The pre-Descemet's layer (Dua's layer, also known as the Dua-Fine layer and the pre-posterior limiting lamina layer): Discovery, characterisation, clinical and surgical applications, and the controversy

Current concepts and recent trends in endothelial keratoplasty

Endothelial keratoplasty (EK) is defined as an umbrella term comprising methods for selective surgical replacement of corneal endothelium and adjacent corneal tissue, which retains healthy portions of a patient's cornea while replacing diseased innermost corneal layer(s) with healthy donor tissue, to achieve corneal dehydration and transparency before the onset of irreversible stromal edema and permanent loss of corneal clarity. Recently, the pathophysiology of corneal decompensation is increasingly being researched upon. Consequent improvement in pharmacotherapy is progressively leading to reduction in the indications of EK. In addition, EK techniques have progressed towards using thinner tissue, optimizing visual outcomes. Improvements have enabled better donor tissue formulation, usage, and attachment, and surgical modifications have enhanced the tissue utilization in difficult clinical scenarios lowering failure and rejection. However, challenges are encountered in various complex clinical scenarios including eyes with prior intraocular surgery, complex anterior chamber anatomy, glaucoma, ocular surface disease etc. These complexities demand tailored surgical strategies, including modifications in graft handling, instrumentation, and postoperative management to ensure success. Attention to these details and addressing patient-specific factors can help improve outcomes in these difficult cases. The choice of procedure depends on multiple factors, including the surgeon's experience, patient's ocular anatomy, and the specific clinical scenario. This review article encompasses the recent developments in this field presenting a comprehensive picture of our modern understanding of the indications, contraindications, surgical techniques, clinical situations, community aspects and future directions pertaining to EK.

Incidence and Factors Related to Double Anterior Chamber Complications After Deep Anterior Lamellar Keratoplasty

Background

Deep anterior lamellar keratoplasty (DALK) has safety advantages over penetrating keratoplasty. However, one of the serious complications of DALK is Descemet membrane (DM) detachment, which can lead to double anterior chamber (DAC) and visual impairment. This study examines the incidence and factors related to the complication of DAC after DALK, including preexisting conditions such as atopic dermatitis (AD).

Methods

This is a retrospective evaluation of all patients who underwent DALK from January 2019 to April 2024 in the Department of Ophthalmology, Fukuoka University Hospital. Cases with DAC postoperatively were analyzed statistically. A total of 85 eyes in 73 patients were included. We excluded eyes with preexisting corneal perforations that required grafts that were less than 6mm in diameter. A binomial logistic predictive model was used to determine factors associated with postoperative DAC. Collated variables were age, AD, preexisting corneal diseases, donor button size, intraoperative DM perforation, and cornea supply source.

Results

Among 85 eyes that underwent DALK, 12 eyes (14.1%) developed postoperative DAC. Binomial regression analysis revealed preexisting corneal diseases (p=0.031) including preoperative DM perforation, infectious keratitis, keratoconus, corneal dystrophy, and corneal scar, intra-operative DM perforation (p=0.049), and AD (p=0.031) to be significant factors associated with DAC. This binomial regression model had 83.3% sensitivity and 78.0% specificity.

Conclusion

AD and preexisting corneal diseases were significant factors in DAC after DALK, and DALK during active infection predisposes to DAC, while intraoperative perforation was also significantly associated. Our study suggests that these factors could be of importance in considering the mechanism of pathogenesis of DM and DAC.

Relationship of posterior peripheral corneal layers and the trabecular meshwork: an immunohistological and anatomical study

BACKGROUND/AIM

With the popularity of endothelial keratoplasty (EK) procedures, Descemet membrane (DM) EK and pre-Descemet EK, considerable work has been done on understanding the posterior corneal anatomy. Most of the information available relates to the central cornea. We evaluated the peripheral cornea to explore the immunohistological and anatomical relationship between the pre-Descemet layer (PDL), DM and trabecular meshwork (TM).

METHODS

Six donor human sclerocorneal discs were studied. PDL, DM and TM were examined by light microscopy, transmission electron microscopy (TEM) and immunohistology. The DM was peeled from the centre to the limit of its peripheral attachment, to reach the transition zone (TZ) between TM and peripheral cornea. Ten-micron sections were stained with antibodies against collagens 1, 2, 3, 4, 5, 6, 12, elastin, myocilin, wnt-1, aquaporin, tenascin C, laminin and integrin alpha 3.

RESULTS

Collagens 2, 3, 4, laminin and myocilin were predominantly seen in the TZ between TM and peripheral cornea. Wnt-1, integrin alpha 3 and tenascin C were highly concentrated in TM. Collagen 1 was present predominantly in the corneal stroma. On TEM; DM was thinner with a denser banded structure spread throughout its thickness in the periphery compared with the central cornea where it presents as the distinct anterior banded layer.

CONCLUSION

The TZ between DM, PDL and TM shows a unique histological structure at the periphery. The collagen and elastin fibres of the TM are continuous with the PDL. The structures are firmly attached to each other. These findings provide structural information that is relevant to the preparation of DMEK donor tissue.

Anatomic Relationship Among Descemet's Membrane, Trabecular Meshwork, Scleral Spur, and Ciliary Muscle

Purpose

The purpose of this study was to examine anatomic relationships between Descemet's membrane (DM) and neighboring tissues.

Methods

Human eyes enucleated due to malignant uveal melanoma were histomorphometrically examined.

Results

In all 50 eyes included in the study (age = 59.2 ± 13.3 years), a cellular tissue (mean thickness at the DM end = 14.2 ± 19.5 µm), originating in the transitional zone, extended into the space between the peripheral DM and corneal stroma for a length of 142 ± 71 µm. This length decreased with the longer part of the DM covered with Hassall-Henle-bodies (beta = -0.30, B = -0.28, 95% confidence interval [CI] = -0.54 to -0.03, P = 0.03) and was not related with age (P = 0.84), axial length (P = 0.94), transitional zone length (P = 0.51), and the DM-scleral spur distance (P = 0.72). The DM thinned toward its end and the DM-like components appeared getting together and merging with transitional zone tissue fibers. The transitional zone length (mean = 267 ± 115 µm) varied from 82 µm to 586 µm, increased with longer DM-scleral spur distance (beta = 0.80, B = 0.67, 95% CI = 0.52 to 0.82, P < 0.001), and was not related with axial length (P = 0.74) or age (P = 0.18). The DM-scleral spur distance (mean = 660 ± 136 µm, range = 302 µm-979 µm) was not related with axial length (P = 0.60) or age (P = 0.06). The scleral spur dimensions (basis = 193 ± 103 µm, height = 151 ± 46 µm, length = 231 ± 75 µm) were not related with the DM-scleral spur distance (all P > 0.35), axial length (all P > 0.07), and age (all P > 0.25). In all eyes, the scleral spur tip was orientated anteriorly, with the longitudinal ciliary muscle inserting at its posterior side.

Conclusions

DM is firmly connected with the transitional zone tissue, and indirectly through the corneoscleral TM, with the scleral spur. With the latter connected through the longitudinal ciliary muscle and Bruch's membrane with the optic disc, the DM is part of an anatomic spherical unit of the globe.

Correlation of Anterior Segment Optical Coherence Tomography and Slit-Lamp Imaging in Infectious Keratitis

PURPOSE

Anterior segment optical coherence tomography (AS-OCT) is increasingly being used to complement slit-lamp biomicroscopy in the evaluation of corneal infections. Our purpose was to analyze, compare, and correlate the clinical signs elicited by these 2 methods in patients with infectious keratitis (IK).

METHODS

Slit-lamp photomicrographs (diffuse and slit beam) and AS-OCT scans were obtained from 20 consecutive patients (21 eyes) with IK. AS-OCT horizontal line scans representing the top, middle, and bottom of the lesions were analyzed and compared with findings seen on slit-lamp photographs. Epithelial defects, thickness, irregularity; presence of infiltrate and its depth; corneal edema or melting; vascularization; Descemet membrane detachment; and presence of keratic precipitates were analyzed with both imaging techniques. AS-OCT features included hyperreflectivity, hyporeflectivity, shadowing, and tissue morphology. Statistical analysis was performed using GraphPad Prism 8.2.1.

RESULTS

AS-OCT was significantly more likely to detect corneal thickening (P < 0.001), epithelial hyperplasia (P = 0.027), infiltrate depth (P < 0.001), presence of inflammatory plaque (P = 0.0002), DM-endothelial complex undulations (P < 0.001), keratic precipitates (P = 0.0006), and Descemet membrane detachment (0.000), than slit-lamp imaging.

CONCLUSIONS

AS-OCT can be a helpful adjunctive test in the evaluation of patients with IK. AS-OCT complements slit-lamp biomicroscopy and photography in the diagnosis and monitoring of IK and may serve an important role in telemedicine compared with slit-lamp photography alone.

What intrinsic factors affect the central corneal thickness?

The cornea is one of the tissues responsible for covering and protecting the inner structures of the eye. Central corneal thickness (CCT) is defined as the distance between the anterior epithelial surface and the posterior surface of the endothelial layer. This parameter plays a very important role regarding intraocular pressure (IOP) measurement, evaluation of corneal uniformity, selection of a suitable technique for corneal refractive surgery and the planning of surgical procedures to overcome corneal disease. This comprehensive review elucidates the multifaceted factors influencing the central corneal thickness. Recognising the impact of these factors not only enhances our understanding of corneal dynamics but also contributes significantly to the refinement of diagnostic and therapeutic strategies in ophthalmology.

A New Device and Method for Endothelial Graft Preparation in Descemet Membrane Endothelial Keratoplasty (DMEK): A Preliminary Feasibility and Technical Evaluation

BACKGROUND

This study compares the preparation time and the macroscopic integrity of Descemet membrane and endothelium keratoplasty (DMEK) grafts prepared using the modified submerged cornea using backgrounds away (SCUBA) technique compared to those prepared with a newly developed artificial chamber device specifically designed for DMEK preparation.

RESEARCH DESIGN AND METHODS

This is a prospective, comparative, randomized, and experimental study. Fifty corneas from 25 donors were used. The inclusion criteria were that both eyes were of the same donor, a scleral ring greater than 3 mm, and corneas unsuitable for clinical use. Preparation time and macroscopic tissue integrity were evaluated at the end of preparation.

RESULTS

The mean preparation time for both techniques was six minutes (p=0.2). The macroscopic integrity of the graft was similar between the inverted artificial chamber device and the modified SCUBA technique (p=1.00).

CONCLUSIONS

The upside-down artificial chamber operating with the upside-down cornea proved reproducible and macroscopically suitable for endothelial graft preparation for the DMEK technique.

Advanced bioengineering strategies broaden the therapeutic landscape for corneal failure

The cornea acts as the eye foremost protective layer and is essential for its focusing power. Corneal blindness may arise from physical trauma or conditions like dystrophies, keratitis, keratoconus, or ulceration. While conventional treatments involve medical therapies and donor allografts-sometimes supplemented with keratoprostheses-these options are not suitable for all corneal defects. Consequently, the development of bioartificial corneal tissue has emerged as a critical research area, aiming to address the global shortage of human cornea donors. Bioengineered corneas hold considerable promise as substitutes, with the potential to replace either specific layers or the entire thickness of damaged corneas. This review first delves into the structural anatomy of the human cornea, identifying key attributes necessary for successful corneal tissue bioengineering. It then examines various corneal pathologies, current treatments, and their limitations. Finally, the review outlines the primary approaches in corneal tissue engineering, exploring cell-free, cell-based, and scaffold-based options as three emerging strategies to address corneal failure.

Self-Assembly Hypoxic and ROS Dual Response Nano Prodrug as a New Therapeutic Approach for Glaucoma Treatments

Glaucoma is an irreversible blinding eye disease characterized by retinal ganglion cell (RGC) death.Previous studies have demonstrated that protecting mitochondria and activating the CaMKII/CREB signaling pathway can effectively protect RGC and axon. However, currently treatments are often unsatisfactory, and the pathogenesis of glaucoma requires further elucidation. In this study, a ROS-responsive dual drug conjugate (OLN monomer) is first designed that simultaneously bonds nicotinamide and oleic acid. The conjugate self-assembled into nanoparticles (uhOLN-NPs) through the aggregation of multiple micelles and possesses ROS scavenging capability. Then, a polymer with a hypoxic response function is designed, which encapsulates uhOLN-NPs to form nanoparticles with hypoxic and ROS responses (HOLN-NPs). Under hypoxia in RGCs, the azo bond of HOLN-NPs breaks and releases uhOLN-NPs. Meanwhile, under high ROS conditions, the thioketone bond broke, leading to the dissociation of nano-prodrug. The released nicotinamide and oleic acid co-scavenge ROS and activate the CaMKII/CREB pathway, protecting mitochondria in RGCs. HOLN-NPs exhibit a significantly superior protective effect on R28 cells in glutamate models of glaucoma. The accumulation of HOLN-NPs in retinal RGCs lead to significant inhibition of RGC apoptosis and axonal damage in vivo. Notably, HOLN-NPs provide a new therapeutic approach for patients with neurodegenerative disease.

Utilization of Ophthalmic Technology and Advances in Endothelial Keratoplasty: A Case Report

INTRODUCTION AND IMPORTANCE

The authors report a case of a 65-year-old male with corneal decompensation associated with poor vision with a recent history of cataract surgery.

CASE PRESENTATION

A patient presented with complaints of poor vision in the left eye. The patient had undergone phacoemulsification surgery 4 months prior to presentation. The presenting best corrected vision was 20/400 in the left eye with the presence of corneal edema and central Descemet's membrane detachment (DMD) extending to the inferior two-thirds of the cornea with a fibrotic demarcation line separating detached Descemet's from intact, attached Descemet's.

CLINICAL DISCUSSION

Anterior segment optical coherence tomography (AS-OCT) confirmed the diagnosis of Type 1 DMD. The patient was managed with femtosecond laser-assisted descematorrhexis with intraoperative AS-OCT, and a ready preloaded Descemet stripping endothelial keratoplasty graft.

CONCLUSIONS

This report emphasizes that many technological advancements in the field can be employed to improve the outcomes of endothelial keratoplasty, especially when fibrosis is associated with the combined PDL and DMD.

Big-bubble DALK: A technique in evolution

Deep anterior lamellar keratoplasty (DALK) is considered a valuablealternative to penetrating keratoplasty (PK) for treatingcorneal disordersthat do not involve theendothelium. DALK preserves the host endothelium, eliminating the risk of endothelial rejection and reducing the risk of late graft failure due to endothelial decay. Despite its not recent introduction, DALK has been considered a difficult, lengthy, and poorly reproducible procedure, limiting its adoption worldwide. With the introduction of the big-bubble technique (BBT) the reproducibility and the time required to complete the procedure were significantly improved, encouraging many surgeons to approach DALK. With BBT air is injected into the stroma to induce separation between the layers of the cornea, facilitating the separation of the diseased or scarred stroma from the healthy endothelium; this allows the creation of a graft-host interface of pristine optical quality, granting clinical results equal to those obtained with PK.Understanding the anatomy and physics behind the big bubble (BB) formation is crucial for thesurgical success of this technique. The discovery of the pre-Descemet's layer (Dua's layer)played a significant role in understanding the principles behindBBformation, considerablyimpacting the safety and reproducibility of the technique. BB formation is influenced by preoperative pathology, trephination size, and instruments used for air injection.Continue advancements have helped to refine BBT's efficacy and reproducibility, broadening its applicability in corneal transplantation whenever the endothelium is healthy.This review provides a detailed account of the procedural steps involved in DALK using the BBT, addressing the most common challenges, highlightingtechnical innovations, and handlingthe most frequent complications.

Strategic Management of Descemet's Membrane Perforation During DALK in Advanced Keratoconus

Objective

To report on the surgical treatment of advanced keratoconus (KC) with stromal scarring in a young male patient with asymmetric disease progression complicated by an intraoperative microperforation of Descemet's membrane (DM) during deep anterior lamellar keratoplasty (DALK).

Methods

The surgical approach consisted of manual descemetic DALK (dDALK), further complicated with DM microperforation. Anterior segment ocular coherence tomography (AS-OCT) was used intraoperatively to locate the site and size of the tear. The surgeon decided not to convert to penetrating keratoplasty (PK), despite stromal scarring, significant ectasia, and variable corneal thickness, but rather to continue the dissection of the stromal bed with maximum precaution.

Results

Postoperatively, visual results improved and reached the best corrected visual acuity of 20/20. Choosing a proper graft dimension and reaching anatomical separation up to the DM were the keys to obtaining such a positive refractive outcome.

Discussions

DALK, the most advanced treatment for KC, was chosen as the ideal option for this young patient due to its advantages over PK: reduced rejection risk, fewer complications, quicker steroid tapering, and faster recovery. However, its steep learning curve remains a challenge for surgeons.

Conclusions

Despite manual DALK being a more challenging and time-consuming procedure than PK, careful dissection of the stromal bed and diligent assessment of the affected DM can provide a better and safer outcome for selected patients. Even if initial postoperative visual results are impressive, the surgeon must pay attention to the patient's future check-ups to swiftly correct any possible complications.

Neurotrophic keratopathy: General features and new therapies

Neurotrophic keratopathy is an uncommon degenerative corneal disorder characterized by compromised corneal sensory innervation resulting in the formation of epithelial defects and nonhealing corneal ulcers. Various treatment modalities are available to stabilize disease progression, improve patient well-being, and prevent vision loss. For eligible patients, medical and surgical reinnervation have emerged as pioneering therapies, holding promise for better management. We present a comprehensive review of the disorder, providing an update relevant to ophthalmologists on pathogenesis, diagnosis, treatment options, and novel therapies targeting pathophysiological pathways.

Drug-eluting contact lenses: Progress, challenges, and prospects

Topical ophthalmic solutions (eye drops) are becoming increasingly popular in treating and preventing ocular diseases for their safety, noninvasiveness, and ease of handling. However, the static and dynamic barriers of eyes cause the extremely low bioavailability (<5%) of eye drops, making ocular therapy challenging. Thus, drug-eluting corneal contact lenses (DECLs) have been intensively investigated as a drug delivery device for their attractive properties, such as sustained drug release and improved bioavailability. In order to promote the clinical application of DECLs, multiple aspects, i.e., drug release and penetration, safety, and biocompatibility, of these drug delivery systems were thoroughly examined. In this review, we systematically discussed advances in DECLs, including types of preparation materials, drug-loading strategies, drug release mechanisms, strategies for penetrating ocular barriers, in vitro and in vivo drug delivery and penetration detection, safety, and biocompatibility validation methods, as well as challenges and future perspectives.

The coordinated activities of collagen VI and XII in maintenance of tissue structure, function and repair: evidence for a physical interaction

Collagen VI and collagen XII are structurally complex collagens of the extracellular matrix (ECM). Like all collagens, type VI and XII both possess triple-helical components that facilitate participation in the ECM network, but collagen VI and XII are distinct from the more abundant fibrillar collagens in that they also possess arrays of structurally globular modules with the capacity to propagate signaling to attached cells. Cell attachment to collagen VI and XII is known to regulate protective, proliferative or developmental processes through a variety of mechanisms, but a growing body of genetic and biochemical evidence suggests that at least some of these phenomena may be potentiated through mechanisms that require coordinated interaction between the two collagens. For example, genetic studies in humans have identified forms of myopathic Ehlers-Danlos syndrome with overlapping phenotypes that result from mutations in either collagen VI or XII, and biochemical and cell-based studies have identified accessory molecules that could form bridging interactions between the two collagens. However, the demonstration of a direct or ternary structural interaction between collagen VI or XII has not yet been reported. This Hypothesis and Theory review article examines the evidence that supports the existence of a functional complex between type VI and XII collagen in the ECM and discusses potential biological implications.

Comparative evaluation of methods for obtaining the stress-free geometry of keratoconus corneas with different levels of severity

A biomechanical model that simulates the physiological pressure load on the cornea without considering the stresses in vivo will result in an overstress or underestimation of the stress field and incorrect deformation of the corneal structure. Therefore, it is essential to propose numerical models that consider the stress-free geometry of the cornea. In this study, the Displacement and Pre-stress methods were compared to obtain the stress-free geometry (S-FG) and the physiological estimated geometry (P-EG), based on the patient-specific geometric behavior and the computational time required to reach each geometry. The same shape and contour conditions were considered in the models obtained from both methods for each of the pathological scenarios analyzed. Both methods behaved differently to obtain the free geometry, and this difference increased with the severity grade of the disease. However, they behaved in a similar way to reach the physiological estimated geometry. The Displacement method required a lower computational cost to reach the free geometry, with both methods presenting a similar computational cost to obtain the physiological geometry. The stress-free geometries obtained by both methods allowed to characterize the existing biomechanical decompensation during the progression of the diseases. In conclusion, the calculation of the stress-free corneal geometry associated to the clinically measured intraocular pressure with the Displacement and Prestress Methods in keratoconus eyes allows the development of accurate and useable models in clinical practice in real time. This displacement method shows some benefits in terms of computational cost.

Clinical Applications of Anterior Segment Optical Coherence Tomography: An Updated Review

Since its introduction, optical coherence tomography (OCT) has revolutionized the field of ophthalmology and has now become an indispensable, noninvasive tool in daily practice. Most ophthalmologists are familiar with its use in the assessment and monitoring of retinal and optic nerve diseases. However, it also has important applications in the assessment of anterior segment structures, including the cornea, conjunctiva, sclera, anterior chamber, and iris, and has the potential to transform the clinical examination of these structures. In this review, we aim to provide a comprehensive overview of the potential clinical utility of anterior segment OCT (AS-OCT) for a wide range of anterior segment pathologies, such as conjunctival neoplasia, pterygium, scleritis, keratoconus, corneal dystrophies, and infectious/noninfectious keratitis. In addition, the clinical applications of AS-OCT (including epithelial mapping) in preoperative planning and postoperative monitoring for corneal and refractive surgeries are discussed.

Main issues in deep anterior lamellar keratoplasty: A systematic narrative review

Deep anterior lamellar keratoplasty (DALK) has emerged as a transformative approach in managing corneal pathologies, notably keratoconus (KC), providing a viable alternative to penetrating keratoplasty (PK). This systematic review explores the intricacies of DALK, comparing its preoperative, intraoperative, and postoperative considerations with PK. Extensive literature searches revealed a wealth of data regarding DALK's advantages and challenges, with an emphasis on graft survival, visual outcomes, and complications. In the preoperative phase, DALK showcases its versatility, catering to a wide spectrum of patients, including those with KC and ocular surface disorders. Intraoperatively, it offers innovative techniques to address emphysema, bubble formation, and Descemet's membrane perforation, all while maintaining a strong focus on patient-centered outcomes. Postoperatively, DALK's lower rejection rates and decreased complications underscore its potential superiority over PK, although unique challenges such as graft failure from nonimmunologic factors demand vigilant management. This comprehensive review not only serves as a valuable resource for ophthalmic surgeons but also sheds light on the evolving landscape of corneal transplantation, highlighting DALK's role as a transformative force in the field.

Phacoemulsification Under the Complex Dua Layer-Descemet-Endothelium for Combined Cataract Surgery and Penetrating Keratoplasty After Failed Deep Anterior Lamellar Keratoplasty

PURPOSE

The aim of this study was to report the surgical management of an eye with a cataract and a failed deep anterior lamellar keratoplasty (DALK) graft. Given the null visualization of the anterior chamber, instead of performing penetrating keratoplasty (PK) combined with open-sky extracapsular extraction, the cleavage plane of the previous DALK was used to expose the transparent complex including Dua layer (DL)-Descemet membrane (DM)-endothelium and to perform phacoemulsification in a closed system; then, PK was completed after the surgical removal of the complex DL-DM-endothelium.

METHODS

This study is a case report.

RESULTS

A 45-year-old woman with corneal opacity due to Acanthamoeba keratitis underwent multiple (n = 2) DALK surgeries. The second DALK graft underwent failure, with the development of severe corneal edema; a dense opacity of the lens was also present. The patient was scheduled for combined PK and cataract surgery. Because the cornea was too opaque to allow closed-system cataract surgery, a partial trephination was performed with the purpose of reopening the old donor-host junction and finding the deep cleavage plane. This maneuver permitted the exposition of the complex DL-DM-endothelium that was completely transparent, thus allowing standard phacoemulsification using the phaco-chop technique. A full-thickness corneal graft was then positioned and sutured.

CONCLUSIONS

This case confirms the toughness of the complex DL-DM-endothelium and reveals the transparency of this complex even in the presence of a failed endothelium, thus highlighting distinct advantages of our surgical approach over the conventional one involving PK combined with open-sky extracapsular extraction.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Current microfluidic platforms for reverse engineering of cornea

According to the World Health Organization, corneal blindness constitutes 5.1% of global blindness population. Surgical outcomes have been improved significantly in the treatment of corneal blindness. However, corneal transplantation is limited by global shortage of donor tissue, prompting researchers to explore alternative therapies such as novel ocular pharmaceutics to delay corneal disease progression. Animal models are commonly adopted for investigating pharmacokinetics of ocular drugs. However, this approach is limited by physiological differences in the eye between animals and human, ethical issues and poor bench-to-bedside translatability. Cornea-on-a-chip (CoC) microfluidic platforms have gained great attention as one of the advanced in vitro strategies for constructing physiologically representative corneal models. With significant improvements in tissue engineering technology, CoC integrates corneal cells with microfluidics to recapitulate human corneal microenvironment for the study of corneal pathophysiological changes and evaluation of ocular drugs. Such model, in complement to animal studies, can potentially accelerate translational research, in particular the pre-clinical screening of ophthalmic medication, driving clinical treatment advancement for corneal diseases. This review provides an overview of engineered CoC platforms with respect to their merits, applications, and technical challenges. Emerging directions in CoC technology are also proposed for further investigations, to accentuate preclinical obstacles in corneal research.

[On the issue of separate designation of the pre-Descemet's layer in the structure of the cornea]

In 2013, based on the results of an experimental pneumodissection of the cornea, English ophthalmologist H. Dua postulated the existence of a previously unknown pre-Descemet's layer (PDL) with unique characteristics. However, the need to revise the traditional concepts of the corneal structure raises reasonable doubts among many researchers. This article discusses the question of whether the structural features of the pre-Descemet's layer can be a sufficient basis for designating it as a separate anatomical unit.