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Correction of Postkeratoplasty Astigmatism by Femtosecond Laser Compared with Mechanized Astigmatic Keratotomy
Correction of Postkeratoplasty Astigmatism by Femtosecond Laser Compared with Mechanized Astigmatic Keratotomy LOUIS HOFFART, HELENE PROUST, FREDERIC MATONTI, JOHN CONRATH, AND BERNARD RIDINGS ● PURPOSE:
To compare the effectiveness of arcuate keratotomy (AK) performed with a femtosecond laser (FSL) or Hanna keratome (Moria, Anthony, France) for correction of postkeratoplasty astigmatism. ● DESIGN: Prospective, randomized study. ● METHODS: This clinical study included 20 eyes. Two groups of 10 eyes underwent AK using an FLS or keratome. Refractive and keratometric astigmatism were evaluated before surgery and 6 months after surgery. The astigmatic changes in the 2 groups were measured through arithmetic and vector analysis (Alpins method). ● RESULTS: Six months after surgery, the mean uncorrected and corrected visual acuities did not change significantly. The mean preoperative refractive cylinder was 8.6 ⴞ 3.0 diopters (D) and 6.7 ⴞ 2.1 D, decreasing to 3.9 ⴞ 2.4 D and 4.7 ⴞ 2.4 D after laser AK and mechanized AK, respectively. The mean arithmetic change was significantly higher after laser AK, with a decrease of ⴚ55.4 ⴞ 20.7% (P ⴝ .011). Vector analysis showed a systematic undercorrection of astigmatism in both groups with a refractive correction index of 0.82 and 0.90 after laser AK and mechanized AK, respectively. Although no statistically significant differences were detected, a wider spread of angle of error and an almost significant difference of mean absolute angle of error (P ⴝ .052) suggest a larger misalignment of treatment during mechanized AK. All cases were uncomplicated after laser AK, 1 microperforation occurred and 1 case with off-center incisions occurred after mechanized AK. ● CONCLUSIONS: AK performed with the femtosecond laser was effective in reducing postkeratoplasty astigmatism and has some advantages over conventional techniques. However, efficacy could be improved by a more accurate nomogram and alignment of treatment. (Am J Ophthalmol 2009;147:779 –787. © 2009 by Elsevier Inc. All rights reserved.)
Accepted for publication Dec 10, 2008. From the Department of Ophthalmology, Hopital de la Timone (L.H., H.P., F.M., J.C., B.R.); and Aix-Marseille 2 University (L.H., F.M., J.C., B.R.), Marseille, France. Inquiries to Louis Hoffart, Hopital de la Timone, 264 rue Saint-Pierre, 13385 Marseille cedex 05, France; e-mail: [email protected] 0002-9394/09/$36.00 doi:10.1016/j.ajo.2008.12.017
©
2009 BY
H
IGH ASTIGMATISM IS ONE OF THE MAJOR ISSUES
that can compromise patient’s visual rehabilitation after penetrating keratoplasty. Numerous procedures have been adopted to correct astigmatic errors, including relaxing procedures, wedge resections, and photorefractive procedures.1–21 Arcuate keratotomy (AK) remains the most commonly used method1,11,13,15,19,22,23 of reducing postkeratoplasty astigmatism. However, no standard method has been established to perform AK, and even with mechanical devices, such as the Hanna keratome, results showed a low reliability.8,9,12,24 Femtosecond laser (FSL) is a step forward in the evolution of corneal surgery, aiming to reduce the deviation of depth and size of corneal incisions to a minimum.25,26 The use of this technology has several advantages, including improved accuracy and safety, associated with enhanced reproducibility.27 In this prospective study, we aimed to test the significant differences in postkeratoplasty astigmatism correction outcomes between FSL-assisted AK and mechanized AK using the Hanna keratome. We studied refractive and keratometric astigmatism through arithmetic and vector analysis.
METHODS PATIENTS WITH HIGH POSTKERATOPLASTY ASTIGMATISM
preventing successful contact lens fitting or spectacle correction were offered secondary relaxing incision surgery. AK procedures were carried out in our department between May 1 and December 31, 2007. Patients were assigned randomly to undergo laser AK or mechanized AK. All patients were informed appropriately about the procedure and signed informed consent statements. To analyze the groups of patients as homogeneously as possible, all patients had to meet specific criteria that have been recommended.28 These criteria included the following: centered graft relative to the corneal light reflex, stable posttransplant astigmatism of at least 3.5 diopters (D), a minimum of 3 months after removal of all sutures before relaxing incision surgery, a minimum of 6 months of follow-up after relaxing incision surgery to avoid reporting early data that may hide possible regression effects, and no wound abnormality such as graft– host edge lift to account for excessive astigmatism.
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RIGHTS RESERVED.
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TABLE 1. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Visual Outcomes Femtosecond Laser Variable
UCVA Initial examination (mean ⫾ SD) Final examination (mean ⫾ SD) P value (Wilcoxon rank-sum test) BSCVA Initial examination (mean ⫾ SD) Final examination (mean ⫾ SD) P (Wilcoxon rank-sum test)
Hanna Keratome
LogMAR
Snellen
LogMAR
Snellen
P value (Mann–Whitney U Test)
0.68 ⫾ 0.27 0.69 ⫾ 0.24 .735
20/95 20/98
0.99 ⫾ 0.43 0.79 ⫾ 0.50 .194
20/194 20/123
.203 .965
0.35 ⫾ 0.25 0.25 ⫾ 0.12 .168
20/45 20/36
0.39 ⫾ 0.35 0.25 ⫾ 0.17 .241
20/49 20/36
.971 .912
BSCVA ⫽ best spectacle-corrected visual acuity; logMAR ⫽ logarithm of the minimum angle of resolution; SD ⫽ standard deviation; UCVA ⫽ uncorrected visual acuity.
FIGURE 1. Bar graph showing a comparison of femtosecond vs mechanized arcuate keratotomy (AK) by gain in Snellen acuity lines with best-spectacle correction.
Arcuate keratotomy procedures were performed by 1 surgeon (L.H.) with a Femtec FSL (20/10 PerfectVision, Heidelberg, Germany) or a Hanna keratome (Moria, Anthony, France). For both techniques, the optical zone diameter and angular length of the AKs were set using a nomogram provided by Hanna and associates.12 All eyes had 2 incisions placed on each steep hemimeridian based on refractive data. The depth of the cut was set at 75% of the optical pachymetry (Orbscan IIz; Bausch & Lomb, Rochester, New York, USA) in the optical zone diameter. For the laser AK procedures, a beam energy of 3.2 to 3.4 J and a spot separation of 3 m were chosen. Under topical anesthesia with 1% tetracaine drops, the laser cut then was performed after the required suction ring was placed on patient’s eye and was centered on the pupil center mark. After completion, AKs were opened widely by dissection of the remaining tissue bridges with a Sinskey manipulator (Moria). The mechanized AK procedures also were performed under topical anesthesia with 1% tetracaine drops. The center of the pupil was marked, and a Mendez protractor was used to identify the horizontal 180 780
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degrees and steep meridian based on the refractive astigmatism steep axis. The instrument was placed on the eye, and the blades were inserted into the cornea. Both incisions were made as a single forward sweep, with no suction. They then were irrigated with balanced salt solution. Patients were treated with topical dexamethasone and tobramycin, and this treatment was tapered from 3 times daily after surgery to once daily at 6 weeks. The following examinations were performed before and after surgery: subjective refraction (cylinder, axis, and spherical equivalent), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSVCA), and automated keratometry were recorded. UCVA and BSCVA were tested using a decimal visual acuity (VA) chart under standardized lighting conditions. Surface regularity index (SRI) values were recorded before surgery and for the last postoperative examination for evaluation of irregular astigmatism. All of the eyes were examined using the OPD-Scan-ARK-10000 (Nidek, Gamagori, Japan). Patients were assessed at 1, 3, and 6 months after surgery. OF
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TABLE 2. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Refractive, Keratometric, and Topographic Outcomes Astigmatism Variable
Refractive cylinder (D) Initial examination Final examination Mean difference P value (Wilcoxon rank-sum Keratometric cylinder (D) Initial examination Final examination Mean difference P value (Wilcoxon rank-sum Spherical equivalent (D) Initial examination Final examination P value (Wilcoxon rank-sum Ocular residual astigmatism Mean ⫾ SD (D) Range (D)a Surface regularity index Initial examination Final examination P value (Wilcoxon rank-sum
P value (Mann–Whitney U Test)
Femtosecond Laser
Hanna Arcitome
6.66 ⫾ 2.12 4.66 ⫾ 2.43 ⫺2.00 ⫾ 2.71 (⫺29.7 ⫾ 30.0%) .038
.089 .529 .011
test)
8.64 ⫾ 2.96 3.85 ⫾ 2.39 ⫺4.79 ⫾ 2.23 (⫺55.4 ⫾ 20.7%) .005
7.42 ⫾ 1.93 4.51 ⫾ 2.41 ⫺2.91 ⫾ 3.19 (⫺35.4 ⫾ 34.7%) .007
.796 .739 1.000
test)
7.01 ⫾ 3.02 3.97 ⫾ 2.38 ⫺3.03 ⫾ 2.42 (⫺40.4 ⫾ 28.6%) .021
⫺2.65 ⫾ 1.96 ⫺3.14 ⫾ 2.07 .374
.579 .436
test)
⫺2.13 ⫾ 2.14 ⫺2.59 ⫾ 1.81 .308 2.56 ⫾ 2.80 0.45 to 4.68
4.05 ⫾ 3.90 1.10 to 6.99
.473
1.41 ⫾ 0.32 1.35 ⫾ 0.17 .508
1.39 ⫾ 0.29 1.34 ⫾ 0.15 .486
.759 .806
test)
D ⫽ diopters; SD ⫽ standard deviation. Boldface values corresponds to P ⬍ .05. a 95% confidence interval.
Mean values and standard deviations of UCVA and BSCVA were calculated after logarithm of the minimum angle of resolution conversion. Refractive measurements from the spectacle plane were vertexed to the corneal plane using a nominal vertex distance of 12.00 mm.29,30 To evaluate the effect of the surgery, the surgically induced astigmatism (SIA) was calculated using the Alpins method.31 The Wilcoxon rank-sum test was used to assess the differences between 2 examinations within the same group, and comparisons of the results between the different techniques were performed by means of the nonparametric Mann–Whitney U test. Correlations were examined with the Pearson correlation test for normally distributed variables and with the Spearman rank test for ordered variables. Unless otherwise noted, continuous variables are reported as mean ⫾ standard deviation. Statistical analyses were performed using SPSS software version 13.0 (SPSS Inc, Chicago, Illinois, USA). All tests of significance were two-tailed with P ⬍ .05 for all tests.
RESULTS TWENTY EYES OF 20 PATIENTS (13 MALES AND 7 FEMALES)
were included in this study. The average age of patients at the time of surgery was 46 ⫾ 19.4 years (range, 22 to 86 VOL. 147, NO. 5
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years). The median time from graft surgery was 2.4 ⫾ 2.2 years (range, 1 to 11 years). The most common preoperative diagnosis was keratoconus in 10 cases (50%), followed by bullous keratopathy in 6 cases (30%), trauma in 2 cases (10%), and infectious keratitis in 2 cases (10%). Incision depth ranged between 405 and 590 m. There were no statistically significant differences in age or gender ratio between groups. Results are presented for refractive and corneal (keratometric) analysis 6 months after surgery. Before surgery, the mean UCVA was 20/95 in the laser AK group and 20/194 (Table 1) in the mechanized AK group (P ⫽ .203). After the procedure, these values were 20/98 and 20/123, respectively (P ⫽ .965). The change in mean UCVA after treatment was nonsignificant in both groups (P ⫽ .735 and P ⫽ .194). The mean preoperative BSCVA was 20/45 in the laser AK group and 20/49 in the mechanized AK group (P ⫽ .971), and the mean postoperative BSCVA was 20/36 in both groups (P ⫽ .912). The change in mean BSCVA also was nonsignificant for all treatments (P ⫽ .168 and P ⫽ .241). In the laser AK group, 70% of eyes gained 1 line or more (30% gained 2 lines or more), BSCVA remained stable in 10% of eyes, and 20% lost 2 Snellen lines of BSCVA. In the mechanized AK group, 80% of eyes gained 1 line or more (50% gained 2 lines or more), BSCVA remain
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TABLE 3. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Alpins Indices Refractive Variable
TIA Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) SIA Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) DV Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) Magnitude of error Arithmetic mean ⫾ SD (D) Rangea AE Arithmetic mean ⫾ SD (degrees) Rangea Absolute AE Absolute mean ⫾ SD (degrees) Rangea CI Geometric mean ⫾ SD Rangea IOS Geometric mean ⫾ SD Rangea CA Geometric mean ⫾ SD Rangea FI Geometric mean ⫾ SD Rangea
Femtosecond Laser
Keratometric
Hanna Keratome
P value
8.64 ⫾ 2.96 6.40 to 10.87 2.98 ⫻ 151
6.66 ⫾ 2.12 5.05 to 8.26 2.49 ⫻ 92
.089
7.37 ⫾ 2.88 5.19 to 9.53 2.13 ⫻ 161
6.86 ⫾ 3.54 6.86 to 9.52 2.86 ⫻ 91
3.85 ⫾ 2.39 2.05 to 5.65 1.21 ⫻ 133
Femtosecond Laser
Hanna Keratome
P value
8.64 ⫾ 2.96 6.40 to 10.87 2.98 ⫻ 151
6.66 ⫾ 2.12 5.05 to 8.26 2.49 ⫻ 92
.089
.853
7.44 ⫾ 2.82 5.31 to 9.56 2.11 ⫻ 163
6.68 ⫾ 3.21 4.25 to 9.09 2.94 ⫻ 85
.684
4.66 ⫾ 2.33 2.82 to 6.49 0.38 ⫻ 178
.529
3.97 ⫾ 2.38 2.17 to 5.76 1.34 ⫻ 132
4.51 ⫾ 2.41 2.69 to 6.32 0.78 ⫻ 151
.739
⫺1.27 ⫾ 3.53 ⫺3.93 to 1.38
0.20 ⫾ 3.22 ⫺2.22 to 2.62
.529
⫺1.20 ⫾ 3.38 ⫺3.74 to 1.35
0.02 ⫾ 2.64 ⫺1.97 to 2.00
.393
⫺2.84 ⫾ 7.38 ⫺8.40 to 2.71
5.02 ⫾ 17.61 ⫺8.25 to 18.29
.089
6.26 ⫾ 20.48 ⫺9.2 to 21.7
3.86 ⫾ 21.38 ⫺12.25 to 19.98
.912
6.78 ⫾ 4.07 3.70 to 9.84
15.83 ⫾ 9.20 8.88 to 22.7
.052
11.67 ⫾ 17.95 ⫺1.86 to 25.21
18.27 ⫾ 11.75 9.4 to 27.13
.089
0.82 ⫾ 0.41 0.60 to 1.23
0.92 ⫾ 0.48 0.77 to 1.40
0.82 ⫾ 0.46 0.58 to 1.27
0.90 ⫾ 0.36 0.73 to 1.28
0.40 ⫾ 0.21 0.29 to 0.60
0.62 ⫾ 0.30 0.47 to 0.93
0.42 ⫾ 0.26 0.29 to 0.67
0.59 ⫾ 0.33 0.44 to 0.94
1.22 ⫾ 0.86 0.76 to 2.05
1.09 ⫾ 0.70 0.72 to 1.78
1.22 ⫾ 0.63 0.88 to 1.84
1.11 ⫾ 1.36 0.38 to 2.42
0.79 ⫾ 0.40 0.58 to 1.19
0.73 ⫾ 0.47 0.51 to 1.21
0.68 ⫾ 0.52 0.40 to 1.26
0.60 ⫾ 0.34 0.53 to 1.04
AE ⫽ angle of error; CA ⫽ coefficient of adjustment; CI ⫽ correction index; D ⫽ diopters; DV ⫽ difference vector; FI ⫽ flattening index; IOS ⫽ index of success; SIA ⫽ surgically induced astigmatism; SD ⫽ standard deviation; TIA ⫽ target-induced astigmatism. a 95% confidence interval.
significant (P ⫽ .011), with an improved outcome for the laser AK group. Preoperative refractive cylinder decreased by more than 1 D in 9 (90%) cases and 7 (70%) cases for the laser AK and mechanized AK groups, respectively, and remained stable (⫾1 D) in 1 (10%) case and 2 (20%) cases and increased by more than 1 D in the remaining case (10%) after mechanical AK. Before surgery, the subjective astigmatism was ⱕ5 D in 20% of the eyes in the laser AK group and 30% in the mechanized AK group, compared with 80% and 40%, respectively, after surgery. The mean change in keratometric cylinder was ⫺3.03 ⫾ 2.42 D (⫺40.4 ⫾ 28.6%; P ⫽ .021) and ⫺2.91 ⫾ 3.19 D (⫺35.4 ⫾ 34.7%; P ⫽ .007) after laser or mechanical AK, respectively. There was no significant difference between both
stable in 10%, and 10% of eyes lost 1 Snellen line of BSCVA (Figure 1). Table 2 shows refractive, keratometric, and topographic measurements before and after AK in both groups. There was no statistically significant difference between groups for preoperative refractive cylinder (P ⫽ .089), keratometric cylinder (P ⫽ .796), spherical equivalent (P ⫽ .579), ocular residual astigmatism (P ⫽ .473), or SRI (P ⫽ .759). Between the preoperative and last examinations, refractive cylinder significantly decreased (P ⫽ .005 and P ⫽ .038) by an average of ⫺4.79 ⫾ 2.23 D (⫺55.4 ⫾ 20.7%) and ⫺2.00 ⫾ 2.71 D (⫺29.7 ⫾ 30.0%) for laser AK and mechanized AK groups, respectively. The difference in magnitude of correction between surgical methods was 782
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FIGURE 2. Illustration comparing femtosecond vs mechanized AK. The astigmatic correction index (surgically induced astigmatism [SIA]/target induced astigmatism [TIA]) for (Left) keratometric and (Right) refractive values displayed at their respective angle-of-error. The rings represent the magnitude of the correction index, and the magnitude step size between rings is 0.50.
FIGURE 3. Scatterplots comparing femtosecond vs mechanized AK. Astigmatic correction index (SIA/TIA) for (Left) keratometric and (Right) refractive data. Solid line represents line of identity. Eyes with points on or above the dotted line achieved at least a 50% reduction in astigmatism.
treatment methods for postoperative refractive cylinder (P ⫽ .529), postoperative keratometric cylinder (P ⫽ .739), or spherical equivalent (P ⫽ .436). Changes in postoperative cylinder values showed a significant correlation with preoperative cylinder values for refractive and keratometric data in the laser AK group (r ⫽ 0.671 and P ⫽ .34, Pearson correlation test, and rs ⫽ 0.815 and P ⫽ .004, Spearman correlation test, respectively). There was no significant variation in spherical equivalent after AK in either group (P ⫽ .308 and P ⫽ .374). The mean preoperative and postoperative SRI values for the laser AK and mechanized AK are reported in Table 2. There was no statistically significant postoperative improvement in SRI (P ⫽ .508 and P ⫽ .486, respectively) in either group after surgery. Refractive and keratometric Alpins indices were calculated separately for each group. Results determined by vector analysis are shown in Table 3. The arithmetic mean SIA magnitude in the laser AK group for refractive (7.37 ⫾ 2.88 D) and keratometric (7.44 ⫾ 2.82 D) were less than the arithmetic mean (8.64 ⫾ 2.96 D) target VOL. 147, NO. 5
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induced astigmatism (TIA). In the mechanized AK group, overcorrection was characterized by mean arithmetic SIA for refraction (6.86 ⫾ 3.54 D) and keratometry (6.68 ⫾ 3.21 D) higher than mean TIA (6.66 ⫾ 2.12 D) and a magnitude of error of more than 0 (0.20 ⫾ 3.22). The amount of SIA for both surgical techniques has been shown not to be significantly different in our study. The summated vector mean of difference vectors (DVs) showed that orientations in the laser AK group for refractive and keratometric values were equivalent (133 and 132 degrees) and that both vector mean magnitudes (1.21 and 1.34 D) were 31.4% and 33.7% of their respective arithmetic mean magnitude; these values suggests some systematic error tendency during treatments. There was no trend of systematic error in the mechanized AK group with different axes and magnitudes for refractive and keratometric DVs. Angle-of-error (AE) analysis (AE arithmetic means) for refractive and keratometric data in both groups showed slight errors (Table 3). However, by examining the absolute refractive AE means, a less favorable outcome on correction alignment was found in the mechanized AK
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group. A significant difference was almost achieved (P ⫽ .052) on refractive absolute AE means between surgical techniques (6.78 ⫾ 4.07 degrees and 15.83 ⫾ 9.20 degrees for FSL and mechanized AK, respectively) and a wider spread of results for the mechanized AK group (8.88 to 22.7 degrees) than in the laser AK group (3.70 to 9.84 degrees) was observed (Figure 2). The lower flattening indexes of the mechanized AK group (0.73 ⫾ 0.47 and 0.60 ⫾ 0.34) than in the laser AK group (0.79 ⫾ 0.40 and 0.60 ⫾ 0.34) are in relation with this treatment misalignment after mechanical keratotomy. Scatterplots of SIA vs TIA are shown in Figure 3. The values showed no correlation in the SIA and TIA scattergrams, and the general undercorrection of astigmatism is more evident by FSL than by mechanical keratotomy and confirmed by a lower correction index in the laser AK group (0.82 ⫾ 0.41and 0.82 ⫾ 0.46) than in the mechanized AK group (0.92 ⫾ 0.48 and 0.90 ⫾ 0.36) for the 2 measurement methods. The coefficient of adjustment (amount required to adjust future treatments) was 1.22 in the laser AK group and between 1.09 and 1.11 in the mechanized AK group. In the mechanized AK group, a microperforation occurred within 1 incision and required suturing. Also, incisions were off center in 1 case as a result of intraoperative patient restlessness. No postoperative complication was observed in laser AK group.
after surgery, with nonsignificant modifications of SRI between preoperative and last postoperative examination (Table 2). We found in our study a significantly (P ⫽ .011) higher reduction (⫺55.4 ⫾ 20.7%) of preoperative refractive cylinder in the laser AK group than in the mechanized AK group (⫺29.7 ⫾ 30.0%). A decrease in refractive and keratometric astigmatism was obtained in 90% and 70% of eyes, and in these eyes, 80% and 40% had less of 5 D of refractive astigmatism after surgery, compared with 20% and 30% before surgery. These cases may qualify for further interventions such as laser in situ or laser subepithelial keratomileusis. Our results are similar to those achieved with freehand AK.4,10,13,23,32,37,38 Hjortdal and Ehlers found a 54% reduction in refractive cylinder with paired AKs in 21 postkeratoplasty eyes, and Hovding found a 49% reduction with transverse keratotomies in 12 postkeratoplasty eyes.4,13 Wilkins and associates recently reported a much higher (70%) reduction in 20 eyes; the greater effect may be from a strict adherence to the 6.0-mm optical zone.19 In our study, the arcuate incisions were placed on a larger optical zone, which may equate to the 6.5-mm optical zone rather than 6.0 mm. It should be noted that the patients in the study by Wilkins and associates also started with a higher mean astigmatic error than our patients did, which also may explain the greater reduction.19 Residual refractive astigmatism (3.85 ⫾ 2.39 D) found in the present study was comparable with that of other reports of mechanized AK. Borderie and associates, in a study of 22 eyes, reported a mean preoperative and postoperative astigmatism of 6.94 and 3.85 D, respectively.8 Hannush and associates reported the results of 29 eyes with a mean preoperative and postoperative astigmatism of 8.8 and 3.2 D, respectively (Hannush S, et al. IOVS 1998;39: S347, ARVO E-Abstract 1612). The Alpins method31,39 was chosen for vector analysis for this study. Refractive, keratometric, and astigmatism data are reported to avoid reporting only refractive changes, which tend to show larger changes.40 The correction plan was targeted on correcting refraction. Thus, the target corneal astigmatism was the minimal keratometric astigmatism remaining after treatment to neutralize refractive astigmatism. The mean ocular residual astigmatism values were 2.56 ⫾ 2.80 D and 4.05 ⫾ 3.90 D for laser AK and mechanized AK, respectively. Because treatment parameters emphasized the elimination of refractive astigmatism (target, 0.00 D), the mean target corneal astigmatism was represented by the mean ocular residual astigmatism. After surgery, the mean corneal astigmatism decreased to 3.97 ⫾ 2.38 D and 4.51 ⫾ 2.41 D, respectively. Thus, the resulting mean corneal astigmatism exceeded ocular residual astigmatism by a factor of 1.55 and 1.11. This imbalance in excessive corneal astigmatism remaining after treatment can be attributed to refractive astigmatism values being the sole consideration in treatment planning, resulting in a proportionately higher reduction in refractive astigmatism than keratometric astigmatism, which is
DISCUSSION THE MAIN OBJECTIVE OF THIS STUDY WAS TO TEST THE
significant differences in surgically generated astigmatism between 2 AK procedures for postkeratoplasty astigmatism correction. Several relaxing incision techniques exist for correction of postkeratoplasty astigmatism, but no standard procedure has been established.3,5,10,13,14,20,22,32–36 However, AK has become a reliable and safe procedure in recent years and the developments in technology and instrumentation combine to allow the planning of corneal surgery with unprecedented accuracy. AK procedures performed with mechanized devices have been shown to provide more reproducible results than freehand techniques,8,12,24 but further improvements may be brought by the use of FSL technology in this indication. In this study, neither UCVA nor BSCVA improved significantly after mechanical or laser AK, although BSCVA increased by 1 line or more of VA in 70% and 80% of cases after laser AK and mechanized AK, respectively. This nonsignificant improvement of VA was probably related to the preoperative irregular corneal astigmatism in all cases, and our results showed no decrease of irregularity in postkeratoplasty topographic astigmatism 784
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FIGURE 4. Photograph comparing femtosecond vs mechanized AK. Direct visualization of the surgical procedure through the laser interface showing a gas bubble between the cornea and applanation lens at the lower keratotomy level.
off-axis from the midpoint of the incision. If corneal astigmatism values were included in the treatment plan, an overall greater reduction in astigmatism would have been achievable. In the mechanized AK group, the arithmetic mean SIA magnitude for refraction (6.86 D) and keratometry (6.68 D) was higher than the arithmetic mean TIA (6.66 D), and it was confirmed by summated vector mean SIA for refractive values (2.86 D ⫻ 92 degrees) and for keratometric values (2.94 ⫻ 85 degrees), in a very close alignment with the TIA (2.49 D ⫻ 91 degrees). However, the geometric mean correction index was between 0.90 and 0.92 and resulted from a lower reduction of astigmatism than the achieved correction in previous studies.14 The mean AE value (5.02 and 3.86 degrees) was consistent with the closeness of the vector mean TIA and SIA axes detailed above, so no significant systematic error of misaligned treatment is evident. However, mean absolute AE values (15.83 and 18.27 degrees) suggest a misalignment of treatment at an individual level, and the difference of mean absolute AE between groups was almost significant (P ⫽ .052). In the laser AK group, a mean refractive correction index of 0.82 resulted from a substantially smaller vector mean of the SIA (2.13 and 2.11 D) compared with the TIA (2.98 D). The summated vector mean of DVs showed that axis in the FSL group for refractive and keratometric values were equivalent (133
and 132 degrees) and that both vector mean magnitudes (1.21 and 1.34 D) were 31.4% and 33.7% of their respective arithmetic mean magnitude. These results suggests some error tendency in the treatments such as systematic misalignment. After laser treatment, the undercorrection of astigmatism was approximately 22%. The systematic proportion of the error fell between 31.4% and 33.7% of the total error measured by the arithmetic mean DV magnitude. These results suggest that a nomogram adjustment to future treatments magnitude (TIAs) should be used by an additional factor (coefficient of adjustment [CA] ⫽ 1.22). The nomogram correction could be achieved by derivation of a nominal value for the TIA close to the average SIA obtained for each standard optical zone and arc length setting. Systematic misalignment should be addressed by such means as preoperative limbal marking, but the direct visualization of the limbus is masked by the suction ring of the laser interface during the surgical procedure (Figure 4), and control of cyclotorsion (or off-axis treatment) could be improved by an embedded device as computerized torsional control, as in actual excimer lasers systems. Moreover, the use of FSL provides depth accuracy even at increased depth settings with a lower mean deviation than the mechanical cut from the planned incision depth.25 These highly reproducible dimensions of the cuts26 will allow accomplishment of deeper incisions and to increase the average SIA in AK procedures. An important factor in determining the outcomes of an astigmatism correction technique on corneal graft is the rate of complications. In our study, all cases in the laser AK group were uncomplicated, as in previous FSL-assisted AK studies.21,26 In the mechanical group, of the 10 procedures performed, 1 case of microperforation occurred and incisions were off-center in 1 case. We found AK performed with FSL to be a relatively easy, safe, and effective means of treating postkeratoplasty astigmatism. In our study, achieved reduction of postkeratoplasty astigmatism in laser AK group was higher for refractive values than those with mechanical procedures. Vector analysis identified a systematic misalignment of laser treatment that need to be addressed, but with a lower mean AE than after mechanical AK. However, related to our small samples, much larger numbers are needed to provide more confident estimates of astigmatism reduction proportions for each surgical method and to adjust correction parameters. Subsequently, these studies could seek other means for improving the alignment of treatment, such as computerized axis control during laser surgery.
THIS STUDY WAS SUPPORTED IN PART BY THE DEPARTMENTAL COUNCIL OF “BOUCHES-DU RHONE” (CG13), MARSEILLE, France. The authors indicate no financial conflict of interest. Involved in design of study (L.H.); conduct of study (L.H.); data collection (H.P.); critical revision of the article (J.C.); administrative and logistical support (B.R., H.P.); and preparation, review, and approval of the manuscript (L.H., J.C.). This study was approved by the Institutional Review Board, Marseille, France. The study was conducted in accord with Good Clinical Practices and the tenets of the Declaration of Helsinki.
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19. Wilkins MR, Mehta JS, Larkin DF. Standardized arcuate keratotomy for post-keratoplasty astigmatism. J Cataract Refract Surg 2005;31:297–301. 20. Troutman RC, Swinger C. Relaxing incision for control of postoperative astigmatism following keratoplasty. Ophthalmic Surg 1980;11:117–120. 21. Kiraly L, Herrmann C, Amm M, Duncker G. Reduction of astigmatism by arcuate incisions using the femtosecond laser after corneal transplantation [in German]. Klin Monatsbl Augenheilkd 2008;225:70 –74. 22. Koffler BH, Smith VM. Corneal topography, arcuate keratotomy, and compression sutures for astigmatism after penetrating keratoplasty. J Refract Surg 1996;12:S306 –S309. 23. Poole TR, Ficker L. Astigmatic keratotomy for post-keratoplasty astigmatism. J Cataract Refract Surg 2006;32:1175– 1179. 24. Hoffart L, Touzeau O, Borderie V, Laroche L. Mechanized astigmatic arcuate keratotomy with the Hanna arcitome for astigmatism after keratoplasty. J Cataract Refract Surg 2007; 33:862– 868. 25. Holzer MP, Rabsilber TM, Auffarth GU. Femtosecond laser-assisted corneal flap cuts: morphology, accuracy, and histopathology. Invest Ophthalmol Vis Sci 2006;47: 2828 –2831. 26. Harissi-Dagher M, Azar DT. Femtosecond laser astigmatic keratotomy for post-keratoplasty astigmatism. Can J Ophthalmol 2008;43:367–369. 27. Touboul D, Salin F, Mortemousque B, et al. Advantages and disadvantages of the femtosecond laser microkeratome [in French]. J Fr Ophtalmol 2005;28:535–546. 28. Millin JA, Maguire LJ. Developing entry criteria for studies of severe post-keratoplasty astigmatism. Am J Ophthalmol 1991;112:666 – 670. 29. Holladay JT, Dudeja DR, Koch DD. Evaluating and reporting astigmatism for individual and aggregate data. J Cataract Refract Surg 1998;24:57– 65. 30. Holladay JT, Moran JR, Kezirian GM. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg 2001;27: 61–79. 31. Alpins N. Astigmatism analysis by the Alpins method. J Cataract Refract Surg 2001;27:31– 49. 32. Krachmer JH, Fenzl RE. Surgical correction of high postkeratoplasty astigmatism. Relaxing incisions vs wedge resection. Arch Ophthalmol 1980;98:1400 –1402. 33. Price FW Jr, Whitson WE. The art of surgical correction for post-keratoplasty astigmatism. Int Ophthalmol Clin 1991;31: 59 – 67. 34. Arffa RC. Results of a graded relaxing incision technique for post-keratoplasty astigmatism. Ophthalmic Surg 1988;19: 624 – 628. 35. Frangieh GT, Kwitko S, McDonnell PJ. Prospective corneal topographic analysis in surgery for post-keratoplasty astigmatism. Arch Ophthalmol 1991;109:506 –510. 36. Karabatsas CH, Cook SD, Figueiredo FC, et al. Surgical control of late post-keratoplasty astigmatism with or without the use of computerized video keratography: a prospective, randomized study. Ophthalmology 1998;105: 1999 –2006.
REFERENCES 1. Seitz B, Naumann GO. Limbus-parallel keratotomies and compression sutures in excessive astigmatism after penetrating keratoplasty. Ger J Ophthalmol 1993;2:42–50. 2. Tuunanen TH, Ruusuvaara PJ, Uusitalo RJ, Tervo TM. Photoastigmatic keratectomy for correction of astigmatism in corneal grafts. Cornea 1997;16:48 –53. 3. Fronterre A, Portesani GP. Relaxing incisions for postkeratoplasty astigmatism. Cornea 1991;10:305–311. 4. Hovding G. Transverse keratotomy in post-keratoplasty astigmatism. Acta Ophthalmol (Copenh) 1994;72:464 – 468. 5. Kirkness CM, Ficker LA, Steele AD, Rice NS. Refractive surgery for graft-induced astigmatism after penetrating keratoplasty for keratoconus. Ophthalmology 1991;98: 1786 –1792. 6. Lazzaro DR, Haight DH, Belmont SC, et al. Excimer laser keratectomy for astigmatism occurring after penetrating keratoplasty. Ophthalmology 1996;103:458 – 464. 7. Ghanem RC, Azar DT. Femtosecond-laser arcuate wedgeshaped resection to correct high residual astigmatism after penetrating keratoplasty. J Cataract Refract Surg 2006;32: 1415–1419. 8. Borderie VM, Touzeau O, Chastang PJ, Laroche L. Surgical correction of post-keratoplasty astigmatism with the Hanna arcitome. J Cataract Refract Surg 1999;25:205–211. 9. Chastang P, Borderie V, Carvajal S, Laroche L. Surgical treatment of astigmatism caused by penetrating keratoplasty using the Hanna arcuate keratome [in French]. J Fr Ophtalmol 1997;20:360 –365. 10. Cohen KL, Tripoli NK, Noecker RJ. Prospective analysis of photokeratoscopy for arcuate keratotomy to reduce postkeratoplasty astigmatism. Refract Corneal Surg 1989;5:388 – 393. 11. Geggel HS. Arcuate relaxing incisions guided by corneal topography for post-keratoplasty astigmatism: vector and topographic analysis. Cornea 2006;25:545–557. 12. Hanna KD, Hayward JM, Hagen KB, et al. Keratotomy for astigmatism using an arcuate keratome. Arch Ophthalmol 1993;111:998 –1004. 13. Hjortdal JO, Ehlers N. Paired arcuate keratotomy for congenital and post-keratoplasty astigmatism. Acta Ophthalmol Scand 1998;76:138 –141. 14. Jacobi PC, Hartmann C, Severin M, Bartz-Schmidt KU. Relaxing incisions with compression sutures for control of astigmatism after penetrating keratoplasty. Graefes Arch Clin Exp Ophthalmol 1994;232:527–532. 15. Koay PY, McGhee CN, Crawford GJ. Effect of a standard paired arcuate incision and augmentation sutures on postkeratoplasty astigmatism. J Cataract Refract Surg 2000;26: 553–561. 16. Krumeich JH, Knuelle A. Circular keratotomy for the correction of astigmatism. Refract Corneal Surg 1992;8:204 – 210. 17. Limberg MB, Dingeldein SA, Green MT, et al. Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989;108:36 – 42. 18. Lustbader JM, Lemp MA. The effect of relaxing incisions with multiple compression sutures on post-keratoplasty astigmatism. Ophthalmic Surg 1990;21:416 – 419.
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37. Lavery GW, Lindstrom RL, Hofer LA, Doughman DJ. The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg 1985;16:165–169. 38. McCartney DL, Whitney CE, Stark WJ, et al. Refractive keratoplasty for disabling astigmatism after penetrating keratoplasty. Arch Ophthalmol 1987;105:954 –957.
39. Alpins NA, Goggin M. Practical astigmatism analysis for refractive outcomes in cataract and refractive surgery. Surv Ophthalmol 2004;49:109 –122. 40. Alpins NA, Tabin GC, Adams LM, et al. Refractive versus corneal changes after photorefractive keratectomy for astigmatism. J Refract Surg 1998;14:386 –396.
REPORTING VISUAL ACUITIES The AJO encourages authors to report the visual acuity in the manuscript using the same nomenclature that was used in gathering the data provided they were recorded in one of the methods listed here. This table of equivalent visual acuities is provided to the readers as an aid to interpret visual acuity findings in familiar units. Table of Equivalent Visual Acuity Measurements Snellen Visual Acuities 4 Meters
6 Meters
20 Feet
Decimal Fraction
LogMAR
4/40 4/32 4/25 4/20 4/16 4/12.6 4/10 4/8 4/6.3 4/5 4/4 4/3.2 4/2.5 4/2
6/60 6/48 6/38 6/30 6/24 6/20 6/15 6/12 6/10 6/7.5 6/6 6/5 6/3.75 6/3
20/200 20/160 20/125 20/100 20/80 20/63 20/50 20/40 20/32 20/25 20/20 20/16 20/12.5 20/10
0.10 0.125 0.16 0.20 0.25 0.32 0.40 0.50 0.63 0.80 1.00 1.25 1.60 2.00
⫹1.0 ⫹0.9 ⫹0.8 ⫹0.7 ⫹0.6 ⫹0.5 ⫹0.4 ⫹0.3 ⫹0.2 ⫹0.1 0.0 ⫺0.1 ⫺0.2 ⫺0.3
From Ferris FL III, Kassoff A, Bresnick GH, Bailey I. New visual acuity charts for clinical research. Am J Ophthalmol 1982;94:91–96.
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Biosketch Louis Hoffart received his MD degree at the Marseille Medical School, France and graduated in 2004 with a Master of Neurosciences. Since 2005, Dr Hoffart worked on his PhD about femtosecond laser interactions in ocular tissues project and has held a fellowship in corneal and external disease in Prof Ridings’ Department of Ophthalmology in Marseille, France. His fields of research are related on corneal surgeries procedures, femtosecond laser physics, and therapeutic procedures.
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To compare the effectiveness of arcuate keratotomy (AK) performed with a femtosecond laser (FSL) or Hanna keratome (Moria, Anthony, France) for correction of postkeratoplasty astigmatism. ● DESIGN: Prospective, randomized study. ● METHODS: This clinical study included 20 eyes. Two groups of 10 eyes underwent AK using an FLS or keratome. Refractive and keratometric astigmatism were evaluated before surgery and 6 months after surgery. The astigmatic changes in the 2 groups were measured through arithmetic and vector analysis (Alpins method). ● RESULTS: Six months after surgery, the mean uncorrected and corrected visual acuities did not change significantly. The mean preoperative refractive cylinder was 8.6 ⴞ 3.0 diopters (D) and 6.7 ⴞ 2.1 D, decreasing to 3.9 ⴞ 2.4 D and 4.7 ⴞ 2.4 D after laser AK and mechanized AK, respectively. The mean arithmetic change was significantly higher after laser AK, with a decrease of ⴚ55.4 ⴞ 20.7% (P ⴝ .011). Vector analysis showed a systematic undercorrection of astigmatism in both groups with a refractive correction index of 0.82 and 0.90 after laser AK and mechanized AK, respectively. Although no statistically significant differences were detected, a wider spread of angle of error and an almost significant difference of mean absolute angle of error (P ⴝ .052) suggest a larger misalignment of treatment during mechanized AK. All cases were uncomplicated after laser AK, 1 microperforation occurred and 1 case with off-center incisions occurred after mechanized AK. ● CONCLUSIONS: AK performed with the femtosecond laser was effective in reducing postkeratoplasty astigmatism and has some advantages over conventional techniques. However, efficacy could be improved by a more accurate nomogram and alignment of treatment. (Am J Ophthalmol 2009;147:779 –787. © 2009 by Elsevier Inc. All rights reserved.)
Accepted for publication Dec 10, 2008. From the Department of Ophthalmology, Hopital de la Timone (L.H., H.P., F.M., J.C., B.R.); and Aix-Marseille 2 University (L.H., F.M., J.C., B.R.), Marseille, France. Inquiries to Louis Hoffart, Hopital de la Timone, 264 rue Saint-Pierre, 13385 Marseille cedex 05, France; e-mail: [email protected] 0002-9394/09/$36.00 doi:10.1016/j.ajo.2008.12.017
©
2009 BY
H
IGH ASTIGMATISM IS ONE OF THE MAJOR ISSUES
that can compromise patient’s visual rehabilitation after penetrating keratoplasty. Numerous procedures have been adopted to correct astigmatic errors, including relaxing procedures, wedge resections, and photorefractive procedures.1–21 Arcuate keratotomy (AK) remains the most commonly used method1,11,13,15,19,22,23 of reducing postkeratoplasty astigmatism. However, no standard method has been established to perform AK, and even with mechanical devices, such as the Hanna keratome, results showed a low reliability.8,9,12,24 Femtosecond laser (FSL) is a step forward in the evolution of corneal surgery, aiming to reduce the deviation of depth and size of corneal incisions to a minimum.25,26 The use of this technology has several advantages, including improved accuracy and safety, associated with enhanced reproducibility.27 In this prospective study, we aimed to test the significant differences in postkeratoplasty astigmatism correction outcomes between FSL-assisted AK and mechanized AK using the Hanna keratome. We studied refractive and keratometric astigmatism through arithmetic and vector analysis.
METHODS PATIENTS WITH HIGH POSTKERATOPLASTY ASTIGMATISM
preventing successful contact lens fitting or spectacle correction were offered secondary relaxing incision surgery. AK procedures were carried out in our department between May 1 and December 31, 2007. Patients were assigned randomly to undergo laser AK or mechanized AK. All patients were informed appropriately about the procedure and signed informed consent statements. To analyze the groups of patients as homogeneously as possible, all patients had to meet specific criteria that have been recommended.28 These criteria included the following: centered graft relative to the corneal light reflex, stable posttransplant astigmatism of at least 3.5 diopters (D), a minimum of 3 months after removal of all sutures before relaxing incision surgery, a minimum of 6 months of follow-up after relaxing incision surgery to avoid reporting early data that may hide possible regression effects, and no wound abnormality such as graft– host edge lift to account for excessive astigmatism.
ELSEVIER INC. ALL
RIGHTS RESERVED.
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TABLE 1. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Visual Outcomes Femtosecond Laser Variable
UCVA Initial examination (mean ⫾ SD) Final examination (mean ⫾ SD) P value (Wilcoxon rank-sum test) BSCVA Initial examination (mean ⫾ SD) Final examination (mean ⫾ SD) P (Wilcoxon rank-sum test)
Hanna Keratome
LogMAR
Snellen
LogMAR
Snellen
P value (Mann–Whitney U Test)
0.68 ⫾ 0.27 0.69 ⫾ 0.24 .735
20/95 20/98
0.99 ⫾ 0.43 0.79 ⫾ 0.50 .194
20/194 20/123
.203 .965
0.35 ⫾ 0.25 0.25 ⫾ 0.12 .168
20/45 20/36
0.39 ⫾ 0.35 0.25 ⫾ 0.17 .241
20/49 20/36
.971 .912
BSCVA ⫽ best spectacle-corrected visual acuity; logMAR ⫽ logarithm of the minimum angle of resolution; SD ⫽ standard deviation; UCVA ⫽ uncorrected visual acuity.
FIGURE 1. Bar graph showing a comparison of femtosecond vs mechanized arcuate keratotomy (AK) by gain in Snellen acuity lines with best-spectacle correction.
Arcuate keratotomy procedures were performed by 1 surgeon (L.H.) with a Femtec FSL (20/10 PerfectVision, Heidelberg, Germany) or a Hanna keratome (Moria, Anthony, France). For both techniques, the optical zone diameter and angular length of the AKs were set using a nomogram provided by Hanna and associates.12 All eyes had 2 incisions placed on each steep hemimeridian based on refractive data. The depth of the cut was set at 75% of the optical pachymetry (Orbscan IIz; Bausch & Lomb, Rochester, New York, USA) in the optical zone diameter. For the laser AK procedures, a beam energy of 3.2 to 3.4 J and a spot separation of 3 m were chosen. Under topical anesthesia with 1% tetracaine drops, the laser cut then was performed after the required suction ring was placed on patient’s eye and was centered on the pupil center mark. After completion, AKs were opened widely by dissection of the remaining tissue bridges with a Sinskey manipulator (Moria). The mechanized AK procedures also were performed under topical anesthesia with 1% tetracaine drops. The center of the pupil was marked, and a Mendez protractor was used to identify the horizontal 180 780
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degrees and steep meridian based on the refractive astigmatism steep axis. The instrument was placed on the eye, and the blades were inserted into the cornea. Both incisions were made as a single forward sweep, with no suction. They then were irrigated with balanced salt solution. Patients were treated with topical dexamethasone and tobramycin, and this treatment was tapered from 3 times daily after surgery to once daily at 6 weeks. The following examinations were performed before and after surgery: subjective refraction (cylinder, axis, and spherical equivalent), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSVCA), and automated keratometry were recorded. UCVA and BSCVA were tested using a decimal visual acuity (VA) chart under standardized lighting conditions. Surface regularity index (SRI) values were recorded before surgery and for the last postoperative examination for evaluation of irregular astigmatism. All of the eyes were examined using the OPD-Scan-ARK-10000 (Nidek, Gamagori, Japan). Patients were assessed at 1, 3, and 6 months after surgery. OF
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TABLE 2. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Refractive, Keratometric, and Topographic Outcomes Astigmatism Variable
Refractive cylinder (D) Initial examination Final examination Mean difference P value (Wilcoxon rank-sum Keratometric cylinder (D) Initial examination Final examination Mean difference P value (Wilcoxon rank-sum Spherical equivalent (D) Initial examination Final examination P value (Wilcoxon rank-sum Ocular residual astigmatism Mean ⫾ SD (D) Range (D)a Surface regularity index Initial examination Final examination P value (Wilcoxon rank-sum
P value (Mann–Whitney U Test)
Femtosecond Laser
Hanna Arcitome
6.66 ⫾ 2.12 4.66 ⫾ 2.43 ⫺2.00 ⫾ 2.71 (⫺29.7 ⫾ 30.0%) .038
.089 .529 .011
test)
8.64 ⫾ 2.96 3.85 ⫾ 2.39 ⫺4.79 ⫾ 2.23 (⫺55.4 ⫾ 20.7%) .005
7.42 ⫾ 1.93 4.51 ⫾ 2.41 ⫺2.91 ⫾ 3.19 (⫺35.4 ⫾ 34.7%) .007
.796 .739 1.000
test)
7.01 ⫾ 3.02 3.97 ⫾ 2.38 ⫺3.03 ⫾ 2.42 (⫺40.4 ⫾ 28.6%) .021
⫺2.65 ⫾ 1.96 ⫺3.14 ⫾ 2.07 .374
.579 .436
test)
⫺2.13 ⫾ 2.14 ⫺2.59 ⫾ 1.81 .308 2.56 ⫾ 2.80 0.45 to 4.68
4.05 ⫾ 3.90 1.10 to 6.99
.473
1.41 ⫾ 0.32 1.35 ⫾ 0.17 .508
1.39 ⫾ 0.29 1.34 ⫾ 0.15 .486
.759 .806
test)
D ⫽ diopters; SD ⫽ standard deviation. Boldface values corresponds to P ⬍ .05. a 95% confidence interval.
Mean values and standard deviations of UCVA and BSCVA were calculated after logarithm of the minimum angle of resolution conversion. Refractive measurements from the spectacle plane were vertexed to the corneal plane using a nominal vertex distance of 12.00 mm.29,30 To evaluate the effect of the surgery, the surgically induced astigmatism (SIA) was calculated using the Alpins method.31 The Wilcoxon rank-sum test was used to assess the differences between 2 examinations within the same group, and comparisons of the results between the different techniques were performed by means of the nonparametric Mann–Whitney U test. Correlations were examined with the Pearson correlation test for normally distributed variables and with the Spearman rank test for ordered variables. Unless otherwise noted, continuous variables are reported as mean ⫾ standard deviation. Statistical analyses were performed using SPSS software version 13.0 (SPSS Inc, Chicago, Illinois, USA). All tests of significance were two-tailed with P ⬍ .05 for all tests.
RESULTS TWENTY EYES OF 20 PATIENTS (13 MALES AND 7 FEMALES)
were included in this study. The average age of patients at the time of surgery was 46 ⫾ 19.4 years (range, 22 to 86 VOL. 147, NO. 5
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years). The median time from graft surgery was 2.4 ⫾ 2.2 years (range, 1 to 11 years). The most common preoperative diagnosis was keratoconus in 10 cases (50%), followed by bullous keratopathy in 6 cases (30%), trauma in 2 cases (10%), and infectious keratitis in 2 cases (10%). Incision depth ranged between 405 and 590 m. There were no statistically significant differences in age or gender ratio between groups. Results are presented for refractive and corneal (keratometric) analysis 6 months after surgery. Before surgery, the mean UCVA was 20/95 in the laser AK group and 20/194 (Table 1) in the mechanized AK group (P ⫽ .203). After the procedure, these values were 20/98 and 20/123, respectively (P ⫽ .965). The change in mean UCVA after treatment was nonsignificant in both groups (P ⫽ .735 and P ⫽ .194). The mean preoperative BSCVA was 20/45 in the laser AK group and 20/49 in the mechanized AK group (P ⫽ .971), and the mean postoperative BSCVA was 20/36 in both groups (P ⫽ .912). The change in mean BSCVA also was nonsignificant for all treatments (P ⫽ .168 and P ⫽ .241). In the laser AK group, 70% of eyes gained 1 line or more (30% gained 2 lines or more), BSCVA remained stable in 10% of eyes, and 20% lost 2 Snellen lines of BSCVA. In the mechanized AK group, 80% of eyes gained 1 line or more (50% gained 2 lines or more), BSCVA remain
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TABLE 3. Comparison of Femtosecond Laser and Mechanical Astigmatic Keratotomy for Postkeratoplasty Astigmatism Correction: Alpins Indices Refractive Variable
TIA Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) SIA Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) DV Arithmetic mean ⫾ SD (D) Rangea Vector mean (D) Magnitude of error Arithmetic mean ⫾ SD (D) Rangea AE Arithmetic mean ⫾ SD (degrees) Rangea Absolute AE Absolute mean ⫾ SD (degrees) Rangea CI Geometric mean ⫾ SD Rangea IOS Geometric mean ⫾ SD Rangea CA Geometric mean ⫾ SD Rangea FI Geometric mean ⫾ SD Rangea
Femtosecond Laser
Keratometric
Hanna Keratome
P value
8.64 ⫾ 2.96 6.40 to 10.87 2.98 ⫻ 151
6.66 ⫾ 2.12 5.05 to 8.26 2.49 ⫻ 92
.089
7.37 ⫾ 2.88 5.19 to 9.53 2.13 ⫻ 161
6.86 ⫾ 3.54 6.86 to 9.52 2.86 ⫻ 91
3.85 ⫾ 2.39 2.05 to 5.65 1.21 ⫻ 133
Femtosecond Laser
Hanna Keratome
P value
8.64 ⫾ 2.96 6.40 to 10.87 2.98 ⫻ 151
6.66 ⫾ 2.12 5.05 to 8.26 2.49 ⫻ 92
.089
.853
7.44 ⫾ 2.82 5.31 to 9.56 2.11 ⫻ 163
6.68 ⫾ 3.21 4.25 to 9.09 2.94 ⫻ 85
.684
4.66 ⫾ 2.33 2.82 to 6.49 0.38 ⫻ 178
.529
3.97 ⫾ 2.38 2.17 to 5.76 1.34 ⫻ 132
4.51 ⫾ 2.41 2.69 to 6.32 0.78 ⫻ 151
.739
⫺1.27 ⫾ 3.53 ⫺3.93 to 1.38
0.20 ⫾ 3.22 ⫺2.22 to 2.62
.529
⫺1.20 ⫾ 3.38 ⫺3.74 to 1.35
0.02 ⫾ 2.64 ⫺1.97 to 2.00
.393
⫺2.84 ⫾ 7.38 ⫺8.40 to 2.71
5.02 ⫾ 17.61 ⫺8.25 to 18.29
.089
6.26 ⫾ 20.48 ⫺9.2 to 21.7
3.86 ⫾ 21.38 ⫺12.25 to 19.98
.912
6.78 ⫾ 4.07 3.70 to 9.84
15.83 ⫾ 9.20 8.88 to 22.7
.052
11.67 ⫾ 17.95 ⫺1.86 to 25.21
18.27 ⫾ 11.75 9.4 to 27.13
.089
0.82 ⫾ 0.41 0.60 to 1.23
0.92 ⫾ 0.48 0.77 to 1.40
0.82 ⫾ 0.46 0.58 to 1.27
0.90 ⫾ 0.36 0.73 to 1.28
0.40 ⫾ 0.21 0.29 to 0.60
0.62 ⫾ 0.30 0.47 to 0.93
0.42 ⫾ 0.26 0.29 to 0.67
0.59 ⫾ 0.33 0.44 to 0.94
1.22 ⫾ 0.86 0.76 to 2.05
1.09 ⫾ 0.70 0.72 to 1.78
1.22 ⫾ 0.63 0.88 to 1.84
1.11 ⫾ 1.36 0.38 to 2.42
0.79 ⫾ 0.40 0.58 to 1.19
0.73 ⫾ 0.47 0.51 to 1.21
0.68 ⫾ 0.52 0.40 to 1.26
0.60 ⫾ 0.34 0.53 to 1.04
AE ⫽ angle of error; CA ⫽ coefficient of adjustment; CI ⫽ correction index; D ⫽ diopters; DV ⫽ difference vector; FI ⫽ flattening index; IOS ⫽ index of success; SIA ⫽ surgically induced astigmatism; SD ⫽ standard deviation; TIA ⫽ target-induced astigmatism. a 95% confidence interval.
significant (P ⫽ .011), with an improved outcome for the laser AK group. Preoperative refractive cylinder decreased by more than 1 D in 9 (90%) cases and 7 (70%) cases for the laser AK and mechanized AK groups, respectively, and remained stable (⫾1 D) in 1 (10%) case and 2 (20%) cases and increased by more than 1 D in the remaining case (10%) after mechanical AK. Before surgery, the subjective astigmatism was ⱕ5 D in 20% of the eyes in the laser AK group and 30% in the mechanized AK group, compared with 80% and 40%, respectively, after surgery. The mean change in keratometric cylinder was ⫺3.03 ⫾ 2.42 D (⫺40.4 ⫾ 28.6%; P ⫽ .021) and ⫺2.91 ⫾ 3.19 D (⫺35.4 ⫾ 34.7%; P ⫽ .007) after laser or mechanical AK, respectively. There was no significant difference between both
stable in 10%, and 10% of eyes lost 1 Snellen line of BSCVA (Figure 1). Table 2 shows refractive, keratometric, and topographic measurements before and after AK in both groups. There was no statistically significant difference between groups for preoperative refractive cylinder (P ⫽ .089), keratometric cylinder (P ⫽ .796), spherical equivalent (P ⫽ .579), ocular residual astigmatism (P ⫽ .473), or SRI (P ⫽ .759). Between the preoperative and last examinations, refractive cylinder significantly decreased (P ⫽ .005 and P ⫽ .038) by an average of ⫺4.79 ⫾ 2.23 D (⫺55.4 ⫾ 20.7%) and ⫺2.00 ⫾ 2.71 D (⫺29.7 ⫾ 30.0%) for laser AK and mechanized AK groups, respectively. The difference in magnitude of correction between surgical methods was 782
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FIGURE 2. Illustration comparing femtosecond vs mechanized AK. The astigmatic correction index (surgically induced astigmatism [SIA]/target induced astigmatism [TIA]) for (Left) keratometric and (Right) refractive values displayed at their respective angle-of-error. The rings represent the magnitude of the correction index, and the magnitude step size between rings is 0.50.
FIGURE 3. Scatterplots comparing femtosecond vs mechanized AK. Astigmatic correction index (SIA/TIA) for (Left) keratometric and (Right) refractive data. Solid line represents line of identity. Eyes with points on or above the dotted line achieved at least a 50% reduction in astigmatism.
treatment methods for postoperative refractive cylinder (P ⫽ .529), postoperative keratometric cylinder (P ⫽ .739), or spherical equivalent (P ⫽ .436). Changes in postoperative cylinder values showed a significant correlation with preoperative cylinder values for refractive and keratometric data in the laser AK group (r ⫽ 0.671 and P ⫽ .34, Pearson correlation test, and rs ⫽ 0.815 and P ⫽ .004, Spearman correlation test, respectively). There was no significant variation in spherical equivalent after AK in either group (P ⫽ .308 and P ⫽ .374). The mean preoperative and postoperative SRI values for the laser AK and mechanized AK are reported in Table 2. There was no statistically significant postoperative improvement in SRI (P ⫽ .508 and P ⫽ .486, respectively) in either group after surgery. Refractive and keratometric Alpins indices were calculated separately for each group. Results determined by vector analysis are shown in Table 3. The arithmetic mean SIA magnitude in the laser AK group for refractive (7.37 ⫾ 2.88 D) and keratometric (7.44 ⫾ 2.82 D) were less than the arithmetic mean (8.64 ⫾ 2.96 D) target VOL. 147, NO. 5
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induced astigmatism (TIA). In the mechanized AK group, overcorrection was characterized by mean arithmetic SIA for refraction (6.86 ⫾ 3.54 D) and keratometry (6.68 ⫾ 3.21 D) higher than mean TIA (6.66 ⫾ 2.12 D) and a magnitude of error of more than 0 (0.20 ⫾ 3.22). The amount of SIA for both surgical techniques has been shown not to be significantly different in our study. The summated vector mean of difference vectors (DVs) showed that orientations in the laser AK group for refractive and keratometric values were equivalent (133 and 132 degrees) and that both vector mean magnitudes (1.21 and 1.34 D) were 31.4% and 33.7% of their respective arithmetic mean magnitude; these values suggests some systematic error tendency during treatments. There was no trend of systematic error in the mechanized AK group with different axes and magnitudes for refractive and keratometric DVs. Angle-of-error (AE) analysis (AE arithmetic means) for refractive and keratometric data in both groups showed slight errors (Table 3). However, by examining the absolute refractive AE means, a less favorable outcome on correction alignment was found in the mechanized AK
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group. A significant difference was almost achieved (P ⫽ .052) on refractive absolute AE means between surgical techniques (6.78 ⫾ 4.07 degrees and 15.83 ⫾ 9.20 degrees for FSL and mechanized AK, respectively) and a wider spread of results for the mechanized AK group (8.88 to 22.7 degrees) than in the laser AK group (3.70 to 9.84 degrees) was observed (Figure 2). The lower flattening indexes of the mechanized AK group (0.73 ⫾ 0.47 and 0.60 ⫾ 0.34) than in the laser AK group (0.79 ⫾ 0.40 and 0.60 ⫾ 0.34) are in relation with this treatment misalignment after mechanical keratotomy. Scatterplots of SIA vs TIA are shown in Figure 3. The values showed no correlation in the SIA and TIA scattergrams, and the general undercorrection of astigmatism is more evident by FSL than by mechanical keratotomy and confirmed by a lower correction index in the laser AK group (0.82 ⫾ 0.41and 0.82 ⫾ 0.46) than in the mechanized AK group (0.92 ⫾ 0.48 and 0.90 ⫾ 0.36) for the 2 measurement methods. The coefficient of adjustment (amount required to adjust future treatments) was 1.22 in the laser AK group and between 1.09 and 1.11 in the mechanized AK group. In the mechanized AK group, a microperforation occurred within 1 incision and required suturing. Also, incisions were off center in 1 case as a result of intraoperative patient restlessness. No postoperative complication was observed in laser AK group.
after surgery, with nonsignificant modifications of SRI between preoperative and last postoperative examination (Table 2). We found in our study a significantly (P ⫽ .011) higher reduction (⫺55.4 ⫾ 20.7%) of preoperative refractive cylinder in the laser AK group than in the mechanized AK group (⫺29.7 ⫾ 30.0%). A decrease in refractive and keratometric astigmatism was obtained in 90% and 70% of eyes, and in these eyes, 80% and 40% had less of 5 D of refractive astigmatism after surgery, compared with 20% and 30% before surgery. These cases may qualify for further interventions such as laser in situ or laser subepithelial keratomileusis. Our results are similar to those achieved with freehand AK.4,10,13,23,32,37,38 Hjortdal and Ehlers found a 54% reduction in refractive cylinder with paired AKs in 21 postkeratoplasty eyes, and Hovding found a 49% reduction with transverse keratotomies in 12 postkeratoplasty eyes.4,13 Wilkins and associates recently reported a much higher (70%) reduction in 20 eyes; the greater effect may be from a strict adherence to the 6.0-mm optical zone.19 In our study, the arcuate incisions were placed on a larger optical zone, which may equate to the 6.5-mm optical zone rather than 6.0 mm. It should be noted that the patients in the study by Wilkins and associates also started with a higher mean astigmatic error than our patients did, which also may explain the greater reduction.19 Residual refractive astigmatism (3.85 ⫾ 2.39 D) found in the present study was comparable with that of other reports of mechanized AK. Borderie and associates, in a study of 22 eyes, reported a mean preoperative and postoperative astigmatism of 6.94 and 3.85 D, respectively.8 Hannush and associates reported the results of 29 eyes with a mean preoperative and postoperative astigmatism of 8.8 and 3.2 D, respectively (Hannush S, et al. IOVS 1998;39: S347, ARVO E-Abstract 1612). The Alpins method31,39 was chosen for vector analysis for this study. Refractive, keratometric, and astigmatism data are reported to avoid reporting only refractive changes, which tend to show larger changes.40 The correction plan was targeted on correcting refraction. Thus, the target corneal astigmatism was the minimal keratometric astigmatism remaining after treatment to neutralize refractive astigmatism. The mean ocular residual astigmatism values were 2.56 ⫾ 2.80 D and 4.05 ⫾ 3.90 D for laser AK and mechanized AK, respectively. Because treatment parameters emphasized the elimination of refractive astigmatism (target, 0.00 D), the mean target corneal astigmatism was represented by the mean ocular residual astigmatism. After surgery, the mean corneal astigmatism decreased to 3.97 ⫾ 2.38 D and 4.51 ⫾ 2.41 D, respectively. Thus, the resulting mean corneal astigmatism exceeded ocular residual astigmatism by a factor of 1.55 and 1.11. This imbalance in excessive corneal astigmatism remaining after treatment can be attributed to refractive astigmatism values being the sole consideration in treatment planning, resulting in a proportionately higher reduction in refractive astigmatism than keratometric astigmatism, which is
DISCUSSION THE MAIN OBJECTIVE OF THIS STUDY WAS TO TEST THE
significant differences in surgically generated astigmatism between 2 AK procedures for postkeratoplasty astigmatism correction. Several relaxing incision techniques exist for correction of postkeratoplasty astigmatism, but no standard procedure has been established.3,5,10,13,14,20,22,32–36 However, AK has become a reliable and safe procedure in recent years and the developments in technology and instrumentation combine to allow the planning of corneal surgery with unprecedented accuracy. AK procedures performed with mechanized devices have been shown to provide more reproducible results than freehand techniques,8,12,24 but further improvements may be brought by the use of FSL technology in this indication. In this study, neither UCVA nor BSCVA improved significantly after mechanical or laser AK, although BSCVA increased by 1 line or more of VA in 70% and 80% of cases after laser AK and mechanized AK, respectively. This nonsignificant improvement of VA was probably related to the preoperative irregular corneal astigmatism in all cases, and our results showed no decrease of irregularity in postkeratoplasty topographic astigmatism 784
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FIGURE 4. Photograph comparing femtosecond vs mechanized AK. Direct visualization of the surgical procedure through the laser interface showing a gas bubble between the cornea and applanation lens at the lower keratotomy level.
off-axis from the midpoint of the incision. If corneal astigmatism values were included in the treatment plan, an overall greater reduction in astigmatism would have been achievable. In the mechanized AK group, the arithmetic mean SIA magnitude for refraction (6.86 D) and keratometry (6.68 D) was higher than the arithmetic mean TIA (6.66 D), and it was confirmed by summated vector mean SIA for refractive values (2.86 D ⫻ 92 degrees) and for keratometric values (2.94 ⫻ 85 degrees), in a very close alignment with the TIA (2.49 D ⫻ 91 degrees). However, the geometric mean correction index was between 0.90 and 0.92 and resulted from a lower reduction of astigmatism than the achieved correction in previous studies.14 The mean AE value (5.02 and 3.86 degrees) was consistent with the closeness of the vector mean TIA and SIA axes detailed above, so no significant systematic error of misaligned treatment is evident. However, mean absolute AE values (15.83 and 18.27 degrees) suggest a misalignment of treatment at an individual level, and the difference of mean absolute AE between groups was almost significant (P ⫽ .052). In the laser AK group, a mean refractive correction index of 0.82 resulted from a substantially smaller vector mean of the SIA (2.13 and 2.11 D) compared with the TIA (2.98 D). The summated vector mean of DVs showed that axis in the FSL group for refractive and keratometric values were equivalent (133
and 132 degrees) and that both vector mean magnitudes (1.21 and 1.34 D) were 31.4% and 33.7% of their respective arithmetic mean magnitude. These results suggests some error tendency in the treatments such as systematic misalignment. After laser treatment, the undercorrection of astigmatism was approximately 22%. The systematic proportion of the error fell between 31.4% and 33.7% of the total error measured by the arithmetic mean DV magnitude. These results suggest that a nomogram adjustment to future treatments magnitude (TIAs) should be used by an additional factor (coefficient of adjustment [CA] ⫽ 1.22). The nomogram correction could be achieved by derivation of a nominal value for the TIA close to the average SIA obtained for each standard optical zone and arc length setting. Systematic misalignment should be addressed by such means as preoperative limbal marking, but the direct visualization of the limbus is masked by the suction ring of the laser interface during the surgical procedure (Figure 4), and control of cyclotorsion (or off-axis treatment) could be improved by an embedded device as computerized torsional control, as in actual excimer lasers systems. Moreover, the use of FSL provides depth accuracy even at increased depth settings with a lower mean deviation than the mechanical cut from the planned incision depth.25 These highly reproducible dimensions of the cuts26 will allow accomplishment of deeper incisions and to increase the average SIA in AK procedures. An important factor in determining the outcomes of an astigmatism correction technique on corneal graft is the rate of complications. In our study, all cases in the laser AK group were uncomplicated, as in previous FSL-assisted AK studies.21,26 In the mechanical group, of the 10 procedures performed, 1 case of microperforation occurred and incisions were off-center in 1 case. We found AK performed with FSL to be a relatively easy, safe, and effective means of treating postkeratoplasty astigmatism. In our study, achieved reduction of postkeratoplasty astigmatism in laser AK group was higher for refractive values than those with mechanical procedures. Vector analysis identified a systematic misalignment of laser treatment that need to be addressed, but with a lower mean AE than after mechanical AK. However, related to our small samples, much larger numbers are needed to provide more confident estimates of astigmatism reduction proportions for each surgical method and to adjust correction parameters. Subsequently, these studies could seek other means for improving the alignment of treatment, such as computerized axis control during laser surgery.
THIS STUDY WAS SUPPORTED IN PART BY THE DEPARTMENTAL COUNCIL OF “BOUCHES-DU RHONE” (CG13), MARSEILLE, France. The authors indicate no financial conflict of interest. Involved in design of study (L.H.); conduct of study (L.H.); data collection (H.P.); critical revision of the article (J.C.); administrative and logistical support (B.R., H.P.); and preparation, review, and approval of the manuscript (L.H., J.C.). This study was approved by the Institutional Review Board, Marseille, France. The study was conducted in accord with Good Clinical Practices and the tenets of the Declaration of Helsinki.
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19. Wilkins MR, Mehta JS, Larkin DF. Standardized arcuate keratotomy for post-keratoplasty astigmatism. J Cataract Refract Surg 2005;31:297–301. 20. Troutman RC, Swinger C. Relaxing incision for control of postoperative astigmatism following keratoplasty. Ophthalmic Surg 1980;11:117–120. 21. Kiraly L, Herrmann C, Amm M, Duncker G. Reduction of astigmatism by arcuate incisions using the femtosecond laser after corneal transplantation [in German]. Klin Monatsbl Augenheilkd 2008;225:70 –74. 22. Koffler BH, Smith VM. Corneal topography, arcuate keratotomy, and compression sutures for astigmatism after penetrating keratoplasty. J Refract Surg 1996;12:S306 –S309. 23. Poole TR, Ficker L. Astigmatic keratotomy for post-keratoplasty astigmatism. J Cataract Refract Surg 2006;32:1175– 1179. 24. Hoffart L, Touzeau O, Borderie V, Laroche L. Mechanized astigmatic arcuate keratotomy with the Hanna arcitome for astigmatism after keratoplasty. J Cataract Refract Surg 2007; 33:862– 868. 25. Holzer MP, Rabsilber TM, Auffarth GU. Femtosecond laser-assisted corneal flap cuts: morphology, accuracy, and histopathology. Invest Ophthalmol Vis Sci 2006;47: 2828 –2831. 26. Harissi-Dagher M, Azar DT. Femtosecond laser astigmatic keratotomy for post-keratoplasty astigmatism. Can J Ophthalmol 2008;43:367–369. 27. Touboul D, Salin F, Mortemousque B, et al. Advantages and disadvantages of the femtosecond laser microkeratome [in French]. J Fr Ophtalmol 2005;28:535–546. 28. Millin JA, Maguire LJ. Developing entry criteria for studies of severe post-keratoplasty astigmatism. Am J Ophthalmol 1991;112:666 – 670. 29. Holladay JT, Dudeja DR, Koch DD. Evaluating and reporting astigmatism for individual and aggregate data. J Cataract Refract Surg 1998;24:57– 65. 30. Holladay JT, Moran JR, Kezirian GM. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg 2001;27: 61–79. 31. Alpins N. Astigmatism analysis by the Alpins method. J Cataract Refract Surg 2001;27:31– 49. 32. Krachmer JH, Fenzl RE. Surgical correction of high postkeratoplasty astigmatism. Relaxing incisions vs wedge resection. Arch Ophthalmol 1980;98:1400 –1402. 33. Price FW Jr, Whitson WE. The art of surgical correction for post-keratoplasty astigmatism. Int Ophthalmol Clin 1991;31: 59 – 67. 34. Arffa RC. Results of a graded relaxing incision technique for post-keratoplasty astigmatism. Ophthalmic Surg 1988;19: 624 – 628. 35. Frangieh GT, Kwitko S, McDonnell PJ. Prospective corneal topographic analysis in surgery for post-keratoplasty astigmatism. Arch Ophthalmol 1991;109:506 –510. 36. Karabatsas CH, Cook SD, Figueiredo FC, et al. Surgical control of late post-keratoplasty astigmatism with or without the use of computerized video keratography: a prospective, randomized study. Ophthalmology 1998;105: 1999 –2006.
REFERENCES 1. Seitz B, Naumann GO. Limbus-parallel keratotomies and compression sutures in excessive astigmatism after penetrating keratoplasty. Ger J Ophthalmol 1993;2:42–50. 2. Tuunanen TH, Ruusuvaara PJ, Uusitalo RJ, Tervo TM. Photoastigmatic keratectomy for correction of astigmatism in corneal grafts. Cornea 1997;16:48 –53. 3. Fronterre A, Portesani GP. Relaxing incisions for postkeratoplasty astigmatism. Cornea 1991;10:305–311. 4. Hovding G. Transverse keratotomy in post-keratoplasty astigmatism. Acta Ophthalmol (Copenh) 1994;72:464 – 468. 5. Kirkness CM, Ficker LA, Steele AD, Rice NS. Refractive surgery for graft-induced astigmatism after penetrating keratoplasty for keratoconus. Ophthalmology 1991;98: 1786 –1792. 6. Lazzaro DR, Haight DH, Belmont SC, et al. Excimer laser keratectomy for astigmatism occurring after penetrating keratoplasty. Ophthalmology 1996;103:458 – 464. 7. Ghanem RC, Azar DT. Femtosecond-laser arcuate wedgeshaped resection to correct high residual astigmatism after penetrating keratoplasty. J Cataract Refract Surg 2006;32: 1415–1419. 8. Borderie VM, Touzeau O, Chastang PJ, Laroche L. Surgical correction of post-keratoplasty astigmatism with the Hanna arcitome. J Cataract Refract Surg 1999;25:205–211. 9. Chastang P, Borderie V, Carvajal S, Laroche L. Surgical treatment of astigmatism caused by penetrating keratoplasty using the Hanna arcuate keratome [in French]. J Fr Ophtalmol 1997;20:360 –365. 10. Cohen KL, Tripoli NK, Noecker RJ. Prospective analysis of photokeratoscopy for arcuate keratotomy to reduce postkeratoplasty astigmatism. Refract Corneal Surg 1989;5:388 – 393. 11. Geggel HS. Arcuate relaxing incisions guided by corneal topography for post-keratoplasty astigmatism: vector and topographic analysis. Cornea 2006;25:545–557. 12. Hanna KD, Hayward JM, Hagen KB, et al. Keratotomy for astigmatism using an arcuate keratome. Arch Ophthalmol 1993;111:998 –1004. 13. Hjortdal JO, Ehlers N. Paired arcuate keratotomy for congenital and post-keratoplasty astigmatism. Acta Ophthalmol Scand 1998;76:138 –141. 14. Jacobi PC, Hartmann C, Severin M, Bartz-Schmidt KU. Relaxing incisions with compression sutures for control of astigmatism after penetrating keratoplasty. Graefes Arch Clin Exp Ophthalmol 1994;232:527–532. 15. Koay PY, McGhee CN, Crawford GJ. Effect of a standard paired arcuate incision and augmentation sutures on postkeratoplasty astigmatism. J Cataract Refract Surg 2000;26: 553–561. 16. Krumeich JH, Knuelle A. Circular keratotomy for the correction of astigmatism. Refract Corneal Surg 1992;8:204 – 210. 17. Limberg MB, Dingeldein SA, Green MT, et al. Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989;108:36 – 42. 18. Lustbader JM, Lemp MA. The effect of relaxing incisions with multiple compression sutures on post-keratoplasty astigmatism. Ophthalmic Surg 1990;21:416 – 419.
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37. Lavery GW, Lindstrom RL, Hofer LA, Doughman DJ. The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg 1985;16:165–169. 38. McCartney DL, Whitney CE, Stark WJ, et al. Refractive keratoplasty for disabling astigmatism after penetrating keratoplasty. Arch Ophthalmol 1987;105:954 –957.
39. Alpins NA, Goggin M. Practical astigmatism analysis for refractive outcomes in cataract and refractive surgery. Surv Ophthalmol 2004;49:109 –122. 40. Alpins NA, Tabin GC, Adams LM, et al. Refractive versus corneal changes after photorefractive keratectomy for astigmatism. J Refract Surg 1998;14:386 –396.
REPORTING VISUAL ACUITIES The AJO encourages authors to report the visual acuity in the manuscript using the same nomenclature that was used in gathering the data provided they were recorded in one of the methods listed here. This table of equivalent visual acuities is provided to the readers as an aid to interpret visual acuity findings in familiar units. Table of Equivalent Visual Acuity Measurements Snellen Visual Acuities 4 Meters
6 Meters
20 Feet
Decimal Fraction
LogMAR
4/40 4/32 4/25 4/20 4/16 4/12.6 4/10 4/8 4/6.3 4/5 4/4 4/3.2 4/2.5 4/2
6/60 6/48 6/38 6/30 6/24 6/20 6/15 6/12 6/10 6/7.5 6/6 6/5 6/3.75 6/3
20/200 20/160 20/125 20/100 20/80 20/63 20/50 20/40 20/32 20/25 20/20 20/16 20/12.5 20/10
0.10 0.125 0.16 0.20 0.25 0.32 0.40 0.50 0.63 0.80 1.00 1.25 1.60 2.00
⫹1.0 ⫹0.9 ⫹0.8 ⫹0.7 ⫹0.6 ⫹0.5 ⫹0.4 ⫹0.3 ⫹0.2 ⫹0.1 0.0 ⫺0.1 ⫺0.2 ⫺0.3
From Ferris FL III, Kassoff A, Bresnick GH, Bailey I. New visual acuity charts for clinical research. Am J Ophthalmol 1982;94:91–96.
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Biosketch Louis Hoffart received his MD degree at the Marseille Medical School, France and graduated in 2004 with a Master of Neurosciences. Since 2005, Dr Hoffart worked on his PhD about femtosecond laser interactions in ocular tissues project and has held a fellowship in corneal and external disease in Prof Ridings’ Department of Ophthalmology in Marseille, France. His fields of research are related on corneal surgeries procedures, femtosecond laser physics, and therapeutic procedures.
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