Purpose
To compare the quality of vision (straylight and contrast sensitivity) after femtosecond laser-assisted Descemet stripping endothelial keratoplasty (FS DSEK) and penetrating keratoplasty (PK).
Design
Prospective, randomized clinical trial.
Methods
setting: Multicenter (5 ophthalmic centers in The Netherlands). study population: Eighty eyes of 80 patients with corneal endothelial dysfunction were included and were randomized to FS DSEK or PK. observation procedures: FS DSEK and PK. main outcome measures: Straylight, contrast sensitivity, astigmatism, uncorrected visual acuity, best spectacle-corrected visual acuity (BSCVA), and visual symptom score.
Results
Straylight at 12 months was 1.37 ± 0.2 logarithm of straylight for FS DSEK and 1.46 ± 0.2 logarithm of straylight for PK ( P = .151). During 12 months of follow-up, there was a significant improvement of straylight and contrast sensitivity after FS DSEK ( P < .001) and PK ( P < .001). The change of straylight and contrast sensitivity correlated significantly with the change of BSCVA after FS DSEK ( r = −0.645; r = 0.580) and PK ( r = −0.370; r = 0.659). The visual symptom score was comparable between the 2 groups during the 12 months of follow-up.
Conclusions
Improvement of straylight and contrast sensitivity was significantly correlated with an improvement of BSCVA. Straylight and contrast sensitivity were improved significantly after FS DSEK and were comparable with those after PK, although BSCVA was slightly better in the PK group.
Penetrating keratoplasty (PK) has been shown to be a successful treatment for restoring vision in eyes with corneal endothelial disease, but disadvantages include a slow visual rehabilitation, high irregular astigmatism, and suture-related problems. In 1956, the first posterior lamellar keratoplasty was performed to replace the deep stromal and endothelial layers and to maintain the anterior part of the cornea. Posterior lamellar keratoplasty was not performed regularly because of difficulties with surgical techniques. After major surgical improvements and innovations in surgical instruments, endothelial keratoplasty replaced PK as the gold standard surgical technique for corneal endothelial disease.
Major advantages of endothelial keratoplasty, compared with PK, are a minimal change in corneal astigmatism, a more predictable postoperative spherical equivalent, and a stable globe more resistant to trauma. In a recent randomized clinical trial of femtosecond laser-assisted Descemet stripping endothelial keratoplasty (FS DSEK) versus PK, we showed that FS DSEK effectively reduces postoperative astigmatism, but we also showed a lower visual acuity as compared with conventional PK.
We hypothesized that the lower visual acuity may be the result of the formation of interface haze at the donor–recipient stromal interface. This haze may result in an increase of intraocular straylight and a decrease of contrast sensitivity. Consequently, a dissatisfaction with the quality of vision and limitations in daily functioning may occur.
This randomized clinical trial was performed to determine intraocular straylight, contrast sensitivity, and subjective visual symptoms after FS DSEK and PK and to correlate these quality-of-vision parameters to the refractive and visual outcomes. A secondary goal of the present study was to test the clinical use of straylight meter in such a demanding setting.
Methods
This randomized, multicenter trial was conducted at 5 ophthalmic centers in The Netherlands. Inclusion criteria were endothelial dysfunction caused by Fuchs endothelial dystrophy, aphakic or pseudophakic bullous keratopathy or posterior polymorphous dystrophy, a minimal age of 18 years, and a best spectacle-corrected visual acuity (BSCVA) lower than 20/50. Patients were excluded if they had undergone previous PK, had human leukocyte antigen typed keratoplasty, or were mentally retarded. The medical history was recorded, and all patients underwent a slit-lamp examination. Preoperative collected data included patient age, gender, refractive error, preoperative lens status, and ocular comorbidities.
Surgical Procedures
The surgical techniques of FS DSEK and PK have been described previously.
Outcome Measures
The primary outcome measures were straylight and contrast sensitivity. Secondary outcome measures included refractive astigmatism, topographic astigmatism, uncorrected visual acuity (UCVA), BSCVA, and visual symptom score. All outcome measures were measured before surgery and at 3, 6, and 12 months of follow-up.
Straylight was measured using a straylight meter (C-Quant; Oculus GmbH, Wetzlar, Germany), which uses a compensation comparison method with a forced-choice technique. Clinical straylight measurement is a relatively new development to quantify quality of vision and was developed originally for visual acuities better than 0.7 logarithm of the minimal angle of resolution (logMAR). However, corneal transplantation patients often have visual acuities worse than that.
The straylight value was expressed as a logarithmic intraocular straylight (log(s)) value. Higher values indicate more straylight and an increased sensitivity to glare. Two consecutive straylight measurements of the study eye and the nonstudy eye were obtained, after which an average amount of logarithmic intraocular straylight was calculated. The instrument derives a reliability value for each measurement, called the expected standard deviation , on the basis of known psychometric principles. A reliable value was defined as an expected standard deviation of less than 0.08 log units. The repeated measures design of the study checked this reliability estimate against true reliability. Straylight values also were compared with a control group obtained from a previous database consisting of age-matched subjects with a clear cornea and no cataract. Eyes that were unable to perform the straylight test before surgery were substituted by the highest preoperative log(s) plus 0.1.
The contrast sensitivity was measured using the Pelli-Robson chart (Clement Clarke Ltd, Harlow, United Kingdom). This chart was chosen from among other available charts for its high reliability and validity compared with sinusoidal grating charts such as the Vistech and Functional Acuity Contrast Test. Patients were tested both monocularly and binocularly, using the best spectacle correction for distance vision on a testing distance of 1 m and a luminance of 85 candelas/m 2 . The last triplet of letters, of which at least 2 letters were seen correctly, was recorded and expressed as a logarithmic contrast sensitivity value. Lower values indicate a better contrast sensitivity.
Topographic astigmatism was measured using the EyeMap corneal topographer (EH-290; Alcon, Fort Worth, Texas, USA). The UCVA and BSCVA were determined using the Early Treatment Diabetic Retinopathy Study letter charts and were converted to logarithm of the minimal angle of resolution measurements. Vision levels of counting fingers, hand movements, light perception, and no light perception were substituted by logarithm of the minimal angle of resolution values of 1.7, 2.0, 2.5, and 3.0, respectively.
Double-vision or distorted vision, glare, halo, blurry vision, and differently looking colors were reported by patients using a validated questionnaire. The grading of symptoms ranged from great deal, moderate amount, little, to none, and a score of 3, 2, 1, or 0 was assigned, respectively. Scores for each of the symptoms then were summed, and this resulted in a visual symptom score ranging from 0 (not at all bothered by any of the symptoms) to 15 (very bothered by all symptoms).
Sample Size
The sample size calculation of the main outcome of this randomized clinical trial has been described previously.
Randomization
All included eyes were assigned randomly to either the FS DSEK or the PK group. The randomization code was generated using a permuted block size of 2. The assigned treatment plans then were sent to the surgeon.
Statistical Analysis
Data were described as mean ± standard deviation for continuous variables and as individual counts and percentages for categorical variables. Differences between groups were analyzed using a Student t test for continuous data. The Pearson chi-square test was used to compare categorical data. Comparisons of preoperative data and postoperative data within a group were performed using a linear regression model. Correlations were assessed using the Pearson correlation coefficient in case of normal distributed data and using the Spearman test in case of abnormal distributed data. A P value of less than .05 was considered to be statistically significant. Statistical analysis was performed using SPSS software for Windows version 15.0 (SPSS, Inc, Chicago, Illinois, USA).
Results
Participant Flow Chart
Eighty eyes of 80 patients were recruited, with 40 eyes in each arm ( Figure 1 ). In the FS DSEK group, 4 patients did not receive the allocated treatment because of significant preoperative events (such as keratitis, corneal ulcers, or both) and eventually were excluded from the study analysis. All patients in the PK group received the allocated treatment.
In the FS DSEK group, 29 eyes were available for analysis at the 12-month follow-up. After surgery, the cornea of 3 eyes remained edematous and did not clear up; this was defined as primary graft failure. Two eyes underwent PK before the 3-month follow-up, and 1 eye underwent repeat FS DSEK after 6 months of follow-up.
Patient Characteristics
Patients characteristics of the FS DSEK and PK group are listed in Table 1 . The mean age of the FS DSEK group and PK group was 69.0 ± 8.8 years and 71.4 ± 11.3 years, respectively ( P = .308). In the FS DSEK group, 21 of 36 patients (58.3%) were diagnosed with Fuchs endothelial dystrophy, and 8 (38.1%) of these 21 patients also had visually significant cataract. These patients either underwent primary cataract extraction with intraocular lens (IOL) implantation (n = 5, 62.5%) followed by the FS DSEK procedure or a combined procedure of FS DSEK and cataract extraction with IOL implantation (n = 3, 37.5%). In the PK group, 20 of 40 patients (50.0%) were diagnosed with Fuchs endothelial dystrophy, and 12 (60.0%) of these 20 patients also had visually significant cataract. Ten (83.3%) of these 12 patients underwent a combined procedure of PK and cataract extraction with IOL implantation, and 2 of the 12 patients (16.7%) underwent a primary cataract extraction with IOL implantation before PK.
| FS DSEK | PK | P Value | |
|---|---|---|---|
| Eyes (n) | 36 | 40 | NA |
| Mean age ± SD (y) | 69.0 ± 8.8 | 71.4 ± 11.3 | .308 |
| No. women (%) | 21 (58.3%) | 27 (67.5%) | .500 |
| Diagnosis | .725 | ||
| Fuchs endothelial dystrophy | 21 (58.3%) | 20 (50.0%) | |
| Pseudophakic bullous keratopathy | 15 (41.7%) a | 19 (47.5%) a | |
| Posterior polymorphous dystrophy | 0 | 1 (2.5%) | |
| Recipient lens status | .996 | ||
| Aphakic | 1 (2.8%) a | 1 (2.5%) a | |
| Phakic | 21 (58.3%) | 21 (52.5%) | |
| Pseudophakic | 14 (38.9%) | 18 (45.0%) | |
| Ocular comorbidity | |||
| Age-related macular degeneration/RPE changes | 12 (33.3%) | 5 (12.5%) | .030 |
| Cataract | 8 (22.2%) | 12 (30.0%) | .442 |
| Glaucoma | 1 (2.8%) | 3 (7.5%) | .357 |
a One aphakic eye with iris-fixated anterior chamber intraocular lens.
Before surgery, 34 patients (85.0%) in the PK group and 30 patients (83.3%) in the FS DSEK group required spectacle correction for distance vision; the remaining patients used no correction. Twelve months after FS DSEK, 23 patients (79.3%) used spectacles and 1 patient (3.4%) used soft contact lenses for distance vision. Five patients (17.2%) did not need a correction. Twelve months after PK, 26 patients (66.6%) used spectacles, 1 patient (2.6%) used a rigid contact lenses for distance vision, and 12 patients (30.8%) did not use a correction, with 7 of the 12 patients being unable to wear a correction because of anisometropia.
Intraocular Straylight
Before surgery, 43% of subjects had a visual acuity lower than the advised limit for straylight measurement (0.7 logMAR). This limit seems a bit strict, because only 11 (30.6%) of 36 patients in the FS DSEK group and 13 (32.5%) of 40 patients in the PK group were unable to complete the straylight test. The mean logMAR BSCVA of these patients’ eyes was significantly higher in comparison with eyes of patients who did complete the test (1.17 ± 0.5 logMAR vs 0.67 ± 0.2 logMAR, respectively [ P < .001], in the FS DSEK group; and 1.00 ± 0.5 logMAR vs 0.59 ± 0.3 logMAR, respectively [ P = .002], in the PK group). Figure 2 shows repeatability of the straylight measurement for all follow-up visits of the study eyes and for the nonstudy eyes ( P < .05 for all 4 comparisons, F test). The repeated-measures standard deviation was 0.07 for the nonstudy eyes. For the study eyes, the repeated-measures standard deviations were slightly higher at 0.10, 0.09, 0.09, and 0.11 for preoperative and postoperative values at 3, 6, and 12 months, respectively. So, the precision of the straylight measurements was not much less in the study eyes as compared with the nonstudy eyes, but the difference was statistically significant ( P < .05 for all comparisons, F test). Repeatability was not dependent on straylight level, as is also evident in Figure 2 .
Preoperative straylight values were not significantly different between the FS DSEK and PK group (1.97 ± 0.4 log(s) vs 1.97 ± 0.4 log(s), respectively; P = .926). During the follow-up, the straylight between the FS DSEK and PK group was comparable (3 months, 1.43 ± 0.2 log(s) vs 1.40 ± 0.2 log(s) [ P = .582]; 6 months, 1.42 ± 0.3 log(s) vs 1.41 ± 0.2 log(s) [ P = .960]; 12 months, 1.37 ± 0.2 vs 1.46 ± 0.2 log(s) [ P = .151]). In both groups, there was a significant improvement of straylight during the 12 months of follow-up (FS DSEK, P < .001; PK, P < .001).
Straylight value as a function of age is shown in Figure 3 . Eyes with too severe corneal edema that were not able to complete the straylight test were substituted by 2.46 log(s), which is notable in Figure 3 . Before surgery, 13.9% (n = 5) of the patients in the FS DSEK group and 12.5% (n = 5) of the patients in the PK group had straylight values within the normal age-matched range, whereas the remaining patients had higher straylight values. Twelve months after FS DSEK and PK, 38.5% (n = 10) and 45.7% (n = 16) of the patients, respectively, had straylight values comparable with the normal age-matched range, and 11.5% (n = 3) and 2.9% (n = 1) of the patients, respectively, had lower straylight values, whereas 50.0% (n = 13) and 51.4% (n = 18) of the patients, respectively, had higher straylight values.
Before surgery, there was a significant correlation between the BSCVA and straylight value in the FS DSEK group ( r = 0.461; P = .005) and PK group ( r = 0.523; P = .001). At 3, 6, and 12 months after surgery, the correlation between BSCVA and straylight value was not significant in the FS DSEK group ( r = 0.260, P = .209; r = 0.214, P = .273; and r = 0.082, P = .696, respectively). In the PK group, the BSCVA was correlated significantly with straylight at 3, 6, and 12 months of follow-up ( r = 0.363, P = .032; r = 0.492, P = .003; and r = 0.569, P < .001).
The change in intraocular straylight and BSCVA values from baseline to 12 months after surgery showed a correlation in the PK group ( r = −0.370; P = .029), and in the FS DSEK group ( r = −0.645; P < .001). An improvement of BSCVA was correlated significantly with a decrease of straylight in both groups.
Contrast Sensitivity
Contrast sensitivities for both groups are shown in Table 2 . Before surgery, 3 (8.3%) of 36 patients in the FS DSEK group and 3 (7.5%) of 40 patients in the PK group were unable to see the highest contrast at 1 m distance. Before surgery, contrast sensitivity of the study eye, fellow eye, and binocularly were not significantly different between the FS DSEK and PK groups.
| FS DSEK, Mean ± SD | PK, Mean ± SD | P Value a | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Study Eye | Fellow Eye | Binocular | Study Eye | Fellow Eye | Binocular | Study Eye | Fellow Eye | Binocular | |
| Before surgery (log(c)) | 0.85 ± 0.4 | 1.26 ± 0.3 | 1.32 ± 0.3 | 0.90 ± 0.3 | 1.22 ± 0.3 | 1.28 ± 0.2 | .594 | .464 | .454 |
| 3 mos (log(c)) | 1.28 ± 0.3 b | 1.27 ± 0.2 | 1.39 ± 0.2 | 1.30 ± 0.3 b | 1.20 ± 0.3 | 1.41 ± 0.2 b | .767 | .316 | .709 |
| 6 mos (log(c)) | 1.22 ± 0.2 b | 1.27 ± 0.2 | 1.41 ± 0.2 | 1.30 ± 0.2 b | 1.21 ± 0.3 | 1.43 ± 0.3 b | .159 | .335 | .710 |
| 12 mos (log(c)) | 1.28 ± 0.2 b | 1.25 ± 0.2 | 1.38 ± 0.2 | 1.31 ± 0.2 b | 1.17 ± 0.3 | 1.45 ± 0.2 b | .572 | .268 | .199 |
| P < .001 c | P = .992 c | P = .365 c | P < .001 c | P = .898 c | P = .006 c | ||||
a P value between FS-DSEK and PK.
b P < .05 versus preoperative in a linear regression model.
c P value of a linear regression model with 3 postoperative periods at the same time in the model.
At 3, 6, and 12 months after surgery, no significant difference in contrast sensitivity was found between the FS DSEK and PK groups. In both the FS DSEK and PK groups, contrast sensitivity of the study eye increased significantly after surgery. The binocular contrast sensitivity improved significantly after PK ( P = .006), but not after FS DSEK ( P = .365).
Before surgery, there was a correlation between BSCVA and contrast sensitivity in both the FS DSEK group ( r = −0.640; P < .001) and PK group ( r = −0.706; P < .001). After FS DSEK and PK, the change in contrast sensitivity from baseline to 12 months after surgery showed a correlation with the change in BSCVA during the same follow-up period ( r = 0.508, P = .009, and r = 0.659, P < .001, respectively).
In the FS DSEK group, the correlation between straylight and contrast sensitivity was r = −0.504 (preoperative, P = .003), r = −0.541 (3-month postoperative, P = .005), r = −0.685 (6-month postoperative, P < .01), and r = −0.054 (12-month postoperative, P = .796). In the PK group, the correlation between straylight and contrast sensitivity was r = −0.434 (preoperative, P = .007), r = −0.492 (3-month postoperative, P = .003), r = −0.534 (6-month postoperative, P = .001), and r = −0.348 (12-month postoperative, P = .040).
Astigmatism
Refractive and topographic astigmatism outcomes are shown in Table 3 . Before surgery, there was no significant difference in refractive and topographic astigmatism between the FS DSEK and PK group. At the 12-month follow-up, both refractive and topographic astigmatism were significantly higher in the PK group compared with the FS DSEK group (refractive, −2.98 diopters [D] vs −1.22 D, respectively; and topographic, 3.67 D vs 1.58 D, respectively). In the FS DSEK group, postoperative refractive and topographic astigmatism values were not significantly different from preoperative values. In the PK group, all postoperative refractive and topographic astigmatism values were significantly higher compared with those before surgery. During follow-up, these values showed a tendency to decrease. After 12 months of follow-up, all sutures had been removed in only 1 eye (2.5%) in the PK group.
| FS DSEK, Mean ± SD | Range | PK, Mean ± SD | Range | P Value a | |
|---|---|---|---|---|---|
| Refractive astigmatism (D) | |||||
| Preoperative | −0.98 ± 1.0 | −3.5 to 0 | −1.27 ± 1.2 | −5.50 to 0 | .275 |
| 3 mos | −1.38 ± 1.2 | −5.0 to 0 | −4.17 ± 3.4 b | −14.0 to 0 | <.001 |
| 6 mos | −1.46 ± 1.3 | −5.0 to 0 | −3.21 ± 1.9 b | −8.00 to 0 | <.001 |
| 12 mos | −1.22 ± 1.1 | −4.0 to 0 | −2.98 ± 2.0 b | −8.75 to 0 | <.001 |
| P = .358 c | P < .001 c | ||||
| Topographic astigmatism (D) | |||||
| Preoperative | 1.38 ± 0.6 | 0.47 to 2.90 | 2.16 ± 1.4 | 0.50 to 6.50 | .577 |
| 3 mos | 1.87 ± 1.1 | 0.25 to 4.30 | 4.59 ± 2.9 b | 1.00 to 15.70 | <.001 |
| 6 mos | 1.72 ± 1.0 | 0.27 to 4.14 | 3.74 ± 1.7 b | 0.50 to 6.83 | <.001 |
| 12 mos | 1.58 ± 1.2 | 0.27 to 6.40 | 3.67 ± 1.8 b | 1.40 to 7.70 | <.001 |
| P = .469 c | P < .001 c |
a P value between FS DSEK and PK.
b P < .05 versus preoperative in a linear regression model.
c P value of a linear regression model with 3 postoperative periods at the same time in the model.
Twelve months after surgery, the percentage of patients with a refractive astigmatism of ≤ 3.0 D was significantly higher in the FS DSEK group compared with the PK group (86.2% vs 51.3%, respectively; P = .004).
Uncorrected Visual Acuity and Best Spectacle-Corrected Visual Acuity
Before surgery and at 3, 6, and 12 months after surgery, there was no significant difference in UCVA between the FS DSEK and PK groups ( Table 4 ). In the FS DSEK group, UCVA was significantly better at all postoperative visits compared with that before surgery. The UCVA in the PK group was significantly improved at 3 and 12 months after surgery compared with that before surgery.
| FS DSEK, Mean ± SD | Range | PK, Mean ± SD | Range | P Value a | |
|---|---|---|---|---|---|
| UCVA (logMAR) | |||||
| Preoperative | 1.01 ± 0.4 (20/200) | 0.22 to 2.0 | 0.88 ± 0.4 (20/150) | 0.40 to 2.0 | .133 |
| 3 mos | 0.80 ± 0.2 (20/125) b | 0.40 to 1.70 | 0.71 ± 0.3 (20/100) b | 0.10 to 1.36 | .144 |
| 6 mos | 0.79 ± 0.3 (20/125) b | 0.40 to 1.70 | 0.79 ± 0.3 (20/125) | 0.14 to 1.36 | .959 |
| 12 mos | 0.73 ± 0.3 (20/102) b | 0.34 to 1.70 | 0.68 ± 0.3 (20/96) b | 0.10 to 1.46 | .539 |
| P = .001 c | P = .045 c | ||||
| BSCVA (logMAR) | |||||
| Preoperative | 0.82 ± 0.4 (20/132) | 0.22 to 2.0 | 0.73 ± 0.4 (20/105) | 0.18 to 2.0 | .316 |
| 3 mos | 0.65 ± 0.3 (20/90) b | 0.22 to 1.70 | 0.40 ± 0.2 (20/50) b | −0.04 to 1.12 | <.001 |
| 6 mos | 0.64 ± 0.3 (20/87) b | 0.26 to 1.70 | 0.35 ± 0.2 (20/44) b | 0 to 0.86 | <.001 |
| 12 mos | 0.55 ± 0.2 (20/70) b | 0.16 to 1.10 | 0.35 ± 0.2 (20/44) b | −0.04 to 0.98 | <.001 |
| P = .004 c | P < .001 c | ||||
| BSCVA gain (logMAR) | |||||
| 3 mos | 0.15 ± 0.4 | −1.06 to 1.34 | 0.33 ± 0.4 | −0.48 to 1.48 | .052 |
| 6 mos | 0.14 ± 0.4 | −1.06 to 1.30 | 0.38 ± 0.4 | −0.40 to 1.46 | .017 |
| 12 mos | 0.24 ± 0.4 | −0.34 to 1.50 | 0.38 ± 0.4 | −0.24 to 1.30 | .103 |
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