What is already known on this topic?
Current techniques for Descemet’s membrane exposure lack reproducibility in addition to challenges in determining incision depth.
What this study adds?
A simplified technique for Descemet’s membrane exposure involving peripheral transconjunctival single-plane sclerocorneal incision yields high reproducibility with easy determination of incision depth via a mirror image or an irregular wrinkle of the Descemet’s membrane.
How this study might affect research, practice, or policy?
This study demonstrates the efficacy of transconjunctival single-plane sclerocorneal incisions for Descemet’s membrane exposure during deep anterior lamellar keratoplasty.
Since the development of the first penetrating keratoplasty (PK), corneal transplantation has been the most common type of organ transplantation (Zirm 1906; Coster and Williams 2005). Despite the dramatic improvement in the complete replacement of severe corneal opacity, there are some disadvantages in PK, such as suture-related problems (higher astigmatism or infection), transplant rejection, glaucoma (steroid-dependent), slower recovery of visual acuity, and rupture due to injury (Hos et al. 2019).
Over the last decade, keratoplasty techniques have evolved rapidly with an increasing number of lamellar surgeries, such as deep anterior lamellar keratoplasty (DALK) and endothelial keratoplasty (EK) (Hos et al. 2019; Flockerzi et al. 2018). Particularly, simple stromal opacity without endothelial dysfunction can be treated with DALK (Reinhart et al. 2011; Ple-Plakon and Shtein 2014). DALK has certain advantages over PK or EK as it causes less endothelial cell density reduction and low immunological graft rejection rates (Ogawa et al. 2016). The greatest difficulty in performing DALK is the surgical learning curve. Anwar’s big-bubble technique and the Melles technique are two major methods to achieve Descemet’s membrane exposure in order for surgeons to perform DALK quickly and easily; however, the incision depth is difficult to determine, and these techniques are not reproducible (Melles et al. 1999; Anwar and Teichmann 2002; Shimazaki et al. 2002; Sugita and Kondo 1997). Even an experienced surgeon risks failure of the procedure due to an incomplete Descemet’s membrane exposure or rupture (Sarnicola et al. 2010; Smadja et al. 2012).
This case series investigated a simplified technique using transconjunctival single-plane sclerocorneal incision, which is familiar to cataract surgeons as well as corneal surgeons (Sugai, Yoshitomi, and Oshika 2010). The purpose of this study was to describe a simple technique for Descemet’s membrane exposure during DALK so as to facilitate an easier learning curve for surgeons.
MATERIALS AND METHODS
This prospective study was performed in accordance with the institutional guidelines, and all the patients provided their informed consent. This study adhered to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of Yokohama Minami Kyosai Hospital Ethical Review Board (Approval no. YKH_26_05_12). Consecutive patients requiring DALK from 2018 July to 2019 March were enrolled in this study. Patients with a history of corneal perforation prior to surgery, ocular surgery, or any pre-existing diseases such as macular degeneration, amblyopia, and advanced glaucoma were excluded.
All surgeries were performed under retrobulbar anaesthesia and the Nadbath facial nerve block. All surgical steps are shown in Figure 1.
First, the host cornea was marked using a trephine (Katena, Denville, NJ, USA) at 7.5 mm. Without a superficial keratectomy, a sclerocorneal pocket was created using a 2.8-mm slit knife, similar to that in a cataract surgery, without perforation as shown in Figure 1A. The most important feature is the incision depth; the incision has to be stopped just prior to the perforation. The average horizontal thickness (x; mm) from limbus to anterior chamber was 1.55 ± 0.21 mm (Fig. 1B); therefore, the slit knife could be stopped just before perforation using a slit knife mark which indicated 1.50 mm from the top of the knife (Fig. 1A). A small slit was created with a disposable knife, and air was injected using a 30-gauge needle (big-bubble formation) at a bevel-down orientation (Anwar and Teichmann 2002) to completely separate the host stroma and the Descemet’s membrane (Fig. 1C, 1D), while ophthalmic viscosurgical devices (OVD) (OPELEAD HV [0.85] 1%) were used to create a space by depressing the Descemet’s membrane. The anterior stroma was divided into four squares (Fig. 1E). The host stroma was carefully removed as was the donor endothelium, and the DALK graft was prepared using a donor punch (Katena) with a diameter of 7.75 mm. The donor graft was sutured using 10-0 nylon (Mani, Tochigi, Japan) by either a running or an interrupted suture technique (Fig. 1F).
Postoperative medications administered were 1.5% levofloxacin (Cravit), 0.1% betamethasone sodium phosphate (Sanbetasone; Santen Pharmaceutical Co., Ltd., Osaka, Japan), and 2% rebamipide ophthalmic solution (Mucosta; Otsuka Pharmaceutical CO., Ltd., Japan, Tokyo), starting at four times per day for 3 months and subsequently tapered. In cases of steroid-related IOP (intraocular pressure) elevation, anti-glaucoma agents were applied.
Patients and examinations
The evaluated outcomes were as follows: best corrected visual acuity (BCVA) (converted to logarithm of the minimal angle of resolution [logMAR] units) pre- and postoperatively (at the last visit after surgery), astigmatism (dioptres [D]) postoperatively (last visit after surgery; evaluated with suture [before suture removal]), success rates of Descemet’s membrane exposure, and incidence of intra- and postoperative complications. Astigmatism was assessed using the autorefractometer ARK-1 (Nidek Co., Ltd, Japan). Cases of conversion to PK were excluded from postoperative clinical course evaluations such as BCVA, corneal astigmatism, and postoperative complications.
Statistical analyses were performed using JMP Pro software version 14.0.0 (SAS Institute, Cary, NC, USA). Statistical significance was defined as p < 0.05. All data were described as means ± standard deviations. For the statistical analyses, BCVA was converted to logMAR units. The Mann–Whitney U test was used to compare the preoperative and postoperative outcomes, namely BCVA and astigmatism.
Four female and seven male patients were included in this study, with an average age of 53.6 ± 16.1 years. Surgical indications were scars (n = 6), corneal dystrophy (n = 3), or keratoconus (n = 2). One patient was excluded from the postoperative analysis of the clinical course owing to the conversion to a PK. The main outcome results for all included cases are shown in Table 1. The average follow-up period was 26.1 ± 16.3 weeks (Table 1).
BCVA significantly improved from 0.83 ± 0.38 logMAR at 20/150 Snellen baseline preoperatively to 0.24 ± 0.12 logMAR at 20/35 Snellen (n = 10, p < 0.001) postoperatively. Postoperative astigmatism was -3.3 ± 1.9 D (n = 10) (Table 1).
Except for unsuccessful separation in one patient (one eye), Descemet’s membrane exposure was successful in 10 of the 11 patients (90.9%) without perforation. Surgery in one eye was unsuccessful due to a large tear in the Descemet’s membrane that made it impossible to complete the DALK and necessitated conversion to a PK. Three out of ten (30%) patients who underwent a DALK showed double chamber formation, wherein spontaneous attachment was obtained. There was no graft rejection or graft failure observed during the follow-up period (Table 1).
This study demonstrated the use of a simple technique, transconjunctival single-plane sclerocorneal incision, which is familiar to ophthalmic and cataract surgeons, to achieve Descemet’s membrane exposure. The technique used in this study allowed high success rates (up to 72.7% [8 of 11 eyes]) in performing the big-bubble technique. In cases of failure, the Descemet’s membrane could still be exposed using an additional OVD injection. Unfortunately, one eye showed Descemet’s membrane rupture that required conversion to a PK.
Previous studies have introduced some novel techniques for DALK, such as the layer-by-layer (manual dissection) (Sugita and Kondo 1997), big-bubble (Anwar and Teichmann 2002), divide-and-conquer (Tsubota et al. 1998), double-bubble (Shimazaki 2010), mirror-image (Melles et al. 1999; Shimmura et al. 2005), and limbal-approach techniques (Senoo 2005). However, all these methods require a steep learning curve, which may affect reproducibility. For instance, the big-bubble technique requires a mastery of the skill to ensure success. Moreover, DALK success rates have been shown to significantly increase with the surgeons’ experience (Sarnicola et al. 2010; Smadja et al. 2012).
The strength of the technique used in this study is its high reproducibility (72.7%), which could be attributed to the depth of the needle injection. In this technique, the depth of insertion could be easily determined by a mirror image or an irregular wrinkle of the Descemet’s membrane. To determine the depth of the slit knife can be developed with experience in performing cataract surgeries. In fact, the use of intraoperative optical coherence tomography revealed that the depth of the first incision performed by intuition with the slit knife or needle injection is adequate to create a big-bubble (Siebelmann, Steven, and Cursiefen 2015).
The limitations of this study include the relatively small number of participants and the lack of a comparison with a control group including other techniques of Descemet’s membrane exposure such as Melles technique, or manual dissection. In this case series, OVD were used in all the eyes to depress the Descemet’s membrane. The relatively high rates of double anterior chamber formation (30%) could be attributed to the use of OVD. Despite the possibility of spontaneous attachment of the host-Descemet’s membrane (Lin et al. 2018), it is important to wash OVD well at the end of surgery.
In conclusion, the current study advocates the efficacy of transconjunctival single-plane sclerocorneal incisions for Descemet’s membrane exposure in DALK.
Ethics approval and consent to participate
This study was approved by the Institutional Review Board (Yokohama Minami Kyosai Hospital Ethical Review Board, Approval no. YKH_26_05_12). All patients provided informed consent for participation.
Consent for publication
All patients provided informed consent for publication.
Availability of data and materials
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.
No. It was not appropriate or possible to involve patients or the public in the design, conduct, reporting, or dissemination plans of this research.
T.H. wrote the manuscript; S.Y. organised the paper. All authors reviewed the paper.
The authors thank Dr. I Oyakawa for providing critical comments concerning this study.