Purpose
To evaluate and compare the visual outcomes and recurrence patterns of corneal stromal dystrophies after excimer laser phototherapeutic keratectomy (PTK) in eyes with and without a corneal graft.
Design
Retrospective, comparative case series.
Methods
setting : Cornea Service, Wills Eye Institute, Philadelphia Pennsylvania. study population : The patients were divided into 2 groups. Group 1 comprised patients with no graft who underwent PTK (22 eyes of 15 patients), and group 2 comprised patients who underwent PTK over a previous full-thickness graft (18 eyes of 14 patients). intervention : All patients underwent PTK for decreased vision, symptoms of recurrent erosions, or both. main outcome measures : Visual outcomes and recurrence patterns of corneal stromal dystrophies.
Results
Preoperative and postoperative best-corrected visual acuities were 0.46 ± 0.25 and 0.51 ± 0.27 ( P = .56), respectively, in group 1 and 0.16 ± 0.13 and 0.21 ± 0.18 ( P = .25), respectively, in group 2. Mean preoperative spherical equivalent was 1.54 ± 2.59 diopters (D) and −5.10 ± 5.81 D ( P = .01) in groups 1 and 2, respectively, and mean postoperative spherical equivalent was 0.44 ± 1.8 D and −1.8 ± 4.25 D ( P = .19) in groups 1 and 2, respectively. There was no statistically significant difference in the efficacy ( P = .73) and safety ( P = .62) indices between the 2 groups. In group 1, mild recurrence was seen in 7 eyes (32%) and significant recurrence was seen in 4 eyes (18%) at a mean of 32 and 47 months after PTK, respectively. In group 2, mild recurrence was seen in 5 eyes (28%) and significant recurrence was seen in 5 eyes (28%) at a mean of 36 and 50 months after PTK, respectively.
Conclusions
PTK improved central corneal clarity, alleviated symptoms resulting from recurrent erosions, and improved visual acuity in both groups.
Excimer laser phototherapeutic keratectomy, popularly known as PTK, was approved by the United States Food and Drug Administration in 1995 for the treatment of various pathologic characteristics of the anterior one third of the cornea. The main goals of performing PTK are to remove or decrease the opacities affecting the visual acuity, to smooth the corneal surface, to improve the adherence of the corneal epithelium, or a combination thereof to help with painful symptoms. Corneal stromal dystrophies usually are first seen in the adolescent or later years and become progressively worse during middle adult life. Patients with corneal stromal dystrophies usually have decreased vision with or without symptoms of recurrent erosions. Based on the location of deposits in stromal corneal dystrophies (eg, granular, lattice, macular, Schnyder), PTK may be a reasonable alternative to delay or avoid anterior lamellar or penetrating keratoplasty (PK). PTK has the definite advantage of being easily repeatable compared with PK, because PK is an intraocular procedure and the prognosis tends to decrease with repeat grafts.
The literature clearly demonstrates the benefits of PTK for the treatment of corneal stromal dystrophies. Two main concerns after the PTK procedure for corneal stromal dystrophies are recurrence of the disease and induced refractive error. Dinh and associates showed a recurrence rate of 23% and 14% for granular and lattice dystrophies, respectively, at 40.3 and 6 months after PTK. Dogru and associates and Amm and Duncker noted induced hyperopia in their series and suggested that limiting the depth of corneal stromal ablation was important to avoid a significant hyperopic shift. Ellies and associates showed that PTK was safe and efficient for recurrent dystrophies after PK. It has also been reported that excimer laser on a graft can lead to anterior segment inflammation, corneal haze, scarring, and graft rejections. The purpose of this study was to evaluate the visual outcomes, recurrence patterns, safety, and efficacy of excimer laser PTK in corneal stromal dystrophy in patients with and without a prior corneal graft.
Methods
All patients with a stromal corneal dystrophy who underwent PTK on the Cornea Service of Wills Eye Institute, Philadelphia, Pennsylvania, for decreased vision, symptoms of recurrent erosions, or both between May 2001 and January 2012 were included in the study. Minimum follow-up was 3 months. This retrospective study was approved by the Institutional Review Board of Wills Eye Institute, Philadelphia, Pennsylvania, and was conducted in strict adherence to the tenets of the Declaration of Helsinki. Preoperative evaluation included complete systemic and ocular history and routine ophthalmic examinations, including uncorrected Snellen distance visual acuity (UCVA), best spectacle-corrected Snellen distance visual acuity (BSCVA), manifest refraction, slit-lamp biomicroscopy, computerized corneal topography (Atlas System model 995; Carl Zeiss Meditec, Dublin, California, USA), ultrasound central corneal pachymetry (Accutome Inc, Malvern, Pennsylvania, USA), Goldman applanation tonometry or Tono-Pen tonometry (Reichert Inc, Depew, New York, USA), and dilated fundus examination. The depth of treatment was determined before surgery by a combination of ultrasound pachymetry and slit-lamp examination results. The percent of corneal involvement was approximated on slit-lamp examination and then was calculated according to the ultrasound pachymetry results. For example, if it was 20% involved and the cornea measured 500 μm, the depth of the pathologic features was estimated to be 100 μm. The patients were divided into 2 groups: group 1 comprised patients with no graft who underwent PTK (22 eyes of 15 patients), group 2 comprised patients who underwent PTK over a previous full-thickness graft (18 eyes of 14 patients).
The PTK procedure was performed with the VISX excimer laser platform (AMO Inc, Santa Ana, California, USA) under topical anesthesia (proparacaine 0.5%). Under sterile precautions, drapes were applied, a lid speculum was placed to the operative eye, and the fellow eye was covered with a protective shield. The goal of the procedure was to clear most of the opacity, not necessarily to remove the entire stromal opacity. In eyes with a smooth epithelial surface, a transepithelial approach was used, whereas in eyes with an irregular epithelial surface, mechanical epithelial debridement was performed, followed by excimer laser ablation. Special care was taken during debridement at the graft-host junction in patients who had undergone PK. A 6.5-mm diameter ablation zone with no transition zone was used for all eyes. The ablation was centered on the entrance pupil. A pulse rate of 6 Hz was used. After approximately two thirds of the expected ablation was performed (based on the preoperative estimated depth of the pathologic area and pachymetry results), patients were examined at the slit lamp, and additional ablation was performed as necessary. Balanced salt solution was used as a masking agent to smooth out the ablation when needed. We find balanced salt solution to be easier and safer to use than a thicker masking agent, although it does need to be reapplied more frequently. The amount of laser treatment was recorded. In certain eyes, especially those with deep ablations and preoperative hyperopia, the surgeon performed an antihyperopia ablation. Using the joystick, a 2-mm diameter ablation zone was moved slowly around the periphery, straddling the central ablation. The total amount of antihyperopia treatment varied between 80 and 120 μm, depending on the degree of expected corneal flattening, as per previous reports. An antihyperopia treatment was performed in 17 eyes in group 1 and in 2 eyes in group 2 ( P < .001). At the end of the procedure, a bandage soft contact lens was placed, which was removed after healing of the epithelial defect, typically after 4 to 5 days. Mitomycin C was not used in any of the eyes.
After surgery, patients were treated with 1 drop of ofloxacin (0.3%), ketorolac (0.5%), and preservative-free artificial tears. In eyes with significant corneal haze after healing of the epithelial defect, a tapering dose of topical prednisolone 1% starting at 4 times daily was used for approximately 4 to 6 weeks. Patients were prescribed acetaminophen with codeine as needed. The patients were followed up at regular intervals. Visual acuity, manifest refraction, and signs and symptoms of recurrent dystrophy were noted. Mild recurrence was characterized by either only slit-lamp evidence of deposits or fewer than 2 episodes of recurrent erosion per month and no decrease in BSCVA. Significant recurrence was characterized by recurrent opacities causing a loss of 2 lines or more of BSCVA or 2 or more episodes of recurrent erosions per month. The safety index and efficacy index were calculated as follows:
Safety index = ean postoperative BSCVA / mean preoperative BSCVA
Efficacy index = mean postoperative UCVA / mean preoperative BSCVA.
Although the primary goal of PTK was to improve BSCVA, significant hyperopic shift is a well-described side effect of PTK for stromal dystrophies that does not show up when analyzing BSCVA, but does when analyzing UCVA.
For statistical analysis, SPSS software version 16.0 for Windows (SPSS Inc, Chicago, Illinois, USA) was used. Snellen visual acuity was converted to logarithm of the minimal angle of resolution units for statistical analysis. Comparisons between groups or variables were performed using nonparametric tests (the Mann–Whitney U test for unpaired samples and the Wilcoxon test for paired samples). Spearman correlations and least squares regression were used to determine the association between different variables. The probability of recurrence of the dystrophy in the 2 groups after PTK was calculated using the Kaplan-Meier method for survival analysis. A P value of less than .05 was considered statistically significant.
Results
Demographics and preoperative characteristics are shown in Table 1 . Group 1 consisted of 19 eyes with granular dystrophy (GD), 2 eyes with macular corneal dystrophy (MCD), and 1 eye with Schnyder corneal dystrophy, and group 2 consisted of 11 eyes with lattice dystrophy (LD), 6 eyes with GD, and 1 eye with MCD. Patient ages ranged from 19 to 71 years (median, 55 years) in group 1 and 50 to 77 years (median, 61 years) in group 2. PTK procedures in group 1 were performed for recurrence of dystrophy after prior PTK in 8 (36%) eyes (6 eyes had undergone 1 prior PTK procedure and 2 eyes had undergone 2 prior PTK procedures) and as a primary procedure in 14 (64%) eyes. In group 2, all the PTK procedures were performed for recurrence of dystrophy in the graft. Previous surgeries included PK performed once in 15 (83%) eyes, PK performed twice in 3 (17%) eyes, and PTK procedures in 6 (33%) eyes. The mean interval between the last surgical intervention and the PTK was 9 ± 4 years for the 8 eyes in group 1 and 12 ± 6 years in group 2 ( P = .32). Preoperative BSCVA, cylinder, mean keratometry, and pachymetry were comparable between the 2 groups ( P > .05). Group 2 eyes had a longer mean follow-up after the PTK (53 ± 31 months) compared with group 1 eyes (31 ± 35 months; P = .03).
| Parameter | Group 1 a | Group 2 b | P Value |
|---|---|---|---|
| Age (y) | 49.8 ± 16.5 (19 to 71) | 62.2 ± 9.3 (50-77) | .05 |
| Gender (M/F) | 7/8 | 6/8 | |
| Laterality (R/L) | 9/13 | 12/6 | |
| BCVA | |||
| logMAR | 0.46 ± 0.25 (0.1 to 1) | 0.51 ± 0.27 (0.18 to 1.2) | |
| Mean Snellen | 20/57 | 20/64 | .56 |
| Sphere (D) | 2.16 ± 1.31 (0.5 to 3.75) | −5.39 ± 6.08 (−15 to 0.75) | .01 |
| Cylinder (D) | 1.63 ± 1.04 (0.75 to 4) | 2.5 ± 1.4 (1.25 to 5) | .18 |
| Spherical equivalent (D) | 1.54 ± 2.59 (−3.75 to 4.12) | −5.10 ± 5.81 (−12.5 to 1.37) | .01 |
| Keratometry (D) | 42 ± 2.5 (36 to 45) | 44 ± 4.5 (36 to 49) | .05 |
| Pachymetry (μm) | 558 ± 54 (480 to 657) | 582 ± 73 (448 to 683) | .34 |
| Follow-up (mos) | 31 ± 35 (3 to 128) | 53 ± 31 (3 to 100) | .03 |
| Indication for PTK (no. of eyes) | |||
| DV | 11 | 9 | |
| Recurrent erosions | 4 | ||
| Both | 11 | 5 |
a Patients with no graft who underwent PTK.
Intraoperative details and postoperative outcomes are shown in Table 2 . There was no difference in the amount of tissue ablation ( P = .11) or the postoperative epithelial healing time ( P = .54) between the 2 groups. There was significant improvement in the postoperative BSCVA compared with the preoperative BSCVA in both groups (group 1, P < .001; group 2, P = .01). Improvements in postoperative BSCVA of 20/40 or better were seen even in eyes with previous recurrent erosions, going from 36% to 91% in group 1 and from 12% to 78% in group 2. There was an increase in the percentage of eyes with BSCVA of 20/40 or better in all the dystrophies in both groups ( Figure 1 ). Mean time to achieve BSCVA was 2.5 ± 1.5 months in group 1 and 2.1 ± 1.5 months in group 2. The postoperative visual outcomes were comparable between the 2 groups ( P > .05). Although group 2 eyes were more myopic than group 1 eyes before surgery ( P = .01), there was no statistically significant difference after surgery between the 2 groups ( P = .85). The change in spherical equivalent (SE) was not statistically different ( P = .39) between the 2 groups. There was a mean improvement of 3.0 ± 1.85 Snellen lines (range, 7 lines better to no improvement) and 2.6 ± 2.72 Snellen lines (range, 7 lines better to 4 lines worse) in groups 1 and 2, respectively. There was no statistically significant correlation between central ablation depth and postoperative spherical power ( P = .96, P = .53), cylinder ( P = .11, P = .25), or SE ( P = .91, P = .51) in groups 1 and 2, respectively. As expected, a statistically significant negative correlation was seen between amount of antihyperopia treatment and spherical power (Spearman correlation, −0.069; P = .02), but not in cylinder ( P = .08) or SE ( P = .38) in group 1. There was no statistically significant difference in the efficacy ( P = .73) and safety ( P = .62) indices between the 2 groups.
