Purpose
To compare the postoperative macular thickness changes using optical coherence tomography (OCT) in eyes that underwent deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PKP).
Design
Prospective, nonrandomized clinical trial.
Methods
Sixty eyes of 60 patients (32 male, 28 female) with keratoconus who underwent corneal transplant surgery in an institutional setting were included in the study. Thirty eyes underwent DALK and 30 eyes underwent PKP. All eyes underwent corrected visual acuity (CVA) measurement and macular thickness measurement using spectral-domain OCT preoperatively, and 1 week, 1 month, 3 months, and 6 months postoperatively. The main outcome measures were CVA and macular thickness.
Results
The DALK group had significantly better mean CVA than that of the PKP group at 1-month ( P < .001), 3-month ( P = .002), and 6-month ( P = .040) follow-ups. The mean macular thickness significantly increased at 1 week after PKP surgery, remained stable at 1-month follow-up, and decreased at 3- and 6-month follow-ups. On the other hand, the mean macular thickness remained stable during 6 months after DALK. Although there was no significant difference between groups preoperatively ( P = .970) and at 6-month follow-up ( P = .339), the PKP group had significantly higher mean macular thickness than that of the DALK group at 1-week ( P < .001), 1-month ( P < .001), and 3-month ( P = .005) follow-ups.
Conclusion
Although mean macular thickness increases and peaks around 1 month and returns back to normal levels at 6 months after PKP surgery, it does not change after DALK.
The concept of deep anterior lamellar keratoplasty (DALK) is that of targeted lamellar replacement of corneal stroma with preservation of the patient’s own endothelium. The visual and optical outcomes of DALK are comparable to penetrating keratoplasty (PKP), particularly when the recipient Descemet membrane is completely bared to provide a smooth interface. As there is no significant manipulation in the anterior chamber, one of the main advantages of DALK surgery is the reduction of the risk of intraocular complications.
Postsurgical macular edema is a well-known complication after cataract surgery. Although the pathogenesis of postsurgical macular edema is unclear, it is mostly associated with intraocular manipulations and prostaglandin release. Macular edema can also be seen after keratoplasty, which can lead to significant vision loss. Optical coherence tomography (OCT) is a fast and noninvasive technique, and it became the preferred diagnostic method of detecting postsurgical macular edema in recent years.
Theoretically, given that there is almost no intraocular manipulation during DALK, the risk of macular edema after DALK surgery would be expected to be lower than that of PKP. In this study, using OCT we compared preoperative and postoperative macular thickness in eyes that underwent DALK with big-bubble technique and PKP.
Methods
The prospective study involved 60 eyes of 60 patients (32 male, 28 female) with keratoconus who underwent uneventful corneal transplant surgery.
Inclusion criteria included patients who had keratoconus and underwent corneal transplant surgery with either PK or DALK. Exclusion criteria were: significant corneal haze or scar, or cataract that will preclude the preoperative or postoperative OCT macular thickness measurement; significant rejection reaction during follow-up; a history of corneal disease other than keratoconus; history of hydrops; abnormal iris; pupil deformation; ocular inflammation; glaucoma; macular degeneration; retinopathy; retinal detachment; neuroophthalmic disease; and a history of previous intraocular surgery.
The diagnosis of keratoconus was based on slit-lamp findings, keratometry, and corneal topography. Thirty eyes of 30 patients (16 male, 14 female) underwent PKP procedure and 30 eyes of 30 patients (16 male, 14 female) underwent DALK surgery. The DALK procedure was performed under local retrobulbar anesthesia using Anwar’s big-bubble technique. A partial trephination with 7.5 or 7.75 mm diameter was performed using the Hessburg-Barron vacuum trephine (Katena Instruments, Denville, New Jersey, USA). After the centration and vacuum, the trephine was set to cut until it reached approximately 400 μm depth (5-6 quarter turns) into the corneal stroma. A 27-gauge disposable needle attached to a 5-mL syringe filled with air was inserted into the central cornea from the trephination. The needle bevel was oriented downward and the needle penetration into the stroma was as deep as possible. The needle was sufficiently inserted to prevent air reflux. Air was injected to produce Descemet membrane detachment. A penetrating stromal corneal incision using a super-sharp blade was then placed in the center of the cornea. The incision was perpendicular to the corneal plane until prolapse of air was observed through the operating microscope. Stromal cuts were made with blunt-tipped microscissors. The residual stroma was then excised with curved scissors along the trephination. After completion of the circumferential incision with corneal scissors, the button was removed. A moist cellulose sponge was placed over the residual cornea, and attention was turned to the donor cornea. After the donor cornea was taken out of the transplant medium, the endothelium was stained with trypan blue and was carefully peeled off using blunt forceps, followed by drying with cellulose sponges. A donor button of 7.75 or 8.0 mm size (0.25 mm larger than the host bed trephination) was trephined (Barron punch trephine; Katena Instruments) and transferred to the host bed. The donor cornea was sutured in place using 10-0 nylon with 16-bite single running suture technique. Subconjunctival injections of 0.5 cc each of cefazoline, gentamicin, and dexamethasone were injected into the fornices at the end of surgery. The patients received ofloxacin (Exocin; Allergan Inc, Irvine, California, USA) drops 4 times a day for 2 weeks and prednisolone acetate 1% drops every 2 hours postoperatively for 3 months, then tapered to 4 times a day until 6-month follow-up.
All patients underwent a full ophthalmologic examination, including manifest refraction, determination of uncorrected visual acuity and corrected visual acuity (CVA), and slit-lamp biomicroscopy; Goldmann applanation tonometry; binocular indirect ophthalmoscopy through dilated pupils; macular thickness measurement using OCT (Carl Zeiss Meditec, Inc, Dublin, California, USA) preoperatively and postoperatively; ultrasonic pachymetry; and computerized videokeratography (Magellan mapper; Nidek Technologies, Gamagori, Japan) preoperatively and postoperatively when needed. Postoperative assessments were performed routinely at 1 day, 1 week, and 1 month, 3 months, and 6 months after surgery. The preoperative, 1-week, 1-month, 3-month, and 6-month follow-ups after corneal transplant surgery were evaluated for this study. The classification of Kim and associates was used for macular changes seen on OCT: group 1: frank cystoid abnormalities within the retina with distortion of the foveal contour; group 2: diffuse thickening of the retina with blunting of the foveal contour but no definite cystoid abnormalities; group 3: subtle intraretinal cystoid abnormalities without substantial increase in retinal thickness or loss of foveal contour.
Data analysis was performed using SPSS for Windows version 11.0 (SPSS, Inc, Chicago, Illinois, USA). Normality was checked by the normal probability plots and Shapiro-Wilk and Kolmogorov-Smirnov tests; the Mann-Whitney U test was performed to compare PKP and DALK outcomes, and Kruskal-Wallis and Wilcoxon signed rank tests were used. Differences were considered to be statistically significant when the P value was < .05.
Results
The mean age of the PKP group was 26.2 ± 6.5 (range: 15 to 40) years, and the mean age of the DALK group was 25.3 ± 6.5 (range: 16 to 40) years. There was no significant difference in mean age between PKP and DALK groups ( P = .614) (Mann-Whitney U test).
All patients were present during each visit. All of the transplanted donor corneas showed a clear interface after DALK with good wound healing in both DALK and PKP groups. There were no significant complications noted during follow-up.
The mean CVA is given in Figure 1 . Compared to preoperative levels, the CVA significantly increased after PKP and DALK surgeries ( P < .001, Kruskal-Wallis test). The CVA at 1-, 3-, and 6-month follow-ups was significantly higher than the preoperative CVA in both groups ( P < .05, Mann-Whitney U test). Although there was no significant difference preoperatively ( P = .825), the DALK group had significantly better CVA than that of the PKP group at 1-month ( P < .001), 3-month ( P = .002), and 6-month ( P = .040) follow-ups.
The mean preoperative macular thickness was 218 ± 17 (range: 190-254) μm in the PKP group and 218 ± 17 (range: 190-260) μm in the DALK group. The mean macular thickness measured using OCT during follow-up is shown in Figure 2 . Compared to preoperative levels, the mean macular thickness significantly increased 1 week after PKP surgery, remained stable at 1-month follow-up, and decreased at 3- and 6-month follow-ups ( P < .001, Kruskal-Wallis test). The macular thickness at 1-week, 1-month, and 3-month follow-ups was significantly higher than the preoperative macular thickness ( P < .01, Mann-Whitney U test), but there was no significant difference in macular thickness between 6-month follow-up and preoperative level ( P = .300, Mann-Whitney U test). On the other hand, the macular thickness remained stable during 6 months after DALK ( P = .457, Kruskal-Wallis test).
The PKP group had significantly higher mean macular thicknesses than those of the DALK group at 1-week and 1- and 3-month follow-ups ( P < .01). The mean postoperative macular thickness, the distribution of postoperative macular thickness during follow-up, the mean increase in macular thickness, and the distribution of the increase in macular thickness in the PKP group are given in the Table . Although 9 of 30 eyes (30%) had an increase in macular thickness more than 34 μm (2 standard deviations of the preoperative mean macular thickness) at 1 month compared to the preoperative levels in the PKP group, none of the 30 eyes (0%) had more than a 34-μm increase in macular thickness at 6-month follow-up. None of the eyes demonstrated cystoid changes in the macula during follow-up and all of the eyes that had an increase in macular thickness were evaluated as group 2 (diffuse thickening of the retina). Figure 3 shows the OCT images of a patient who demonstrated increase in macular thickness after PKP surgery. All eyes in the DALK group were within ±10 μm of the preoperative values during each follow-up.
| 1 Week | 1 Month | 3 Months | 6 Months | |
|---|---|---|---|---|
| Postoperative macular thickness | ||||
| Mean macular thickness (μm) | 247 ± 24 | 248 ± 23 | 234 ± 18 | 223 ± 19 |
| ≥ 250 μm [n (%)] | 15 (50) | 14 (47) | 8 (27) | 5 (17) |
| ≥ 230 μm [n (%)] | 22 (73) | 20 (67) | 13 (43) | 12 (40) |
| Increase in macular thickness | ||||
| Mean increase (μm) | 28 ± 13 | 30 ± 14 | 16 ± 10 | 5 ± 7 |
| ≥ 50 μm [n (%)] | 1 (3) | 3 (10) | 0 (0) | 0 (0) |
| ≥ 40 μm [n (%)] | 7 (23) | 8 (27) | 1 (3) | 0 (0) |
| ≥ 34 μm a [n (%)] | 12 (40) | 9 (30) | 1 (3) | 0 (0) |
| ≥ 30 μm [n (%)] | 13 (43) | 15 (50) | 5 (17) | 0 (0) |
| ≥ 20 μm [n (%)] | 21 (60) | 22 (73) | 12 (40) | 3 (10) |
| ≥ 10 μm [n (%)] | 29 (97) | 30 (100) | 23 (77) | 9 (30) |
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