INTRODUCTION
The cornea is a transparent, avascular tissue covered by nonkeratinized stratified epithelium that is responsible for maintaining a smooth ocular surface for normal vision. Corneal stem cells, adult somatic stem cells located at the limbus are bestowed with the capability of maintaining corneal health.[1,2] Partial or total limbal stem cells (LSCs) lead to persistent epithelial defects, vascularization of the cornea, conjunctivalization of the cornea, corneal scarring, melting, ulceration, and perforation of the cornea. Thus, cornea becomes unable to maintain its surface epithelial integrity. The management of LSC deficiency (LSCD) is crucial because patients with these abnormalities generally are poor candidates for conventional corneal transplantation.[3,4,5,6] LSC transplantation (LSCT) has been the primary procedure for managing LSCD. Several techniques have been reported for LSCT, such as conjunctival-limbal autograft,[7] kerato-limbal allografts,[8] and cultivated limbal epithelial transplantation.[9] However, major limitations of using these techniques are in cases of bilateral diseases, low resource settings, and lack of laboratory support. Recently, Sangwan et al. have introduced a new simplified LSCT technique, called simple limbal epithelial transplantation (SLET), as an alternative to LSCD.[10]
To date, the data on allogenic SLET (alloSLET), especially living-related allogenic SLET for bilateral LSCD and the outcomes of SLET associated with other causes of LSCD are limited. Therefore, in this study we aim to evaluate the efficacy of both autoSLET and alloSLET in patients with different causes of LSCD.
MATERIALS AND METHODS
Study design and participants
This prospective intervention study was performed at tertiary care center in eastern India from April 2019 to March 2020 according to the principles of the Declaration of Helsinki. The study was approved by the ethics committee and written informed consent was obtained from the patients of >18 years of age and in case of minors' consent was obtained from their legal guardians.
The inclusion criteria of the study were (1) age ≥5 years; (2) clinical LSCD (partial LSCD ≥180° or total) based on the slit-lamp examination (presence of conjunctivalization, persistent/recurrent epithelial defects, ocular surface inflammation, scarring, and neovascular invasion onto the central corneal 5-mm zone); (3) duration of LSCD for more than ≥3 months; (4) Schirmer I-test ≥10 mm. Patient with LSCD for <3 months, severe dry eye, acute inflammation, age <5 years, immunocompromised, lid disorders, uncontrolled glaucoma, evidence of infection, taking treatment for other systemic illness, and patients who could not comply with the follow-up were excluded from study.
Surgical technique
Auto simple limbal epithelial transplantation
Adult patients were operated under peribulbar anesthesia, while children under 16 years were administered general anesthesia. The conjunctiva overlaying the cornea, the perilimbal subconjunctival tissue, any symblepharon and sub-conjunctival fibrotic tissue were removed and further resected 1–2 mm away from the limbus. The human amniotic membrane (hAM) was placed over the bare ocular surface with the stromal side down and the edge was well aligned with the conjunctival rim before fixing with the fibrin glue (TISSEEL, Baxter AG, Vienna, Austria). A limbal lenticule of 2 mm × 2 mm with adjacent conjunctiva was harvested from the healthy fellow donor eye and placed in balanced salt solution. It was cut into 10–12 small pieces using Vannas scissor and placed on hAM with the epithelial side up in a circular fashion around the center of the cornea avoiding the visual axis. The transplants were fixed in place using fibrin glue. A soft bandage contact lens was placed on both the donor and recipient eyes. Thereafter, appropriately sized conformer or symblepharon ring was applied and temporary tarsorrhaphy was done.
Allo simple limbal epithelial transplantation
The procedure was similar to autoSLET except the limbal tissue was harvested from living related donor or from a recently acquired graft of nonoptical quality or the donor corneoscleral rim of a corneal transplant performed on the same day.
Postoperative care and follow-up
Topical preservative-free Moxifloxacin 0.5% was used four times a day till epithelization was completed. Topical preservative-free prednisolone acetate 1% was used four times a day for the first 3 months, and slowly tapered during the next months in autoSLET whereas it was tapered to once daily and continued indefinitely in patients who underwent alloSLET. In addition, in all cases of alloSLET oral prednisone 1–2 mg/kg body weight that was tapered within 6 weeks. Oral cyclosporin 5–10 mg/kg body weight was added when additional immunosuppression required. All patients were followed weekly during the 1st month, monthly for 6 months, then every 3 months.
Outcome measures
The primary outcome measure was defined by stable epithelialized ocular surface, lack of vascularization in the central cornea, decrease in corneal vascularization (extent of reduction in vascularization in clock hours), and forniceal reconstruction of the recipient eye. Secondary outcome measures were improvement in visual acuity and complications.
RESULTS
Thirty-one eyes of 31 patients (20 men and 11 women) underwent SLET surgery (15 autoSLET, 16 alloSLET). The mean age was 35.8 ± 16.8 years. The demographic data from all patients are summarized in Table 1. The most common etiology in patients who undergone SLET was chemical injury (11, 35.5%) followed by Stevens–Johnson syndrome/Toxic Epidermal Necrolysis (SJS/TEN) (9, 29.0%). The most common cause of bilateral LSCD was SJS/TEN. Successful SLET was achieved in 64.5% of all cases. The average visual acuity was found to be 1.7 ± 0.7 logMAR preoperatively which improved to 1.5 ± 0.5 logMAR at 3 months and to 1.2 ± 0.6 logMAR at 6 months respectively (P < 0.05). Corneal clarity was assessed and mean corneal clarity grading was found to be a mean of 1.5 ± 1.1 preoperatively which improved to 2.1 ± 0.8 at 3 months and 2.5 ± 1.3 at 6 months, respectively (P < 0.05). Corneal vascularization was reduced from 9.8 ± 3.6 clock to 1.5 ± 2.1 clock hours at 3 months and 2.4 ± 3.3 clock hours at 6 months follow-up (P < 0.05) [Figure 1]. Out of 31 patients, only 19 patients had symblepharon release and recovered significantly (P < 0.05). None of the donor's eye developed any LSCD defect. Mild chemosis and congestion were were cleared off at the end of 1 week, re-epithelization occurred.
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Figure 1: Outcome of SLET. (a)-Preoperative LSCD, (b)-Day 1 postoperative, (c)-Day 15 postoperative, (d)-3 months postoperative, (e)-6 months postoperative. SLET: Simple limbal epithelial transplantation, LSCD: Limbal stem cell deficiency
Table 1: Various parameters of pre- and post-operative period in patients who underwent simple limbal epithelial transplantation
In postoperative period, we experienced various consequences are summarized in Table 2 and Figure 2. The most common was hemorrhage under hAM found in 14 patients which got resolved with time. Focal vascularization was seen in five patients while 11 patients suffered from complications such as LSC migration, infective keratitis, filamentary keratitis, pyogenic granuloma, persistent epithelial defect and 4 cases of alloSLET had irreversible rejection.
Figure 2: Consequences in postoperative periods of SLET. (a)-Haemorrhage under hAM, (b)-Loss of BCL with LSC migration, (c)-PED, (d)-Viral keratitis, (e)-Pyogenic granuloma, (f)-Rejection with PED. SLET: Simple limbal epithelial transplantation, hAM: Human amniotic membrane, BCL: Bandage contact lens, LSC: Limbal stem cell, PED: Persistant epithelial defect
Table 2: Consequences in postoperative periods of simple limbal epithelial transplantation
DISCUSSION
The ocular surface disorder may result from loss of numbers or function of LSCs or dysfunction of the limbal niche and is referred clinically as LSCD. LSCD occurs in many ocular disorders such as acid and alkali burn, aniridia, SJS, contact lens-induced keratopathy, and ocular cicatricial pemphigoid.[2,3] In LSCD, the conjunctival epithelium migrates across the limbus leading to “conjunctivalization” of the cornea with the appearance of goblet cells and an irregular and unstable epithelium causing the cornea to become opaque thus affecting vision. This is accompanied by inflammation, vascularization, and severe discomfort.[4]
Several techniques have been used for restoring LSCs. Recently in 2012, the novel technique “SLET” has been published by Sangwan et al.[10] that showed direct transplantation of LSC without any ex vivo expansion of stem cells. Since then, many studies have validated the results of SLET [Table 3] and documented success rates ranging from 25% by Mittal et al.[11] to 83.8% by Basu et al.[12]
Table 3: Comparison of simple limbal epithelial transplantation done in various study
This study aimed to analyze the outcome of SLET in LSCD. Thirty-one SLET was performed for different etiology, the most common being chemical injury (35.5%). Male patients have outnumbered female patients which is similar with other studies also. The majority of earlier documented studies showed the outcomes of autoSLET only, however, in this study, 16 patients had bilateral disease requiring alloSLET. Hence, we could see the efficacy of SLET in both unilateral LSCD as well as bilateral LSCD using auto allogenic donor tissue from a living relative.
In our study, successful outcome was 64.5% which is low as compared to previously documentation of 83.8% by Basu et al.[12] and 70% by Gupta et al.[13] This was probably due to the inclusion of both autoSLET and alloSLET and only 6 months' follow-up were done. Illiteracy, ignorance, and poor compliance can be other factors affecting outcome.
The median duration of follow-up was 6 months which is comparable to other studies. No intraoperative consequences were seen. Early consequences like hemorrhage under hAM were seen in 14 patients. In the postoperative period, the most common consequence was focal vascularization indicating the need of an intense immunosuppressant.
CONCLUSION
Ocular surface restoration with the SLET method was found safe and effective. SLET is a simple, useful surgery to restore LSC and it does not require any specialized center and can be done in a center with limited resources.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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