Bowman\'s layer is an acellular layer in the anterior stroma found in the corneas of humans, most other primates, chickens, and some other species. Many other species, however, including the rabbit, dog, wolf, cat, tiger, and lion, do not have a Bowman\'s layer. Millions of humans who have had photorefractive keratectomy over the past thirty plus years have had Bowman\'s layer removed by excimer laser ablation over their central cornea without apparent sequelae. A prior study showed that Bowman\'s layer does not contribute significantly to mechanical stability within the cornea. Bowman\'s layer does not have a barrier function, as many cytokines and growth factors, as well as other molecules, such as EBM component perlecan, pass bidirectionally through Bowman\'s layer in normal corneal functions, and during the response to epithelial scrape injury. We hypothesized that Bowman\'s layer represents a visible indicator of ongoing cytokine and growth factor-mediated interactions that occur between corneal epithelial cells (and corneal endothelial cells) and stromal keratocytes that maintain the normal corneal tissue organization via negative chemotactic and apoptotic effects of modulators produced by the epithelium on stromal keratocytes. Interleukin-1 alpha, produced constitutively by corneal epithelial cells and endothelial cells, is thought to be one of these cytokines. Bowman\'s layer is destroyed in corneas with advanced Fuchs\' dystrophy or pseudophakic bullous keratopathy when the epithelium becomes edematous and dysfunctional, and fibrovascular tissue commonly develops beneath and/or within the epithelium in these corneas. Bowman\'s-like layers have been noted to develop surrounding epithelial plugs within the stromal incisions years after radial keratotomy. Although there are species-related differences in corneal wound healing, and even between strains within a species, these differences are not related to the presence or absence of Bowman\'s layer.

Purpose: To characterize the three-dimensional (3D) thickness profile and age-related changes of Bowman\'s layer (BL), and endothelium/Descemet\'s membrane (En/DM) complex among healthy individuals using Corneal Microlayer Tomography (CML-T), and to describe its repeatability and accuracy.Methods: Sixty-six eyes of 41 healthy volunteers; 27 eyes (< 40 years old), and 39 eyes (>40 years old) were imaged using HD-OCT. Automatic and manual segmentation of the corneal layers was performed, and 3D thickness maps were generated, using custom-built CML-T software. A regional analysis of mean thickness parameters between the 2 age groups was performed. A regression analysis was used to assess the correlation between age, and thickness maps. Intraclass Correlation Coefficients (ICC), Coefficients of Variation (COV), and Bland-Altman plots were used to assess the reliability of the repeated measurements in 198 locations.Results: CML-T successfully mapped the BL and En/DM in all included eyes. Thickness maps showed a significant increase in corneal thickness (CT), BL thickness (BMT), and En/DM complex thickness (DMT) toward the periphery with a mean difference 28 µm (p < .001), 1.1 µm (p < .001), and 1.4 µm (p < .001), respectively. There was a strong correlation between age and central DMT (r = 0.61; p < .001), while there was no correlation between age and both CT, and BMT. ICC values ranged from 0.9 (BMT) to 0.997 (DMT), and from 0.808 (BMT) to 0.979 (CT) for intraoperator repeatability of manual measurements, and the accuracy of auto matic measurements, respectively. COV values were lower than 7.5% in all cases.Conclusion: CML-T is a novel tool that can generate 3D-thickness maps of both BL and En/DM. CT, BMT, and DMT increase toward the periphery in healthy corneas. DMT increases with aging, while BMT does not. We also report excellent repeatability, accuracy and good agreement between automatic and manual measurements.

BACKGROUND: To investigate thickness changes in the corneal epithelium and Bowman\'s layer after overnight silicone hydrogel contact lens (CL) wear by using ultra-high resolution optical coherence tomography (UHROCT).
METHODS: Eleven subjects without CL wearing history were recruited for this study. An UHROCT was used to measure the thickness of the epithelium (ET), Bowman\'s layer (BT), stroma (ST), and total cornea (CCT) at the center of both eyes. A silicone hydrogel CL was inserted in the right eye of each subject, and the fellow non-CL wearing left eye served as the control. The lens was inserted at 9:30 pm and removed at 8:00 am the next morning. The subjects were evaluated at 9:00 pm (baseline), 9:30 pm (lens insertion), 10:00 pm (before sleep), 7:00 am (waking), 7:30 am, and 8:00 am (lens removal).
RESULTS: Compared to the lens insertion level, the ET of the lens-wearing eye increased by 5.73% at eye opening (P = 0.001). The ET of the non-CL wearing eye and the BT in both eyes did not change after overnight CL wear. Compared to baseline, the CCT of the lens-wearing eye increased by 2.87% upon waking (P = 0.003) and recovered 30 min later (P = 0.555). In contrast, compared to baseline, the CCT of the non-CL wearing eye did not increase upon waking (P = 0.105).
CONCLUSIONS: By using UHROCT, we found that overnight CL wear induced different swelling responses in the various sublayers of the cornea.
BACKGROUND: Retrospectively registered. Registration number: ChiCTR1800015115 . Registered 07 March 2018.

Surgical management of keratoconus (KC) has undergone a paradigm shift in the last two decades and component corneal transplantation technique of deep anterior lamellar keratoplasty has established itself as a modality of choice for management of advanced cases of KC. Every now and then, new minimalist modalities are being innovated for the management of KC. On the same lines, a new technique, Bowman\'s layer transplantation, for surgical management of moderate to advanced KC has been reported in recent years. The procedure has shown to be beneficial in reducing ectasia in advanced KC with minimal intraoperative and postoperative complications. In this review, we intend to describe available information and literature with reference to this new surgical technique - Bowman\'s layer transplantation.

Our aim was to examine the associations between the cornea morphological parameters, endothelial cell density, and anterior chamber measurements.
This observational study included 50 eyes of 50 healthy volunteers. The thicknesses of corneal epithelium, Bowman\'s layer, stroma, Descemet\'s membrane-endothelium complex, and pre-ocular tear film were measured by means of anterior segment optical coherence tomography. The keratometry (K), corneal volume (CV), corneal optical densitometry (COD), iridocorneal angle (ICA), anterior chamber depth (ACD), and anterior chamber volume (ACV) measurements were taken by the Scheimpflug anterior segment imaging. The corneal endothelial cell density and percentage of hexagonality were measured by specular microscopy.
The COD was only correlated with the thickness of Bowman\'s layer (r = -0.30, p = 0.035). The hexagonal endothelial cell percentage was correlated with the thickness of the pre-ocular tear film (r = -0.50, p < 0.001), ACD (r = 0.40, p = 0.004), and ACV (r = 0.34, p = 0.015). The corneal epithelium thickness was associated with the ACD (r = 0.30, p = 0.034), ACV (r = 0.34, p = 0.018), K-flat (r = -0.35, p = 0.013), and K-steep (r = -0.29, p = 0.038) readings.
The anterior chamber morphological parameters (i.e., ACV, ACD) were significantly positively correlated with the hexagonal endothelial cell percentage and corneal epithelium thickness in healthy adults.

A morphological and morphometric study of the adult zebrafish ocular surface was performed to provide a comprehensive description of its parts and to evaluate its similarity to the human.
The eyes of adult zebrafish were processed for light, transmission and scanning electron microscopy, and for immunohistochemical stain of corneal nerves; a morphometric analysis was also performed on several morphological parameters.
The corneal epithelium was formed by five layers of cells. No Bowman\'s layer could be demonstrated. The stroma consisted of lamellae of different thickness with few keratocytes. The Descemet\'s membrane was absent as the flat and polygonal endothelial cells directly adhered to the deepest corneal lamella. The immunohistochemical stain of neurofilaments failed to demonstrate corneal nerve fibers. The conjunctival epithelium was stratified, overlying the stroma formed by a subepithelial and a deep layer, this latter connected to the scleral cartilage. In the peripheral cornea and in the conjunctiva, many goblet and rodlet cells were observed. The morphometric analysis showed that the peripheral cornea epithelium was thicker when compared to the other parts of the ocular surface, with smaller superficial cells. Desmosomes and hemidesmosomes in the conjunctiva were significantly fewer in number than the other parts of the ocular surface. The stroma was thinner in the conjunctiva than in the cornea, while corneal lamellae were thicker in the intermediate stroma.
The zebrafish ocular surface showed significant differences compared to the human, such as the absence of Bowman\'s layer, Descemet\'s membrane and corneal nerve fibers, the reduced stromal thickness, and the presence of rodlet cells. On the basis of these original findings, it is suggested that the use of the zebrafish as a model for studying normal or pathological human corneas should be undertaken with particular caution.

OBJECTIVE: To report the in vivo laser confocal microscopy findings of a cornea with osteogenesis imperfecta (OI) with special attention to the abnormality of Bowman\'s layer and sub-Bowman\'s fibrous structures (K-structures).
METHODS: Two patients (67-year-old male and his 26-year-old son) with OI type I were included in this study. Slit lamp biomicroscopic and in vivo laser confocal microscopic examinations were performed for both patients. Central corneal thickness and central endothelial cell density were also measured.
RESULTS: Although the corneas looked clear with normal endothelial density for both eyes in both patients, they were quite thin (386 μm oculus dexter (OD) (the right eye) and 384 μm oculus sinister (OS) (the left eye) in the father and 430 μm OD and 425 μm OS in the son). In both patients, slit lamp biomicroscopic and in vivo laser confocal microscopic examination showed similar results. Anterior corneal mosaics produced by rubbing the eyelid under fluorescein were completely absent in both eyes. In vivo laser confocal microscopy revealed an absent or atrophic Bowman\'s layer; a trace of a presumed Bowman\'s layer and/or basement membrane was barely visible with high intensity. Additionally, K-structures were completely absent in both eyes.
CONCLUSIONS: The absence of K-structures and fluorescein anterior corneal mosaics strongly suggested an abnormality of Bowman\'s layer in these OI patients.

BACKGROUND: The purpose of this study was to report Acanthamoeba encystment in Bowman\'s layer in Japanese cases of persistent Acanthamoeba keratitis (AK).
METHODS: Laser confocal microscopic images of the cornea were obtained in vivo from 18 consecutive eyes from 17 confirmed AK patients. Retrospectively, 14 cases treated over 4 months were categorized as a nonpersistent group and three cases that required prolonged therapy for more than 6 months were categorized as a persistent group. Clinical outcomes based on final best-corrected visual acuity were retrospectively analyzed, and selected confocal images were evaluated qualitatively for abnormal findings.
RESULTS: The final best-corrected visual acuity was significantly lower (P < 0.01) for patients in the persistent group compared with that in the nonpersistent group. At the initial visit, in vivo confocal microscopy demonstrated Acanthamoeba cysts exclusively in the epithelial layer in both the nonpersistent group (80%) and the persistent group (100%). At a subsequent follow-up visit, numerous Acanthamoeba cysts were observed in the epithelial cell layer and in Bowman\'s layer in all patients with persistent AK, but Acanthamoeba cysts were undetectable in all cases with nonpersistent AK tested.
CONCLUSIONS: Invasion of cysts into Bowman\'s layer was characteristically observed in patients with persistence of AK. This finding suggests that invasion of Acanthamoeba cysts into Bowman\'s layer may be a useful predictor for a persistent clinical course.