifts.
The purpose of our study was to characterize refractive changes after DMEK triple procedures and assess differences in preoperative parameters between eyes with and without hyperopic shift.
Patients and Methods
A retrospective chart review was done of DMEK triple procedures performed between January 2014 and February 2018 by three corneal surgeons (SH, MM, SNY) at a tertiary care center in Vancouver, British Columbia, Canada. Consecutive patients with at least 6 months of follow-up and available preoperative data including visual acuity, biometry, and corneal topography were included in the study. Among 6 patients who underwent DMEK triple in both eyes during the study period, one eye was randomly excluded to avoid inter-eye correlation bias.
The primary outcome measure was the percentage of eyes that were within ±0.50 and ±1.00 D of target refraction. The secondary outcome measure was differences in preoperative parameters such as central corneal thickness, anterior curvature, axial length, and intraocular lens formula used between eyes with hyperopic surprise of greater than 0.50 D and eyes without hyperopic surprise. Snellen corrected distance visual acuity (CDVA) was also abstracted and converted to logMAR notation for statistical purposes. A P value of .05 was considered statistically significant based on two-sided tests. The Wilcoxon signed-rank test was used to compare means of repeated measurements, and the Mann-Whitney U test was used to compare means of independent samples. Statistical analysis was performed using R software ( http://CRAN.r-project.org).
The study complied with the tenets set forth by the Declaration of Helsinki. The study was approved by the University of British Columbia and Vancouver Island Health Clinical Research Ethics Boards.
Intraocular lens power calculations were performed using recorded biometry and Haigis, Holladay 2, Barrett, and SRK2 formulas, depending on the surgeon's preference, as well as the enVista and Tecnis toric formulas for toric lenses. Refractive targets were adjusted myopically by approximately 0.50 D in anticipation of a hyperopic shift. Intraocular lenses used included the Tecnis ZBC00 lens (Abbott Medical Optics) in 56 eyes; Atkis SP NS-60G lens (Nidek) in 8 eyes; enVista MX60T toric lens (Bausch & Lomb, Inc) in 2 eyes; Tecnis ZCT225 toric lens (Abbott Medical Optics) in 1 eye; and Tecnis ZCT400 toric lens (Abbott Medical Optics) in 1 eye. Preoperative and postoperative central corneal thickness measurements were obtained using the DGH Pachmate 2 (Axis Medical Canada, Inc).
Surgical technique was similar between all surgeons. All donor tissue was obtained from the Eye Bank of British Columbia, Canada, and stored in Optisol GS (Bausch & Lomb, Inc). All DMEK grafts were prepared by the surgeon prior to commencing the case. The donor preparation techniques have been described previously.8
Briefly, the cataract was removed using standard phacoemulsification techniques and the intraocular lens was placed in the capsular bag. Next, Descemet membrane was stripped and removed under cohesive viscoelastic using a reverse hook. The viscoelastic was removed and Miochol (Miochol E; Bausch & Lomb, Inc) was injected into the anterior chamber to constrict the pupil. The graft was loaded into a glass pipet (Geuder AG) and injected into the anterior chamber. The main incision was closed with a single 10-0 nylon suture and the graft unfolded using a no-touch technique. Once the correct orientation was confirmed with the F mark, air or 20% SF6 gas was injected into the anterior chamber. Following a 10-minute complete anterior chamber fill, air or gas was replaced with balanced salt solution until clear of the inferior pupil margin or iridotomy.
The eye was checked at the slit lamp after 1 hour in the supine position and, if acceptable, patients were discharged home with instructions to position supine for 24 to 48 hours. Follow-up was performed at 1 day, 1 week, and 1, 3, and 6 months. Postoperative drop regimen included moxifloxacin 0.5% (Apo Moxifloxacin; Apotex, Inc) four times per day for 1 week or until epithelial healing. Prednisolone acetate 1% (ratio Prednisolone 1%, TEVA Canada LIM) was administered either four or eight times daily depending on the surgeon's preference for the first week. Subsequently, the regimen was four times daily for the first month and tapered to once daily by the fourth month. Nepafenac (Nevanac; Novartis Pharmaceuticals Canada, Inc) was also prescribed four times daily for 1 month.
There were 68 eyes of 68 patients included in the study. The indication for DMEK in all eyes (100%) was Fuchs endothelial dystrophy. The mean patient age was 66.5 ± 8.6 years. Forty-four of 68 cases (65%) were female.
The mean target refraction was −0.69 D (interquartile range [IQR]: −0.80 to −0.50 D). Postoperatively at 6 months, 47% (32 of 68) and 63% (43 of 68) of eyes were within ±0.50 and ±1.00 D of target refraction, respectively. A total of 37% (25 of 68) of eyes were greater than 1.00 D from the target refraction. Of the eyes that were greater than 0.50 D from the target refraction, 78% (28 of 36) were hyperopic surprises and 22% (8 of 36) were myopic surprises. A summary of the errors in postoperative spherical equivalent refraction compared to target is provided in Figure 1. A scatterplot of attempted versus achieved spherical equivalent refraction is provided in Figure 2. Mean spherical equivalent at 6 months was −0.14 ± 1.26 D, representing a mean hyperopic shift of 0.55 D from the target refraction.
Error in spherical equivalent refraction relative to target refraction. D = diopters
Attempted versus achieved spherical equivalent refraction in Descemet membrane endothelial keratoplasty combined with cataract surgery. D = diopters
Mean CDVA was 0.47 ± 0.21 logMAR (20/59 ± 10.5 letters) preoperatively and 0.15 ± 0.13 logMAR (20/28 ± 6.5 letters, P < .001) at 6 months postoperatively. After excluding 1 eye with amblyopia and 1 eye with advanced optic neuropathy, the mean 6-month CDVA was 0.14 ± 0.11 logMAR (20/28 ± 5.5 letters). There was no significant difference in CDVA between eyes within ±0.50 D of target refraction (0.12 ± 0.11 logMAR; 20/26 ± 5.5 letters) versus eyes deviating over 0.50 D target refraction (0.15 ± 0.11 logMAR; 20/28 ± 5.0 letters, P = .22). More than 50% of eyes gained three or more lines of Snellen visual acuity postoperatively (Figure 3).
Change in corrected distance visual acuity (CDVA) relative to preoperative CDVA.
Preoperative parameters including axial length, anterior mean keratometry, anterior maximum keratometry, and central corneal thickness were compared between eyes with and without hyperopic surprise compared to target refraction (Table 1). Among 45 eyes with preoperative central corneal thickness values available, analysis showed that eyes with hyperopic surprise had greater preoperative central corneal thickness. There was no significant difference found in axial length or anterior curvature. To further examine the relationship between preoperative central corneal thickness and postoperative refractive shift, a Spearman's correlation coefficient was calculated. This analysis revealed a modest but statistically significant positive correlation between these two variables (r = 0.37, P = .01). To determine whether the change in central corneal thickness from preoperatively to postoperatively also correlated with refractive shift, a Pearson's correlation coefficient was calculated after confirming normality of data with the Shapiro-Wilk test. This analysis showed a modest positive correlation that approached statistical significance (r = 0.34, P = .06; n = 31). There was no significant difference in change in mean keratometry in eyes with hyperopic surprise greater than 0.50 D compared to eyes without hyperopic surprise (−0.53 ± 1.17 vs −0.28 ± 0.66 D, P = .35). There was also no difference in change in maximum keratometry between groups (−0.72 ± 1.26 vs −0.87 ± 0.93 D, P = .87).
Differences in Preoperative Measurements Between Eyes With and Without Hyperopic Surprise Compared to Target Refraction (> 0.50 D)
Eighteen of 45 eyes (40%) had a preoperative central corneal thickness of 640 µm or greater. Twelve of these 18 eyes (67%) had a hyperopic shift greater than 0.50 D compared to target refraction. None of the 18 eyes had a myopic shift (range: −0.09 to +2.89 D). The mean refractive shift among eyes with preoperative central corneal thickness of 640 µm or greater was significantly greater than eyes with preoperative central corneal thickness of less than 640 µm (+1.20 ± 0.92 vs +0.40 ± 0.99 D, P = .02). The overall mean central corneal thickness was 630 ± 57 µm preoperatively and 525 ± 48 µm at 6 months postoperatively (P < .001).
An exploratory analysis was undertaken to determine the effect of an additional 0.50 D myopic adjustment of target refraction in eyes with preoperative central corneal thickness of 640 µm or greater. Mean refractive surprise would have been reduced from +1.20 ± 0.92 to +0.70 ± 0.92 D. In addition, 61% of eyes (11 of 18) would have been within ±1.00 D of target refraction, compared to 44% (8 of 18) without additional adjustment. Finally, 44% of eyes (8 of 18) would have been within ±0.50 D of target refraction, with 1 eye converting to myopic surprise, compared to 39% (7 of 18) without additional adjustment. Figure 4 demonstrates the effect of an additional 0.50 D of myopic adjustment of target refraction on postoperative spherical equivalent in eyes with pre-operative central corneal thickness of 640 µm or greater.
Effect of an additional 0.50 diopters (D) of myopic adjustment of target refraction on postoperative spherical equivalent in eyes with preoperative central corneal thickness of 640 µm or greater.
Intraocular lens power calculations were performed using the Haigis (n = 40), Holladay 2 (n = 20), Barrett (n = 3), enVista toric (n = 2), Tecnis toric (n = 2), and SRK2 (n = 1) formulas. Excluding eyes that used the Barrett, SRK2, and toric formulas given the low sample size, 6 of 20 (30%) of Holladay 2 formulas resulted in hyperopic surprise greater than 0.50 D compared to target refraction, and 18 of 40 (45%) of Haigis formulas resulted in hyperopic surprise. This difference was not statistically significant (chi-square = 1.25, P = .26).
Among 4 eyes with toric lenses implanted, refractive astigmatism was reduced in all cases, from a mean 2.75 ± 0.79 to 1.56 ± 0.90 D. Preoperative topographic astigmatism was similar to the preoperative refractive astigmatism at 2.33 ± 0.56 D. Uncorrected distance visual acuity at 6 months postoperatively was 20/40 or better in 75% (3 of 4). CDVA improved from 0.40 ± 0.17 logMAR (20/50 ± 8.5 letters) preoperatively to 0.14 ± 0.05 logMAR (20/28 ± 2.5 letters) postoperatively. Given the small sample size, statistical comparisons were not performed.
Refractive outcomes of DMEK triple reported in previous studies are summarized in Table 2.
Summary of Previous Studies on Refractive Changes After DMEK Triple
This study aimed to characterize refractive changes after DMEK triple and assess differences in preoperative parameters in eyes with and without hyperopic surprise. In our sample, we found that 47% and 63% of eyes 6 months postoperatively were within ±0.50 and ±1.00 D of target refraction, respectively. Our findings are comparable to previous studies, which reported 54.5% of eyes within ±1.00 D,14 30% and 50% of eyes within ±0.50 and ±1.00 D,15 and 38% of eyes within ±0.50 D.16 More than 40% of eyes in our sample had a hyperopic shift compared to the target refraction by greater than 0.50 D. Hyperopic shift in previous studies of DMEK triple has been reported at rates and magnitudes of 31% of eyes greater than 1.25 D17 and 46% of eyes greater than 0.50 D.16 The amount of refraction adjustment preferred by surgeons to account for this hyperopic shift ranges from approximately −0.50 to −1.00 D.14–17 The surgeons in our study generally performed a myopic adjustment of 0.50 D. In previous studies, a myopic adjustment between 0.50 and 1.00 D seemed to result in comparable refractive outcomes.
Our patients had a mean postoperative CDVA of 20/28, with more than 50% of eyes gaining three or more lines of Snellen visual acuity, confirming that DMEK triple can provide excellent visual outcomes. Prior studies have reported a mean long-term postoperative visual acuity ranging from 20/28 to 20/31.14,17,18 No significant differences in CDVA were found between eyes close to emmetropia versus eyes with hyperopic or myopic surprise, similar to findings reported by Cheung et al.17
We found that preoperative central corneal thickness was higher in eyes with hyperopic surprise, with a positive correlation between preoperative central corneal thickness and refractive shift. Interestingly, a greater hyperopic shift was seen among eyes with a preoperative central corneal thickness of 640 µm or greater, and none of the eyes with a preoperative central corneal thickness less than 640 µm had a myopic shift. This suggests that a greater myopic target refraction may be warranted in eyes with a preoperative central corneal thickness greater than 640 µm. Prior studies have also reported an association with preoperative central corneal thickness and hyperopic shift.16,17 Our findings support the hypothesis proposed by Ham et al13: as central corneal thickness increases with greater edema, the posterior stroma swells and flattens centrally, causing an oblate posterior surface and a myopic shift. After endothelial keratoplasty, the edema improves and the posterior cornea steepens, causing hyperopic shift.13 This hypothesis is also supported by studies that have shown eyes with hyperopic shift had significantly greater preoperative posterior Q values,16,17 where a value greater than 0 indicates an oblate surface that is flatter centrally than peripherally. Furthermore, preoperative posterior curvature has been found to be flatter in patients with hyperopic surprise.17,18 It is worthwhile to note that some studies have not found a significant correlation between preoperative central corneal thickness and the degree of refractive shift.15,18
We did not find any significant differences in anterior curvature or axial length between eyes with and without hyperopic surprise, consistent with prior studies.16–18 We also did not find any significant differences between eyes that used the Haigis versus Holladay 2 formulas for intra-ocular lens power calculation, although Haigis formulas trended toward a higher rate of hyperopic surprise. One study of DMEK alone found that the highest difference in target refraction by ray-tracing versus formula calculation among third-generation formulas was with the Haigis formula.19 Further research may help determine whether the Haigis formula may lead to more hyperopic surprises. To our knowledge, no previous studies have compared the accuracy of power calculations in DMEK triple among various formulas. Refractive outcomes from previous studies appear to be comparable, with a variety of formulas reported, including Holladay 2,15 Haigis,14,16,18 and SRK/T.16
We reported a small sample of 4 eyes that had toric intraocular lens implantation. Although statistical comparisons were not performed, we found reduced astigmatism in all cases. Given that anterior corneal curvature does not change significantly with DMEK,13 we are able to use standard intraocular lens formula calculations, including for toric lenses. Our initial cases show toric lenses can be effective, but further research is needed to clarify the indications and outcomes of their use in DMEK triple procedures.
Limitations of our study include its retrospective nature and lack of information on the posterior corneal profile. Follow-up in this study was limited to 6 months, but studies have shown stability in spherical equivalent within this time period.15,20 Therefore, we believe our refractive outcomes to hold true long-term. Although we found a statistically significant relationship between pre-operative central corneal thickness and refractive shift, it should be noted that there is wide variability in normal central corneal thickness. Given the lack of data on baseline central corneal thickness before the onset of stromal edema in Fuchs dystrophy, calculating the precise amount of corneal edema was not possible. Our analysis did not focus on eyes with myopic surprise, and given the paucity of literature addressing this subgroup, further work is needed to predict myopic surprises.
A total of 47% of eyes in our sample achieved within 0.50 D of target refraction after DMEK triple, with 41% of eyes having a hyperopic shift of greater than 0.50 D. Eyes with hyperopic surprise had on average thicker corneas preoperatively, and eyes with a central corneal thickness of greater than 640 µm preoperatively had greater hyperopic shift. For eyes with significant preoperative corneal edema, a more myopic target refraction may help optimize refractive outcomes. As our collective experience with DMEK triple grows, future large studies that attempt to create a nomogram incorporating various preoperative parameters may help optimize refractive outcomes for this procedure.
- Flockerzi E, Maier P, Böhringer D, et al. all German Keratoplasty Registry Contributors. Trends in corneal transplantation from 2001 to 2016 in Germany: a report of the DOG-Section Cornea and its keratoplasty registry. Am J Ophthalmol. 2018;188:91–98. doi:10.1016/j.ajo.2018.01.018 [CrossRef]
- Chan SWS, Yucel Y, Gupta N. New trends in corneal transplants at the University of Toronto. Can J Ophthalmol. 2018;53(6):580–587. doi:10.1016/j.jcjo.2018.02.023 [CrossRef]
- Burkhart ZN, Feng MT, Price FW Jr, Price MO. One-year outcomes in eyes remaining phakic after Descemet membrane endothelial keratoplasty. J Cataract Refract Surg. 2014;40(3):430–434. doi:10.1016/j.jcrs.2013.08.047 [CrossRef]
- Chaurasia S, Price FW Jr, Gunderson L, Price MO. Descemet's membrane endothelial keratoplasty: clinical results of single versus triple procedures (combined with cataract surgery). Ophthalmology. 2014;121(2):454–458. doi:10.1016/j.ophtha.2013.09.032 [CrossRef]
- Chamberlain W, Lin CC, Austin A, et al. Descemet Endothelial Thickness Comparison Trial: a randomized trial comparing ultrathin Descemet stripping automated endothelial keratoplasty with Descemet membrane endothelial keratoplasty. Ophthalmology. 2019;126(1):19–26. doi:10.1016/j.ophtha.2018.05.019 [CrossRef]
- Duggan MJ, Rose-Nussbaumer J, Lin CC, Austin A, Labadzinzki PC, Chamberlain WD. Corneal higher-order aberrations in Descemet membrane endothelial keratoplasty versus ultrathin DSAEK in the Descemet endothelial thickness comparison trial: a randomized clinical trial. Ophthalmology. 2019;126(7):946–957. doi:10.1016/j.ophtha.2019.02.007 [CrossRef]
- Woo JH, Ang M, Htoon HM, Tan D. Descemet membrane endothelial keratoplasty versus Descemet stripping automated endothelial keratoplasty and penetrating keratoplasty. Am J Ophthalmol. 2019;207:288–303. doi:10.1016/j.ajo.2019.06.012 [CrossRef]
- Singh A, Zarei-Ghanavati M, Avadhanam V, Liu C. Systematic review and meta-analysis of clinical outcomes of Descemet membrane endothelial keratoplasty versus Descemet stripping endothelial keratoplasty/Descemet stripping automated endothelial keratoplasty. Cornea. 2017;36(11):1437–1443. doi:10.1097/ICO.0000000000001320 [CrossRef]
- Terry MA, Shamie N, Chen ES, et al. Endothelial keratoplasty for Fuchs' dystrophy with cataract: complications and clinical results with the new triple procedure. Ophthalmology. 2009;116(4):631–639. doi:10.1016/j.ophtha.2008.11.004 [CrossRef]
- Covert DJ, Koenig SB. New triple procedure: Descemet's stripping and automated endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation. Ophthalmology. 2007;114(7):1272–1277. doi:10.1016/j.ophtha.2006.12.030 [CrossRef]
- Jun B, Kuo AN, Afshari NA, Carlson AN, Kim T. Refractive change after descemet stripping automated endothelial keratoplasty surgery and its correlation with graft thickness and diameter. Cornea. 2009;28(1):19–23. doi:10.1097/ICO.0b013e318182a4c1 [CrossRef]
- Guerra FP, Anshu A, Price MO, Giebel AW, Price FW. Descemet's membrane endothelial keratoplasty: prospective study of 1-year visual outcomes, graft survival, and endothelial cell loss. Ophthalmology. 2011;118(12):2368–2373. doi:10.1016/j.ophtha.2011.06.002 [CrossRef]
- Ham L, Dapena I, Moutsouris K, et al. Refractive change and stability after Descemet membrane endothelial keratoplasty: effect of corneal dehydration-induced hyperopic shift on intraocular lens power calculation. J Cataract Refract Surg. 2011;37(8):1455–1464. doi:10.1016/j.jcrs.2011.02.033 [CrossRef]
- Laaser K, Bachmann BO, Horn FK, Cursiefen C, Kruse FE. Descemet membrane endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation: advanced triple procedure. Am J Ophthalmol. 2012;154(1):47–55.e2. doi:10.1016/j.ajo.2012.01.020 [CrossRef]
- Schoenberg ED, Price FW Jr, Miller J, McKee Y, Price MO. Refractive outcomes of Descemet membrane endothelial keratoplasty triple procedures (combined with cataract surgery). J Cataract Refract Surg. 2015;41(6):1182–1189. doi:10.1016/j.jcrs.2014.09.042 [CrossRef]
- Fritz M, Grewing V, Böhringer D, et al. Avoiding hyperopic surprises after Descemet membrane endothelial keratoplasty in Fuchs dystrophy eyes by assessing corneal shape. Am J Ophthalmol. 2019;197:1–6. doi:10.1016/j.ajo.2018.08.052 [CrossRef]
- Cheung AY, Chachare DY, Eslani M, Schneider J, Nordlund ML. Tomographic changes in eyes with hyperopic shift after triple Descemet membrane endothelial keratoplasty. J Cataract Refract Surg. 2018;44(6):738–744. doi:10.1016/j.jcrs.2018.04.040 [CrossRef]
- Augustin VA, Weller JM, Kruse FE, Tourtas T. Can we predict the refractive outcome after triple Descemet membrane endothelial keratoplasty?Eur J Ophthalmol. 2019;29(2):165–170. doi:10.1177/1120672118785282 [CrossRef]
- Alnawaiseh M, Zumhagen L, Rosentreter A, Eter N. Intraocular lens power calculation using standard formulas and ray tracing after DMEK in patients with Fuchs endothelial dystrophy. BMC Ophthalmol. 2017;17(1):152. doi:10.1186/s12886-017-0547-7 [CrossRef]
- van Dijk K, Rodriguez-Calvo-de-Mora M, van Esch H, et al. Two-year refractive outcomes after Descemet membrane endothelial keratoplasty. Cornea. 2016;35(12):1548–1555. doi:10.1097/ICO.0000000000001022 [CrossRef]
Differences in Preoperative Measurements Between Eyes With and Without Hyperopic Surprise Compared to Target Refraction (> 0.50 D)
|Preoperative Measurements||Hyperopic Surprise||No Hyperopic Surprise||Pa|
|Central corneal thickness (µm)||648 ± 60||613 ± 49||.04|
|Anterior K mean (D)||43.80 ± 1.40||43.90 ± 1.80||.35|
|Anterior K max (D)||44.30 ± 1.50||44.50 ± 1.90||.43|
|Axial length (mm)||24.04 ± 1.07||23.72 ± 1.47||.31|
Summary of Previous Studies on Refractive Changes After DMEK Triple
|Study||No. of Eyes||Follow-up (Months)||Target Refraction (D), Mean ± SD||Postoperative Spherical Equivalent (D), Mean ± SD||Summary of Refractive Outcomes|
|Laaser et al14 (2012)||61||6||−0.53 ± 0.95||0.90 ± 1.50||54.5% ±1.00 D of emmetropia at 6 months|
|Schoenberg et al15 (2015)||108||Mean 11.9||−0.56 ± 0.12 (after adjusting −0.50)||Not specified||30% ±0.50 D, 50% ±1.00 D of target|
|Cheung et al17 (2018)||62||3 to 6||Mean −1.03 (goal −0.75 to −1.00)||+0.70 ± 0.60 D in hyperopic, −1.00 ± 0.90 D in non-hyperopic||31% > +1.25 D from target|
|Fritz et al16 (2019)||112||Median 10||Median −0.43||Median −0.06 D (IQR −0.63 to 0.56 D)||38% ±0.50 D of target, 46% > +0.50 D, 17% >+1.00 D, 79% ±1.00 D of target|
|Augustin et al18 (2019)||152||9.3 ± 3.9||Not specified||Not specified||Mean +1.24 ± 1.07 D of target (−1.81 to +4.12 D)|
|Current study (2020)||68||6||Mean −0.69 (IQR: −0.80 to −0.50)||−0.14 ± 1.26 D||47% ±0.50 D, 63% ±1.00 D of target|