The Efficacy of Sutureless Amnion Membrane Transplantation for Corneal Epithelialization in Delayed Corneal Healing: A Systematic Review

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Abstract

Materials and Methods

A comprehensive systematic literature search was done via PubMed, Cochrane Library, Embase, ProQuest, and a secondary search through reference lists to identify relevant articles published up to June 1, 2024. The keywords were developed based on the PICOS (population, intervention, comparison, study design) framework (Table 1).

Table 1

PICOS framework

Based on the PICOS framework of the study, systematic literature searching encompassed a comprehensive set of primary keywords and their related terms. These terms included ocular surface disease, sutureless AMT, and corneal epithelialization. The specifics of the search terms utilized in each database are outlined in Table 2. Furthermore, reference lists from each study were carefully examined to identify potentially relevant articles.

Table 2

Search terms in each database

This study adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines [17]. Each study included in the review was assessed according to the 2011 Levels of Evidence by the Oxford Centre of Evidence-Based Medicine (Table 3) [18]. A study was included if it met the following criteria: (1) samples with delayed corneal healing disorders (includes persistent epithelial defect (PED), recalcitrant keratitis or corneal ulcer, corneal thinning or perforation, moderate to severe dry eyes with signs of ocular surface inflammation, chemical burn ocular injury, and other); (2) observe corneal epithelialization as one of the outcomes; and (3) AMT without suture fixation. Studies with sutureless AMT using cyanoacrylate or fibrin glue were excluded from this review.

Table 3

2011 Levels of Evidence by the Oxford Centre of Evidence-Based Medicine

Results

Using the search method, we identified 72 articles for inclusion in this systematic and meta-analysis study. A total of 14 studies met the inclusion and exclusion criteria (Fig. 1 and Table 4) [4,7,19–30]. The studies were published from the year 2012 until 2023. A total of 517 eyes (454 patients) were included in the studies, with the average age of 56.4 ± 7.6 years. These studies evaluated the efficacy and safety of sutureless AMT for treating delayed corneal healing, such as PED (three studies, 21.4%) [7,28,29], moderate to severe dry eye disease (DED; two studies, 14.3%) [26,27], chemical eye injury (two studies, 14.3%) [19,21], corneal ulcer (two studies, 14.3%) [4,22], herpetic epithelial keratitis (one study, 7.1%) [23], Sjögren syndrome (one study, 7.1%) [30], Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN; one study, 7.1%) [25], and unspecified ocular surface diseases (two studies, 14.3%) [20,24]. Average follow-up durations ranged from 1 to 50 months. These studies reported improvements in visual acuity, corneal epithelialization, symptoms improvement, and complications following sutureless AMT.

Fig. 1

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) flowchart of the studies selection process.

Table 4

Study characteristics

One randomized clinical trial was done by Liang et al. [19] comparing sutureless AMT fixed with modifiable polymethyl methacrylate (PMMA) symblepharon ring with control group using conventional sutured AMT method. A study by Suri et al. [20] reviewed six articles evaluating self-retained cryopreserved AM (S-CAM; Prokera, Bio-Tissue) in various ocular surface diseases. Eleven studies were retrospective observational studies [4,7,22–30] and one was prospective observational study [21].

Overall, complete epithelialization occurred in 64.4% of eyes. Good efficacy, determined by more than 80% had complete corneal epithelialization, was observed in SJS/TEN (100%), herpetic epithelial keratitis (100%), DED (91.1%), corneal ulcer (84.0%), and Sjögren syndrome (83.3%). Whereas unsatisfactory results were obtained in the chemical injury group (64.5%) and the PED group (47.2%). Based on the diagnosis, PED and DED groups had the largest sample size (238 and 112 eyes, respectively), followed by chemical eye injury, corneal ulcer, SJS/TEN, and herpetic epithelial keratitis groups. In the chemical injury group, complete epithelialization occurred in 92.3% with grades I to II and only in 10.0% with grades III to IV (Roper-Hall classification) after 1 month of observation [19,21]. According to a study by Sell et al. [7] in PED eyes, risk factors of complete epithelialization failures were neurotrophic keratopathy (67.7%), lagophthalmos/eyelid malposition (26.8%), and limbal stem cell deficiency (LSCD; 20.0%).

From the 14 studies, the most common sutureless AMT type was S-CAM (eight studies, 57.1%) [4,7,20,23,24,26,27,30]. Based on the type of sutureless AM device, S-CAM group (306 eyes) had the largest sample size, followed by AM with BCL (146 eyes) and modified symblepharon ring (65 eyes). The highest to lowest successful outcomes were reported as follows: modified symblepharon ring (81.4%), S-CAM (65.7%), and AM with BCL (54.8%).

The complications recorded overall were sterile infiltrate in nine eyes (1.8%), corneal perforation in three eyes (0.6%), worsened epithelial defect due to ring trauma in two eyes (0.4%), and central corneal scarring in one eye (0.2%). The most frequent adverse effects overall were pain (15 of 517 eyes, 2.9%), displaced AM or lost ring (9 of 517 eyes, 1.7%). According to each group, the most common adverse effect was pain.

Discussion

AM has been utilized in ophthalmology since the early 1990s, to address various corneal epithelial defects. These include PED due to LSCD, corneal ulcers, chemical burns, and others [20]. AM plays an important role in promoting corneal re-epithelialization, reducing inflammation and fibrosis, preventing structural damage, inhibiting vascularization, and reducing scar [19,20]. AM consists of five layers: an epithelial monolayer supported by a basement membrane, an extracellular matrix stromal layer consisting of an acellular compact layer and sparsely populated fibroblast layer. Underneath it, a spongy layer acts as the interface between the fibroblastic layer of the amnion and the reticular layer of the chorion [10].

The effectiveness of AM in ocular surface reconstruction can be attributed to several key properties. Firstly, it has a mechanical function that supports the growth of epithelial cells on the ocular surface. Structural proteins, such as laminin, fibronectin, and collagens in the amnion extracellular matrix and basement membrane act as a scaffold in which cells can interact to promote epithelial regeneration [22]. Secondly, the application of AM stromal matrix upregulates matrix metalloproteinases which reduces the proliferation of corneal, limbal, and conjunctival fibroblasts, inducing an antifibrotic effect. Third, AM expresses anti-inflammatory and regulatory mediators that could remove infiltrating inflammatory cells. Additionally, AM also has antibacterial and antiviral properties. AM stimulates epithelialization by producing growth factors, such as epithelial growth factor, hepatocyte growth factor, and keratinocyte growth factor [31]. Collagen composition of AM basement membrane resembles that of conjunctiva and cornea, therefore allowing the epithelial cells to easily replicate. AM also reinforces the adhesion of basal epithelial cells, promotes cell differentiation, and prevents epithelial cell apoptosis [10].

AM may be used temporarily or permanently. As a temporary patch, AM is used like a “biological bandage” with onlay technique. The tissue underneath the membrane is given an opportunity to heal, and subsequently the membrane becomes detached from the surface of the cornea. As a permanent graft, AM is used with inlay technique. The neighboring epithelial cells migrate over top of the AM, rather than underneath it and the AM then becomes part of the subepithelial substrate. There is also a combination of both techniques, the sandwich technique, which is used mainly if the ocular surface has deep and extensive corneal defect [32,33]. The main purpose of the onlay is to protect the inlay and promote its epithelialization. Sutured AM enables more options of AM applications techniques, while the sutureless AM may limit some of these purposes. Sutured AM method can be used for applying single-layered or multilayered AM graft [34].

The use of sutured AMT can be advantageous in ocular disease cases which need the benefit of suturing against the sutureless AMT. In cases which require longer usage and wider coverage of ocular surface, such as severe LSCD and PED, sutured AMT may be favorable as they provide firmer attachment and stable fixation to the corneal surface [11,19]. It is important for the AM graft to be kept still and not easily dislodged by eyelid movement as this might affect the degradation rate of the graft. [11]. Moreover, sutured AMT can promote the migration of the epithelium over the top of the AM and minimize free potential space between the graft and ocular surface, therefore decrease the chance for foreign bodies to accumulate underneath the graft and achieve optimal ocular surface environment to heal [33].

Even though, corneal sutures may take longer surgery duration, induce postoperative pain and discomfort, and increase the risk of suture-associated complications, such as infections, suture abscess, granuloma formation, or tissue necrosis. The inflammatory effect of corneal suture can lead to unsuccessful attempt at repairing, especially if the corneal damage is caused by inflammatory disease. These suture-related complications can be minimized with the use of fewer stitches and larger pieces of AM (a single 5 × 10 cm compared to multiple 3.5- or 5-cm square pieces) as described in a study of patients with SJS/TEN by Ma et al. [35]. The study shows that patient with the aforementioned technique had fewer postsyndromic ocular complications, reduced surgical time, decreased intraoperative bleeding, reduced costs, and longer AM dissolution. Another study which included patients with severe ocular surface disease has introduced a suturing technique modification of continuous blanket sutures in order to decreased suture-related complications, minimized surgery-induced astigmatism, and give better aesthetics appearance compared to traditional interrupted or continuous sutures [36]. More recent study has showed an octagonal modified continuous suturing technique which has the same advantage of fewer sutures as the study mentioned before [34]. To avoid sutured AM complications, decrease surgical time, and reduce potential postoperative pain, sutureless method have been developed [19].

Complete epithelialization was observed to be most effective in patients with herpetic epithelial keratitis (100%), SJS/TEN (100%), DED (91.1%), corneal ulcers (84.0%), and Sjögren syndrome (83.3%). One study which observed herpetic epithelial keratitis included only four patients [23]. Herpetic epithelial keratitis is caused by herpes simplex virus type 1. This virus can continue replicating in cells or it can enter latency, by traveling to trigeminal ganglion by way of corneal nerves. Corneal sensation diminished in the affected eye due to associated decline in sub-basal corneal nerves. Disruption in corneal sensation and diminished corneal nerves induces neurotrophic keratopathy, which can result in PED [37]. In the study by Cheng et al. [23], CAM was used as it can be placed in-office to avoid treatment delay, reduce suture-induced inflammation, and the risk of surgical complication. Its efficacy in herpetic epithelial keratitis may be due to CAM properties: (1) nonspecific antiviral immunity of the placenta; (2) anti-inflammatory action to activated neutrophils, macrophages, and lymphocytes; (3) reduced production of proinflammatory cytokines and chemicals (interleukin 12 [IL-12], tumor necrosis factor α [TNF-α], nitric oxide synthase, interferon γ [IFN-γ], IL-2); and (4) nerve growth factor to promote nerve regeneration [38–41]. This in conjunction with oral acyclovir may accelerate restoration of normal corneal epithelium to reduce the potential adverse event from topical corticosteroid or other immunosuppressive treatment [23]. Another study by Brijacak et al. [42] observed 18 eyes with epithelial defect or corneal ulcer due to herpetic keratitis which did not respond well with conventional treatment (acyclovir oral or ointment). After underwent sutured AMT, complete epithelialization was shown in 16 of 18 eyes (89.0%) in 16.4 days (range, 10–30 days). These studies demonstrated the advantages of AM properties in healing epithelial defects due to herpetic keratitis, resulting in favorable outcomes both with and without the use of sutures.

Studies including SJS/TEN population in this review shows successful outcome of corneal epithelialization (20 of 20 eyes, 100%) following AMT in acute stage [25]. The acute stage of SJS/TEN, which is the first 2 weeks after onset, is thought to be a T-cell mediated type IV hypersensitivity reaction, in which causes intense immune dysregulation with extensive keratinocyte apoptosis [43]. In this stage, mucous membranes of the whole body are disrupted, including the eye. The inflammation in the conjunctiva or cornea tends to be relentless and prolonged. It may further destroy corneal epithelial stem cells at the limbus, leading to LSCD [44]. Corneal epithelial defect indicates severe grade of ocular involvement in acute stage of SJS/TEN [45]. Conventional treatments may consist of lubrications, antibiotics, steroids, cyclosporine, and periodic release of symblepharons [44]. AMT is another approach in the early stages of SJS/TEN to suppress inflammation, prevent ulcer formation, and promote healing. AM has the potential to reduce inflammation and scarring, as well as to promote growth of limbal epithelial stem cells. Innate immunity is suppressed by AM through trapping mononuclear and polymorphonuclear granulocytes within its stromal matrix and inducing them to undergo rapid apoptosis. Acquired immunity is modulated by suppressing reactive immune responses and down regulating inflammatory cytokines production. AM also secretes anti-inflammatory cytokines to reduce scarring [46].

DED is associated with ocular surface inflammation with upregulation of proinflammatory cytokines, such as IL-1β, IL-6, IL-8, TNF-α, IFN-γ, and metalloproteinases. Therapeutic effect of S-CAM can be attributed to multiple mechanisms of action. First, it acts as a bandage to keep the eye moist. Second, it controls ocular surface inflammation with its anti-inflammatory properties. Third, it regenerates the corneal nerves [26]. In addition, S-CAM, in which contains polycarbonate ring, stimulates more blinking that helps achieving balanced and consistent tear distribution [27].

Successful outcome was good in patients with corneal ulcer (84.0%), in which two studies were included. The study by Meduri et al. [22] observed 12 eyes with severe corneal thinning, descemetocele, or perforation due to underlying disease of SJS or ocular cicatricial pemphigoid. Patients with corneal infectious diseases were excluded. The study by Brocks et al. [4] observed 13 eyes (13 patients) with nonhealing corneal ulcers despite prior conservative treatment with artificial tears, antibiotics or antivirals, ointments, steroids, nonsteroidal anti-inflammatory drugs, BCL, and mydriatics. Ulcers were located centrally (54%), peripherally (23%), or both (23%). The underlying diseases were mostly neurotrophic keratitis (69%) caused by acoustic neuroma removal (one eye), lagophthalmos (three eyes), herpetic infection (three eyes), and advanced diabetes mellitus (two eyes). Other etiologies were autoimmune disease (15%), chemical burn (8%), and dry eye (8%). In the study, corneal ulcers were mostly caused by noninfectious etiologies. A previous study done by Casalita et al. [47] showed good results of sutured AM in patients with infectious corneal ulcers. The successful outcome rate was higher in bacteria etiology (100%) and Acanthamoeba (100%), than in fungal (50%). Complete healing was achieved in ulcers with no perforation (92%), perforation <1 to 5 mm (86%), or perforation >1 to 5 mm (80%).

In patients with chemical injuries and PED, the outcomes of corneal epithelialization were less favorable, with rates of 64.5% and 48.3%, respectively. In studies with moderate to severe ocular chemical injury, corneal defect accompanied with disruption of palpebral fissure, entropion, and trichiasis, which make the AM easily dry and rupture. The study by Liang et al. [19] showed that the sutureless AM had higher rate of complete epithelial closure rate and shorter time to epithelial closure than the sutured AM in treating acute ocular burn grade III to V (Dua classification criteria). However, patients with grade VI had poor prognosis when treated with any AM [48]. The type of chemical affects the prognosis. Almost all patients with alcohol (100%) and acidic (75%) chemical injury attained best-corrected visual acuity of >20/60, while only 14% did in the alkali group. According to Lotfy et al. [21], there was statistically significant difference of complete corneal healing between eyes with Roper-Hall classification grades I to II and grades III to IV (p = 0.01). The lower grade of chemical burn gains more benefit from AM than in eyes with more severe injury. The use of dehydrated AM with BCL was not effective in restoring ocular surface integrity in eyes with Roper-Hall classification grade IV chemical injury.

Studies involving PED patients mostly used dehydrated AM as the sutureless AM method [7,28,29]. For PEDs that did not resolve, surgical intervention was often necessary, including tarsorrhaphy alone or in combination with other procedures. These surgeries aimed to address the underlying causes of PED, such as ethylenediaminetetraacetic acid for band keratopathy, or ocular surface stem cell transplantation for LSCD. Increased sutureless AM failure was noted in patients with two or more risk factors. These risk factors included LSCD, neurotrophic keratopathy, floppy eyelids, lagophthalmos/malposition of the eyelid, focal corneal thinning, underlying band keratopathy, or inflammatory disease state requiring systemic/topical immunosuppression for treatment (rheumatoid arthritis, graft-versus-host disease, SJS, scleritis, and uveitis) [7].

There are various forms of sutureless AMT devices, such as modified symblepharon ring, S-CAM, and sutureless AM graft mounted with BCL. Modified symblepharon ring has the best outcome of complete corneal epithelialization (81.4%), including modified PMMA ring and modified nasogastric tube ring [19,25]. Modified PMMA symblepharon ring is an annular device with a gap in the inferior part which benefits oxygen exchanging, drug delivery, and prevent from running off. The inferior gap also helps to observe the healing process of the ocular surface and drains fluid from under the AM to maintain compact attachment between the AM and the ocular surface [19]. Whereas, the other study used pediatric nasogastric tube (8F, Bicakcilar) as a ring on the eyelids over the superior and inferior orbital rims, approximately 8 to 9 cm. Then, the tube is cut 1 cm longer than the approximate length with one blunt end and one oblique end. The oblique end fitted into the blunt end to form a ring. These rings can extend to the conjunctival fornices and tarsi, which enlarged the AM coverage area. This feature is favorable in chronic inflammatory cases, such as chemical injury and SJS/TEN. This method of AM application can lower the occurrence of symblepharon, in addition to promote corneal healing. Modified nasogastric tube symblepharon ring may also be a fast and inexpensive option for sutureless AMT [25]. Symblepharon occurrence difference using modified PMMA ring (14 of 39 eyes, 38.46%) and sutured AM (22 of 36 eyes, 61.11%) was statistically significant (p < 0.05) in the study by Liang et al. [19].

Prokera is a S-CAM, clipped to a dual polycarbonate ring system. In cryopreservation, the AM is placed in a storage medium containing cryoprotectants and frozen to −80 °C. This method is thought to inhibit proinflammatory cells, suppress T-cell activation, and inhibit giant cell formation [49–51]. It preserves extracellular matrix, including proteoglycans and growth factors, collagens, fibronectin, and laminin that play an important role in tissue regeneration and healing. It acts as a biological bandage, with the stromal side in contact with the cornea. The ring is similar to a symblepharon ring with an inner diameter of 16 mm and outer diameter of 21 mm [7].

The advantages of S-CAM Prokera compared to sutured AM are easier application, less time-consuming, can be performed in the clinic, and well-tolerated by patients [20]. Disadvantages of this device may result from poor apposition to ocular surface in cases with lower eyelid ectropion, that required a sutured AMT with tarsorrhaphy. Prokera may also cover a limited area of the perilimbal conjunctiva and does not cover the palpebral conjunctiva, thus does not prevent cicatrizing complications, such as entropion and trichiasis. Whereas sutured AM can cover entire bulbar and palpebral surfaces. Another method of sutureless AM is dehydrated AM which is secured with separate BCL. Dehydration preservation methods involve air or heat to remove the moisture and dehydrate the AM tissue, followed by gamma irradiation to sterilize the tissue. Dehydrated AM may lose parts of the extracellular matrix and certain biological components. Dehydrated AM can be stored at room temperature and only requires a small droplet of balanced salt solution to be rehydrated before application. In contrast, CAM must be stored in the frozen state which is more expensive during transportation. Omnigen (NuVision Biotherapies), a vacuum-dehydrated AM, has a diameter of 16 mm and is secured with BCL Omnilenz (NuVision Biotherapies). Dehydrated AM can be placed with ease in the office along with BCL to cover the AM, thus protecting the AM from mechanical effects of the eyelids. Suri et al. [20] reported that 17.1% of the patients reported discomfort from using Prokera, whereas Mimouni et al. [28] reported 89% of the eyes achieved resolution of PEDs with none of the patients experienced discomfort from the AM graft secured with BCL.

The use of a separate BCL to retain AM graft on the ocular surface may lead to better patient comfort than using a conformer ring. In this review, pain was recorded in 3.5% of patients with the AM with BCL group, similar to 3.4% in the Prokera group. Although Liang et al. [19] did not report the frequency of pain felt by the patient using modified symblepharon ring, the disadvantages of separate BCL to retain AM graft include possibility of AM displacement under the separate BCL [20].

This systematic review of studies on sutureless AM treatment reveals several limitations. One significant issue is the variability in sample sizes across the studies, which ranged from 4 to 220 eyes. Such discrepancies can have a profound impact on the reliability and generalization of the results. For instance, while the herpetic epithelial keratitis group reported an outcome of 100% complete epithelialization, this finding was based on a very small sample of only four eyes. This limited sample size raises concerns about the conclusions drawn.

Another significant limitation of this review is the lack of randomized controlled trials comparing sutured and sutureless AMT. There was only one randomized controlled trial available in the chemical injury group, which restricts the ability to draw robust conclusions. These limitations underscore the need for more comprehensive studies to better understand the efficacy and safety of sutureless AMT for various delayed corneal healing disorders.

Moreover, the outcomes reported in the studies were not entirely available, such as AM application duration, time to AM dissolution, and time to complete epithelialization. This may affect the applicability of the review. Complete data would provide a more comprehensive understanding and allow a definitive conclusion regarding its efficacy and safety in treating various delayed corneal healing disorders. Therefore, future research with more detailed outcome, comparing sutureless AMT with sutured method as the control group, may be needed to better inform the efficacy and safety of sutureless AM graft.

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