Journal of Refractive Surgery

Therapeutic Refractive Surgery 

Femtosecond Laser–Assisted Small Incision Sutureless Intrastromal Lamellar Keratoplasty (SILK) for Corneal Transplantation in Keratoconus

Kishore R. Pradhan, MD; Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Ryan S. Vida, OD, FAAO; Timothy J. Archer, MA(Oxon), DipCompSci(Cantab), PhD; Shashwat Dhungel, MD; Purushottam Dhungana, Moptom, OD, FLVC; Glenn I. Carp, MBBCh, FCOphth (SA)

Abstract

PURPOSE:

To describe a femtosecond laser–assisted small incision sutureless intrastromal lamellar keratoplasty in an eye with severe keratoconus and report on the outcome with a 1-year follow-up.

METHODS:

A 20-year-old man with a history of keratoconus presented for evaluation at the Tilganga Institute of Ophthalmology, Kathmandu, Nepal. The patient had previously undergone a deep anterior lamellar keratoplasty in the left eye. Examination of the right eye revealed an uncorrected distance visual acuity (UDVA) of counting fingers with a manifest refraction of −5.00 −3.50 × 170, giving a corrected distance visual acuity (CDVA) of 20/80. Thinnest pachymetry was 425 µm and progression of both anterior and posterior corneal elevation tomography and maximum keratometry was noted compared to examination 2 years prior. The VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) was used to prepare the donor and recipient cornea. The donor graft was inserted into the recipient through the 3-mm small incision. No sutures were applied.

RESULTS:

At 2 weeks postoperatively, UDVA was 20/50 with a manifest refraction of −1.00 −5.00 × 145 (20/32). One year postoperatively, UDVA was 20/80 with a manifest refraction of −2.50 −3.50 × 125 (20/40−2), with the maximum keratometry decreasing from 64.08 to 56.74 diopters.

CONCLUSIONS:

This femtosecond laser–assisted sutureless intrastromal corneal transplantation technique may provide an option to improve the quality of vision for some patients with keratoconus, affording a simpler postoperative follow-up course compared to traditional anterior lamellar or full-thickness corneal transplantation.

[J Refract Surg. 2019;35(10):663–671.]

Abstract

PURPOSE:

To describe a femtosecond laser–assisted small incision sutureless intrastromal lamellar keratoplasty in an eye with severe keratoconus and report on the outcome with a 1-year follow-up.

METHODS:

A 20-year-old man with a history of keratoconus presented for evaluation at the Tilganga Institute of Ophthalmology, Kathmandu, Nepal. The patient had previously undergone a deep anterior lamellar keratoplasty in the left eye. Examination of the right eye revealed an uncorrected distance visual acuity (UDVA) of counting fingers with a manifest refraction of −5.00 −3.50 × 170, giving a corrected distance visual acuity (CDVA) of 20/80. Thinnest pachymetry was 425 µm and progression of both anterior and posterior corneal elevation tomography and maximum keratometry was noted compared to examination 2 years prior. The VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany) was used to prepare the donor and recipient cornea. The donor graft was inserted into the recipient through the 3-mm small incision. No sutures were applied.

RESULTS:

At 2 weeks postoperatively, UDVA was 20/50 with a manifest refraction of −1.00 −5.00 × 145 (20/32). One year postoperatively, UDVA was 20/80 with a manifest refraction of −2.50 −3.50 × 125 (20/40−2), with the maximum keratometry decreasing from 64.08 to 56.74 diopters.

CONCLUSIONS:

This femtosecond laser–assisted sutureless intrastromal corneal transplantation technique may provide an option to improve the quality of vision for some patients with keratoconus, affording a simpler postoperative follow-up course compared to traditional anterior lamellar or full-thickness corneal transplantation.

[J Refract Surg. 2019;35(10):663–671.]

Lamellar transplantation, both penetrating and non-penetrating, has proven to be effective in rehabilitating vision for a wide variety of conditions, including keratoconus.1–3 The risk of graft rejection has been shown to be lower when recipient endothelial tissue remains intact, as in deep anterior lamellar keratoplasty (DALK).2,4 Improved surgical techniques, including big-bubble and Descemet's bearing DALK, have made this technique the first-line choice for many corneal specialists.5–7

The first published femtosecond laser–assisted anterior lamellar keratoplasty (FALK)8 used the IntraLase femtosecond laser (Johnson & Johnson, New Brunswick, NJ) to prepare the donor and recipient cornea to achieve better apposition between the donor graft and recipient bed. Femtosecond laser–assisted corneal transplantations have since been reported to have good safety9 and visual outcomes10 while decreasing the number of sutures required compared to manual DALK.11

These innovations in keratoplasty may have particular relevance in the developing world, where routine corneal transplantation is hindered by tissue supply, difficulties in achieving appropriate short- and long-term patient follow-up, and access to quality spectacles or specialty contact lenses. In Nepal, where the incidence of microbial keratitis is 799 in 100,000,12 full-thickness and lamellar corneal transplantations form an important part of ophthalmic surgical practice. Postoperative care is often limited by financial, geographic, and infrastructural barriers. Consequently, these patients may be at higher risk of suture-related complications, such as infection, neovascularization, and trauma.

A keratoplasty technique that may decrease or eliminate the need for sutures has the potential to improve patient outcomes and lower rates of postoperative complications in this environment. Additionally, if reduced postoperative astigmatism could be achieved, improved uncorrected distance visual acuity (UDVA) and simpler visual rehabilitation with spectacles could reduce the substantial challenges faced in environments where patients may have limited access to more sophisticated contact lens and refractive surgical options. To the best of our knowledge, we report the first case of a femtosecond laser–assisted small incision sutureless intrastromal lamellar keratoplasty (SILK) for keratoconus.

Case Report

A 20-year-old man first presented to the refractive surgery unit at the Tilganga Institute of Ophthalmology, Kathmandu, Nepal, in 2015 for a refractive surgery evaluation. The manifest refraction and corrected distance visual acuity (CDVA) was −6.25 −3.50 × 175 (20/63) in the right eye and −6.25 −3.75 × 178 (20/63) in the left eye. Pentacam corneal tomography (Oculus Optikgeräte, Wetzlar, Germany) showed steep corneas with increased posterior corneal elevation. The patient was informed of the diagnosis of keratoconus, advised that he was not a candidate for corneal refractive surgery, and advised to seek corneal specialist advice. Due to a lack of funds, the patient was unable to further explore this option.

Two years later, he returned with a complaint of decreased vision in the right eye more than the left eye. An updated history revealed he had undergone DALK in the left eye since his last visit. The UDVA was counting fingers with a manifest refraction of −5.50 −3.50 × 170 (20/80) in the right eye and 20/200 with a manifest refraction of 0.00 −6.00 × 10 (20/40) in the left eye. A rigid gas permeable contact lens improved his CDVA to 20/20 in both eyes but all attempts to wear the lenses had failed due to poor tolerance.

A slit-lamp evaluation of the right eye revealed a steep cornea with central Vogt's striae. The left eye revealed DALK surgery with a single loose suture remaining inferotemporally. The graft was healthy with no scarring or haze. Pentacam corneal tomography of the right eye showed an increase in anterior and posterior corneal elevation compared to the examination 2 years prior (Figure 1). As seen in Figure 2, Atlas corneal topography (Carl Zeiss Meditec, Jena, Germany) of the right eye showed a maximum keratometry (Kmax) reading of 64.08 diopters (D) with 12.46 D of corneal astigmatism. The left eye showed 9.00 D of corneal astigmatism remaining after DALK. Minimum corneal pachymetry in the right eye was 425 µm as measured by RTVue corneal optical coherence tomography (OCT) (Optovue, Fremont, CA).

Pentacam corneal tomography (Oculus Optikgeräte, Wetzlar, Germany) from the 2017 visit, 2015 visit, and associated difference maps for anterior corneal evaluation (top row) and posterior corneal elevation (bottom row). There is progression noted on both surfaces.

Figure 1.

Pentacam corneal tomography (Oculus Optikgeräte, Wetzlar, Germany) from the 2017 visit, 2015 visit, and associated difference maps for anterior corneal evaluation (top row) and posterior corneal elevation (bottom row). There is progression noted on both surfaces.

A series of corneal topography, optical coherence tomography B-scans, corneal pachymetry maps, and epithelial thickness maps covering the preoperative visit and 1 day, 1 week, 2 week, and 12 months postoperatively.

Figure 2.

A series of corneal topography, optical coherence tomography B-scans, corneal pachymetry maps, and epithelial thickness maps covering the preoperative visit and 1 day, 1 week, 2 week, and 12 months postoperatively.

Given the change in tomography, the increase in Kmax, and the decrease in CDVA, it was decided that surgical intervention was appropriate for the right eye. Treatment options to provide a more definitive improvement included classic DALK or penetrating keratoplasty. Due to the significant postoperative corneal astigmatism leading to difficulty finding a functional vision correction option for the left eye, the patient was not eager to proceed with another DALK or a more invasive penetrating keratoplasty. Our previous experience with lenticule implantation together with published data from other groups provided the concept to extrapolate this to a lenticule implant.13–16 After comprehensive discussion with the patient regarding our prior lenticule implantation experience and review of the literature on this technique, it was decided the combination of FALK with lenticule implantation was a reasonable option. This technique had the potential to be less invasive without ruling out the possibility of proceeding to more conventional transplantation if necessary (ie, performing a keyhole-based stromal transplant, maintaining Bowman's layer and the endothelial layer, with the possibility of needing to proceed to a DALK/FALK or penetrating keratoplasty if unsuccessful).

Sutureless Transplant Procedure

Video 1 (available in the online version of this article) includes all subsequent steps of the transplantation procedure, which are explained in detail below.

Treatment Planning

The aim of the treatment was to increase the corneal thickness by first removing a portion of the keratoconic cornea and replacing it with a thicker donor button. A secondary aim was to produce a degree of central flattening to help reduce the Kmax, regularize the cornea, and possibly reduce the myopic refraction of the eye by performing a 50-µm myopic excimer laser ablation in the donor button before insertion through the small incision. The stages in the treatment plan are shown in Figure 3 for the donor cornea and Figure 4 for the recipient cornea.

Diagrammatic representation of the steps involving donor tissue preparation. (A) The initial deep interface and side cut using the deep anterior lamellar keratoplasty software module. The button was then prepared for laser by removing the epithelium. (B) A 50-µm myopic ablation was performed that removed Bowman's layer and (C) provided a small amount of central flattening.

Figure 3.

Diagrammatic representation of the steps involving donor tissue preparation. (A) The initial deep interface and side cut using the deep anterior lamellar keratoplasty software module. The button was then prepared for laser by removing the epithelium. (B) A 50-µm myopic ablation was performed that removed Bowman's layer and (C) provided a small amount of central flattening.

Diagrammatic representation of the steps involving recipient tissue preparation. (A) The initial deep interface and side cut using the deep anterior lamellar keratoplasty software license. A suction loss was generated when the side cut was 65% completed. (B) A laser in situ keratomileusis software license was used to create the anterior cut of the lenticule. The hinge was set to 330°. (C) The tissue removal was planned to leave 125 µm of anterior corneal stromal tissue and 140 µm of posterior corneal tissue. (D) The donor stromal lenticule was implanted into the recipient through the same small incision.

Figure 4.

Diagrammatic representation of the steps involving recipient tissue preparation. (A) The initial deep interface and side cut using the deep anterior lamellar keratoplasty software license. A suction loss was generated when the side cut was 65% completed. (B) A laser in situ keratomileusis software license was used to create the anterior cut of the lenticule. The hinge was set to 330°. (C) The tissue removal was planned to leave 125 µm of anterior corneal stromal tissue and 140 µm of posterior corneal tissue. (D) The donor stromal lenticule was implanted into the recipient through the same small incision.

Similar to the standard protocol for DALK, the treatment plan was to leave 140 µm of residual stromal tissue (approximately one-third of the full thickness) below the graft to minimize the risk of endothelial cell damage. To provide structural stability, the treatment plan was to leave 140 µm above the graft, consisting of 85 µm of stroma and approximately 55 µm of epithelium. Therefore, the donor stromal button would need to have a final thickness of 220 µm to reach the goal of a 500-µm total corneal thickness postoperatively (140 + 220 + 140 = 500). Taking into account the tissue that would be removed by the excimer laser ablation (50 µm), the donor stromal button would need to be 270 µm.

Given the tissue swelling that would take place in an average donor cornea while in storage medium, it was decided that the corneal pachymetry would be artificially raised by 50%. Therefore, it was calculated that a donor button of 400 µm would need to be fashioned to result in a 270-µm button after tissue deturgescence.

Donor Cornea Preparation

A donor cornea arrived at the onsite eye bank (Tilganga Eye Bank) stored in dextran and chondroitin sulphate solution. The cornea was retrieved from a 26-year-old man, 6 hours after time of death. The recipient patient was notified and scheduled for treatment the next day. The donor cornea was placed in an artificial anterior chamber under the VisuMax femtosecond laser (Carl Zeiss Meditec). The epithelium was removed using a blunt spatula. The donor cornea was docked to the VisuMax and the DALK software module was used to create a corneal button that was 7.75 mm in diameter and 400 µm in thickness (Figure 3A). The donor button was then taken to the MEL 80 excimer laser (Carl Zeiss Meditec) and a 50-µm myopic ablation was performed in the central 6.5-mm zone (Figures 3B–3C).

Recipient/Patient Preparation

In brief, an intrastromal button was created in the recipient cornea using a combination of the DALK and laser in situ keratomileusis (LASIK) flap software modules. The DALK module allowed for the posterior interface and side cut to be created, but stopping the side cut before reaching the epithelium. Then the LASIK flap software module would be used to create the anterior interface of the intrastromal button and a small access incision.

The DALK module was programmed with a depth of 285 µm and a diameter of 7.5 mm, to leave 140 µm of residual stroma, as described above. The DALK module begins by cutting the deep posterior interface followed by the side cut. The side cut is created from deep to superficial, so a timed release of the foot pedal was planned with 4 seconds from completion, leaving 140 µm to the front corneal surface, as seen in Figure 4A. The timed stop for the DALK side cut had been calculated and rehearsed using pig corneal studies.

Next, the LASIK software module was used to create the anterior interface of the intrastromal button and a small incision. The flap was set to a thickness of 140 µm with a diameter of 9 mm (possible by setting the contact glass in the software to an L-size contact glass). The flap hinge arc length was programmed as 330°, which created a small incision of arc length 30° (approximately 3 mm); femtosecond laser cutting occurred only over a 30° region superotemporally, thus producing a small access incision rather than a traditional LASIK flap (Figure 4B). The recipient cornea's stromal button was separated by blunt dissection and removed through the small incision using techniques developed for standard SMILE (Figure 4C).

Tissue Transplantation

The donor stromal button was inserted into the patient's cornea through the 3-mm small incision (Figure 4D). The incision had to be slightly enlarged from 3 to 4 mm using curved corneal scissors. Once inserted, the donor lenticule was manipulated using a LASIK flap lifter until it appeared smooth and centered within the pocket. No sutures were applied.

The patient wore plastic shields while sleeping for 7 nights. The patient was instructed to use sodium chloride 5% eye drops (Beximco Pharmaceuticals Ltd, Dhaka, Bangladesh) in addition to the standard protocol for broad-spectrum prophylaxis, which includes tobramycin and dexamethasone (Tobradex; Alcon Laboratories, Inc., Fort Worth, TX) and ofloxacin (Exocin; Allergan Ltd, Marlow, United Kingdom) four times daily for the first week.

Postoperative Examination

1 Day. The patient returned the next morning for a postoperative visit and complained of blurry vision but had no pain or discomfort. The CDVA was 20/400 with a manifest refraction of +6.00 −9.00 × 10. Slit-lamp examination revealed diffuse corneal edema with moderate stromal haze (Figure 5). The graft was well centered and extended 360° and the epithelium over the small incision was completely healed. Central corneal pachymetry was approximately 1,000 µm as measured by OCT. The anterior interface of the transplant tissue was 149 µm from the surface, similar to the planned depth of 140 µm. Due to the thickness of the central cornea, it was difficult to identify a clear posterior interface of the transplant tissue, but the transplant thickness was estimated as 600 µm, indicating it was swollen relative to the planned thickness of 220 µm. The residual stromal bed under the button was also edematous, measuring approximately 285 µm compared to the planned thickness of 140 µm.

(Left) Slit-lamp photograph 1 day after treatment showing moderate stromal edema and (right) 2 weeks after treatment showing a clear and centered graft with mild residual stromal edema.

Figure 5.

(Left) Slit-lamp photograph 1 day after treatment showing moderate stromal edema and (right) 2 weeks after treatment showing a clear and centered graft with mild residual stromal edema.

1 Week. The patient returned for a 5-day follow-up visit, at which time the UDVA had improved to 20/63 in the right eye. The CDVA was 20/50 with a manifest refraction of 0.00 −5.50 × 145. A slit-lamp examination showed improvement but still persistent corneal edema with mild diffuse stromal haze. As seen in Figure 2, Atlas corneal topography showed 7.52 D of corneal astigmatism and a total central corneal thickness of 683 µm as measured on the OCT B-scan. The epithelium was thin centrally at 33 µm. All postoperative medications were discontinued as per standard protocol.

2 Weeks. At the 2-week visit, the UDVA was 20/80. The CDVA improved to 20/32 with a manifest refraction of −1.00 −5.00 × 145. A slit-lamp examination showed continued improvement in residual corneal edema and a decrease in stromal haze (Figure 5). As can be seen in Figure 2, corneal topography showed a continued decrease in corneal astigmatism of 6.82 D compared to 7.52 D at the 1-week visit. The total corneal pachymetry was the same as at the 1-week visit, measuring approximately 680 µm by corneal OCT. The epithelial maps showed continued remodeling and thickening, with the minimum increasing from 33 µm at the 1-week visit to 43 µm.

6 Months. The patient was seen again at 1, 3, and 6 months with progressively improved parameters. At the 6-month visit, the UDVA was 20/80 in the right eye. The CDVA was 20/32 with a manifest refraction of −1.25 −4.00 × 125. A slit-lamp examination showed a well-centered and well-healed stromal graft. The graft tissue was clear with no significant residual edema visible at the slit lamp. Atlas corneal topography showed 3.50 D of regular corneal astigmatism with a Kmax reading of 57.08 D. Total corneal pachymetry had decreased to 625 µm and an epithelial thickness map showed a relatively regular central 6-mm zone with mild central thinning.

1 Year. The patient was seen for a 1-year postoperative visit and reported stable vision in the right eye (Table A, available in the online version of this article). The UDVA was 20/80 with a manifest refraction of −2.50 −3.50 × 125 (20/40−2). Slit-lamp examination showed a clear and stable graft. As seen in Figure 2, Atlas corneal topography measured the Kmax to be 56.74 D, which was 7.34 D flatter than the preoperative Kmax of 64.08 D. Corneal astigmatism was 5.43 D, which was 7.03 D less than the preoperative value of 12.46 D.

Patient's Visual Outcomes in the Right Eye

Table A:

Patient's Visual Outcomes in the Right Eye

As can be seen in Figure 2, the total corneal thickness by OCT was 617 µm, which was 117 µm thicker than the planned thickness of 500 µm. The anterior interface of the transplant tissue was 127 µm from the surface. The stromal transplant thickness was 332 µm, 122 µm thicker than the planned thickness of 220 µm. The residual stromal bed under the button was 158 µm, which was 18 µm thicker than the planned thickness of 140 µm. The epithelial thickness profile was reasonably regular, with a central zone of epithelium 3 to 4 µm thinner than the paracentral zone.

As can be seen in Figure 6, the Pentacam preoperative to 1-year postoperative difference map shows a significant regularization in the posterior elevation, demonstrating a reduction in astigmatism. The maximum elevation was slightly increased, but the range between the maximum and minimum elevation was greatly reduced.

Pentacam corneal tomography (Oculus Optikgeräte, Wetzlar, Germany) showing the posterior elevation from the preoperative visit in 2017, 1-year postoperative visit in 2018, and difference map. There is improvement in regularity in the midperiphery with a small amount of central elevation.

Figure 6.

Pentacam corneal tomography (Oculus Optikgeräte, Wetzlar, Germany) showing the posterior elevation from the preoperative visit in 2017, 1-year postoperative visit in 2018, and difference map. There is improvement in regularity in the midperiphery with a small amount of central elevation.

The patient was not interested in any further refractive treatment and was offered a pair of spectacles, as the CDVA was better than UDVA, but preferred functioning with unaided vision for most daily activities.

Discussion

This SILK treatment approach builds on the previously reported concept of lenticule implantation.13–16 The ability to perform such a graft through a small incision obviates the need for sutures, and the remaining host tissue and interfaces appear to have healed with sufficient optical clarity to provide a visual result comparable to that of classic DALK. In this case, the patient recovered with relative ease, without complications, and both UDVA and CDVA not only significantly improved but nearly fully recovered by 1 week postoperatively.

The target postoperative corneal thickness planned was approximately 500 µm, a 75-µm increase from the preoperative pachymetry of 425 µm. The imprecision in predicting the graft thickness is to be expected due to unknown donor hydration and lamellar expansion, as well as an unknown final level of deturgescence of the donor button achieved by the physiological apparatus of the host cornea. We estimated that donor tissue swelling can cause an artificial increase in pachymetry up to 50%. Given the cornea was stored in a dextran and chondroitin sulphate solution for less than 24 hours, a 50% increase was used in the laser treatment planning calculations.17–19 The donor lenticule was 350 µm (400 µm donor button – 50 µm myopic ablation). If the tissue was swollen by 50%, the actual thickness of the button would be 230 µm. Therefore, the postoperative total corneal thickness would be the sum of the donor stromal button (230 µm) + recipient tissue above the implant (140 µm) + recipient tissue below the implant (140 µm), which equals 510 µm. However, the final total corneal thickness was measured to be 617 µm. The actual final measurements were 332 µm (intrastromal button) + 158 µm (tissue below the button) + 127 (tissue above the button). This difference shows that the estimated 50% increase in corneal pachymetry when taking into account donor corneal swelling was too high.

Because use of donor stromal lenticules is increasing and new methods for corneal refractive and disease treatment have been reported, it is important to consider a standard procedure for lenticule preparation. Although it is not as important in the current case where improving refraction was not the main outcome measure, lenticule preparation is important if the main goal is refractive improvement. For example, Damgaard et al.20 reported standardized lenticule donor tissue preparation by using a 5-hour settling period between removal from the storage solution and excimer laser ablation.

One of the main challenges to suture-based transplantation in developing countries is the occurrence of a broken suture or infected suture site, which can easily result in infectious keratitis, tissue rejection, or even endophthalmitis due to lack of access to care or proper ocular medications. In addition to an increased risk of infection, careful and thoughtful removal of sutures is an important factor for controlling postoperative astigmatism.21–23 In suture-based transplantation, suture-related complications (albeit few) have been reported between 1.0% and 4.5%. Risks associated with sutures can include induction of irregular astigmatism, abscess and infection, tissue erosion, and inflammation.24–26 Although the best spectacle corrected vision may not be as good as with penetrating keratoplasty, by eliminating the use of sutures the current technique may provide a significant advantage for patients requiring corneal transplantation in difficult environments where follow-up is more challenging.

Additionally, as a result of the combination of donor tissue and recipient-based astigmatism, there is a possibility that a patient ends up with high or irregular astigmatism.27,28 Advanced laser treatment techniques or specialty contact lenses may be an option to regularize the cornea and improve functional vision for these patients in developed countries.28 Although irregular or high postoperative corneal astigmatism is less than ideal for any patient, it is even more problematic for patients with little or no access to specialty care or vision correction needs. A procedure that would offer better refractive outcomes and less dependence on contact lenses or spectacles would be advantageous for all surgeons and individuals.

Similar to classic DALK, this procedure spares the host endothelium. This confers several benefits in transplantation surgery in developing countries in that the quality of the donor endothelial cell layer is less important and therefore the cost of the tissue may be less and the access more readily available. In addition to availability and cost advantages, the risk of rejection is lower1 and visual rehabilitation is quicker.

Other potential advantages of the current technique relating to preserving the anterior corneal lamellae may include minimizing the reduction of the structural integrity of the globe as a whole, as well as preservation of the anterior corneal nerve plexus, thereby potentially reducing the incidence of neurotrophic complications after transplantation.29,30

Ganesh and Brar13 and Mastropasqua et al.14 have demonstrated that lenticular addition without recipient corneal stromal tissue removal can improve visual quality for patients with keratoconus. Further work in this area with large series and longer follow-up is important. Replacing the recipient corneal stroma with stroma from a healthy cornea may not change the progression of the disease. Histopathologically, keratoconus has been associated with changes in Bowman's layer.31,32 So, although the clinical relevance of these findings is not well understood, if changes in Bowman's layer play a role in progression of the disease, then replacing stromal tissue may only act to temporarily bolster corneal integrity but not change the progressive nature of the disease.

In addition to the changes on the anterior surface, the procedure achieved a regularization of the posterior surface. This provides several optical advantages to the eye, and generally speaking posterior surface coma and cylinder are not correctable by any other means. Further study into the effects of sutureless transplant on back surface regularization will be of great interest.

Finally, the eligibility for this type of procedure will depend largely on the severity of the keratoconus and hence distortion of the cornea, which can directly affect the accuracy of cutting out an even block-button from the recipient. Although the femtosecond laser has been shown to be effective in corneas with mild anterior stromal scars,8 more pronounced corneal scarring would prevent adequate femtosecond laser cutting, thus also limiting the applicability of this technique.

This first case report of SILK may prove useful in the armamentarium of the corneal surgeon for several corneal pathologies. This case study should encourage further studies to establish the full risk profile and feasibility and eligibility for patients with keratoconus and non-keratoconic corneal disease.

References

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Patient's Visual Outcomes in the Right Eye

Visit DateUDVAManifest RefractionCDVA
PreoperativeCounting fingers−5.50 −3.50 × 17020/80
1 day postoperativeCounting fingers+6.00 −9.00 × 1020/400
1 week postoperative20/63+0.00 −5.50 × 14520/50
2 weeks postoperative20/80−1.00 −5.00 × 14520/32
1 month postoperative20/80−2.00 −5.00 × 13520/40
3 months postoperative20/80−1.50 −5.50 × 12520/40
6 months postoperative20/80−1.25 −4.00 × 12520/32
12 months postoperative20/80−2.50 −3.50 × 12520/40−2
Authors

From Tilganga Institute of Ophthalmology, Kathmandu, Nepal (KRP, SD, PD); London Vision Clinic, London, United Kingdom (DZR, RSV, TJA, GIC); Columbia University Medical Center, New York, New York (DZR); Sorbonne Université, Paris, France (DZR); and Biomedical Science Research Institute, Ulster University, Coleraine, United Kingdom (DZR).

Dr. Reinstein is a consultant for Carl Zeiss Meditec (Carl Zeiss Meditec AG, Jena, Germany) and has a proprietary interest in the Artemis Insight 100 technology (ArcScan Inc., Morrison, Colorado) through patents administered by the Cornell Center for Technology Enterprise and Commercialization (CCTEC), Ithaca, New York. Drs. Pradhan and Carp receive travel expenses from Carl Zeiss Meditec. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (KRP, DZR, RSV, TJA, GIC); data collection (KRP, DZR, RSV, TJA, SD, PD, GIC); analysis and interpretation of data (KRP, DZR, RSV, TJA, SD, PD, GIC); writing the manuscript (KRP, DZR, RSV, TJA); critical revision of the manuscript (SD, PD, GIC); statistical expertise (DZR, TJA)

Correspondence: Dan Z. Reinstein, MD, MA(Cantab), FRCSC, London Vision Clinic, 138 Harley Street, London W1G 7LA, United Kingdom. E-mail dzr@londonvisionclinic.com

Received: April 24, 2019
Accepted: August 26, 2019

10.3928/1081597X-20190826-01

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