Allograft corneal ring segment for keratoconus management: Istanbul nomogram clinical results

Outcomes after Implantation of KeraNatural, a Sterile Corneal Allograft Intrastromal Ring Segment (CAIRS), in Eyes with Keratoconus

PURPOSE

To assess and describe the outcomes of corneal allograft intrastromal ring segment (CAIRS) implantation in eyes with keratoconus.

METHODS

In this retrospective analysis, we examined the early postoperative results of CAIRS (KeraNatural) implantation after cutting a corneal tunnel with a femtosecond laser device (Ziemer Z6) in patients with keratoconus. Outcome measures included best-corrected distance visual acuity (BCDVA), spherical equivalent (SE), maximal keratometry (Kmax), refractive astigmatism (RA), higher-order aberrations (HOAs), and root mean square total aberrations (total RMS), evaluated both before and a variable time after surgery, ranging from at least 30 days to 338 days, with a mean follow-up time of 141.1 ± 79.9 days postoperatively.

RESULTS

A total of 17 eyes with keratoconus of 16 patients (mean age of 36.2 ± 17.3 years) were treated. In one eye, previous corneal UVA cross-linking (CXL) was reported in the medical history, and 9 eyes underwent adjunctive CXL at least 1 month postoperatively due to previously documented progressive disease. BCDVA (mean ± SD) improved from preoperative values of 0.43 ± 0.16 logMAR to 0.19 ± 0.14 logMAR postoperatively (p < 0.001). Furthermore, the results show a significant decrease in spherical and astigmatic refraction, with the mean SE decreasing from - 2.9 ± 4.7 D to - 0.7 ± 3.6 D (p = 0.004). Mean RA slightly changed from - 3.42 ± 2.18 D to - 2.51 ± 2.31 D (p = 0.13). Additionally, mean Kmax significantly decreased from 57.3 ± 5.5 D to 51.4 ± 5.7 D (p < 0.001). In the comparison of pre- to postoperative HOA and total RMS values at 4, 5, and 6 mm, a slight tendency for improvement was found; however, these changes were not statistically significant (p > 0.05, each).

CONCLUSION

CAIRS implantation reduced corneal ectasia and improved BCDVA in patients with keratoconus. This highlights its potential as an effective visual rehabilitation strategy, particularly for patients who are intolerant to wearing contact lenses.

Corneal Tissue Addition Keratoplasty for the Treatment of Keratoconus: A Review

Keratoconus, characterized by loss of corneal structural integrity causing stromal thinning, has both surgical and nonsurgical management options. While corneal cross-linking is being increasingly used to halt the progression of keratoconus, it is reserved for patients with milder disease and thicker corneas. Tissue addition keratoplasty has recently emerged as a treatment option for patients with more advanced keratoconus. Studies of available tissue addition keratoplasty techniques, including Bowman layer transplantation, corneal allogenic intrastromal ring segments, and intralamellar keratoplasty, show flattening of corneal keratometry and improved visual outcomes, with increased rates of contact lens fitting. The purpose of this review is to discuss available options regarding tissue addition keratoplasty.

Long-Term Results of Sterile Corneal Allograft Ring Segments Implantation in Keratoconus Treatment

PURPOSE

To evaluate the efficacy and safety of sterile corneal allograft ring segments implantation for the treatment of keratoconus by analyzing long-term visual, refractive, and tomographic clinical outcomes.

METHODS

This prospective study included 62 eyes of 49 patients with keratoconus who underwent corneal allograft ring segments implantation at Istanbul Medipol University Faculty of Medicine between February 2020 and August 2022. Surgical outcomes using the Istanbul nomogram were evaluated in patients preoperatively and postoperatively at 1 month, 6 months, 1 year, and 3 years. Outcomes measured were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), spherical refraction (SR), cylindrical refraction (CR), topographic keratometric values, and corneal thickness at the thinnest point.

RESULTS

Preoperative mean UDVA and CDVA (LogMAR) were 0.96 ± 0.50 and 0.72 ± 0.47, respectively, and increased to 0.41 ± 0.34 and 0.22 ± 0.19 at the last visit ( P < 0.001). There was a significant decrease in SE, SR, and keratometric values postoperatively ( P < 0.001). There was no difference in CR and thinnest corneal thickness values ( P = 0.333 and 0.154, respectively). The stromal and epithelial thicknesses measured by anterior segment optical coherence tomography were stabilized at 6 months and 1 year, respectively. No major complications or side effects were observed intraoperatively or postoperatively.

CONCLUSIONS

This study demonstrated that sterile corneal allograft ring segments implantation is a safe and feasible treatment for keratoconus, yielding notable long-term visual outcomes with minimal implant-related complications.

Visual and Topographic Outcomes After Corneal Allogeneic Intrastromal Ring Segments for Keratoconus: A Systematic Review and Meta-Analysis

PURPOSE

Corneal allogeneic intrastromal ring segments (CAIRS) are a novel therapeutic approach to treat ectatic diseases such as keratoconus and improve visual acuity as well as corneal topography. This analysis aimed to evaluate the visual outcomes and corneal topography changes after CAIRS implantation for keratoconus.

DESIGN

Systematic Review and Meta-Analysis.

METHODS

In this systematic literature review and meta-analysis (ID: CRD42024612508) original peer-reviewed clinical studies on the effect of CAIRS in eyes with keratoconus were included. Exclusion criteria were preimplanted ring segments, ectatic diseases other than keratoconus, as well as no reported pre- or postoperative outcome parameters. Cochrane, Embase, PubMed and Web of Science libraries were screened in November 2024 by 2 researchers independently. The risk of bias was assessed using the Evidence Project risk of bias tool. The primary effect measure was the difference in corrected distance visual acuity (CDVA) before and after CAIRS. Additionally, changes in uncorrected distance visual acuity (UDVA), spherical equivalent (SE), cylinder, flat keratometry, steep keratometry, maximum keratometry (Kmax), mean keratometry, thinnest corneal thickness, and higher order aberrations (HOAs) after CAIRS were analyzed and compared using a random effects model. In addition, postoperative complications were documented.

RESULTS

Fourteen clinical studies with a total of 442 eyes were included in the meta-analysis. The mean improvement in CDVA was 0.37 logMAR (95% CI: 0.28, 0.46; 14 studies; n = 442 eyes). UDVA improved by 0.43 logMAR (95% CI: 0.34, 0.55; 11 studies; n = 427 eyes). SE improved by 4.59 D (95% CI: 3.35, 5.84; 12 studies; n = 430 eyes). Kmax was reduced by -4.49 D (95% CI: -6.05, -2.92; 13 studies; n = 439 eyes) and total HOAs decreased by -0.33 µm (95% CI: -0.62, -0.03; 6 studies; n = 171 eyes). One severe adverse event (0.2%) reported was an acute rejection, which necessitated explantation.

CONCLUSIONS

This meta-analysis demonstrates that CAIRS transplantation is an effective procedure that can significantly improve UDVA, CDVA, and topographic outcomes in keratoconus eyes with low complication rates.

A Manual Technique for Corneal Allogeneic Intrastromal Ring Segments Without a Femtosecond Laser

PURPOSE

To evaluate the outcomes of corneal allogeneic intrastromal ring segments (CAIRS) using a simplified manual technique for treating keratoconus.

METHODS

This prospective case series included 5 eyes from 5 patients with keratoconus (4 males, 1 female, mean age 32.5 ± 10.6 years) treated with manual CAIRS. Surgeries were performed under local anesthesia by a single surgeon. An intrastromal pocket for donor tissue implantation was manually created using a spatula, and donor corneas were prepared using a Jacobs CAIRS trephine. Corneal parameters, including higher-order aberrations, coma, and spherical aberrations at a 6 mm diameter, were measured using optical coherence tomography (CASIA SS-1000, Tomey, Japan). Anterior and posterior corneal indices, subjective refractive power, cylinder, spherical equivalent, best-corrected visual acuity (BCVA; logarithm of the minimum angle of resolution [logMAR]), and central corneal thickness. Intra- and postoperative complications were also analyzed.

RESULTS

Over a mean follow-up of 6.4 ± 2.9 months, no complications occurred. BCVA improved from 0.74 ± 0.44 logMAR preoperatively to 0.19 ± 0.66 logMAR (P = 0.043). The maximum keratometry (Kmax) value decreased from 63.6 ± 8.3D preoperatively to 59.6 ± 6.8D postoperatively (P = 0.043). Spherical equivalent improved from -11.2 ± 5.8D to -5.3 ± 3.1D (P = 0.043), and astigmatism reduced from -5.0 ± 3.4D to -3.3 ± 2.9D. Total corneal higher-order aberrations decreased from 5.6 ± 1.6D to 4.2 ± 1.6D postoperatively (P = 0.043).

CONCLUSIONS

Manual CAIRS is an effective treatment when a femtosecond laser is not available.

Implantation of Opposing Dual Corneal Allogeneic Intrastromal Ring Segments With Topography-Guidance: A Novel Method for Improved Corneal Reshaping

PURPOSE

To present the outcomes of topography-guided opposing dual-segment KeraNatural implantation in patients with keratoconus with symmetrical corneal cones.

METHODS

This study evaluated 6 eyes from 5 patients who had undergone dual allogeneic intrastromal ring segment (corneal allogeneic intrastromal ring segment) opposite horizontal implantation surgery based on topographic cone location with a follow-up period ranging from 6 months to 3 years. Preoperative and postoperative measurements, including visual acuity, refractive, topographic keratometric values, and central corneal thickness, were analyzed.

RESULTS

Corrected distance visual acuity increased from 0.93 ± 0.58 preoperatively to 0.33 ± 0.14 postoperatively and Kmax decreased from 57.87 ± 1.87 to 55.47 ± 1.62 diopters. No significant complications were reported during the follow-up period.

CONCLUSIONS

This study investigates the outcomes of dual KeraNatural implantation in patients with keratoconus with symmetrical cones. The findings from this study may yield enhanced outcomes, necessitating additional exploration and possible implementation as a new standard in keratoconus surgery.

Femtosecond Laser-Assisted Graft Preparation and Implantation of Corneal Allogeneic Intrastromal Ring Segments for Corneal Ectasia: 1-Year Results

PURPOSE

To evaluate the outcomes of patients treated with corneal allogeneic intrastromal ring segments cut with femtosecond laser (Femto-CAIRS) without concomitant corneal crosslinking.

METHODS

Patients with keratoconus treated with Femto-CAIRS at the American University of Beirut Medical Center were included (May 2022-January 2023). A proprietary software program was developed on the femtosecond laser to cut allogeneic segments. Visual, refractive, tomographic, aberrometric, and epithelial data by anterior segment optical coherence tomography were measured at baseline and 1, 3, 6, and 12 months postoperatively.

RESULTS

20 eyes of 15 patients were included and followed up for 12 months. The manifest refraction spherical equivalent and cylinder improved from -6.79 ± 4.9 diopter (D) and -4.25 ± 1.8 D to -1.88 ± 2.9 D ( P < 0.001) and -2.64 ± 1.4 D ( P = 0.01) 12 months postoperatively, respectively. 75% of eyes gained 3 or more corrected distance visual acuity lines, most of which (65%) gained 4 lines or more 12 months postoperatively. The maximum keratometry and vertical coma decreased by 5.2 D ( P < 0.001) and 1 μm ( P = 0.001), respectively, 3 months postoperatively and remained stable until 12 months. The largest anterior stromal elevation over the central 5-mm diameter decreased from 36.0 ± 18.2 μm preoperatively to 19.9 ± 9.25 μm at 1 week postoperatively ( P < 0.001) and remained relatively stable. Epithelial thickness over the cone increased relative to baseline starting 1 month postoperatively and becoming stable after 6 months while the mean epithelial thickness central to the ring peaked at 1 month after which it decreased to reach a plateau at 6 months.

CONCLUSIONS

The Femto-CAIRS procedure improves visual and tomographic parameters and allows repeatable and safe results with the possibility of customization for individualized management.

A Technique of Multiple Corneal Allogeneic Ring Segments Prepared From a Single Corneal Graft: A Case Series

PURPOSE

To describe a novel technique for preparing multiple corneal allogeneic ring segments (CAIRS) from a single corneal graft using femtosecond laser technology.

METHODS

This is a case series of 10 eyes from 10 patients with keratoconus who underwent FS-assisted CAIRS implantation using corneas from 4 donors at the Hospital Foundation Adolphe de Rothschild-Noémie de Rothschild institute. A preoperative and postoperative examination was performed at 1 day, 1 week, and 1 month. Anterior segment OCT and corneal tomography with aberrometric and pachymetric analyses were performed at each visit. Visual, refractive, and topographic parameters were extracted. The thickness and width of implanted CAIRS were analyzed.

RESULTS

Patients were classified according to keratoconus severity: group A (maximal keratometry Kmax <75D) and group B (Kmax >75D). At 1 month postoperatively, both groups A and B showed a significant decrease in mean keratometry by 4.78 ± 1.57D and 12.87 ± 4.62D, respectively. Total and higher order aberrations decreased by 5.66 ± 4.55 and 0.65 ± 1.54 in group A and by 9.45 ± 9.15 and 0.49 ± 1.39 in group B, respectively. The corrected distance visual acuity improved by 4.8 ± 1.7 lines in group A. Visual improvement was not significant in group B. One eye in group B exhibited acute rejection and required explantation.

CONCLUSIONS

FS-assisted multiple CAIRS implantation using a single corneal graft maximizes the utilization of viable corneal tissue. CAIRS implantation is an effective and biocompatible therapeutic alternative, particularly in cases of moderate to advanced keratoconus with Kmax <75D.

Crosslinked All-Femtosecond Laser-Cut Corneal Allogenic Intracorneal Ring Segments (AFXL CAIRSs): Pilot Ex Vivo Study and Report of First Two Cases Performed in Italy

Objectives: This pilot ex vivo study and first clinical experience in Italy evaluate the impact of using pre-implantation crosslinking on all-femtosecond laser-cut corneal allogenic intracorneal ring segments (AFXL CAIRSs). Methods: Six human donor eye-bank corneas were used for this preclinical ex vivo human study. Three donor (D) corneas were used for AFXL CAIRSs. First, they were prepared with an IntraLase™ femtosecond laser (Johnson & Johnson, New Brunswick, NJ, USA). The allogenic tissue rings were crosslinked before implantation with Riboflavin-UV-A accelerated crosslinking protocol (ACXL) with a 0.1% HPMC Riboflavin isotonic solution (Vibex Rapid, Glaukos-Avedro, Burlington, MA, USA) and a new KXL UV-A emitter (Glaukos-Avedro, USA). Three corneas were used as recipients (Rs) of the AFXL CAIRSs. After completing the ex vivo phase, IRB approval and signing a specific informed consent, the first two Italian patients were treated. A single ACXL CAIRS was implanted in a 51-year-old male with 53.53 D K steep, 363 μm minimum corneal thickness (MCT) and a double ACXL CAIRS was implanted in a 46-year-old male patient with 58.30 D K steep, 443 μm MCT. The longest follow-up was at three months. Results: Crosslinking of the segments enhanced tissue stiffness and grip, facilitating manipulation and CAIRS insertion into the recipient tunnels, and the yellowish color of the crosslinked segments improved visibility. The segment's thickness and volume remained unaltered during the follow-up. Both patients improved UDVA and BSCVA. K steep and High-Order Aberrations (HOAs) were reduced and MCT increased. Conclusions: Pre-implantation ACXL facilitated CAIRS insertion preserving dimensions and volume during the follow-up, rendering this important step a promising candidate in method standardization. Functional data and MCT improved significantly without adverse events.

Clinical outcomes of femtosecond laser-assisted corneal allogenic intrastromal ring segment (CAIRS) in the treatment of keratoconus

BACKGROUND

To evaluate the results of corneal allogenic intrastromal ring segment (CAIRS) implantation in keratoconus.

METHODS

The medical records of patients with keratoconus who underwent CAIRS implantation were reviewed. The CAIRS, prepared by trephination from the donor cornea, was implanted into a tunnel created using the femtosecond laser. The depth of the tunnel was 200 μ; the inner diameter of the tunnel was 4.5 mm; and the outer diameter was 7 mm. Uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), keratometry, minimum corneal thickness (CT), endothelial cell density (ECD), and high order aberration values were recorded preoperatively and at the 1st, 3rd, and 6th months postoperatively.

RESULTS

A total of 23 eyes of 23 patients were included in the study. Preoperative UCVA (0.08 ± 0.01) and BCVA (0.25 ± 0. 11) values improved postoperatively and reached 0.40 ± 0.05 and 0.68 ± 0.09, respectively, at the end of the 6-month follow-up period (p1 < 0.001, p2 = 0.016; respectively). A statistically significant flattening of all keratometric values was observed in the postoperative period compared to preoperatively (p < 0.001 for all). There were no statistical differences between CT and ECC values at the preoperative and postoperative visits (p1 = 0.654, p2 = 0.769; respectively). In addition, coma aberration values were lower than the preoperative values at all postoperative visits (p < 0.05 for all).

CONCLUSIONS

These results suggest that CAIRS implantation is a safe treatment option with good visual and keratometric outcomes for suitable patients with keratoconus.

Asymmetric All-Femtosecond Laser-Cut Corneal Allogenic Intrastromal Ring Segments

PURPOSE

To describe a novel technique for cutting asymmetric allogenic segments using the femtosecond laser for the management of cases of keratoconus with non-coinciding astigmatism and coma axes.

METHODS

Four eyes of 2 patients with irregular keratoconus and asymmetric allogenic segments were included. Visual, refractive, tomographic, and aberrometric outcomes, and optical coherence tomography (OCT) sections were measured preoperatively and 6 months postoperatively. Evaluations included slit-lamp examination, manifest refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuity, and simulated and maximum anterior keratometry (Kmax) using anterior segment OCT.

RESULTS

Spherical and cylindrical refractive errors decreased from -2.38 ± 2.96 and -2.94 ± 2.16 to -1.81 ± 2.77 (P = .04) and -1.75 ± 2.07 (P = .01) diopters (D), respectively, 6 months postoperatively. There was an average gain of three lines of CDVA. Kmax decreased from 50.02 ± 1.99 to 47.89 ± 3.05 D (P= .03) and coma from 1.05 ± 0.21 to 0.21 ± 0.19 D (P = .01).

CONCLUSIONS

Asymmetric femtosecond laser-cut allogenic segments allow a higher level of customization based on size, shape, and arc length, in contrast to the limited range of available synthetic asymmetrical segments. [J Refract Surg. 2023;39(12):856-862.].

Efficacy and safety of intracorneal allogenic ring segment implantation in keratoconus: 1-year results

BACKGROUND

To evaluate the safety and efficacy of corneal allogenic intrastromal ring segments in the management of keratoconus patients.

METHODS

The retrospective, nonrandomized, interventional case series consisted of 65 keratoconic eyes of 49 consecutive patients who had ring segment-shaped corneal allografts (KeraNatural®) implanted in intrastromal tunnels created using a femtosecond laser. The main outcome measures were uncorrected visual acuity (UCVA), corrected distant visual acuity (CDVA), refraction, keratometry, and pachymetry. Computed tomography scans of the corneal surfaces were also performed preoperatively as well as 3, 6 and 12 months postoperatively.

RESULTS

Mean age was 29.5 ± 7.3 years (median 29, range: 20-52 years). The mean UCVA improved from 0.91 ± 0.50 logMAR preoperatively to 0.40 ± 0.24 logMAR postoperatively at 6 month follow-up (p < 0.01) and the mean CDVA improved from 0.87 ± 0.20 logMAR preoperatively to 0.27 ± 0.06 logMAR postoperatively (p < 0.01). The mean spherical equivalent improved from -8.82 ± 4.57 to -3.45 ± 4.81D (p < 0.01). Average Keratometry decreased from 49.23 ± 5.22 preoperatively to 45.63 ± 4.89 D postoperatively (p < 0.01). Mean anterior and posterior maximum elevation were also decreased significantly (p < 0.01). In one patient, dislocation of the graft towards the tunnel incision site and dehiscense at the tunnel entrance were observed in the first week of the operation. Yellow-white deposits were observed in the segment tunnels in five cases after 6 months.

CONCLUSION

This study demonstrated that implantation of corneal allograft ring segments is a viable alternative treatment for keratoconus with safety and good visual results.

Extended Dehydration of Corneal Allogenic Intrastromal Ring Segments to Facilitate Insertion: The Corneal Jerky Technique

PURPOSE

The aim of this study was to describe a new technique to facilitate the insertion of corneal allogenic intrastromal ring segments.

METHODS

A single-segment corneal allogenic intrastromal ring segment (CAIRS) was trephined from donor corneas and allowed to markedly dehydrate for 75 minutes before the start of the procedure with a room humidity of 35% to 45%. The duration of the insertion step and the intrastromal segment size at 1 week as measured by optical coherence tomography were compared with previously performed single-segment CAIRS procedures using the conventional technique.

RESULTS

A total of 41 eyes of 36 patients underwent 1-segment CAIRS insertion of the same trephination size (750 µm). Fifteen eyes underwent the conventional insertion procedure, and 26 eyes had a dehydrated segment inserted. The time taken to insert the CAIRS analyzed by surgical video recording starting after the femtosecond tunnel creation and initiation of the insertion to the segment ironing step was 282 ± 103 and 97 ± 23 seconds for the conventional and the dehydrated segment technique, respectively ( P < 0.001). Anterior segment optical coherence tomography performed 1 week postoperatively revealed similar segment thickness and width of 471.3 ± 54.1 μm and 1285.1 ± 191.0 μm for the conventional allogenic segments and 483.4 ± 58.3 μm and 1227.2 ± 165.2 μm for the dehydrated segments ( P = 0.515 and 0.314, respectively).

CONCLUSIONS

Markedly dehydrated corneal allogenic segments are easier and faster to insert than the nondehydrated ones while maintaining similar sizes intrastromally. This dehydration technique makes the procedure similar to the one with synthetic segments and hence reduces the learning curve.

Corneal Allogenic Intrastromal Ring Segments (CAIRS) for Corneal Ectasia: A Comprehensive Segmental Tomography Evaluation

PURPOSE

To evaluate the visual, refractive, and tomographic results of patients with corneal ectasia treated with corneal allogenic intrastromal ring segments (CAIRS) insertion without concomitant corneal cross-linking.

METHODS

Fifty-two eyes from 39 patients with stable corneal ectasia and unsatisfactory visual acuity with contact lenses were included. All patients underwent CAIRS insertion with no concomitant corneal procedure at the American University of Beirut Medical Center between September 2019 and July 2022. Visual, refractive, topographic, aberrometric, epithelial, stromal, and segment thickness data were measured relative to baseline at 1 week, 1 month, and at least 3 months postoperatively. Evaluations included slit-lamp examination, manifest refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuity, and tomography using anterior segment optical coherence tomography.

RESULTS

Mean follow-up time was 6.9 ± 5.2 months. UDVA and CDVA improved from 0.97 ± 0.47 and 0.56 ± 0.19 preoperatively to 0.52 ± 0.21 (P < .001) and 0.23 ± 0.19 (P < .001) 3 months postoperatively. Manifest refraction spherical equivalent and cylinder improved from -6.71 ± 6.51 and -4.02 ± 2.24 diopters (D) preoperatively to -3.78 ± 4.07 D (P < .001) and -2.35 ± 1.98 D (P < .001) 3 months postoperatively, respectively. Maximum anterior keratometry and vertical coma decreased from 58.09 ± 7.92 D and 1.56 ± 1.09 µm to 52.48 ± 6.69 D (P < .001) and 0.43 ± 0.77 µm, respectively (P < .001). Corneal epithelium thickened proximal to the allogenic segment by 7.25 µm (P < .001), whereas stromal elevation at the cone decreased from 38.61 ± 18.5 to 23.82 ± 13.4 µm, respectively (P < .001). No major complications were observed and only 1 eye lost one line of CDVA.

CONCLUSIONS

Treatment of corneal ectasia with CAIRS improved visual, refractive, topographic, and tomographic parameters. Epithelial thickening central to CAIRS, along with anterior stromal flattening is postulated to contribute to tomographic flattening and regularization. [J Refract Surg. 2023;39(11):767-776.].

Bowman Layer Transplantation for Treating Keratoconus-Preliminary Findings

(1) Background: Mid-stromal isolated Bowman layer transplantation aims to reduce and stabilize corneal ectasia in patients with advanced, progressive keratoconus. The purpose of this review is to evaluate the effectiveness and safety of this new surgical technique. (2) Methods: Following the PRISMA statement and checklist, we searched Medline, the Cochrane Controlled Trials Register, and Embase and used a broad systematic search strategy according to the Cochrane Collaboration. (3) Results: Eight studies with a total number of 120 eyes of 106 patients met our inclusion criteria. One month after Bowman layer transplantation, patients with keratoconus showed a significant decrease in the measured simulated keratometry (-4.74 D [95% CI -6.79 to -2.69]) and the maximum keratometry (-7.41 D [95% CI -9.64 to -5.19]), which remained significant one year postoperatively (-2.91 D [95% CI -5.29 to -0.53] and -5.80 D [-8.49 to -3.12]). Intra- and postoperative complications were observed in 3% and 9% of the patients, respectively. An estimated success rate of 75% to 85% was achieved by experienced surgeons at 5 to 8 years postoperatively. (4) Conclusions: Bowman layer transplantation may be an effective and safe treatment option in patients with advanced, progressive keratoconus. Additional multicenter prospective interventional studies are needed to confirm these preliminary findings.