A comprehensive light and ultrastructural examination of the cornea in Domestic Pigs (Sus scrofa domesticus) revealed four distinct layers: the anterior epithelium, corneal stroma, Descemet\'s membrane and endothelium. Although Bowman\'s layer was not distinctly identified through histology, histochemical analysis indicated the presence of a rudimentary Bowman\'s layer, possibly vestigial from evolution. Scanning electron microscopy of the outer corneal surface unveiled two cell types, characterized by micro-projections, with light cells exhibiting shorter, thicker projections compared to dark cells. Examination of the inner surface via scanning electron microscopy demonstrated an endothelial layer devoid of cilia and microvilli, yet faint round to oval elevations were observed, potentially representing cell nuclei. Transmission electron microscopy unveiled that basal cells of the anterior epithelium closely adhered to the basement membrane, featuring half desmosomes along the basal surface. These basal cells extensively interconnected through interdigitations and a few desmosomes. The superficial cell layer consisted of a few rows of closely attached flat cells, forming a leak-proof layer with zona occludens. The outermost cells of this layer displayed fine projections to enhance the surface area, facilitating tear film distribution. At lower magnification, Transmission electron microscopy of the corneal stroma revealed alternating light and dark bands, with light bands representing transverse sections of collagen fibril lamellae and dark bands corresponding to longitudinal or oblique sections. Spindle-shaped keratocytes (fibroblasts) were identified as the primary stromal cells, intermingled between the lamellae, and featured long processes in close contact with neighbouring keratocytes. Overall, the histomorphology of the pig cornea resembles that of the human cornea except indistinct Bowman\'s membrane. This detailed understanding of the normal corneal structure in pigs hold great significance for biomedical research, providing a valuable reference for studies involving this animal model.

UNASSIGNED: To review the atypical development of Salzmann\'s nodular degeneration (SND) after two cases of laser in situ keratomileusis (LASIK) and one case of photorefractive keratomileusis (PRK), and to highlight the pathophysiology of SND and its treatment.
UNASSIGNED: Three cases of SND (two following LASIK performed with microkeratomes and one following PRK) were reviewed and Pubmed.gov and internet searches were performed.
UNASSIGNED: SND is myofibroblast-generated fibrosis in the subepithelial space between the epithelium and Bowman\'s layer that develops years or decades after traumatic, surgical, infectious, or inflammatory injuries to the cornea in which the epithelial basement membrane is damaged in one or more locations and does not fully regenerate. It is hypothesized based on these cases, and the previous immunohistochemistry of other investigators, that myofibroblast precursors, such as fibrocytes or corneal fibroblasts, that enter the subepithelial space are driven to develop into myofibroblasts, which slowly proliferate and extend the fibrosis, by transforming growth factor-beta from epithelium and tears that passes through the defective epithelial basement membrane. These myofibroblasts and the disordered collagens, and other extracellular matrix components they produce, make up the subepithelial opacity characteristic of SND. Nodules are larger accumulations of myofibroblasts and disordered extracellular matrix. If the injury is associated with damage to the underlying Bowman\'s layer and stroma, as in LASIK flap generation, then the myofibroblasts and fibrosis can extend into Bowman\'s layer and the underlying anterior stroma.
UNASSIGNED: SND fibrosis often extends into Bowman\'s layer and the anterior stroma if there are associated Bowman\'s defects, such as incisions or lacerations. In the latter cases, SND frequently cannot be removed by simple scrape and peel, as typically performed for most common SND cases, but can be trimmed to remove the offending tissue. This condition is more accurately termed Salzmann\'s subepithelial fibrosis. [J Refract Surg. 2024;40(5):e279-e290.].

BACKGROUND: The in vivo characterisation of corneal epithelial tissue morphology is of considerable importance for diagnosis, disease prognosis, and the development of a treatment strategy for ocular surface diseases. In contrast to many alternative methods, in vivo corneal confocal microscopy (CCM) not only provides a macroscopic description of the corneal tissue but also allows its visualisation with cellular resolution. However, the translation of CCM from research to clinical practice is significantly limited by the complex and still largely manual operation of available CCM systems. In addition, for cross-sectional images, and analogously to conventional slit lamp microscopy, volume data must be acquired in time-consuming depth scans due to the frontal orientation of the image field in CCM, from which depth slices can subsequently be calculated. The pure acquisition time is already in the range of seconds, and additionally, motion artefacts have to be corrected in a sophisticated way.
METHODS: This paper presents the concept and optics simulation of a new imaging technique based on a swept-source laser in combination with special chromatic optics. Here, the laser periodically changes its wavelength and is focused at different depths due to the wavelength-dependent aberration of the chromatic optics.
RESULTS: The optics simulation results promise good optical resolution at a total imaging depth of 145 µm.
CONCLUSIONS: The long-term goal is cell-resolving in vivo corneal confocal microscopy in real time with differently oriented sectioning directions.
UNASSIGNED: Die In-vivo-Charakterisierung der Morphologie des Epithelgewebes der Kornea ist von erheblicher Bedeutung für die Diagnostik, die Krankheitsprognose und die Entwicklung einer Behandlungsstrategie bei Oberflächenerkrankungen des Auges. Im Gegensatz zu vielen alternativen Methoden bietet die In-vivo-Konfokalmikroskopie der Kornea (CCM) nicht nur eine makroskopische Beschreibung des kornealen Gewebes, sondern ermöglicht dessen Darstellung mit zellulärer Auflösung. Die Translation der CCM von der Forschung in die klinische Praxis ist jedoch durch die komplexe und bisher weitgehend manuelle Bedienung der verfügbaren CCM-Systeme erheblich eingeschränkt. Für Tiefenschnittbilder, analog zur konventionellen Spaltlampenmikroskopie, müssen außerdem aufgrund der frontalen Orientierung des Bildfeldes bei der CCM in aufwendigen Tiefenscans Volumenaufnahmen erzeugt werden, aus denen sich anschließend Tiefenschnitte berechnen lassen. Bereits die reine Aufnahmedauer liegt hierbei im Bereich von Sekunden, zusätzlich müssen Bewegungsartefakte aufwendig korrigiert werden.
METHODS: Dieser Beitrag stellt das Konzept und die Optiksimulation eines neuen Bildgebungsverfahrens auf Basis eines Swept-Source-Lasers in Verbindung mit einer speziellen chromatischen Optik vor. Hierbei verändert der Laser periodisch seine Wellenlänge und wird aufgrund der wellenlängenabhängigen Aberration der chromatischen Optik in unterschiedlichen Tiefen fokussiert.
UNASSIGNED: Die Ergebnisse der Optiksimulation versprechen eine gute optische Auflösung bei einer Abbildungstiefe von insgesamt 145 µm.
UNASSIGNED: Das langfristige Ziel ist die konfokalmikroskopische zellauflösende In-vivo-Bildgebung der Kornea in Echtzeit mit verschieden orientierten Schnittrichtungen.

*Correspondence, Stephen Kaye: s.b.kaye@liverpool.ac.uk PURPOSE: To assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain (LF-SD) optical coherence tomography (OCT) for the clinical in vivo measurement of Bowman\'s layer thickness in subjects with and without keratoconus.
METHODS: Patients with keratoconus and volunteers with no corneal disease were included. The thickness of Bowman\'s layer was measured in the clinic. An in vivo graph search image segmentation of the central cornea was obtained at the normal interface vector orientation. The Mirau-UHR-LF-SD-OCT system used has an axial resolution down to 2.4 µm in air (1.7 µm in tissue), with an A-scan speed of 204.8 kHz and a signal to noise ratio (sensitivity) of 69 (83) dB.
RESULTS: 40 patients with keratoconus and 20 healthy volunteers were included. The repeatability of mean Bowman\'s and epithelial thicknesses were 0.3 and 1.0 µm, respectively. The measured 95% population range for Bowman\'s layer thickness was 13.7 to 19.6 µm for healthy (mean 16.65, SD 1.48) and 10.94 to 16.99 for 23 of the keratoconics (mean 13.96 SD 1.51) (p<0.05).
CONCLUSIONS: The measured thicknesses of Bowman\'s layer using the Mirau-UHR-LF-SD-OCT were both accurate, with the range for healthy in vivo thicknesses matching prior confocal and OCT systems of varying axial resolutions and repeatable. Bowman\'s layer was significantly thinner in patients with keratoconus. Bowman\'s layer can be accurately measured in the clinical setting using a Mirau-UHR-LF-SD-OCT and can be useful for disease monitoring.

*Correspondence, Stephen Kaye: s.b.kaye@liverpool.ac.uk PURPOSE: To assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain (LF-SD) optical coherence tomography (OCT) for the clinical in vivo measurement of Bowman\'s layer thickness in subjects with and without keratoconus.
METHODS: Patients with keratoconus and volunteers with no corneal disease were included. The thickness of Bowman\'s layer was measured in the clinic. An in vivo graph search image segmentation of the central cornea was obtained at the normal interface vector orientation. The Mirau-UHR-LF-SD-OCT system used has an axial resolution down to 2.4 µm in air (1.7 µm in tissue), with an A-scan speed of 204.8 kHz and a signal to noise ratio (sensitivity) of 69 (83) dB.
RESULTS: 40 patients with keratoconus and 20 healthy volunteers were included. The repeatability of mean Bowman\'s and epithelial thicknesses were 0.3 and 1.0 µm, respectively. The measured 95% population range for Bowman\'s layer thickness was 13.7 to 19.6 µm for healthy (mean 16.65, SD 1.48) and 10.94 to 16.99 for 23 of the keratoconics (mean 13.96 SD 1.51) (p<0.05).
CONCLUSIONS: The measured thicknesses of Bowman\'s layer using the Mirau-UHR-LF-SD-OCT were both accurate, with the range for healthy in vivo thicknesses matching prior confocal and OCT systems of varying axial resolutions and repeatable. Bowman\'s layer was significantly thinner in patients with keratoconus. Bowman\'s layer can be accurately measured in the clinical setting using a Mirau-UHR-LF-SD-OCT and can be useful for disease monitoring.

The purpose of this study was to assess the accuracy, repeatability, and performance limits of in vivo Mirau ultrahigh axial resolution (UHR) line field spectral domain (LF-SD) optical coherence tomography (OCT) for the measurement of Bowman\'s and epithelial thickness, and to provide a reference range of these values for healthy corneas.
Volunteers with no history and evidence of corneal disease were included in this study. An in vivo graph search image segmentation of the central cornea was obtained at the normal interface vector orientation. The Mirau-UHR-LF-SD-OCT system used has an axial resolution down to 2.4 µm in air (1.7 µm in tissue), with an A-scan speed of 204.8 kHz and a signal to noise ratio (sensitivity) of 69 (83) dB.
Nine volunteers were included, one of whom wore contact lenses. The repeatability of mean Bowman\'s and epithelial thicknesses were 0.3 and 1.0 µm, respectively. The measured 95% population range for healthy in vivo thickness was 13.7 to 19.6 µm for the Bowman\'s layer, and 41.9 to 61.8 µm for the epithelial layer.
The measured thicknesses of Bowman\'s layer and the corneal epithelium using the Mirau-UHR-LF-SD-OCT were both accurate, with the range for healthy in vivo thicknesses matching prior confocal and OCT systems of varying axial resolutions, and repeatable, equaling the best value prior reported.
T1. Development of a commercially viable clinical UHR OCT technology, enabling accurate measurement and interpretation of Bowman\'s and epithelial layer thickness in clinical practice.

OBJECTIVE: To evaluate the feasibility and report long-term outcomes with Bowman\'s membrane relaxation (BMR) for enhancing the residual refractive error following femtosecond intrastromal lenticule implantation (FILI).
METHODS: BMR was performed using a Hessburg-Barron trephine to create a circular incision into the Bowman\'s membrane and anterior corneal fibers up to the depth of approximately 120 to 130 µm. After enhancement, clinical outcomes were analyzed for a mean period of 36 months (range: 14 to 57 months).
RESULTS: Four eyes of 3 patients (mean age: 29 years) underwent enhancement with BMR for a significant residual refractive error of +2.25 diopters (D) spherical equivalent following FILI for high hyperopia (mean spherical equivalent: +7.00 D). After BMR, the residual refraction reduced to +0.31 D, resulting in improvement in uncorrected distance visual acuity from 0.55 to 0.33 logMAR. The mean front keratometry values increased from 46.20 to 49.30 D, and the mean back keratometry values increased from -5.90 to -6.30 D following BMR, the latter returning to the baseline (pre-FILI) value of -6.30 D. An increase in Q-value with a corresponding increase in higher order aberrations was observed. Corneal biomechanics indicated reduction of stiffness and other parameters after enhancement. No intraoperative or postoperative complications were noted.
CONCLUSIONS: BMR may be an effective technique for enhancement of residual hyperopia following tissue addition techniques such as FILI. BMR may reverse the posterior curvature changes, negating the steepening effect of the anterior cornea following tissue addition, potentially aiding in the enhancement. [J Refract Surg. 2022;38(2):134-141.].

To identify global gene expression changes in the corneal epithelium of keratoconus (KC) patients compared to non-KC myopic controls.
RNA-sequencing was performed on corneal epithelium samples of five progressive KC and five myopic control patients. Selected results were validated using TaqMan quantitative PCR (qPCR) on 31 additional independent samples, and protein level validation was conducted using western blot analysis on a subset. Immunohistochemistry was performed on tissue microarrays containing cores from over 100 KC and control cases. WNT10A transcript levels in corneal epithelium were correlated with tomographic indicators of KC disease severity in 15 eyes. Additionally, WNT10A was overexpressed in vitro in immortalized corneal epithelial cells.
WNT10A was found to be underexpressed in KC epithelium at the transcript (ratio KC/control = 0.59, P = 0.02 per RNA-sequencing study; ratio = 0.66, P = 0.03 per qPCR) and protein (ratio = 0.07, P = 0.06) levels. Immunohistochemical analysis also indicated WNT10A protein was decreased in Bowman\'s layer of KC patients. In contrast, WNT10A transcript level positively correlated with increased keratometry (Kmax ρ = 0.57, P = 0.02). Finally, WNT10A positively regulated COL1A1 expression in corneal epithelial cells.
A specific Wnt ligand, WNT10A, is reduced at the mRNA and protein level in KC epithelium and Bowman\'s layer. This ligand positively regulates collagen type I expression in corneal epithelial cells. The results suggest that WNT10A expression in the corneal epithelium may play a role in progressive KC.

OBJECTIVE: 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.

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.