Femtosecond laser-assisted corneal transplantation

Abstract

Corneal transplantation is the only surgical option to improve symptoms and vision in patients with severe corneal opacification. With the evolution and development of keratoplasty techniques, corneal surgeons can perform customized keratoplasty, with complex graft–host junctions to promote wound healing and accelerate visual rehabilitation. Femtosecond laser (FSL) enable customization of the thickness and shape of the graft has been used for trephination of both donor and recipient corneas and for creating special wound configurations. In this review, we have summarized the intraoperative application and postoperative outcomes of FSL-assisted keratoplasties, including penetrating keratoplasty, anterior lamellar keratoplasty (ALK), deep ALK, Descemet stripping automated endothelial keratoplasty (EK), and Descemet membrane EK. Although FSL allows for the customization and precision in keratoplasty, several concerns, such as cost-effectiveness, limit its wider clinical adoption. Hence, more work is required to weigh the advantages and limitations of the FSL applications in corneal transplantation.

Introduction

Corneal transplantation is one of the most effective procedures to improve poor vision due to corneal opacification, resulting from corneal pathologies such as infections, trauma, or degenerative diseases,[1] with an estimated 185,000 procedures performed globally each year.[2] Corneal transplantation includes penetrating keratoplasty (PK), anterior lamellar keratoplasty (ALK), deep ALK (DALK), Descemet stripping automated endothelial keratoplasty (DSAEK), and Descemet membrane endothelial keratoplasty (DMEK). In PK, the full-thickness cornea is removed and replaced with a healthy donor, while in ALK, DALK, DSAEK, and DMEK, the diseased corneal layers are replaced by the graft and the healthy corneal tissue is preserved.

The emergence of femtosecond laser (FSL), which produces photodisruption, with near-infrared light, to emit many adjacent pulses to cut tissue, with minimal damage to collateral tissues,[3] has allowed great advances in ocular surgery. FSLs were first used to create corneal flaps, for laser in situ keratomileusis (LASIK), for the correction of refractive errors.[4] It has subsequently been used for lens capsulotomy and fragmentation in cataract surgery,[5] the creation of conjunctival grafts[6] in pterygium surgery,[7,8] as well as various types of corneal transplantation.[9]

In FSL-assisted keratoplasty, the FSL attempts to achieve a precise corneal trephination of both recipient and donor, as well as the desired wound configurations owing to its ability to create precise vertical, horizontal, and oblique cuts in the cornea.[10] Compared to manual techniques, FSL may provide more accurate corneal cutting and more complex corneal wound profiles, improving the safety, accuracy, and refractive status as well as leading to faster and better visual and tectonic outcomes in the early postoperative period (up to 6 months).[11-13] In addition, FSLs have been shown to precisely trephine the host and donor corneas in DALK and DSAEK.[14,15] It provides a precise and reproducible plane of dissection at the desired depth in corneal stroma.[16] These may lead to faster and better visual rehabilitation. However, the FSL cannot penetrate opaque tissue, and deep lamellar cutting may result in irregular surfaces due to poor penetration.[17]

In this review, we will discuss the application of FSL in assisting PK, DALK, hemi-automated lamellar keratoplasty (HALK), DSAEK, and DMEK. We summarize the results of intraoperative trephination of the recipient and donor corneas for the creation of particular wound configurations, postoperative visual and refractive outcomes, wound healing, graft rejection or failure, as well as comparison with conventional surgery.

Femtosecond Laser-assisted Penetrating Keratoplasty

Numerous experimental and clinical trials have demonstrated the advantages of FSL-assisted PK over conventional PK.[18-20] The customized incisions created by FSL have increased surface area and interlocking surfaces, which theoretically provide improved donor–recipient alignment and faster wound healing, as well as reduced wound leakage in certain configuration.[21] Buratto and Böhm reported that FSL-assisted PK provided a better donor–recipient apposition, earlier suture removal, and a faster visual recovery with low degrees of astigmatism in the early period postoperatively.[9] However, no significant difference was observed in the visual outcomes between FSL-assisted and conventional PK after the 6-month postoperative follow-up period.[2,13] The induction of less astigmatism may be due to the geometry of the donor–recipient matching being more physiological and requiring less tight sutures.[12] Compared to manual suction trephine, it has been shown that there is less intraocular pressure (IOP) variation and less damage to endothelial cells during FSL trephination.[22] A technique combining an FSL anvil-like trephination pattern with the laser welding procedure was effective for performing FSL-assisted PK. The large donor–recipient interface provided by the anvil-profiled shape might also contribute to good preservation of the recipient’s endothelial cell density.[9,22,23] However, FSL-assisted PK and manual PK seem to be comparable regarding the postoperative spherical equivalent, graft rejection and failure rate, and the incidence of postoperative complications, including wound leakage and graft dehiscence.[24]

The alteration of cutting angulation and accurate reproducibility of FSL allows various customized trephination patterns for performing FSL-assisted PK.[9] There is an increasing number of studies being conducted to develop more ideal cut shapes, such as zig-zag, top-hat, mushroom, and Christmas tree incisions [Figure 1], to enhance the alignment and attachment of the wound for sutureless corneal transplantation.[10] All these wound shapes are biomechanically more stable and create more healing surface area than conventional straight cuts from manual PK.[25,26]

Figure 1.

Schematic diagram of different cutting configurations. From top to bottom: “Zig-zag” incision; “Mushroom” incision; “Top-hat” incision;” Christmas tree” incision

A retrospective review has shown that zig-zag wound configuration created by FSL resulted in a lower manifest and topographical astigmatism, although the graft rejection and failure rates were similar to those of conventional PK.[18] Zig-zag configuration may provide a smooth transition between the donor and the recipient, and the wound strength could be enhanced by this configuration.[27] Faster visual recovery and better visual outcomes have been observed in keratoconus patients who had FSL-assisted PK compared with those who had mechanical PK during the 6-month follow-up postoperatively.[28] In another study evaluating the postoperative visual acuity and astigmatism by three different suture patterns in zig-zag PK, better visual acuity was observed in the running suture group than in simple interrupted and combined sutures groups after full suture removal.[27] Running suture adjustment may play a role in controlling postoperative astigmatism compared to selective interrupted suture removal.

FSL-produced top-hat incision is also feasible. It provides superior incision integrity and greater mechanical stability than manual half-top-hat PK. Trephination can be performed easily and with minimal tissue trauma, achieving good optical results.[29-31] It also results in less endothelial cell loss, faster suture removal, less astigmatism, and better best spectacle-corrected visual acuity, in comparison with the manual top-hat keratoplasty.[32] The FSL-assisted top-hat wound configuration for PK was reported to be the most mechanically stable compared with the traditional method and mushroom, zig-zag, and Christmas tree configurations in a laboratory model.[26] The posterior peripheral flange in the top hat acts as a posterior valve to prevent wound leakage and showed more resistance than other wound configurations. Moreover, the creation of the peripheral flange in top-hat PK enabled the transplantation of more endothelial cells. In addition, top-hat keratoplasty seems to have fewer immunological graft reactions (6.6% in Fuchs’ dystrophy) than mushroom trephination (21.8% in keratoconus) after 14 months.[33] This might be the result of a perfect match between the donor and recipient, which minimized the exposure of the donor tissue antigens to the aqueous humor.[32]

Mushroom keratoplasty combines the refractive advantage of a large keratoplasty with the immunologic advantage of a small keratoplasty. A mushroom-shaped graft is created by FSL with a larger anterior than posterior portion, hence FSL-assisted mushroom keratoplasty may have a mechanical advantage over regular PK.[34] The increased surgical wound area due to the mushroom shape of donor and recipient tissues results in fast healing and improved wound integrity.[35] Compared to conventional PK, FSL mushroom-shaped incision results in less postoperative astigmatism and more endothelial cells preserved in patients with keratoconus, but with similar postoperative best-corrected visual acuity (BCVA).[36,37] The multiplanar fit between the donor and recipient allows early suture removal and visual rehabilitation. The finite element analysis investigating various edge shapes created during PK demonstrated that zig-zag shape had the highest ratios of stresses and minimal dioptric power value, suggesting the best wound healing and the best optical outcomes.[38]

Research on Christmas tree configuration is scarce. One laboratory study on 22 human corneoscleral buttons showed the zig-zag shape and the Christmas tree configuration has no mechanical advantage over the traditional PK after evaluating the wound bursting pressure.[26]

Regardless of the wound configurations, FSL-assisted PK has the disadvantage of deformation of the cornea due to the need for vacuum and flat applanation of the cornea during the cutting process [Figure 2].[39] As keratoconic corneas are less rigid, thinner, and steeper, this might cause oval trephination apertures as well as corneal deformation and shift of the thinnest point during the laser programming.[40,41] In keratoconus eyes, donor and recipient edges may not align perfectly.[39] FSL-assisted keratoplasty with a liquid interface technique seems to be a promising method to reduce the stress on the donor and recipient during trephination, which is a safe procedure and can potentially improve graft alignment.[42] Donner and Schmidinger showed that FSL-assisted PK using a liquid–patient interface decreased stress on donor and recipient tissues and lowered areas of DM folds with a faster time to reach the vacuum in porcine eyes.[43] Our group has also demonstrated that the liquid interface technique induced significantly less IOP rise and variation than a flat interface, with minimal endothelial cell and stromal tissue damage, especially when high laser energy was used, suggesting that a liquid interface was a preferable choice in corneal transplantation.[21] Comparison of intra-ocular pressure changes with liquid or flat applanation interfaces in a femtosecond laser platform (PMID: 26439499).

Figure 2.

Descemet’s folds were observed due to the applanation from the laser handpiece during femtosecond laser-assisted deep anterior lamellar keratoplasty on intraoperative optical coherence tomography images

Femtosecond Laser-assisted Anterior Lamellar Keratoplasty

Over the past two decades, ALK has replaced PK, in the treatment of corneal diseases where the endothelium is not involved. Compared to PK, ALK is an extraocular procedure with the potential for early removal of sutures and discontinuation of topical corticosteroids, which can effectively reduce the risk of endothelial rejection.[44] In eyes with anterior corneal pathology, ALK is the preferred surgical option to replace the anterior layers of the cornea only and preserve healthy corneal tissue of the receipt. FSL-assisted ALK has been shown to improve uncorrected distance visual acuity (UCVA) and BCVA,[45,46] when FSLs were used for both donor and recipient dissections. A clinical study including 19 eyes with FSL-assisted ALK for the treatment of superficial corneal opacities demonstrated that the quality of vision improved and the visual outcomes remained stable during the 1-year follow-up, indicating that FSL-assisted ALK was a safe and efficient procedure.[47]

Yoo et al. used a sutureless technique in FSL-assisted ALK. This was made possible by the precise cutting of the donor and recipient corneas using a FSL, which allowed close apposition of the graft and recipient bed and improved UCVA and BCVA after surgery.[46] Long-term results showed that FSL-assisted sutureless ALK remains stable for 72 months postoperatively.[48] Instead of creating a horizontal lamellar bed interface in donor and recipient corneas during sutureless anterior lamellar keratoplasty, Sharma et al. reported a modified technique to obtain better apposition and healing, in which the side-cut angle of donor and recipient was modified to 45°, so that the margins of the donor can be tucked in under the recipient bed.[50]

HALK is a specific form of ALK, performed in patients with irregular anterior surfaces, and thin or eccentrically steep cornea, especially for patients with anterior-mid corneal scars because of previous keratitis or corneal dystrophy.[51] In manual HALK, the recipient bed lamellar is dissected manually, and the donor is prepared using a microkeratome.[52] HALK provides good visual outcomes and graft survival in short and long-term follow-ups.[51] The main advantage of FSL-assisted HALK is the ability to evenly remove the anterior stromal pathology and to customize the size and thickness of the donor graft for optimal optical and postoperative outcomes.[51,52] FSL-assisted HALK has shown high accuracy at the depth of trephination in the side cuts, which has contributed to achieving a dissection plane below the stromal pathology [Figure 3]. However, the FSL can only be used in cases where there is no dense scar tissue or the transparency of the cornea is reduced due to the limited penetration.[53] A modification of FSL-assisted ALK, in patients with dense corneal scars, is to avoid the creation of a lamellar cut, where there may be incomplete penetration of the laser due to the scar, and instead to perform a ring cut around the scar [Figure 4]. This will enable accurate depth precision of the lamellar dissection, and the remaining uncut area is removed with a sharp crescent technique in the usual manner.

Figure 3.

A patient with granular type II (Avellino) corneal dystrophy underwent femtosecond laser-hemi-automated lamellar keratoplasty (FSL-HALK). Preoperative slit-lamp photo showing linear lattice deposits and granular deposits in stroma (a). Preoperative anterior segment optical coherence tomography (OCT) image showing hyperreflective deposits in stroma (b). Intraoperative OCT images during FSL-HALK showing the lamellar dissection plane below the deposits (c)

Figure 4.

A patient with a corneal scar in the central cornea underwent femtosecond laser-anterior lamellar keratoplasty. Instead of cutting a complete lamellar cut, where there may be incomplete penetration, a ring cut around the scar was used. This allows an accurate depth precision of the lamellar dissection, and the remaining uncut area is removed with a manual technique

Femtosecond Laser-assisted Deep Anterior Lamellar Keratoplasty

DALK is one form of ALK in which the majority of the stroma of the cornea is removed with sparing of the posterior corneal layers, including Descemet membrane (DM) and endothelium. One retrospective review reported that FSL-assisted DALK provided faster visual rehabilitation and improved visual outcomes and emmetropization of the manifest refraction.[54] Compared to manual trephine-assisted DALK, FSL-assisted DALK has shown comparable visual and refractive outcomes but more pronounced corneal wound healing responses at the side cut [Figure 5]. This activated cornea wound healing may allow for earlier removal of sutures in FSL-assisted DALK.[55] In patients with advanced keratoconus, the accurate control of the diameter and depth of side cuts in FSL-assisted DALK accelerates epithelial healing and visual acuity rehabilitation after surgery, compared with vacuum trephine-assisted DALK.[56]

Figure 5.

A patient with keratoconus underwent femtosecond laser (FSL)-assisted deep anterior lamellar keratoplasty (DALK). Preoperative Pentacam images demonstrating corneal steepening, posterior elevation and thinning (a). Intraoperative optical coherence tomography images during FSL-assisted DALK showing the programmed lamellar cut (yellow line), vertical trephination (green lines) and intrastromal tunnel creation (purple line) (b). Slit-lamp photo at 8 months postoperatively showing clear cornea and no signs of wound dehiscence (c)

Analysis of a retrospective interventional case series has reported that intraoperative DM perforation occurred in 25.9% of FSL-assisted DALK cases, compared to 45.4% of manual DALK cases. Intraoperative conversion to PK was seen in 3.4% of FSL-assisted DALK cases, as compared to 24.5% of manual DALK cases.[14] In patients with keratoconus, the preparation of the host using a FSL may decrease the risk of intraoperative DM perforation [Figure 6]. Overall, FSL-assisted DALK has reduced the frequency of DM ruptures and improved the short- and long-term outcomes with respect to postoperative astigmatism, earlier suture removal, increased wound strength, and healing, compared to manual techniques.[57]

Figure 6.

A patient with keratoconus underwent femtosecond laser (FSL)-assisted mushroom deep anterior lamellar keratoplasty (DALK). Preoperative Pentacam images demonstrating corneal inferior steepening and posterior elevation (a). Intraoperative optical coherence tomography (OCT) images showing the preset lamellar cut (yellow line), intrastromal tunnel (purple line), and vertical trephination (green lines) with mushroom configuration on the patient (b). Slit-lamp photo at 1 month after FSL-assisted DALK showing the good wound alignment at the graft–host junction (c). Anterior segment OCT image at postoperative 1 month showing the Mushroom shaped configuration (d)

With the use of the FSL-assisted incisional configuration, the advantages of stepped corneal wounds, found in PK, can be extended to DALK.[58] Zig-zag incisions created by FSL may provide an interlocking wound configuration facilitating accurate apposition and greater surface area for healing in DALK.[59] Compared to conventional DALK with big bubble (BB) technique, the use of the zig-zag incision can accurately show the depth of air needle in the posterior stroma, as the lamellar ring cut and posterior side cut allow the surgeon to know the exact depth of the needle insertion, thereby reducing the risk of DM perforation.[60] The angled anterior donor and recipient junctions allow a smooth transition for the improvement of visual outcomes. Even if the DM is perforated, it can be easily converted to a full-thickness zigzag PK, preserving the advantage of wound seal. A series of 7 eyes has demonstrated that the use of the FSL to perform a mushroom-shaped incision is feasible in DALK for patients with keratoconus, corneal ectasia, or scarring.[58] Compared to manual trephination, earlier recovery of the vision was achieved with mushroom configuration, although there was no significant difference in the mean BCVA at 6 months and 1 year postoperatively.[61] Using a decagonal trephination profile on both donor and recipient corneas for FSL-assisted DALK has also shown good visual and refractive outcomes.[62] An advantage of a decagonal incision is to avoid the rotation or decentration of the circular cut, resulting in a stable matching of the graft and recipient. If the dissection of deep stroma fails and there is a need to convert to PKP, the benefits of the FSL incision are retained.[60]

In DALK, the separation of deep corneal stroma from DM is achieved by the creation of a BB technique. The FSL could standardize the BB technique in DALK by presetting the depth, length, and angulation of the intrastromal tunnel, minimizing the risk of intraoperative complications and reducing the learning curve for surgeons.[19,63-65] Compared with manual intrastromal tunnel creation, the rate of successful BB formation was higher, and the surgery time was shorter in the tunnel created by FSL.[66,67] A case series of intrastromal tunnel created by FSL with the depth set at 80% of the cornea showed that all eyes were successfully pneumatically dissected and formed type 1 BB without DM perforation or conversion to PK.[65] These studies demonstrated that FSL provided a safe and repeatable method of creating an intracorneal channel at specific depths, and could be used as a guide for the insertion of the DALK cannula.[68] Our previous study has also demonstrated the safety and effectiveness of the creation of BB with an optical coherence tomography (OCT)-integrated FSL system. An OCT-integrated FSL system allowed visualization of the location and depth of the tunnel predetermined, to precisely and safely assist in injecting the air toward the DM to form BB. This was particularly advantageous in keratoconus patients, where thin and ecstatic areas can be avoided.[41]

Femtosecond Laser-assisted Endothelial Keratoplasty

Endothelial keratoplasty (EK) is becoming increasingly popular as a treatment for endothelial diseases such as Fuchs’ dystrophy and bullous keratopathy. EK, including DSAEK and DMEK, greatly reduces the risk of postoperative rejection and complications compared to PK.[69,70] However, the development of EK is limited due to the operation being challenging and long learning curve for ophthalmologists.[71] Furthermore, limitations of the microkeratome in conventional EK are inevitable, including poor depth adjustments and thickness reproducibility of grafts.[15] FSL-assisted EK (FSL-EK) effectively reduces postoperative astigmatism and wound healing-related problems, by creating a standardized stromal interface in the donor corneas.[72]

Femtosecond Laser-assisted Descemet Stripping Automated Endothelial Keratoplasty

The thickness of graft in conventional DSAEK is about 150–250 um, and the DSAEK graft regularity and thickness are related to postoperative HOAs that would limit visual rehabilitation.[73] Some studies have shown that the microkeratome lamellar dissection provided smoother interfaces compared with FSL in donor tissue preparation.[74,75] To optimize the interface quality, some investigators proposed that double-pass ablation of the bed using FSL significantly improved the smoothness of the interface and the ease of donor lenticule peeling and removal.[76,77] The first clinical results of the application of combined FSL and microkeratome-assisted DSAEK have shown that this new technique is consistently able to obtain very thin and smooth grafts (<100 mm), excellent visual outcomes, and good endothelial cell counts with good reproducibility. The DSAEK grafts were prepared by two successive cuts: the first, of variable thickness, was made with FSL and the second with a 300 mm microkeratome head. This procedure not only avoids the variability of a double microkeratome cut but also reduces the risk of a rough stromal bed and endothelial damage caused by a double FSL cut.[78]

Trinh et al. compared the interface quality of the endothelial graft prepared by four different techniques: mechanical microkeratotomy, a single pass with FSL, a double FSL lamellar cut, and combined FSL lamellar dissection with excimer laser surface photoablation, a procedure named femtosecond and excimer laser-assisted endothelial keratoplasty (FELEK). The results showed that FELEK was the most efficient method to obtain a thin and smooth endothelial graft with a high level of safety and accuracy, which has refined the limitations observed in DSAEK.[79]

In addition to the applanation with the laser lens, the laser energy itself may cause tissue damage, leading to 3%–9% additional endothelial cell loss.[80] Corneal endothelial damage was likely to increase using a 150-kHz FSL when the remaining depth was <70 μm. When the remaining depth was <100 μm, peeling off the anterior stroma could also damage corneal endothelial cells.[81] However, endothelial cell loss remained relatively stable up to 12 months after FSL-assisted ultrathin DSAEK, in a large case series of 120 patients.[81] No correlation between cell loss and corneal graft thickness has been observed, indicating corneal graft preparation by the FSL was safe.[82] In order to minimize the endothelial cell loss, one group modified the technique with FSL cutting the side cuts but then manually dissecting an endothelial graft. The authors found that 98% of the grafts survived at 24 months, and this approach might be considered a feasible choice in patients with endothelial dysfunction.[83]

The compression of lamellae with the applanation cone may result in inaccuracy in the depth of FSL firing, during a transepithelial approach to obtain grafts.[84] Due to the greater possibility of laser energy scattering, deeper stromal cutting presents a greater challenge to the accuracy and smoothness of interface quality.[81] To eliminate the limitation, some surgeons have proposed an “endothelial approach” to harvest endothelial grafts.[85] The endothelial side of the cornea was laterally flattened and mounted upside down on an artificial chamber to improve incision quality, which also provided thinner and more regular grafts.[86] A case series demonstrated that FSL cutting from the endothelial side could provide planar and thin posterior lamellar grafts with good endothelial viability, but interface haze negatively affected the visual outcome.[85] It may be due to the generation of collagen fibril strands by the parallel organization of the collagen fibrils in the posterior part of the stroma when the tissue was cut with a FSL. In the transendothelial approach, the coating with viscoelastic materials could protect the endothelial cells from damage during the posterior laser dissection.[84] To further refine the donor preparation of posterior lamellar keratoplasty, our group used low-pulse energy, high-frequency FSL to produce consistently ultrathin grafts with smooth interface and uniform shape.[87]

Femtosecond Laser-assisted Descemet Membrane Endothelial Keratoplasty

Due to only DM and endothelium being transplanted in DMEK, donor preparation is more challenging and time-consuming. It is difficult to unfold the extremely thin tissue into the right orientation, which leads to higher rates of graft dislocation.[11] Using an artificial anterior chamber with the grafts being mounted with endothelial side down, DMEK grafts can be prepared by using a FSL to make a partial thickness deep circular cut through the endothelium, DM, and posterior stroma.[88] The graft tissue was then flipped, and the DM edge was then delineated and lifted from the stroma.

FSL has also been used to perform the descemetorhexis in receipts, and the higher postoperative precision of the FSL-descemetorhexis compared to manual descemetorhexis was observed using OCT images.[89] FSL has shown comparable safety and efficacy to that of manual descemetorhexis with apparently low detachment and rebubble rates. The possible mechanism is that FSL creates an even interface, which allows the graft to adhere better, and FSL-induced inflammation may promote tissue adherence.[90] Moreover, FSL-descemetorhexis may be effective management in PK graft failure, since making complete descemetorhexis across the PK graft may be more difficult than that in virgin corneas, and the remnant Descemet may lead to incomplete graft adherence.[91-93] The precision of the FSL-descemetorhexis also obviates the need to oversize the rhexis diameter in relation to the graft and thus leaves less denuded stroma to be populated by migrating endothelial cells,[94] helping to prolong the graft survival. Jardine et al. showed that the endothelial cell loss was higher in FSL-descemetorhexis DMEK than conventional DMEK and DSAEK graft preparation, possibly due to greater tissue manipulation.[95] However, the laser energy may scatter in opaque corneas such as bullous keratopathy during the descemetorhexis and if the laser applanation is flat, the invariable fold in the DM will affect the quality, accuracy, and shape of the cut.

Femtosecond Laser-assisted Deep Lamellar Endothelial Keratoplasty

Deep Lamellar Endothelial Keratoplasty (DLEK) was a treatment option for patients with corneal endothelial diseases associated with the opacification of the posterior stroma, while the anterior and mid-stroma are not affected. In DLEK, the affected endothelium, DM, and a thin lamella of posterior corneal stroma are replaced by a healthy graft of donor corneal tissue. However, the procedure was gradually abandoned due to the challenging host lamellar dissection, and also due to the introduction of DS(A)EK. However, in certain situations, this procedure could be advantageous, especially if there is posterior stromal scarring. The introduction of FSL would make this procedure more feasible with the creation of laser-assisted posterior side cut.[96] Alió del Barrio et al. described a combined surgical approach incorporating FSL-DLEK with DMEK for a patient with posterior corneal scarring secondary to viral endotheliitis. A two-step FSL-DLEK in which a manual lamellar dissection plane was created 1 week before the EK surgery through a 5-mm superior scleral incision. FSL-DLEK was performed thereafter by creating an intersecting posterior lamellar side cut.[96,97] We herein also illustrate one case. A patient with poor vision due to residual posterior corneal opacity after DALK underwent FSL-assisted DLEK combined with standard DMEK [Figure 7a and b]. In this case, the FSL was used to create a posterior lamellar side cut of 7.5 mm diameter with a posterior corneal thickness of 108 μ [Figure 7c]. Recipient tissue was separated using the deep lamellar dissection plane from the previous DALK and removed. Standard DMEK was performed thereafter. Four months after the procedure, the cornea was clear with the resolution of corneal opacity [Figure 7d and e]. This case demonstrates the utility of FSL for the preparation of the recipient tissue precisely with deep corneal stromal scarring. The posterior trephination starts from the anterior chamber and passes anteriorly through the DM till the desired posterior stromal depth. The host lamellar can be removed with a single posterior side cut.

Figure 7.

A postoperative deep anterior lamellar keratoplasty (DALK) case receiving femtosecond laser (FSL)-assisted Deep Lamellar Endothelial Keratoplasty (DLEK) combined with standard DMEK. Slit-lamp photo after DALK showing residual deep central stromal scar (a). Anterior segment optical coherence tomography (OCT) image after DALK showing the precise depth of remnant corneal scar (b). Intraoperative images: Posterior lamellar side cut using Ziemer Z8 femtosecond laser in the recipient. In-built OCT scans in 8 meridians and the depth of laser adjusted to include posterior corneal thickness of 108 μ (c). Slit-lamp photo 4 months after FSL-DLEK and DMEK showing clear transparent cornea (d). Anterior segment OCT image 4 months after FSL-assisted deep lamellar DMEK showing well-attached corneal graft with complete restoration of corneal clarity (e)

Limitations

However, there are limitations that need to be considered. One limitation is the challenge posed by scarred tissue, which can affect the penetration of FSL, and the accessibility of FSL would limit the widespread use of FSL technology. Moreover, regardless of the type of corneal transplantation, using a FSL platform stands a less favorable position in the aspect of cost-effectiveness.[98,99] In addition, many lasers are not in the main operating theater (OT), where transplants are performed, and are often in the refractive OT, hence requiring patient movement. This, and the large footprint of many of the lasers, may limit access to this technology for patients undergoing transplantation.

Conclusions

While FSL-assisted keratoplasty has demonstrated various advantages over conventional surgery, such as precise wound preparation and improved outcomes, it faces limitations related to scarred tissue, limited accessibility, and cost-effectiveness. Further research is necessary to establish the clear efficacy of FSL technology in corneal transplantation and determine whether it can become a commonly adopted alternative to manual keratoplasty in routine practice.

Declaration of patient consent and Ethical approval

The patient consent is waived by IRB (approval number: SingHealth 2020/2061).

Data availability statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Financial support and sponsorship

Nil.

Conflicts of interest

Prof. (Dr.) Jodhbir S. Mehta, an editorial board member at Taiwan Journal of Ophthalmology, had no role in the peer review process of or decision to publish this article. The other authors declared no conflicts of interest in writing this paper.