Bowman Layer Onlay Grafting: Proof-of-Concept of a New Technique to Flatten Corneal Curvature and Reduce Progression in Keratoconus.

PURPOSE: The aim of this study was to describe a new surgical technique for flattening the corneal curvature and to reduce progression in eyes with advanced progressive keratoconus (KC) by using Bowman layer (BL) onlay grafting and to report on the preliminary outcomes of this procedure. METHODS: In this prospective interventional case series, 5 patients with advanced progressive KC underwent BL onlay grafting. After removal of the epithelium, a BL graft was placed and "stretched" onto the stroma, and a bandage lens was placed to cover the BL graft. In 1 case, BL onlay grafting could be performed immediately after ultraviolet corneal crosslinking; all other eyes were ineligible for ultraviolet corneal crosslinking. Best spectacle- and/or best contact lens-corrected visual acuity, refraction, biomicroscopy, corneal tomography, anterior segment optical coherence tomography, and complications were recorded at 1 week and at 1, 3, 6, 9, and 12 to 15 months postoperatively. RESULTS: All 5 surgeries could be performed successfully. Average maximum keratometry went from 75 diopters (D) preoperatively to 70 D at 1 year postoperatively. All eyes showed a completely reepithelialized and a well-integrated graft. Best spectacle-corrected visual acuity improved at least 2 Snellen lines (or more) in 3 of 5 cases and best contact lens-corrected visual acuity remained stable, improving by 3 Snellen lines in case 1 at 15 months postoperatively. Satisfaction was high, and all eyes again had full contact lens tolerance. CONCLUSIONS: BL onlay grafting may be a feasible surgical technique, providing up to -5 D of corneal flattening in eyes with advanced KC.

Intrastromal Allogeneic Inclusions for the Management of Keratoconus: A Review of Current Literature.

ABSTRACT: A new therapeutic alternative has been developed in the past 6 years to treat severe keratoconus in young patients. Those patients had only corneal transplantation as an option, but now a variety of surgical alternatives in the form of allogeneic corneal inclusions have bloomed and are becoming more popular. Although Bowman layer transplantation is the most studied technique, recent studies have described different options with very promising preliminary results. Mostly all the techniques described improve corneal curvature, visual acuity, pachymetry, contact lens tolerance, and foremost, manage to avoid or postpone corneal transplantation. Very few complications have been described so far, which makes these techniques not only feasible but also safe. Herein, we focus on reviewing recently published studies describing these techniques and their first results.

In Vivo Confocal Microscopy Findings in Bowman Layer Transplantation.

PURPOSE: To report the in vivo confocal microscopy (IVCM) findings of a case who underwent femtosecond laser-assisted Bowman layer transplantation (BLT). METHODS: This is a case report. RESULTS: In a 25-year-old man with previous diagnosis of keratoconus in whom a BLT was performed using the femtosecond laser-assisted technique, IVCM (Confoscan 4; Fortune Technologies, Vigonza, Italy) was performed 3 months after surgery, obtaining a sequence of 4 digitalized images of the total thickness of the cornea, from the epithelium to the endothelium, and then backward. The images were analyzed with the Navis v. 3.5.0. system (NIDEK, Multi-Instrument Diagnostic System, Japan). In the anterior stroma, before arriving to the graft interphase, activated keratocytes could be observed with higher reflectivity. In this first image of the anterior interphase, a homogenous hyporreflective image could be observed. In the interior of the graft, no keratocytes were found and some hyperreflective particles were present. In addition to the anterior, the posterior interphase presented bright particles. CONCLUSIONS: This is the first report that documents a BLT using IVCM.

Bowman Layer Onlay Graft for Reducing Fluctuation in Visual Acuity After Previous Radial Keratotomy.

PURPOSE: To describe the clinical outcome of a first patient undergoing Bowman layer (BL) transplantation with an onlay graft to reduce fluctuation in visual acuity and refractive error after previous radial keratotomy (RK) surgery. METHODS: In 2018, a 66-year-old woman presented with complaints of long-standing diurnal fluctuation in best-spectacle corrected visual acuity (BSCVA) after RK in 1983. After the removal of host epithelium, a BL graft was positioned onto the host cornea. BSCVA, Scheimpflug-based corneal tomography, and anterior segment optical coherence tomography were evaluated up to 12 months postoperatively. RESULTS: The surgery and postoperative course were uneventful. After surgery, the subjective complaints of visual fluctuation were reduced from 10 to 3 on a scale from 1 to 10. BSCVA (20/40; 0.5) did not change from preoperative to postoperative. Corneal tomography showed an overall central corneal steepening of 5.9 diopters. Biomicroscopy, Scheimpflug imaging, and anterior segment optical coherence tomography showed a completely epithelialized and well-integrated graft, with some minor epithelial remnants located in the preexisting keratotomy incisions. CONCLUSIONS: BL onlay grafting may have the potential to manage patients with subjective complaints of diurnal fluctuation in visual acuity after previous RK.

Potential benefits of modified corneal tissue grafts for keratoconus: Bowman layer 'inlay' and 'onlay' transplantation, and allogenic tissue ring segments.

PURPOSE OF REVIEW: Keratoconus can be surgically challenging, especially in advanced cases. Classic corneal transplantation techniques, may often be associated with complications. New alternative procedures like isolated Bowman layer transplantation (as a corneal stromal inlay or as a corneal onlay) and corneal allogenic intrastromal ring segments (CAIRS) have recently shown promising results. The aim of this review is to describe the main new surgical developments for treating keratoconus. RECENT FINDINGS: Intrastromal Bowman layer transplantation has recently shown to be effective in halting keratoconus progression and maintaining visual acuity with contact lenses, at least up to 5-7 years postoperatively. Because intrastromal dissection can be challenging, we have recently developed a technique that allows using Bowman layer grafts as an onlay, that is positioned onto the patient's anatomical Bowman layer or anterior stroma, achieving comparable results as with Bowman layer inlay transplantation. CAIRS may also be an effective treatment, improving visual acuity, corneal surface parameters and keratoconus progression. SUMMARY: There are currently some new alternative treatments such as isolated Bowman layer inlay or onlay transplantation and CAIRS, both of which seem effective at treating keratoconus and which may offer a less invasive surgical approach.

The comparison of visual outcomes, aberrations, and Bowman's layer micro-distortions after femtosecond laser small-incision lenticule extraction (SMILE) for the correction of high and moderate myopia and myopic astigmatism.

BACKGROUND: This study compares the clinical outcomes of femtosecond laser small-incision lenticule extraction (SMILE) for the correction of myopia and myopic astigmatism greater than - 10 D, and - 10 D or less respectively. METHODS: 60 eyes/patients were equally selected into group 1 (myopia and myopic astigmatism of - 10 D or less) and group 2 (myopia and myopic astigmatism of over - 10 D), both of which were treated with SMILE. Visual and refractive outcomes, corneal higher-order aberrations, and Bowman's layer micro-distortions were evaluated preoperatively, 3 months, and 6 months postoperatively. RESULTS: LogMAR corrected distance visual acuity (CDVA) of group 1 and group 2 was - 0.069 ± 0.047 and - 0.053 ± 0.073 6 months postoperatively (P = 0.48). 100% eyes in group 1 and 97% in group 2 were within 1 D of targeted correction (P = 0.45). Meanwhile, 100% eyes in group 1 and 97% in group 2 had an uncorrected distance visual acuity of 20/25 or better (P = 0.20). Changes in corneal higher-order aberrations root mean square, coma, and trefoil were similar between the two groups but spherical aberration was higher in group 2 (P < 0.01). Micro-distortions were observed in 53% in group 1 and 77% in group 2. More micro-distortions were observed in group 2 (3.40 ± 2.66) than in group 1 (2.07 ± 2.29) (P = 0.041). The total number of micro-distortions was not correlated with postoperative CDVA (P = 0.77). CONCLUSIONS: Visual outcomes showed similar results of SMILE for myopic correction of > - 10 D and ≤ - 10 D. Refractive outcomes showed slightly under-correction in higher myopic eyes. Higher myopic treatment tends to induce more spherical aberrations. Micro-distortions had no impact in visual and refractive outcomes.

Update on Bowman layer transplantation.

PURPOSE OF REVIEW: Bowman layer transplantation is a novel technique that may stabilize progressive ectatic corneal changes in eyes with keratoconus, which are too steep or too thin for ultraviolet corneal crosslinking or intracorneal ring segments. In this way, patients can maintain stable vision with contact lenses, and avoid or postpone more invasive corneal transplants, such as penetrating keratoplasty or deep anterior lamellar keratoplasty. This review aims to summarize the currently available literature on Bowman layer transplantation. RECENT FINDINGS: Bowman layer transplantation seems to be a promising, minimally invasive procedure for managing advanced keratoconus with a reported 5-year success rate of 84%. The procedure allows patients to maintain acceptable visual acuity with glasses or contact lens correction. Although graft preparation and surgical technique can be challenging, adaptation of technologies, such as femtosecond laser and intraoperative anterior segment optical coherence tomography, may help overcome these barriers to enable Bowman layer transplantation to become a more widely adopted procedure. SUMMARY: Bowman layer transplantation may offer an alternative, less invasive treatment option for eyes with advanced, progressive keratoconus.

Bowman layer transplantation using a femtosecond laser.

We describe a variation of the original manual Bowman layer transplantation technique. After the isolation of the graft, a stromal pocket is created using a femtosecond laser. With the use of this technology, which entails preservation of the conjunctiva and the non-use of sutures, we avoid the scleral approach. The femtosecond laser proved to be a feasible surgical support of this technique.

Epi-Bowman Blunt Keratectomy Versus Diluted EtOH Epithelial Removal in Myopic Photorefractive Keratectomy: A Prospective Contralateral Eye Study.

PURPOSE: To compare the outcomes and complications of Epi-Bowman blunt keratectomy (EBK) using a blunt epikeratome (Epi-Clear, Orca Surgical, Israel), with alcohol delamination of the corneal epithelium during photorefractive keratectomy (PRK) in contralateral eyes. METHODS: This prospective, randomized contralateral eye study included 44 eyes of 22 patients undergoing PRK for bilateral myopia or myopic astigmatism. In each patient, epithelial delimitation was performed using an Epi-Clear epikeratome EBK (EBK group) on 1 eye and diluted ethanol (EtOH) on the fellow eye (EtOH group). Postoperative pain, epithelial healing, epithelial profile, and visual outcome were compared between the 2 groups. RESULTS: The mean postoperative pain scores were 0.37 ± 0.25 for the EBK group and 0.82 ± 0.22 for the EtOH group (P = 0.043). The mean epithelial defect size at day 3 postoperatively was 1.61 ± 1.46 and 2.25 ± 1.69 mm, respectively (P = 0.034). The postoperative 3-month remaining mean spherical equivalent was 0.04 ± 0.49 diopters for the EBK group and 0.21 ± 0.26 D for the EtOH group (P = 0.520). There was no significant difference in UCVA and BCVA between the groups. CONCLUSIONS: Our data suggest that this novel EBK device and technique may minimize postoperative pain, accelerate re-epithelialization, and offer earlier visual recovery, compared with EtOH when used for myopic PRK.

New Surgical Modality for Management of Corneal Perforation Using Bowman Membrane.

PURPOSE: To describe a new surgical modality, "Bowman membrane tuck-in," for management of small to medium sized corneal perforation of a noninfectious etiology. METHODS: Two patients with corneal perforation of a noninfectious etiology and less than 4 mm in size underwent Bowman membrane tuck-in, a new surgical procedure. In this technique, Bowman membrane harvested from the donor cornea was tucked inside the stromal pocket of host tissue, which was prepared by 360-degree anterior stromal lamellar dissection. Patients were followed up for 6 months and were examined for best-corrected visual acuity, epithelialization time, anterior chamber stability, and graft-related complications. RESULTS: During 6-month follow-up, best-corrected visual acuity improved from PL+ (positive) to 20/120 and 20/200 in patient 1 and patient 2, respectively, and epithelialization was completed within a 2-week period in both patients. Surgery was uneventful in both cases; however, anterior chamber re-formation and graft repositioning were performed in patient 1. None of the patients showed signs of rejection or graft failure at 6-month follow-up. CONCLUSIONS: Bowman membrane tuck-in is an effective sutureless and glueless technique for management of corneal perforation of a noninfectious etiology, which may be used in emergency settings for the management of noninfectious corneal perforation of size less than 4 mm.

Direct measurement of anterior corneal curvature changes attributable to epithelial removal in keratoconus.

PURPOSE: To compare the tomography of the corneal epithelium and Bowman layer in eyes with moderate to severe keratoconus before and after epithelial debridement. SETTING: University hospital tertiary referral center. DESIGN: Prospective case series. METHODS: Dual-channel Scheimpflug combined with Placido-disk tomography was used to measure the corneal variables in eyes with keratoconus having corneal crosslinking immediately before and after epithelial debridement. The differences in pachymetry, axial keratometry, astigmatism magnitude, asphericity, total corneal power, and spherical aberrations were computed. RESULTS: The study comprised 30 eyes of 30 patients. After epithelial removal, the central (0.0 to 4.0 mm) and midperipheral (4.0 to 7.0 mm) corneal zones were significantly thinner mean (21 µm ± 14 [SD] and 35 ± 44 µm, respectively). The mean anterior axial flat keratometry (K) (+1.71 diopters [D]), steep K (+2.14 D), maximum K (+2.13 D), corneal astigmatism (+1.11 D), asphericity (-0.31), and total corneal power changes (+2.03 D) were significantly different after epithelial debridement. There were no significant changes in posterior corneal flat K or steep K, posterior corneal astigmatism, or posterior asphericity. There were no significant differences in the mean astigmatic axis (anterior or posterior corneal surface) or spherical aberration after epithelial debridement. CONCLUSIONS: In eyes with moderate to severe keratoconus, the tomography of Bowman layer was significantly steeper than that of the epithelium; thus, epithelial debridement increased the magnitude of anterior corneal keratometry, astigmatism, and prolateness. These data suggest that the corneal epithelium smooths the underlying Bowman layer irregularity in keratoconus.

Technical feasibility of isolated Bowman layer graft preparation by femtosecond laser: a pilot study.

PURPOSE: To evaluate the technical feasibility of isolated Bowman layer (BL) graft preparation by femtosecond laser (FSL) and to compare the ultrastructural morphology to manually dissected grafts. METHODS: Five whole globes were placed in custom-made eye holders and debrided of epithelium. After programming a dissection depth of 20 µm, the FSL was docked into position and 5 isolated BL grafts were created. From 5 additional globes, corneoscleral buttons were procured, mounted in artificial anterior chambers, and stripped of BL via the previously described manual technique. Three specimens from both series were randomly selected and assigned to transmission electron microscopy for ultrastructural evaluation and thickness measurements. RESULTS: All dissections were uneventful and 10 total grafts were produced: 5 by FSL and 5 by manual dissection. Mean graft thickness was 37 (±8.6) µm (n = 3) for the FSL group and 11.7 (±1.6) µm (n = 3) for the manually dissected group. Transmission electron microscopy revealed a thick but relatively smooth posterior cut edge in the FSL group, versus a virtually isolated BL with irregular rests of dispersed stroma in the manually dissected group. CONCLUSIONS: Femtosecond laser may have potential for harvesting intact BL and with a smooth posterior surface, but accompanied by variable amounts of anterior stroma owing to technical limitations.

Corneal Densitometry and Higher Order Aberrations After Bowman Layer Transplantation: 1-Year Results.

PURPOSE: To evaluate corneal densitometry and higher order aberrations (HOAs) up to 1 year after Bowman layer (BL) transplantation. METHODS: This was a retrospective study carried out at a tertiary referral center. Fifteen eyes of 14 patients who underwent BL transplantation for advanced keratoconus and had at least 1 year of follow-up were examined before BL transplantation and postoperatively at 1 day, 1 week, and 1, 3, 6, and 12 months. Corrected distance visual acuity (CDVA) with spectacles and contact lenses, anterior and posterior HOAs, and corneal densitometry were analyzed. RESULTS: One year after surgery, average logarithm of the minimum angle of resolution of spectacle-CDVA changed from 1.35 (±0.46) preoperatively to 0.96 (±0.32, P < 0.001), whereas average logarithm of the minimum angle of resolution of CDVA with contact lens remained stable after surgery (P = 0.126). Anterior and posterior HOA root mean square decreased from 3.08 ± 0.59 to 2.67 ± 0.71 µm and 7.32 ± 2.20 to 6.30 ± 2.18 µm, respectively (P < 0.05). Spherical aberration ((Equation is included in full-text article.)) improved on both anterior and posterior corneal surfaces (P < 0.001). After 1 year, corneal backscattering values showed an increase as compared with preoperative values mostly involving the central and posterior layers of the cornea, with a peak 1 month after surgery (P < 0.005 in zones 2-6 and 6-10 mm). No correlation between HOAs or corneal backscatter and CDVA was found. CONCLUSIONS: Corneal HOAs, especially spherical aberration, decreased for both anterior and posterior corneal surfaces after BL transplantation, whereas corneal backscattering increased, mostly in the central and posterior layers, where the graft has been placed. Changes in HOAs and corneal backscattering did not correlate with CDVA.

Safety and Efficacy of Epi-Bowman Keratectomy in Photorefractive Keratectomy and Corneal Collagen Cross-Linking: A Pilot Study.

PURPOSE: The purpose of this study is to compare the efficacy and safety of Epi-Bowman Keratectomy (EBK) using Epi-clear™ epikeratome with a mechanical scraper for corneal epithelium debridement during photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL). METHODOLOGY: Sixty eyes of 30 patients undergoing PRK and 44 eyes of 44 patients undergoing CXL were included in this study. In the PRK group, one eye of each patient underwent EBK and the other eye epithelial debridement with a mechanical scraper. In the CXL group, 22 eyes of 22 patients underwent EBK and the other 22 eyes with a mechanical scraping to remove the epithelium. Intra-operative spectral domain optical coherence tomography (SD OCT; Bioptigen Inc, Durham, NC) was performed to evaluate the integrity of Bowman's membrane following epithelial removal. The time taken for epithelial removal, post-operative pain score using the Wong-Baker's pain scale, time for epithelial healing, and the epithelial profile using the Optovue (Optovue Inc. Fremont, CA) during the healing was observed and analyzed between the two groups and subgroups. RESULTS: Intra-operative SD OCT showed a smooth and undamaged Bowman's membrane when EBK was performed. Post-operative pain was significantly less (p < 0.01 in the PRK group and p < 0.001 in the CXL group) with faster epithelial healing (p < 0.001 in the PRK group and p < 0.0001 in the CXL group) in the EBK subgroup as compared with the mechanical scraper subgroup. Epithelial profiling during the healing phase showed an edematous epithelium in the initial 2 weeks in the mechanical scraper subgroup while the EBK subgroup showed minimal epithelial edema lasting up to a week with regularized and smooth corneal epithelium healing. CONCLUSION: Epi-Bowman Keratectomy appears to be an effective and safe method of corneal epithelial debridement with negligible damage to Bowman's membrane and the surrounding epithelium leading to early healing thereby reducing the post-operative pain and complications.

The Impact of Flap Creation Methods for Sub-Bowman's Keratomileusis (SBK) on the Central Thickness of Bowman's Layer.

PURPOSE: To determine the impact of flap creation methods for sub-Bowman's keratomileusis (SBK) on central Bowman's layer thickness. METHODS: SBK flaps were made by Moria microkeratome for 20 subjects and by femtosecond (FEMTO) laser for 21 subjects. Corneal sublayer thicknesses were measured by ultra-high resolution optical coherence tomography before SBK and at 1 day, 1 week, 2 weeks, and 1 month afterwards. Each subject was imaged twice on each visit. Thicknesses of central epithelium, Bowman's layer, flap, and total cornea were calculated using a custom-made automated image processing algorithm. The repeatability of sublayer thickness measurements was tested by the intraclass correlation coefficient (ICC) and by the coefficient of repeatability (CoR) at 1 week post-SBK. RESULTS: ICCs of the Moria and FEMTO groups were ≥ 0.959 and ≥ 0.961 respectively for all sublayer measurements. The segmentation CoRs were less than 6.78% and 5.63% respectively. For both groups, microdistortions were present in the epithelium and Bowman's layer after SKB. The flap thickness of the Moria group was 9.8 µm (95% confidence interval: 4.8 - 14.8 µm) thinner than the FEMTO group one day after SBK (independent samples t-test, P < 0.05). Bowman's layer became thicker by 1.6 ± 1.1 µm and 1.7 ± 1.6 µm one day post-SBK for the Moria and FEMTO groups (repeated ANOVA, P < 0.05) and then remained stable. Corneal and sublayer thickness were similar between the two groups. CONCLUSIONS: Central Bowman's layer thickness increased 1 day post-SBK. Flap creation by Moria microkeratome and femtosecond laser did not have significantly different impacts on Bowman's layer thickness following SBK. TRIAL REGISTRATION: Chinese Clinical Trial Registry (ChiCTR) NO: ChiCTR-OCH-14004525.

Longitudinal comparison of outcomes after sub-Bowman keratomileusis and laser in situ keratomileusis: randomized, double-masked study.

PURPOSE: To compare the outcomes of sub-Bowman keratomileusis (100-µm flap) and laser in situ keratomileusis (LASIK) (120-µm flap) using 150-kHz femtosecond laser. DESIGN: Randomized, double-masked, contralateral clinical trial. METHODS: One hundred patients (200 eyes) with myopia or myopic astigmatism were included. Postoperative examinations were performed at week 1 and months 1, 3, 6, and 12. Main outcome measures included postoperative uncorrected (UCVA) and best-corrected distance visual acuity (BCVA); manifest refraction spherical equivalent; efficacy and safety indices; corneal thickness; and complications. RESULTS: The mean age of patients was 33.9 ± 7.9 years. Overall, the preoperative UCVA, BCVA, and manifest refraction spherical equivalent were 1.349 ± 0.332, -0.022 ± 0.033, and -5.81 ± 1.61 diopters, respectively. No significant difference was observed in preoperative (P ≥ .226) or intraoperative parameters (P ≥ .452) between both groups, except residual stromal thickness (P < .001). The UCVA, manifest refraction spherical equivalent, and central corneal thickness stabilized by 1 week, while the thinnest corneal thickness stabilized by 3 months postoperatively. There was no significant difference between both groups for any parameter during all follow-up visits (P ≥ .132) except the 3-month safety index, which was better in the sub-Bowman keratomileusis group (P = .007). Soft opaque bubble layer was noted intraoperatively in 12 cases (7, 100-µm group; 5, 120-µm group; P = .577). No postoperative complications were observed. CONCLUSIONS: Our study did not find any differences in the visual and refractive outcomes between femtosecond-assisted sub-Bowman keratomileusis and LASIK. Both surgeries resulted in quick visual recovery as early as 1 week postoperatively.

Development of the continuous curvilinear lenticulerrhexis technique for small incision lenticule extraction.

PURPOSE: To develop and evaluate the new continuous curvilinear lenticulerrhexis (CCL) technique for small incision lenticule extraction. METHODS: Thirty-one eyes of 20 patients with myopia were included in the study. The CCL technique for lenticule extraction was developed and used in 16 eyes of 10 patients (CCL group). The traditional technique of lenticule extraction was used in 15 eyes of 10 patients (traditional group). Uncorrected and corrected distance visual acuity, manifest refraction, lenticule quality, the duration of the extraction procedure, microdistorsions in Bowman's layer under optical coherence tomography (Optovue OCT; Optovue, Inc., Fremont, CA), and adverse events were evaluated at 1 day and 1 month postoperatively. RESULTS: At the first postoperative month, all eyes in both groups had an uncorrected distance visual acuity of 1.0 or better. The safety indices were 1.12 and 1.09 for the CCL and traditional groups, respectively. The efficacy indices were 1.06 and 1.09 for the CCL and traditional groups, respectively. All lenticules in the CCL group had intact, round margins, whereas one lenticule in the traditional group had a microdefect margin. There was no statistically significant difference in duration of lenticule extraction or microdistorsions in Bowman's layer. No eyes in the CCL group developed diffuse lamellar keratitis, as compared to one eye in the traditional group. CONCLUSIONS: The CCL technique exhibited excellent safety and efficacy for myopia correction, suggesting CCL is a promising technique that merits further development and study.