|Year : 2014 | Volume
| Issue : 3 | Page : 166-172
Comparative study between DALK using the big-bubble technique and penetrating keratoplasty in corneal stromal opacities
Amr S Abdel Hakeem, Tarek A Katamish, Dalia H Abdel Raouf, Hoda A Abdel Monem
Department of Ophthalmology, Kasr El Aini Hospital, Cairo University, Cairo, Egypt
|Date of Submission||07-Apr-2014|
|Date of Acceptance||25-Jul-2014|
|Date of Web Publication||30-Dec-2014|
Dalia H Abdel Raouf
Department of Ophthalmology, Kasr El Aini Hospital, Cairo University, 8 Mohei el din street, Dokki, Cairo 12311
Source of Support: None, Conflict of Interest: None
To compare between deep anterior lamellar keratoplasty (DALK) using the big-bubble technique and penetrating keratoplasty (PK) in terms of visual and refractive outcomes, endothelial cell density (ECD), and contrast sensitivity in patients with corneal stromal opacities.
A prospective interventional comparative study was carried out from April 2011 to August 2012. The follow-up duration was 12 months postoperatively.
Patients and methods
Thirty eyes of 30 patients presenting to the outpatient clinic in Kasr El Aini Hospital, Cairo University who fulfilled the inclusion criteria were studied. The inclusion criteria were as follows: best-corrected visual acuity (BCVA) less than 6/36, with an intact endothelium/descemet membrane complex by ultrasound biomicroscopy. The exclusion criteria were as follows: full-thickness corneal pathology involving the descemet membrane, endothelial dysfunction, intraocular pathology, ectatic corneal conditions, previous intraocular surgeries, lid abnormalities, active keratitis, or dry eye. They were divided into two groups: group A included 15 patients in whom the big-bubble technique was used successfully and group B included 15 patients operated upon by PK. Postoperative follow-up was carried out with group masking in terms of the following: BCVA, refraction, ECD contrast sensitivity using the Functional Acuity Contrast test, contrast sensitivity chart, intraocular pressure, and ultrasound biomicroscopy assessment of graft thickness.
All patients completed the 12-month follow-up. The significance level was set at P-value less than or equal to 0.05. ECD showed a greater decrease in the PK group, with the mean ECD attained at 3 months in the DALK group compared with the PK group reaching a statistically significant level at the end of the 12 months (P = 0.001). The mean refractive astigmatism and the mean number of days needed for the cornea to clear were significantly less (P = 0.035 and 0.001 respectively) in the big-bubble DALK group. In terms of BCVA, the final mean graft thickness, postoperative contrast sensitivity, and intraocular pressure, there was no significant difference between both groups (P > 0.05).
The big-bubble technique is superior to PK in terms of ECD, mean refractive astigmatism, and early corneal clarity.
Keywords: big-bubble, deep anterior lamellar keratoplasty, endothelial cell density, lamellar keratoplasty, penetrating keratoplasty
|How to cite this article:|
Abdel Hakeem AS, Katamish TA, Abdel Raouf DH, Abdel Monem HA. Comparative study between DALK using the big-bubble technique and penetrating keratoplasty in corneal stromal opacities. J Egypt Ophthalmol Soc 2014;107:166-72
|How to cite this URL:|
Abdel Hakeem AS, Katamish TA, Abdel Raouf DH, Abdel Monem HA. Comparative study between DALK using the big-bubble technique and penetrating keratoplasty in corneal stromal opacities. J Egypt Ophthalmol Soc [serial online] 2014 [cited 2020 Feb 21];107:166-72. Available from: http://www.jeos.eg.net/text.asp?2014/107/3/166/148133
| Introduction|| |
Traditionally, penetrating keratoplasty (PK) has commonly been used as the definitive treatment for a variety of corneal pathologies, such as bullous keratopathy, keratoconus, corneal degenerations, and dystrophies. This technique of corneal transplantation is a safe and effective treatment, with numerous studies reporting good visual results after surgery . However, PK adversely affects the structural and immunological integrity of the eye, which can result in traumatic wound dehiscence and endothelial graft rejection .
The concept of lamellar keratoplasty (LK) is not new. However, it had been abandoned and largely replaced by the time-honored technique of PK because LK is technically demanding, time consuming, and yields suboptimal visual outcomes because of interface irregularity arising from manual lamellar dissection .
Recent improvements in surgical instruments and the introduction of new techniques of maximum depth of corneal dissection as well as inherent advantages such as preservation of globe integrity and elimination of endothelial graft rejection have resulted in the reintroduction of deep anterior lamellar keratoplasty (DALK) as an acceptable alternative to conventional PK .
In comparison with PK, DALK avoids most complications associated with an open-system surgery, such as anterior synechia, expulsive hemorrhage, and endophthalmitis. The criteria for donor cornea tissue selection are less stringent in DALK compared with PK .
Therefore, DALK has been introduced as a possible alternative to PK in eyes with keratoconus and stromal opacities attributable to dystrophies, degenerations, trauma, and microbial keratitis .
Because of the increasing numbers of DALK surgeries in recent years, comparison of visual and optical outcomes after DALK and PK has been a research subject of interest. Although some studies have reported visual outcomes to be comparable , several others have documented less favorable results after DALK surgery . In this study, we aimed to contribute toward the current information on the visual and optical performance outcomes in patients undergoing DALK or PK for corneal stromal opacities, which is also a less studied indication as compared with keratoconus.
| Patients and methods|| |
This is a prospective interventional comparative study carried out on 30 eyes of 30 patients with corneal stromal opacities who attended the outpatient clinic of Kasr El Aini Hospital, Cairo University from April 2011 to August 2012.
Best-corrected visual acuity (BCVA) less than 6/36, with an intact endothelium/descemet membrane complex by ultrasound biomicroscopy (UBM) and anterior segment OCT.
(1) Ectatic corneal conditions.
(2) Intraocular pathology (e.g. dense cataract, glaucoma, uveitis, etc.).
(3) Full-thickness corneal pathology involving the descemet membrane.
(4) Endothelial dysfunction.
(5) Lid abnormalities, active keratitis, or dry eye.
(6) Previous intraocular surgeries.
Patients were divided into two groups: In group A, 15 eyes with corneal stromal opacities of the first 15 patients who attended the outpatient clinic and fulfilled the inclusion criteria were operated by DALK using the big-bubble technique. In group B, 15 eyes with corneal stromal opacities of the next 15 patients who attended the outpatient clinic and fulfilled the inclusion criteria were operated by PK.
The research followed the tenets of the Declaration of Helsinki. After an explanation of the nature and the possible consequences of the study, including the advantages, disadvantages, risks of possible complications, and periodic follow-up for 12 months after the surgery, was provided, all participants provided written informed consent for intervention. The research was approved by the Research Ethical Committee of the faculty of medicine of Cairo University.
All patients were subjected to an assessment of history and ophthalmological examination including measurement of the BCVA, intraocular pressure (IOP) measurement with Goldman's applanation tonometry, slit-lamp examination, fundus examination, anterior segment OCT, and UBM of the cornea to assess the depth of the corneal opacity and to study the DM/endothelial complex, corneal pachymetry, corneal topography to exclude an ectatic corneal condition, B-scan ultrasonography for vitreoretinal evaluation, and VEP and ERG if needed.
All surgeries in each group were performed by the same surgeon with standardization of the technique in each surgery.
For group A, Anwar's big-bubble technique of DALK was performed by the second author as follows: ~80% of corneal thickness was trephined and a 27- or 30-G needle (bevel facing downward), attached to a 5 ml syringe, was inserted into the deep stroma aiming toward the center of the cornea. Air was gently injected into the deep stroma until a round, well-demarcated big bubble was formed extending to the borders of trephination. After big-bubble formation, debulking of the anterior two-thirds of the corneal stroma was performed using a crescent blade. This was followed by excision of the remaining stroma using blunt scissors .
For group B, PK was performed by the third author as follows: a graft was prepared using the selected punch. The difference between the punch and the trephine was 0.5 mm, with the combinations used being either 7.5 and 8.0 or 7.25 and 7.75. Near full-thickness corneal trephination was performed using a suction trephine, and then a superblade was used to enter the anterior chamber. Full-thickness removal of host cornea was completed using curved scissors, followed by suturing the graft in place using four initial 10/0 nylon stay sutures. Finally, suturing was completed using 16 interrupted 10/0 nylon.
The primary outcome measures were the BCVA and contrast sensitivity.
The Secondary outcome measures were the refraction status, the clinical clarity of the graft, the graft thickness, and wound coaptation using UBM, endothelial cell count by specular microscopy, and corneal topography using an NIDEK Magillan Mapper, NIDEK Co., LTD. JAPAN, Difference scan.
Patients received postoperative follow-up at 1 week, 1, 3, 6, and 12 months postoperatively for the following parameters: BCVA, contrast sensitivity using the Functional Acuity Contrast test, contrast sensitivity chart, IOP, UBM, specular microscopy, and corneal topography. Selective suture removal was performed in case of loose sutures and sutures causing repeated inflammation and vascularization.
Data were statistically described in terms of means ± SD, median and range, or frequencies and percentages when possible. Comparison of numerical variables in the study groups was carried out using the Mann-Whitney U-test. The χ2 -test was performed to compare categorical data. The significance level was set at P-value 0.05 or less. Statistical calculations were carried out using the computer program statistical package for the social science 15.0 (SPSS Inc., Chicago, Illinois, USA).
| Results|| |
A total of 18 patients (60%) were men (10 in group A and eight in group B) and 12 patients (40%) were women (five in group A and seven in group B) (P = 0.705). In group A, the mean age at the time of surgery was 34.13 ± 10.8, with an age range of 18-57 years, whereas in group B, the mean age at the time of surgery was 30.42 ± 15.3 years, with an age range of 20-58 years. [Table 1] shows the distribution of patients in both groups according to the etiology of corneal scarring.
Other preoperative data including the BCVA, corneal pachymetry, depth of stromal opacities, and IOP are presented in [Table 2], in which it is clear that there were statistically insignificant differences between the groups studied in the variables mentioned.
Postoperative best-corrected visual acuity
0The difference between the DALK group and the PK group is shown in [Table 3]. The mean BCVA was significantly better in the DALK group at 1, 3, and 6 months postoperatively, whereas the improvement was faster in PKP group in early postoperative period. Finally, at 12 months, the BCVA showed a statistically insignificant difference between both groups.
|Table 3 Comparison between best-corrected visual acuity results of both groups over time |
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[Table 3] and [Figure 1] show that visual stabilization occurred around 6 months after DALK, whereas at the end of the 12-month follow-up period, the PK group had not yet shown visual stabilization.
|Figure 1: Comparison of the postoperative best-corrected visual acuity (BCVA) in logMAR units between deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PK) groups.|
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Postoperative refractive outcomes
Topographic astigmatism was calculated as the difference between K1 and K2 values; comparison of the mean spherical equivalent, mean refractive astigmatism, and mean topographic astigmatism between the DALK and the PK group at all follow-up visits showed that the only significant results were those of the mean refractive astigmatism values at 6 and 12 months postoperatively. [Figure 2] shows the change in the mean spherical equivalent over time in both groups. This shows a trend toward more myopia over time in the DALK group and a trend towards less myopia over time in the PK group. The difference between the DALK group and the PK group in refractive astigmatism is shown in [Table 4].
|FIgure 2: Change in the mean spherical equivalent over time in the two groups. DALK, deep anterior lamellar keratoplasty; PK, penetrating keratoplasty.|
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|Table 4 Refractive outcomes of deep anterior lamellar keratoplasty versus penetrating keratoplasty |
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Postoperative endothelial cell density outcomes
Endothelial cell density (ECD) was measured by specular microscopy (cells/mm 2 ). As shown in [Table 5], ECD showed a greater decrease in the PK group, with the mean ECD starting off at 2501 ± 323 at 3 months in the DALK group compared with 2348 ± 280 in the PK group (P = 0.156). At the end of the 12-month follow-up period, the mean ECD had decreased to 2386 ± 255 in the DALK group and to 1770 ± 299 in the PK group (P = 0.001).
|Table 5 A comparison of endothelial cell density between the two groups over time |
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The ECD stabilized in the DALK group at 6 months postoperatively, whereas in the PK group, it continued to decrease throughout the 12-month follow-up period. This can be seen in [Figure 3], which shows the change in ECD over time in both study groups.
|Figure 3: Decrease in endothelial cell density over time in the two groups studied. DALK, deep anterior lamellar keratoplasty; PK, penetrating keratoplasty.|
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Postoperative ultrasound biomicroscopy data
In terms of the average wound thickness, the mean wound thickness at 12 months in the DALK group was 0.78 ± 0.0.9 mm, which was significantly lower than that of the PK group, 0.898 ± 0.17 mm (P = 0.043). However, the final mean graft thickness at 12 months was 520 ± 93 μm in the DALK group compared with 560 ± 61 μm in the PK group (P = 0.836). It was observed that the overall corneal thickness in the DALK group was lower (but not to a statistically significant degree) than that in the PK group.
Postoperative corneal clarity
In the DALK group, the mean number of days needed for the cornea to clear was 6.5 ± 8.5 days. In the PK group, the number of days needed was 11.64 ± 4.7 days (P = 0.001).
For postoperative contrast sensitivity and IOP, there was no significant difference between both groups (P > 0.05).
| Discussion|| |
Several studies have been carried out to determine the advantages of performing DALK compared with PK, and in 2011, Reinhart et al.  carried out a literature review for the American Academy of Ophthalmology, where they chose 11 studies that they considered particularly useful for comparison of the visual, refractive, early postoperative ECD results, and surgical complications of the two procedures.
In our study, the mean postoperative BCVA showed a significant difference between both groups, with BCVA in the DALK group being better at 1, 3, and 6 months. Finally, at 12 months postoperatively, the mean BCVA of both groupsshowed insignificant difference
(P = 0.224). This indicates that the mean BCVA for the PK group improved over time, whereas that of the DALK group stabilized earlier.
Similarly, Borderie et al.  compared PK with DALK for corneal stromal diseases (including keratoconus) and reported that comparison of DALK with PK for the best-spectacle corrected logMAR visual acuity showed no significant differences at all postoperative time points . In contrast, Cheng et al.  compared DALK with PK for corneal stromal diseases and reported that at 3 and 6 months postoperatively, the BCVA was significantly better in the PK group compared with the DALK group. However, the BCVA continued to improve in the DALK group and was not significantly different from the PK group 12 months postoperatively . Wu et al. , reported no significant difference in the number of patients operated for herpetic corneal scar between the DALK and PK groups; there was a statistically significant difference between both groups, with a significantly higher number of patients with a BCVA of at least 0.1 in the DALK group (P = 0.01) and a significantly higher number of patients with a BCVA of less than 0.1 in the PK group (P = 0.01) . Finally, in the review by Reinhart et al. , of the 11 comparative studies included, there was no significant difference in the postoperative BCVA between the DALK and PK groups in six studies [4,13-17]. There was better BCVA in the DALK group in one study  and better BCVA in the PK group in four studies [1, 6, 7, 18]. It is worth noting that the study that reported better postoperative vision in the DALK group had the largest number of eyes in each group (150/150) .
In terms of the refractive outcomes, in our study, there was a significant difference in the mean refractive astigmatism values at 6 and 12 months postoperatively, where the DALK group showed si gnificantly less mean refractive astigmatism (P = 0.043 and 0.035, respectively). There was no significant difference in the mean refractive astigmatism at 1 and 3 months of follow-up. There were no significant differences in topographic astigmatism or spherical equivalent at any time during the follow-up, but there was a trend toward more myopia over time in the DALK group and a trend toward less myopia over time in the PK group.
These results are similar to those published by Ardjomand et al. , for keratoconus patients, where they reported higher myopia and lower astigmatism in the DALK group compared with the PK group, but the difference was not statistically significant . However, Cheng et al.  reported less myopia over time for both groups. Reinhart et al. , in the 11 studies that they reviewed, as well as Sari Sφπόtlό et al.  reported no significant differences between the DALK and PK groups in any postoperative visual and refractive parameters.
Our study indicated that the ECD showed a greater decrease in the PK group, with the mean ECD starting off at 3 months. The ECD in the PK group was statistically lower than that of the DALK group at 6 months (P = 0.049), whereas at the end of the 12-month follow-up period, the mean ECD showed a highly significant difference between the two groups (P = 0.001). The ECD of the DALK group stabilized after 6 months, whereas that of the PK group continued to decrease throughout the 12-month follow-up period.
These results were in agreement with those of Cheng et al. , who reported continuous postoperative endothelial cell loss in both groups. The ECD was significantly lower in the PK group (P = 0.007) at 12 months postoperatively. Similarly, Borderie et al.  reported that the ECD was significantly higher in the DALK group than in the PK group at all postoperative time points (P < 0.001). The average 5-year postoperative endothelial cell loss was −22.3% in the DALK group and -50.1% in the PK group (P < 0.0001) . Wu et al.  reported that postoperative corneal ECD was steady in the full-bed DLK group, whereas it decreased continuously in the PK group. Similarly, Bahar et al.  reported a significantly lower ECD at the 12-month follow-up in the PKP group versus the DALKgroup
(P < 0.0001) . In the review by Reinhart et al. , six of the 11 studies in the DALK/PK comparison group evaluated postoperative ECD of the host corneal endothelium for the DALK groups and of the donor graft endothelium for the PK groups. All showed significantly higher ECD in the DALK groups: at 12 months postoperatively [13,18], at 24 months , at 3 years , and at all intervals up to 5 years . The ECD data for the DALK/PK comparative studies highlight significant differences between these surgical techniques, with consistently higher ECD in post-DALK eyes compared with post-PK eyes .
Another noteworthy point is that in our study, the ECD stabilized in the DALK group at 6 months postoperatively, whereas in the PK group, it continued to decrease throughout the 12-month follow-up period. This is in agreement with results reported by Shimazaki , who conducted a randomized-controlled trial comparing DALK and PK and found stabilization of EC loss 6 months after a DALK procedure. In addition, van Dooren et al.  reported an initial decrease in ECDs of ~11% in 6 months, followed by a physiologic rate of cell loss. However, Cheng et al.  found no evidence for EC loss stabilization within 12 months of a DALK procedure. A longer follow-up may be needed to further evaluate the time of stabilization of EC loss in DALK and PK.
In terms of the central graft thickness following DALK and PK, our study found an insignificant difference in the final mean graft thickness at 12 months (P = 0.836).
Similar to our results, Shimazaki  reported that the corneal thickness was less in the DALK group than the PK group throughout the observation period, but the difference was not statistically significant. Borderie et al.  reported that the average central corneal thickness was higher in the PK group than in the DALK group after 12 months (P < 0.001).
In our study, there was also no significant difference in contrast sensitivity between the DALK and PK groups at any grating frequency (P > 0.05). This is in agreement with the findings reported by Sari Sφπόtlό et al. , where no significant differences in photopic contrast sensitivity were found for each of the spatial frequencies between the DALK and the PK groups for keratoconus patients. However, mesopic contrast sensitivity for three cycles/degree was significantly higher in the DALK group (P < 0.01). For the remaining spatial frequencies in the mesopic condition, no significant differences were detected . Similarly Ardjomand et al.  reported no significant difference in contrast sensitivity between the DALK and PK groups for keratoconus patients (P = 0.38).
| Conclusion|| |
Our results confirm that DALK offers the huge advantage of preserving the recipient endothelium with significantly higher ECD and greater incidence of graft survival after DALK than after PK. Furthermore, the preservation of a healthy recipient endothelium allows earlier discontinuation of steroids after surgery and a reduced incidence of immunologic rejection. However, DALK is a technically more difficult procedure that requires an experienced surgeon and has a slower learning curve than PK. Thus, DALK can be considered a challenging, yet rewarding alternative to PK in all patients with corneal stromal pathologies not involving the descemet/endothelial complex.
| Acknowledgements|| |
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]