The IC3D classification of the corneal dystrophies

Characterization of Directional Reflectance in Corneal Tissue: A Comprehensive Optical Coherence Tomography Analysis

Purpose

To characterize the directional reflectance properties of the cornea using optical coherence tomography (OCT) imaging and develop a mathematical model describing corneal reflectance as a function of depth and incidence angle across different corneal layers.

Methods

A retrospective analysis was conducted on OCT scans from normal subjects using the Visionix Avanti OCT system (840 nm). Reflectance values for the epithelium, Bowman's layer, stroma, and endothelium/Descemet's membrane were extracted and analyzed as functions of incidence angle and corneal depth. Reflectance distributions were assessed for normality. Exponential functions were fitted to the mean and 97th percentile reflectance data to model directional reflectance for each corneal layer.

Results

Reflectance values exhibited non-normal leptokurtic distributions with right-tailed skewness, requiring non-parametric methods for percentile calculations. The exponential model incorporating angular dependence achieved R² values of 0.987 and 0.963 for mean and 97th percentile reflectance, respectively. The mean reflectance of the epithelium was modeled by a single exponential function, with half-reflectance angles of 15.9° to 26.6°. The stromal layers required two exponential components, with the anterior stroma exhibiting the highest reflectance and most pronounced directionality (half-reflectance angle of 0.17°). The 97th percentile reflectance differed, with higher reflectance values in the middle and posterior stroma. No statistically significant age or gender related variability in reflectance was measured.

Conclusions

This study provides a detailed mathematical model of corneal directional reflectance, highlighting the importance of incidence angle and layer depth in OCT image analysis.

Translational Relevance

The developed cornea reflectance model may improve OCT-based diagnostics by identifying early microstructural changes, aiding in the diagnosis and management of corneal diseases.

Healing the cornea: Exploring the therapeutic solutions offered by MSCs and MSC-derived EVs

Affecting a large proportion of the population worldwide, corneal disorders constitute a concerning health hazard associated to compromised eyesight or blindness for most severe cases. In the last decades, mesenchymal stem/stromal cells (MSCs) demonstrated promising abilities in improving symptoms associated to corneal diseases or alleviating these affections, especially through their anti-inflammatory, immunomodulatory and pro-regenerative properties. More recently, MSC therapeutic potential was shown to be mediated by the molecules they release, and particularly by their extracellular vesicles (EVs; MSC-EVs). Consequently, using MSC-EVs emerged as a pioneering strategy to mitigate the risks related to cell therapy while providing MSC therapeutic benefits. Despite the promises given by MSC- and MSC-EV-based approaches, many improvements are considered to optimize the therapeutic significance of these therapies. This review aspires to provide a comprehensive and detailed overview of current knowledge on corneal therapies involving MSCs and MSC-EVs, the strategies currently under evaluation, and the gaps remaining to be addressed for clinical implementation. From encapsulating MSCs or their EVs into biomaterials to enhance the ocular retention time to loading MSC-EVs with therapeutic drugs, a wide range of ground-breaking strategies are currently contemplated to lead to the safest and most effective treatments. Promising research initiatives also include diverse gene therapies and the targeting of specific cell types through the modification of the EV surface, paving the way for future therapeutic innovations. As one of the most important challenges, MSC-EV large-scale production strategies are extensively investigated and offer a wide array of possibilities to meet the needs of clinical applications.

Systematic ocular phenotyping of 8,707 knockout mouse lines identifies genes associated with abnormal corneal phenotypes

PURPOSE

Corneal dysmorphologies (CDs) are typically classified as either regressive degenerative corneal dystrophies (CDtrs) or defective growth and differentiation-driven corneal dysplasias (CDyps). Both eye disorders have multifactorial etiologies. While previous work has elucidated many aspects of CDs, such as presenting symptoms, epidemiology, and pathophysiology, the genetic mechanisms remain incompletely understood. The purpose of this study was to analyze phenotype data from 8,707 knockout mouse lines to identify new genes associated with the development of CDs in humans.

METHODS

8,707 knockout mouse lines phenotyped by the International Mouse Phenotyping Consortium were queried for genes associated with statistically significant (P < 0.0001) abnormal cornea morphology to identify candidate CD genes. Corneal abnormalities were investigated by histopathology. A literature search was used to determine the proportion of candidate genes previously associated with CDs in mice and humans. Phenotypes of human orthologues of mouse candidate genes were compared with known human CD genes to identify protein-protein interactions and molecular pathways using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING), Protein Analysis Through Evolutionary Relationships (PANTHER), and Kyoto Encyclopedia of Genes and Genomes.

RESULTS

Analysis of data from 8,707 knockout mouse lines identified 213 candidate CD genes. Of these, 37 (17%) genes were previously known to be associated with CD, including 14 in the mouse, 16 in humans, and 7 in both. The remaining 176 (83%) genes have not been previously implicated in CD. We also searched publicly available RNAseq data and found that 131 of the total 213 (61.5%) were expressed in adult human corneal tissue. STRING analysis showed several interactions within and between candidate and established CD proteins. All cellular pathways of the established genes were found in the PANTHER analysis of the candidate genes. Several of the candidate genes were implicated in corneal disease, such as TGF-ß signaling. We also identified other possible underappreciated mechanisms relevant to the human cornea.

CONCLUSIONS

We identified 213 mouse genes that resulted in statistically significant abnormal corneal phenotypes in knockout mice, many of which have not previously been implicated in corneal pathology. Bioinformatic analyses implicated candidate genes in several signaling pathways which are potential therapeutic targets.

[The latest IC3D classification of corneal dystrophies-Overview and changes of the 3rd edition]

The International Committee on Classification of Corneal Dystrophies (IC3D) was founded in 2005 to address difficulties arising from the outdated nomenclature for corneal dystrophies (CD) and to correct misconceptions in the literature. For each of the 22 CDs, a separate template was created to represent the current clinical, pathological and genetic knowledge of the disease. In addition, each template contains representative clinical photographs as well as light and electron microscopic images and, if available, confocal microscopic and coherence tomographic images of the respective CD. After the first edition was published in 2008, the revised version followed in 2015. The third edition of the IC3D was published as open access in February 2024. The latest edition is intended to serve as a reference work in everyday clinical practice and facilitate the diagnosis of CD, which might sometimes be difficult. This article provides an overview of the diagnostic and treatment principles of CD and presents the IC3D and its changes over time.

Exploring single-cell RNA sequencing as a decision-making tool in the clinical management of Fuchs' endothelial corneal dystrophy

Single-cell RNA sequencing (scRNA-seq) has enabled the identification of novel gene signatures and cell heterogeneity in numerous tissues and diseases. Here we review the use of this technology for Fuchs' Endothelial Corneal Dystrophy (FECD). FECD is the most common indication for corneal endothelial transplantation worldwide. FECD is challenging to manage because it is genetically heterogenous, can be autosomal dominant or sporadic, and progress at different rates. Single-cell RNA sequencing has enabled the discovery of several FECD subtypes, each with associated gene signatures, and cell heterogeneity. Current FECD treatments are mainly surgical, with various Rho kinase (ROCK) inhibitors used to promote endothelial cell metabolism and proliferation following surgery. A range of emerging therapies for FECD including cell therapies, gene therapies, tissue engineered scaffolds, and pharmaceuticals are in preclinical and clinical trials. Unlike conventional disease management methods based on clinical presentations and family history, targeting FECD using scRNA-seq based precision-medicine has the potential to pinpoint the disease subtypes, mechanisms, stages, severities, and help clinicians in making the best decision for surgeries and the applications of therapeutics. In this review, we first discuss the feasibility and potential of using scRNA-seq in clinical diagnostics for FECD, highlight advances from the latest clinical treatments and emerging therapies for FECD, integrate scRNA-seq results and clinical notes from our FECD patients and discuss the potential of applying alternative therapies to manage these cases clinically.

Macular corneal dystrophy with iridofundal coloboma in the same patient: a unique combination

A young a presented with painless, progressive diminution of vision in both eyes (BE). Slit lamp examination revealed the presence of a single central corneal opacity in the right eye and multiple corneal opacities of varying sizes in the left eye (LE), limited to the anterior-mid corneal stroma. Microcornea with reduced central corneal thickness and complete inferonasal iris coloboma along with inferior fundal coloboma, sparing both the disc and macula, were noted in BE. A diagnosis of BE macular corneal dystrophy (MCD) and iridofundal coloboma (IFC) was made. The patient underwent LE sutureless anterior lamellar therapeutic keratoplasty. On histopathological examination, the excised corneal tissue revealed stromal lamellar disarray with positive colloidal iron staining, strongly suggestive of MCD. Whole-exome sequencing revealed the presence of a likely pathogenic carbohydrate sulfotransferase 6 (CHST6) mutation, confirming the diagnosis of MCD. This concurrent presence of IFC with a corneal stromal dystrophy is previously unreported in the literature, to the best of our knowledge.

Epithelial recurrent erosion dystrophy (ERED) from the splice site altering COL17A1 variant c.3156C>T in families of Finnish-Swedish ancestry

PURPOSE

To describe four Finnish families with epithelial recurrent erosion dystrophy (ERED) caused by the pathogenic variant c.3156C>T in collagen type XVII alpha 1 chain gene (COL17A1).

METHODS

Eleven affected and two unaffected individuals underwent clinical ophthalmological examination, anterior segment photography, and corneal topography. Two of them underwent phototherapeutic keratectomy (PTK). Genetic analysis included both next-generation and Sanger sequencing. Specimens from the manual keratectomy of one patient were available for ophthalmic pathologic examination, including immunohistochemistry.

RESULTS

The common splice-site altering synonymous variant c.3156C > T, p.(Gly1052=) in COL17A1 was confirmed in 15 individuals with ERED from the four families. Subepithelial corneal scarring grades varied and increased with age, leading to decreased best-corrected visual acuity. PTK improved vision in 58- and 67-year-old individuals without reactivating the disease. The keratectomy specimens showed an uneven epithelium and a spectrum of basement membrane abnormalities, including breaks, fragmentation, multiplication and entrapment within the subepithelial scar, reflecting recurrent erosions. The stromal cells consisted of varying proportions of bland and activated fibroblasts and myofibroblasts, reflecting different ages of scars. The family with the largest number of known affected generations originated from Southern Sweden.

CONCLUSION

The phenotype in the Finnish ERED families is consistent with earlier reports of the c.3156C > T variant, although the severity has varied between reports. The phenotype may be modulated by other genes. This study suggests a likely founder effect of the variant in both Finnish and Swedish populations due to their shared population histories. If vision is compromised, PTK can be considered especially in older patients.

IC3D Classification of Corneal Dystrophies-Edition 3

PURPOSE

The International Committee for the Classification of Corneal Dystrophies (IC3D) was created in 2005 to develop a new classification system integrating current information on phenotype, histopathology, and genetic analysis. This update is the third edition of the IC3D nomenclature.

METHODS

Peer-reviewed publications from 2014 to 2023 were evaluated. The new information was used to update the anatomic classification and each of the 22 standardized templates including the level of evidence for being a corneal dystrophy [from category 1 (most evidence) to category 4 (least evidence)].

RESULTS

Epithelial recurrent erosion dystrophies now include epithelial recurrent erosion dystrophy, category 1 ( COL17A1 mutations, chromosome 10). Signs and symptoms are similar to Franceschetti corneal dystrophy, dystrophia Smolandiensis, and dystrophia Helsinglandica, category 4. Lisch epithelial corneal dystrophy, previously reported as X-linked, has been discovered to be autosomal dominant ( MCOLN1 mutations, chromosome 19). Classic lattice corneal dystrophy (LCD) results from TGFBI R124C mutation. The LCD variant group has over 80 dystrophies with non-R124C TGFBI mutations, amyloid deposition, and often similar phenotypes to classic LCD. We propose a new nomenclature for specific LCD pathogenic variants by appending the mutation using 1-letter amino acid abbreviations to LCD. Pre-Descemet corneal dystrophies include category 1, autosomal dominant, punctiform and polychromatic pre-Descemet corneal dystrophy (PPPCD) ( PRDX3 mutations, chromosome 10). Typically asymptomatic, it can be distinguished phenotypically from pre-Descemet corneal dystrophy, category 4. We include a corneal dystrophy management table.

CONCLUSIONS

The IC3D third edition provides a current summary of corneal dystrophy information. The article is available online at https://corneasociety.org/publications/ic3d .

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.

[Intracorneal selective stromal transplantation]

Deep anterior lamellar keratoplasty or penetrating keratoplasty are currently considered the optimal methods of surgical treatment of stromal dystrophies and corneal degeneration. Despite certain advantages and benefits of these methods, they also have significant limitations: involvement of superficial corneal layers in the surgery, need for suturing, development of post-keratoplasty astigmatism etc.

PURPOSE

This study aimed to test and describe the new method of closed sutureless keratoplasty (intracorneal selective stromal transplantation), which was indicated in isolated dystrophic and degenerative pathology of the stroma.

MATERIAL AND METHODS

Intracorneal selective stromal transplantation was performed in a 62-year-old patient with stromal degeneration and intact corneal layers between the altered stroma and the Descemet's membrane posteriorly, and the Bowman's layer anteriorly. The patient also had immature senile cataract. Corneal stroma was removed and replaced with a graft in the optical center of the lens, while the endothelium, the Descemet's membrane and the Bowman's layer remained intact.

RESULTS

The proposed technique of intracorneal selective stromal transplantation makes it possible to replace only the pathologically altered stroma through closed surgical approach, without affecting the anterior and posterior surfaces of the cornea. Best-corrected visual acuity has increased in the patient from 0.01 to 0.6, while mean endothelial cell density has not changed in the course of 24-months follow-up.

CONCLUSION

The proposed keratoplasty method can be used in patients with dystrophy or degeneration of the corneal stroma and preserved endothelial cells, intact Descemet's membrane and Bowman layer. Since the superficial corneal layers are not involved during the surgery, intracorneal selective stromal transplantation combined the advantages of both deep anterior lamellar keratoplasty and endothelial keratoplasty. The biologically favorable result in this first clinical case allows a preliminary conclusion on the technical possibility and functional effectiveness of the proposed method, but further long-term observation and more clinical cases are required.

Pathogenicity and Function Analysis of Two Novel SLC4A11 Variants in Patients With Congenital Hereditary Endothelial Dystrophy

Purpose

The purpose of this study was to explore the pathogenicity and function of two novel SLC4A11 variants associated with congenital hereditary endothelial dystrophy (CHED) and to study the function of a SLC4A11 (K263R) mutant in vitro.

Methods

Ophthalmic examinations were performed on a 28-year-old male proband with CHED. Whole-exome and Sanger sequencing were applied for mutation screening. Bioinformatics and pathogenicity analysis were performed. HEK293T cells were transfected with the plasmids of empty vector, wild-type SLC4A11, and SLC4A11 (K263R) mutant. The transfected cells were treated with SkQ1. Oxygen consumption, cellular reactive oxygen species (ROS) level, mitochondrial membrane potential, and apoptosis rate were measured.

Results

The proband had poor visual acuity with nystagmus since childhood. Corneal foggy opacity was evident in both eyes. Two novel SLC4A11 variants were detected. Sanger sequencing showed that the proband's father and sister carried c.1464-1G>T variant, and the proband's mother and sister carried c.788A>G (p.Lys263Arg) variant. Based on the American College of Medical Genetics (ACMG) guidelines, SLC4A11 c.1464-1G>T was pathogenic, whereas c.788A>G, p.K263R was a variant of undetermined significance. In vitro, SLC4A11 (K263R) variant increased ROS level and apoptosis rate. Decrease in mitochondrial membrane potential and oxygen consumption rate were remarkable. Furthermore, SkQ1 decreased ROS levels and apoptosis rate but increased mitochondrial membrane potential in the transfected cells.

Conclusions

Two novel heterozygous pathogenic variants of the SLC4A11 gene were identified in a family with CHED. The missense variant SLC4A11 (K263R) caused mitochondrial dysfunction and increased apoptosis in mutant transfected cells. In addition, SkQ1 presented a protective effect suggesting the anti-oxidant might be a novel therapeutic drug.

Translational Relevance

This study verified the pathogenicity of 2 novel variants in the SLC4A11 gene in a CHED family and found an anti-oxidant might be a new drug.

The miR-183/96/182 cluster is a checkpoint for resident immune cells and shapes the cellular landscape of the cornea

PURPOSE

The conserved miR-183/96/182 cluster (miR-183C) regulates both corneal sensory innervation and corneal resident immune cells (CRICs). This study is to uncover its role in CRICs and in shaping the corneal cellular landscape at a single-cell (sc) level.

METHODS

Corneas of naïve, young adult [2 and 6 months old (mo)], female miR-183C knockout (KO) mice and wild-type (WT) littermates were harvested and dissociated into single cells. Dead cells were removed using a Dead Cell Removal kit. CD45+ CRICs were enriched by Magnetic Activated Cell Sorting (MACS). scRNA libraries were constructed and sequenced followed by comprehensive bioinformatic analyses.

RESULTS

The composition of major cell types of the cornea stays relatively stable in WT mice from 2 to 6 mo, however the compositions of subtypes of corneal cells shift with age. Inactivation of miR-183C disrupts the stability of the major cell-type composition and age-related transcriptomic shifts of subtypes of corneal cells. The diversity of CRICs is enhanced with age. Naïve mouse cornea contains previously-unrecognized resident fibrocytes and neutrophils. Resident macrophages (ResMφ) adopt cornea-specific function by expressing abundant extracellular matrix (ECM) and ECM organization-related genes. Naïve cornea is endowed with partially-differentiated proliferative ResMφ and contains microglia-like Mφ. Resident lymphocytes, including innate lymphoid cells (ILCs), NKT and γδT cells, are the major source of innate IL-17a. miR-183C limits the diversity and polarity of ResMφ.

CONCLUSION

miR-183C serves as a checkpoint for CRICs and imposes a global regulation of the cellular landscape of the cornea.

Matrix Metalloproteinases and the Pathogenesis of Recurrent Corneal Erosions and Epithelial Basement Membrane Dystrophy

Matrix metalloproteinases (MMPs) are a group of proteolytic enzymes which are members of the zinc endopeptidase family. They have the ability to degrade extracellular matrix elements, allowing for the release of binding molecules and cell migration. Although metalloproteinases regulate numerous physiological processes within the cornea, overexpression of metalloproteinase genes and an imbalance between the levels of metalloproteinases and their inhibitors can contribute to the inhibition of repair processes, the development of inflammation and excessive cellular proliferation. The involvement of MMPs in the pathogenesis of dystrophic corneal diseases needs clarification. Our analyses focus on the involvement of individual metalloproteinases in the pathogenesis of recurrent corneal erosions and highlight their impact on the development of corneal epithelial basement membrane dystrophy (EBMD). We hypothesize that abnormalities observed in patients with EBMD may result from the accumulation and activation of metalloproteinases in the basal layers of the corneal epithelium, leading to basement membrane degradation. A barrier formed from degradation materials inhibits the normal migration of epithelial cells to the superficial layers, which contributes to the development of the aforementioned lesions. This hypothesis seems to be lent support by the elevated concentrations of metalloproteinases in the corneal epithelium of these patients found in our previous studies on the relationships between MMPs and recurrent corneal erosions.

Endoplasmic reticulum stress: molecular mechanism and therapeutic targets

The endoplasmic reticulum (ER) functions as a quality-control organelle for protein homeostasis, or "proteostasis". The protein quality control systems involve ER-associated degradation, protein chaperons, and autophagy. ER stress is activated when proteostasis is broken with an accumulation of misfolded and unfolded proteins in the ER. ER stress activates an adaptive unfolded protein response to restore proteostasis by initiating protein kinase R-like ER kinase, activating transcription factor 6, and inositol requiring enzyme 1. ER stress is multifaceted, and acts on aspects at the epigenetic level, including transcription and protein processing. Accumulated data indicates its key role in protein homeostasis and other diverse functions involved in various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, achromatopsia, cataracts, ocular tumors, ocular surface diseases, and myopia. This review summarizes the molecular mechanisms underlying the aforementioned ocular diseases from an ER stress perspective. Drugs (chemicals, neurotrophic factors, and nanoparticles), gene therapy, and stem cell therapy are used to treat ocular diseases by alleviating ER stress. We delineate the advancement of therapy targeting ER stress to provide new treatment strategies for ocular diseases.

Mini-Review: Clinical Features and Management of Granular Corneal Dystrophy Type 2

Granular corneal dystrophy type 2 (GCD2) is an autosomal dominant corneal stromal dystrophy that is caused by p.Arg124His mutation of transforming growth factor β induced (TGFBI) gene. It is characterized by well demarcated granular shaped opacities in central anterior stroma and as the disease progresses, extrusion of the deposits results in ocular pain due to corneal epithelial erosion. Also, diffuse corneal haze which appears late, causes decrease in visual acuity. The prevalence of GCD2 is high in East Asia including Korea. Homozygous patients show a severe phenotype from an early age, and the heterozygote phenotype varies among patients, depending on several types of compound heterozygous TGFBI mutations. In the initial stage, conservative treatments such as artificial tears, antibiotic eye drops, and bandage contact lenses are used to treat corneal erosion. Different surgical methods are used depending on the depth and extent of the stromal deposits. Phototherapeutic keratectomy removes anterior opacities and is advantageous in terms of its applicability and repeatability. For deeper lesions, deep anterior lamellar keratoplasty can be used as the endothelial layer is not always affected. Recurrence following these treatments are reported within a wide range of rates in different studies due to varying definition of recurrence and follow-up period. In patients who have undergone corneal laser vision-correction surgeries such as photorefractive keratectomy, LASEK, or LASIK including SMILE surgery, corneal opacity exacerbates rapidly with severe deterioration of visual acuity. Further investigations on new treatments of GCD2 are necessary.

A Novel 13q12 Microdeletion Associated with Familial Syndromic Corneal Opacification

Progressive corneal opacification can result from multiple etiologies, including corneal dystrophies or systemic and genetic diseases. We describe a novel syndrome featuring progressive epithelial and anterior stromal opacification in a brother and sister and their mildly affected father, with all three family members having sensorineural hearing loss and two also with tracheomalacia/laryngomalacia. All carried a 1.2 Mb deletion at chromosome 13q12.11, with no other noteworthy co-segregating variants identified on clinical exome or chromosomal microarray. RNAseq analysis from an affected corneal epithelial sample from the proband's brother revealed downregulation of XPO4, IFT88, ZDHHC20, LATS2, SAP18, and EEF1AKMT1 within the microdeletion interval, with no notable effect on the expression of nearby genes. Pathway analysis showed upregulation of collagen metabolism and extracellular matrix (ECM) formation/maintenance, with no significantly down-regulated pathways. Analysis of overlapping deletions/variants demonstrated that deleterious variants in XPO4 were found in patients with laryngomalacia and sensorineural hearing loss, with the latter phenotype also being a feature of variants in the partially overlapping DFNB1 locus, yet none of these had reported corneal phenotypes. Together, these data define a novel microdeletion-associated syndromic progressive corneal opacification and suggest that a combination of genes within the microdeletion may contribute to ECM dysregulation leading to pathogenesis.

Variant Landscape of 15 Genes Involved in Corneal Dystrophies: Report of 30 Families and Comprehensive Analysis of the Literature

Corneal dystrophies (CDs) represent a group of inherited diseases characterized by the progressive deposit of abnormal materials in the cornea. This study aimed to describe the variant landscape of 15 genes responsible for CDs based on a cohort of Chinese families and a comparative analysis of literature reports. Families with CDs were recruited from our eye clinic. Their genomic DNA was analyzed using exome sequencing. The detected variants were filtered using multi-step bioinformatics and confirmed using Sanger sequencing. Previously reported variants in the literature were summarized and evaluated based on the gnomAD database and in-house exome data. In 30 of 37 families with CDs, 17 pathogenic or likely pathogenic variants were detected in 4 of the 15 genes, including TGFBI, CHST6, SLC4A11, and ZEB1. A comparative analysis of large datasets revealed that 12 of the 586 reported variants are unlikely causative of CDs in monogenic mode, accounting for 61 of 2933 families in the literature. Of the 15 genes, the gene most frequently implicated in CDs was TGFBI (1823/2902, 62.82% of families), followed by CHST6 (483/2902, 16.64%) and SLC4A11 (201/2902, 6.93%). This study presents, for the first time, the landscape of pathogenic and likely pathogenic variants in the 15 genes responsible for CDs. Awareness of frequently misinterpreted variants, such as c.1501C>A, p.(Pro501Thr) in TGFBI, is crucial in the era of genomic medicine.

Identifying and categorizing compounds that reduce corneal transforming growth factor beta induced protein levels: a scoping review

INTRODUCTION

Transforming growth factor beta induced (TGFBI) gene mutations have been reported as the cause of a group of genetically inherited, visually debilitating, corneal dystrophies (CD). A scoping literature review to identify and categorize compounds that inhibit corneal TGFBI expression and/or promote TGFBIp degradation was performed. Emphasis was given to their potential to be used as a cost-effective approach via drug repurposing.

AREAS COVERED

We performed a thorough search of original peer-reviewed literature using electronic bibliographic databases and selected articles according to a set of criteria. The total number of articles retrieved from the search terms applied to the databases was 2344. The number of relevant full-text articles included added up to 19. We identified 16 compounds that can theoretically reduce the levels of mutant TGFBIp in human corneal cells.

EXPERT OPINION

Currently, the only temporary treatments available for this condition are lubricant drops and surgery. Here, we explored the crosstalk between cascades that regulate TGFBI expression and identified compounds that target these pathways. Compounds that inhibit DNA synthesis and function, increase elimination of TGFBIp or bind to mutant TGFBIp were also explored with the aim of highlighting promising compounds that can be used in future cost-effective drug-repurposing studies.

Update on the Corneal Dystrophies-Genetic Testing and Therapy

ABSTRACT

One major purpose of the IC3D Corneal Dystrophy Nomenclature Revision was to include genetic information with a goal of facilitating investigation into the pathogenesis, treatment, and perhaps even prevention of the corneal dystrophies, an ambitious goal. Over a decade has passed since the first publication of the IC3D Corneal Dystrophy Nomenclature Revision. Gene therapy is available for an early-onset form of inherited retinal degeneration called Leber congenital amaurosis, but not yet for corneal degenerations. We review the current state of affairs regarding our original ambitious goal. We discuss genetic testing, gene therapy [RNA interference (RNAi) and genome editing], and ocular delivery of corneal gene therapy for the corneal dystrophies. Why have gene therapy techniques not yet been introduced for the corneal dystrophies?

Corneal Epithelial Thickness Mapping in the Diagnosis of Ocular Surface Disorders Involving the Corneal Epithelium: A Comparative Study

PURPOSE

The purpose of this study was to analyze the role of corneal epithelial thickness (ET) mapping provided by spectral domain optical coherence tomography in the diagnosis of ocular surface disorders (OSDs) involving the corneal epithelium.

DESIGN

This was a retrospective comparative study.

METHODS

Institutional settings are as follows. Study population includes 303 eyes with an OSD and 55 normal eyes (controls). Observation procedures include spectral domain optical coherence tomography with epithelial mapping in the central 6 mm. Main outcome measures include ET map classification (normal, doughnut, spoke-wheel, localized/diffuse, and thinning/thickening patterns) and ET data and statistics (minimum, maximum, and SD). A quantitative threshold was determined with receiver operating curves to distinguish pathological from normal corneas. Sensitivity and specificity of classification and quantitative data were calculated using all eyes to assess the ability to distinguish corneas with a given corneal disorder from other conditions.

RESULTS

Classification of full agreement between 3 readers was obtained in 75.4% to 99.4% of cases. Main OSD features were keratoconus (135 eyes), doughnut pattern (sensitivity/specificity = 56/94%), and max-min ET ≥ 13 μm (84/43%); limbal deficiency (56 eyes), spoke-wheel pattern (66/98%), and max-min ET ≥ 14 μm (91/59%); epithelial basement membrane dystrophy (55 eyes), inferior thickening pattern (55/92%), and central ET > 56 μm (53/81%); dry eye (21 eyes), superior thinning pattern (67/88%), and minimal ET ≤ 44 μm (86/48%); pterygium (10 eyes), nasal thickening pattern (100/86%), and nasal ET > 56 μm (80/71%); and in situ carcinoma (11 eyes), max ET > 60 μm (91/60%), and ET SD >5 μm (100/58%).

CONCLUSIONS

The epithelial map pattern recognition combined with quantitative analysis of ET is relevant for the diagnosis of OSDs and for distinguishing various OSDs from each other. Deep learning analysis of big data could lead to the fully automated diagnosis of these disorders.

Corneal irregularity and visual function using anterior segment optical coherence tomography in TGFBI corneal dystrophy

The purpose of this study was to evaluate corneal irregular astigmatism of patients with granular and lattice corneal dystrophy (GCD and LCD). 70 GCD, 35 LCD, and 81 control eyes were included. Anterior and posterior corneal topographic data obtained from anterior segment optical coherence tomography were expanded into four components via Fourier harmonic analysis. These components were compared with healthy eyes and the association between each component and best-corrected visual acuity (BCVA) was investigated. Anterior and posterior components increased in both GCD and LCD eyes. Anterior and posterior components of GCD2, anterior of LCD type 1 (LCD1), posterior of LCD type IIIA (LCD 3A), and type IV (LCD4) significantly increased. BCVA was significantly associated with anterior and posterior components in LCD eyes but not in GCD. The anterior components of LCD1, anterior and posterior of LCD3A, and posterior of LCD4 , were positively correlated with BCVA. As conclusions, in GCD eyes, anterior and posterior components differed from those of the control but BCVA was not significantly associated with them. In LCD eyes, the anterior and posterior components increased, and BCVA was significantly associated with the anterior and posterior components.

Update on Pediatric Corneal Diseases and Keratoplasty

Managing pediatric corneal disorders is challenging as the prognosis of pediatric keratoplasty depends on several factors. Advancements in the genetic basis of congenital corneal diseases and investigations in congenital corneal conditions provide a better understanding of pediatric corneal conditions. Surgeons performing keratoplasty in children now have a choice of various techniques. Evolving surgical techniques of anterior lamellar and endothelial keratoplasties has expanded the management interventions in these pediatric corneal morbidity conditions; however, considerable concerns still exist in association with corneal transplantation in infants and children. Outcomes in pediatric keratoplasty depend upon the preoperative indications, the timing of surgical intervention, intraoperative and postoperative factors including the patient/care givers' compliance. Factors such as low scleral rigidity, higher rate of graft failure, need for frequent examinations under anesthesia, and difficulty in optimal visual acuity assessment still remain a considerable challenge in pediatric scenarios. In children, deprivation amblyopia as a result of the corneal opacification can adversely affect visual development, causing dense amblyopia. Outcomes to surgical interventions for management of corneal opacification in children is further compromised by the pre-existing amblyopia apart from the concerns of refractive outcome of the graft. Graft rejection, graft infection, amblyopia, and glaucoma continue to be serious concerns. In recent years both anterior and posterior lamellar keratoplasty techniques are being increasingly performed in pediatric eyes, which offer advantages in the form of lower risk of graft rejection. The timing of surgery, careful case selection, cautious intraoperative approach, and optimal postoperative management can improve the anatomical and functional outcome in difficult cases.

Optimization of the Ocular Surface Through Treatment of Ocular Surface Disease Before Ophthalmic Surgery: A Narrative Review

Ocular surface disease commonly exists in individuals requiring ophthalmic surgery and may compromise the structure and function of ocular surface components. Ophthalmic surgery may further affect the ocular surface by injuring the epithelium and sensory nerves, disrupting the tear film, or causing local inflammation. Medical management of ocular surface disease prior to ophthalmic surgery aids in reducing inflammation, resolving infection, improving epithelial pathology, stabilizing the tear film, and easing patient symptoms, promoting positive long-term outcomes and minimizing the incidence of postoperative complications. This review summarizes frequently encountered ocular surface diseases and available preoperative medical management options, discusses common ophthalmic surgeries and their effects on the ocular surface, examines potential postoperative complications, and defines recommendations for postoperative ocular surface maintenance.

Recurrence and Visual Outcomes of Phototherapeutic Keratectomy in Lattice Corneal Dystrophy: A Cohort Study

PURPOSE

To evaluate recurrence and visual outcomes of phototherapeutic keratectomy (PTK) in lattice corneal dystrophy.

METHODS

Kaplan-Meier survival analyses were retrospectively performed. Recurrence was defined as central biomicroscopic findings of recurrence with decreased visual acuity: loss of at least two lines or visual acuity ≤ 20/40) at any time during the follow-up.

RESULTS

Twenty-two virgin eyes and 10 with previous keratoplasty (20 patients; 13 women and 7 men) were studied during a mean of 4.7 ± 3.5 years (range: 11 months to 18 years). One and 5 years after the first PTK (PTK1), 1 of 32 and 12 of 32 eyes, respectively, recurred. The cumulative probabilities of recurrence were 3%, 48%, and 89% in the whole sample at 1, 5, and 10 years, respectively. All cases in the virgin group and 8 eyes in the previous keratoplasty group improved their visual acuity. There were no significant differences in recurrence probability between groups (log-rank test; P = .86). A second PTK (PTK2) was performed in 15 of 32 eyes, with 6 postoperative recurrences recorded. The cumulative probabilities of recurrence in the whole sample were 18%, 30%, and 44% at 1, 3, and 5 years, respectively. Visual acuity improved in 11 of 13 eyes in the virgin group and 2 of 2 eyes in the previous keratoplasty group. Recurrence probability after PTK1 and PTK2 was similar in the whole sample (log-rank test; P = .637). Persistent graft edema after PTK1 in one eye was the only complication found.

CONCLUSIONS

PTK can be an effective, safe, and repeatable treatment to delay keratoplasty in symptomatic lattice corneal dystrophy. [J Refract Surg. 2022;38(1):43-49.].

[Clinical and morphological characteristics of corneal epithelial dystrophy (clinical observations)]

This paper presents clinical observations that can be regarded as degeneration of the basement membrane of the corneal epithelium. Difficulties in identifying such forms of corneal dystrophies, on the one hand, are associated with limitation and polymorphism of the clinical picture, and, on the other hand, with insufficient information content of the basic diagnostic methods (i.e. the methods used during the initial examination). The presented clinical cases allow singling out the alarming and pathognomonic signs of the disease in the diagnostic algorithm. In the first case, attention should be paid to biomicroscopic changes in the superficial layers of the cornea and the optical defects, which can be regarded as a manifestation of an irregularity of corneal refraction. Identification of pathognomonic signs of the disease is possible on the basis of a detailed, close-to-morphological study of the structure of superficial corneal layers using confocal microscopy and optical coherence tomography. At the same time, the localization of the detected changes at the level of epithelial basement membrane and its basal sections is of crucial significance for substantiating the diagnosis. In addition, according to the literature data, recurrent erosions of the cornea of unclear etiology should be attributed to presumptive signs of degenerative changes in the basement membrane of the epithelium.

Macular corneal dystrophy related to novel mutations of CHST6 in a Chinese family and clinical observation after penetrating keratoplasty

BACKGROUND

Macular corneal dystrophy (MCD) is a rare corneal stromal dystrophy with bilateral progressive vision loss. The pathogenic gene of MCD is carbohydrate sulfotransferase 6 (CHST6). Herein, we report a novel missense mutation and a rare exon deletion mutation in the CHST6 gene in a Chinese family with MCD.

METHODS

Genomic DNA was extracted from the peripheral blood, and next generation sequencing was used to analyse the gene sequence. The pathogenic mutations were identified in all affected family members. The proband successively received binocular penetrating keratoplasty (PKP), and the corneas were examined by histopathology and colloidal iron staining to prove the diagnosis. A long-term follow-up was made to observe the changes after PKP.

RESULTS

Genetic analysis demonstrated hemizygous mutations in the proband, including a novel c.520A>C (p.K174Q) missense mutation and a rarely reported exon 3 deletion mutation, which were co-segregated with the MCD phenotypes in the pedigree. The positive colloidal iron staining confirmed the diagnosis of MCD in the proband. However, the clinical phenotype and pathological manifestation of both eyes were different from each other because of complicated keratitis in the left eye. During the nine years of follow-up, visual acuity was improved significantly, and the cornea was transparent without rejection and postoperative recurrence in both eyes.

CONCLUSIONS

The novel hemizygous mutations were thought to contribute to the loss of CHST6 function, which induced typical clinical and pathological features of MCD. PKP was an effective treatment for MCD.

Long-Term Observation of Deep Anterior Lamellar Keratoplasty in Patients with Post-LASIK Granular Corneal Dystrophy Type 2: Two Case Reports

INTRODUCTION

Laser-assisted in situ keratomileusis (LASIK) exacerbates granular corneal dystrophy type 2. Post-LASIK granular corneal dystrophy type 2 is treated by several surgical techniques. To the best of our knowledge, no report has addressed the results of deep anterior lamellar keratoplasty in affected patients. Here, we report our experience regarding deep anterior lamellar keratoplasty treatment of patients with post-LASIK granular corneal dystrophy type 2.

METHODS

We describe two Japanese women who underwent deep anterior lamellar keratoplasty to treat corneal opacities that worsened after LASIK.

RESULTS

One patient had a family history of corneal dystrophies. During the initial visit to our clinic, numerous fine opacities were found at the LASIK flap interface in both patients. The clinical findings were compatible with post-LASIK granular corneal dystrophy type 2. Both patients underwent deep anterior lamellar keratoplasty by one of the authors (T.C.). In both procedures, the surgeon used a visco-dissection technique and successfully removed the whole corneal stroma. Histopathological examination of the excised corneal button from each eye revealed amyloid and hyaline deposits at the LASIK flap interface. Neither patient experienced recurrent corneal opacity during the follow-up visit at 8 years (patient 1) and 6 years (patient 2).

CONCLUSION

Deep anterior lamellar keratoplasty can be used for the treatment of post-LASIK granular corneal dystrophy type 2. Removal of the entire host stroma may be important for the prevention of recurrent corneal opacity.

Characterization of a dual media system for culturing primary normal and Fuchs endothelial corneal dystrophy (FECD) endothelial cells

Primary cultures of human corneal endothelial cells (HCECs) are an important model system for studying the pathophysiology of corneal endothelium. The purpose of this study was to identify and validate an optimal primary culture model of normal and Fuchs endothelial corneal dystrophy (FECD) endothelial cells by comparing cell morphology and marker expression under different media conditions to in vivo donor tissues. Primary and immortalized HCECs, isolated from normal and FECD donors, were cultured in proliferation media (Joyce, M4, Bartakova) alone or sequentially with maturation media (F99, Stabilization 1, M5). CD56, CD73 and CD166 expressions were quantified in confluent and matured cell lines by flow cytometry. HCECs that were allowed to proliferate in Joyce's medium followed by maturation in low-mitogen containing media yielded cells with similar morphology to corneal endothelial tissues. Elevated expression of CD56 and CD166 and low expression of CD73 correlated with regular, hexagonal-like HCEC morphology. CD56:CD73 > 2.5 was most consistent with normal HCEC morphology and mimicked corneal endothelial tissue. Immortalization of normal HCECs by hTERT transduction showed morphology and CD56:CD73 ratios similar to parental cell lines. HCECs established from FECD donors showed reduced CD56:CD73 ratios compared to normal HCECs which coincided with reduced uniformity and regularity of cell monolayers. Overall, a dual media system with Joyce's medium for proliferation and a low-mitogen media for maturation, provided normal cultures with regular, hexagonal-like cell morphologies consistent with corneal endothelial cells in vivo. CD56:CD73 expression ratio >2.5 was predictive of in vivo-like cellular morphology.

Functional study of SCCD pathogenic gene UBIAD1 (Review)

Schnyder's crystalline corneal dystrophy (SCCD) is a rare autosomal dominant genetic disorder that is characterized by progressive corneal opacity, owing to aberrant accumulation of cholesterol and phospholipids in the cornea. A number of SCCD affected families have been reported in the world since 1924, when it was first described. In 2007, the molecular basis of SCCD was demonstrated to be associated with a tumor suppressor, UbiA prenyltransferase domain-containing 1 (UBIAD1), which was isolated from the bladder mucosa and demonstrated to be involved in vitamin K₂ and CoQ10 biosynthesis. This sterol triggers the binding of UBIAD1 to 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGCR) at endoplasmic reticulum (ER) membranes, which is regulated by an intracellular geranylgeranyl diphosphate (GGpp) molecule. The inability of SCCD-associated UBIAD1 to bind GGpp results in the consistent binding of UBIAD1 to HMGCR at ER membranes. This binding leads to HMGCRs being redundant. Therefore, they cannot be degraded through ER-associated degradation to synthesize abundant cholesterol in tissue cells. Excess corneal cholesterol accumulation thus leads to SCCD disease. After decades, the efforts of numerous ophthalmologists and scientists have helped clarify the molecular basis and pathogenesis of SCCD, which has guided the effective diagnosis and treatment of this genetic disorder. However, more studies need to be conducted to understand the pathogenesis of SCCD disease from a genetic basis by studying the defective gene, UBIAD1. Results would guide effective diagnosis and treatment of the inherited eye disease.

Macular Corneal Dystrophy: An Updated Review

Macular Corneal Dystrophy is an autosomal recessive form of corneal dystrophy due to a mutation in CHST6 gene, which results in abnormal proteoglycan synthesis. There is accumulation of abnormal glycosaminoglycans in the corneal stroma and endothelium. The deposition results in progressive loss of corneal transparency and visual acuity. The histopathology shows characteristic alcian blue positive deposits. Management in the cases with visual loss requires keratoplasty either full thickness or lamellar. The decision about the ideal type of keratoplasty depends on age and pre-operative clinical features. Although prognosis after keratoplasty is good, recurrences can occur. Future research should be targeted towards gene therapy in this condition.

Clinical Profile and Demographic Distribution of Corneal Dystrophies in India: A Study of 4198 Patients

PURPOSE

To describe the clinical profile and demographic distribution of corneal dystrophy in patients presenting to a multitier ophthalmology hospital network in India.

METHODS

This cross-sectional hospital-based study included 2,151,584 new patients presenting between March 2012 and December 2019 (∼8 year period). Patients with a clinical diagnosis of corneal dystrophy in at least 1 eye were included as cases. The data were collected by using an electronic medical record system.

RESULTS

Overall, 4198 new patients (0.20%) were diagnosed with corneal dystrophy. The prevalence rates were 0.19% in children (age < 16 years) and 0.20% in adults. Most patients were women (51.86%). The mean age of the patients was 43.61 ± 21.39 years. Most patients (18.79%) were between 61 and 70 years of age. The most common anatomical location of the dystrophy was endothelium (51.71%), followed by stroma (43.55%) and Bowman membrane/epithelium (4.73%). The most common corneal dystrophy was Fuch endothelial corneal dystrophy (41.89%). Most eyes had mild or no visual impairment (43.43%). Of the 8193 eyes, 998 eyes (12.18%) underwent a corneal surgery. Among those who underwent surgical intervention, endothelial keratoplasty was the most commonly performed surgical procedure (52%), followed by penetrating keratoplasty (22%).

CONCLUSIONS

Corneal dystrophy is a rare disease, affecting patients seeking eye care in India. Endothelial dystrophies were the most common, followed by stromal dystrophies. Among the stromal dystrophies, macular dystrophy was the most common. At initial presentation, visual impairment was mild to moderate in most patients, and surgical intervention was needed in 12.18% of the eyes during the study period.

Laser refractive surgery in corneal dystrophies

Twenty-eight case reports and case series published between 2000 and 2019 concerning laser refractive surgery in patients with corneal dystrophies, resulting in 173 eyes from 94 patients, were included in this systematic review. Best results were achieved in posterior corneal polymorphous and Cogan dystrophy. Unfavorable results were found in Avellino dystrophy and Fuchs endothelial corneal dystrophy (FECD). Photorefractive keratectomy was not indicated in Meesmann and Avellino dystrophy. Laser in situ keratomileusis was indicated in posterior polymorphous corneal dystrophy but not in FECD, Avellino, or Cogan dystrophy. Small-incision lenticule extraction and other dystrophies such as lattice, fleck, Lisch, or François did not achieve enough scientific evidence to report any recommendation.

Evaluation of the Genetic Variation Spectrum Related to Corneal Dystrophy in a Large Cohort

AIMS

To characterize the genetic landscape and mutation spectrum of patients with corneal dystrophies (CDs) in a large Han ethnic Chinese Cohort with inherited eye diseases (IEDs).

METHODS

Retrospective study. A large IED cohort was recruited in this study, including 69 clinically diagnosed CD patients, as well as other types of eye diseases patients and healthy family members as controls. The 792 genes on the Target_Eye_792_V2 chip were used to screen all common IEDs in our studies, including 22 CD-related genes.

RESULTS

We identified 2334 distinct high-quality variants on 22 CD-related genes in a large IEDs cohort. A total of 21 distinct pathogenic or likely pathogenic mutations were identified, and the remaining 2313 variants in our IED cohort had no evidence of CD-related pathogenicity. Overall, 81.16% (n = 56/69) of CD patients received definite molecular diagnoses, and transforming growth factor-beta-induced protein (TGFBI), CHTS6, and SLC4A11 genes covered 91.07, 7.14, and 1.79% of the diagnosed cases, respectively. Twelve distinct disease-associated mutations in the TGFBI gene were identified, 11 of which were previously reported and one is novel. Four of these TGFBI mutations (p.D123H, p.M502V, p.P501T, and p.P501A) were redefined as likely benign in our Han ethnic Chinese IED cohort after performing clinical variant interpretation. These four TGFBI mutations were detected in asymptomatic individuals but not in CD patients, especially the previously reported disease-causing mutation p.P501T. Among 56 CD patients with positive detected mutations, the recurrent TGFBI mutations were p.R124H, p.R555W, p.R124C, p.R555Q, and p.R124L, and the proportions were 32.14, 19.64, 14.29, 10.71, and 3.57%, respectively. Twelve distinct pathogenic or likely pathogenic mutations of CHTS6 were detected in 28 individuals. The recurrent mutations were p.Y358H, p.R140X, and p.R205W, and the proportions were 25.00, 21.43, and 14.29%, respectively. All individuals associated with TGFBI were missense mutations; 74.19% associated with CHTS6 mutations were missense mutations, and 25.81% were non-sense mutations. Hot regions were located in exons 4 and 12 of TGFBI individuals and located in exon 3 of CHTS6 individuals. No de novo mutations were identified.

CONCLUSION

For the first time, our large cohort study systematically described the variation spectrum of 22 CD-related genes and evaluated the frequency and pathogenicity of all 2334 distinct high-quality variants in our IED cohort. Our research will provide East Asia and other populations with baseline data from a Han ethnic population-specific level.

Genotypic Homogeneity in Distinctive Transforming Growth Factor-Beta Induced (TGFBI) Protein Phenotypes

Background: To evaluate the distribution of the transforming growth factor-beta induced (TGFBI) corneal dystrophies in a multi-ethnic population in Singapore, and to present the different phenotypes with the same genotype. Methods: This study included 32 patients. Slit lamp biomicroscopy was performed for each patient to determine the disease phenotype. Genomic DNA was extracted from the blood samples and the 17 exons of the TGFBI gene were amplified by PCR and sequenced bi-directionally for genotype analysis. Results: Regarding phenotypes, the study patients comprised 11 (34.4%; 8 with R555W and 3 with R124H mutation) patients with granular corneal dystrophy type 1 (GCD1), 6 (18.8%; 5 with R124H and 1 with R124C mutation) patients with GCD2, 13 (40.6%; 7 with R124C, 2 with H626R, 2 with L550P, 1 with A620D and 1 with H572R) patients with lattice corneal dystrophy (LCD) and 2 (6.3%; 1 with R124L and 1 with R124C) patients with Reis-Bückler corneal dystrophy. Regarding genotype, R124H mutation was associated with GCD2 (5 cases; 62.5%) and GCD1 (3 cases; 37.5%). R124C mutation was associated with LCD (7 cases; 87.5%) and GCD2 (1 case; 12.5%). All the 8 cases (100%) of R555W mutation were associated with GCD1. Conclusions: Although the association between genotype and phenotype was good in most cases (65.7%; 21 of 32 patients), genotype/phenotype discrepancy was observed in a significant number.

Corneal Dystrophy in Dutch Belted Rabbits as a Possible Model of Thiel-Behnke Subtype of Epithelial-Stromal TGFβ-Induced Corneal Dystrophy

The International Committee for Classification of Corneal Dystrophies (IC3D) categorized corneal dystrophies in humans using anatomic, genotypic, and clinicopathologic phenotypic features. Relative to the IC3D classification, a review of the veterinary literature confirmed that corneal dystrophy is imprecisely applied to any corneal opacity and to multiple poorly characterized histologic abnormalities of the cornea in animals. True corneal dystrophy occurs in mice with targeted mutations and spontaneously in pet dogs and cats and in Dutch belted (DB) rabbits, but these instances lack complete phenotyping or genotyping. Corneal dystrophy in DB rabbits can be an important confounding finding in ocular toxicology studies but has only been described once. Therefore, the ophthalmology and pathology of corneal dystrophy in 13 DB rabbits were characterized to determine whether the findings were consistent with or a possible model of any corneal dystrophy subtypes in humans. Slit lamp and optical coherence tomography (OCT) imaging were used to characterize corneal dystrophy over 4 months in young DB rabbits. The hyperechoic OCT changes correlated with light microscopic findings in the anterior stroma, consisting of highly disordered collagen fibers and enlarged keratocytes. Histochemical stains did not reveal abnormal deposits. Small clusters of 8 to 16 nm diameter curly fibers identified by transmission electron microscopy were consistent with Thiel-Behnke (TBCD) subtype of epithelial-stromal transforming growth factor β-induced dystrophies. Sporadic corneal dystrophy in DB rabbits appears to be a potential animal model of TBCD, but genotypic characterization will be required to confirm this categorization.

Mutation-Independent Allele-Specific Editing by CRISPR-Cas9, a Novel Approach to Treat Autosomal Dominant Disease

CRISPR-Cas9 provides a tool to treat autosomal dominant disease by non-homologous end joining (NHEJ) gene disruption of the mutant allele. In order to discriminate between wild-type and mutant alleles, Streptococcus pyogenes Cas9 (SpCas9) must be able to detect a single nucleotide change. Allele-specific editing can be achieved by using either a guide-specific approach, in which the missense mutation is found within the guide sequence, or a protospacer-adjacent motif (PAM)-specific approach, in which the missense mutation generates a novel PAM. While both approaches have been shown to offer allele specificity in certain contexts, in cases where numerous missense mutations are associated with a particular disease, such as TGFBI (transforming growth factor β-induced) corneal dystrophies, it is neither possible nor realistic to target each mutation individually. In this study, we demonstrate allele-specific CRISPR gene editing independent of the disease-causing mutation that is capable of achieving complete allele discrimination, and we propose it as a targeting approach for autosomal dominant disease. Our approach utilizes natural variants in the target region that contain a PAM on one allele that lies in cis with the causative mutation, removing the constraints of a mutation-dependent approach. Our innovative patient-specific guide design approach takes into account the patient's individual genetic make-up, allowing on- and off-target activity to be assessed in a personalized manner.

A pathogenic variant in the transforming growth factor beta I (TGFBI) in four Iranian extended families segregating granular corneal dystrophy type II: A literature review

OBJECTIVES

Granular and lattice corneal dystrophies (GCDs & LCDs) are autosomal dominant inherited disorders of the cornea. Due to genetic heterogeneity and large genes, unraveling the mutation is challenging.

MATERIALS AND METHODS

Patients underwent comprehensive clinical examination, and targeted next-generation sequencing (NGS) was used for mutation detection. Co-segregation and in silico analysis was accomplished.

RESULTS

Patients suffered from GCD. NGS disclosed a known pathogenic variant, c.371G>A (p.R124H), in exon 4 of TGFBI. The variant co-segregated with the phenotype in the family. Homozygous patients manifested with more severe phenotypes. Variable expressivity was observed among heterozygous patients.

CONCLUSION

The results, in accordance with previous studies, indicate that the c.371G>A in TGFBI is associated with GCD. Some phenotypic variations are related to factors such as modifier genes, reduced penetrance and environmental effects.

TGF-β1 enhanced myocardial differentiation through inhibition of the Wnt/β-catenin pathway with rat BMSCs

OBJECTIVES

To investigate and test the hypotheses that TGF-β1 enhanced myocardial differentiation through Wnt/β-catenin pathway with rat bone marrow mesenchymal stem cells (BMSCs).

MATERIALS AND METHODS

Lentiviral vectors carrying the TGF-β1 gene were transduced into rat BMSCs firstly. Then several kinds of experimental methods were used to elucidate the related mechanisms by which TGF-β1 adjusts myocardial differentiation in rat BMSCs.

RESULTS

Immunocytochemistry revealed that cTnI and Cx43 expressed positively in the cells that were transduced with TGF-β1. The results of Western blot (WB) test showed that the levels of intranuclear β-catenin and total β-catenin were all significantly decreased. However, the cytoplasmic β-catenin level was largely unchanged. Moreover, the levels of GSK-3β were largely unchanged in BMSCs, whereas phosphorylated GSK-3β was significantly decreased in BMSCs. When given the activator of Wnt/β-catenin pathway (lithium chloride, LiCl) to BMSCs transducted with TGF-β1, β-catenin was increased, while phosphorylated β-catenin was decreased. In addition, cyclinD1, MMP-7, and c-Myc protein in BMSCs transducted with Lenti-TGF-β1-GFP were significantly lower.

CONCLUSION

These results indicate that TGF-β1 promotes BMSCs cardiomyogenic differentiation by promoting the phosphorylation of β-catenin and inhibiting cyclinD1, MMP-7, and c-Myc expression in Wnt/β-catenin signaling pathway.

Rare stromal corneal dystrophic diseases in Oman: A clinical and histopathological analysis for accurate diagnosis

INTRODUCTION

Corneal dystrophy (CD) encirclements a heterogeneous group of genetically determined corneal diseases. Many features still remain unknown.

AIM

The purpose of this study was to highlight the clinical and the histopathological aspects of rare stromal CDs and to assess the clinical and the histopathological roles in their diagnosis.

PATIENTS AND METHODS

This study incorporated 10 eyes of six patients, clinically diagnosed as follows: four patients with bilateral lattice stromal CD (8 eyes) and two patients, each one eye, one with macular and the other with granular-type CD. Histopathological examination with applications of many special stains was done in four eyes (4 patients) after penetrating keratoplasty.

RESULTS

The histopathological examination was in concordance with the clinical diagnosis of three examined corneas and revealed first eye with lattice dystrophy, second eye with macular dystrophy, and third eye with granular dystrophy. The fourth examined cornea was not that in concordance with the clinical diagnosis of lattice CD as it showed mixed stromal CD patterns of granular, macular, and lattice types.

CONCLUSION

Histopathological assessment of corneal dystrophy cases, subjected to keratoplasty is recommended to avoid missing cases with mixed stromal corneal dystrophy. Also, using low magnification slit lamp alone in the clinical assessment of the corneal opacity appeared to be limited mode and thus, the imaging corneal methods such confocal microscopy and high-definition optical coherence tomography are recommended for future cases especially in cases with unclassic query diagnosis.

Descemet Stripping Endothelial Keratoplasty in Pediatric Patients with Congenital Hereditary Endothelial Dystrophy

PURPOSE

To report the long-term outcomes of Descemet stripping endothelial keratoplasty (DSEK) with suture-assisted donor lenticule insertion performed in different age groups for pediatric patients with congenital hereditary endothelial dystrophy (CHED).

DESIGN

Retrospective case series.

METHODS

Pediatric patients with CHED who underwent DSEK from January 2010 to January 2016 were enrolled. Patients were divided into 2 groups according to their ages: the infant group and the child group. Long-term clinical outcomes and complications were compared.

RESULTS

Thirty eyes of 16 patients were included: 19 eyes (10 patients) in the child group and 11 eyes (6 patients) in the infant group. The average duration of follow-up was 4.08 ± 1.90 years (range 2.5-8.5 years). Corneal transparency scores of the 2 groups on postoperative day 7 were not statistically different. The average postoperative best-corrected visual acuity (BCVA) in the infant group (logMAR 0.32 ± 0.11) was better than that in the child group (logMAR 0.54 ± 0.20; (P = .01). Thirty-three percent of cases in the child group and 86% of cases in the infant group had postoperative BCVA achieved or better than logMAR 0.4. Average endothelial cell loss in the child group was 31.21% ± 9.17%. Lenticule detachment occurred in 3 cases in the child group.

CONCLUSIONS

Improved visual outcomes could be achieved in infant patients with CHED after DSEK without significant complications. Suture-assisted donor lenticule insertion techniques, Descemet membrane stripping, and postoperative sedation are advocated technical points.

Amyloidosis and Ocular Involvement: an Overview

Purpose: To describe the ophthalmic manifestations of amyloidosis and the corresponding therapeutic measures.Methods: The 178 patients included in the study had different types of amyloidosis, diagnosed at a single internal medicine institution (Bari, Italy). To provide a comprehensive review of the types of amyloidosis that can be associated with ocular involvement, the images and clinical descriptions of patients with amyloidosis structurally related to gelsolin, keratoepithelin and lactoferrin were obtained in collaborations with the ophthalmology departments of hospitals in Mainz (Germany) and Helsinki (Finland).Results: Overall, ocular morbidity was detected in 41 of the 178 patients with amyloidosis (23%). AL amyloidosis was diagnosed in 18 patients with systemic disease, 3 with multiple myeloma, and 11 with localized amyloidosis. AA amyloidosis was detected in 2 patients with rheumatoid arthritis and 3 with Behçet syndrome, and transthyretin amyloidosis in 4 patients. The treatment of AL amyloidosis is based on chemotherapy to suppress the production of amyloidogenic L-chains and on surgical excision of orbital or conjunctival masses. AA amyloidosis is managed by targeting the underlying condition. Vitreous opacities and additional findings of ocular involvement in patients with transthyretin amyloidosis indicate the need for pars plana vitrectomy. Gelsolin amyloidosis, characterized by lattice corneal amyloidosis and polyneuropathy, results in recurrent keratitis and corneal scarring, such that keratoplasty is inevitable. In patients with lattice corneal dystrophies associated with amyloid deposits of keratoepithelin fragments, corneal transparency is compromised by deposits of congophilic material in the subepithelial layer and deep corneal stroma. Patients with established corneal opacities are treated by corneal transplantation, but the prognosis is poor because recurrent corneal deposits are possible after surgery. In patients with gelatinous drop-like dystrophy, the amyloid fibrils that accumulate beneath the corneal epithelium consist of lactoferrin and can severely impair visual acuity. Keratoplasty and its variants are performed for visual rehabilitation.Conclusion: A routine ophthalmic follow-up is recommended for all patients with established or suspected amyloidosis, independent of the biochemical type of the amyloid. Close collaboration between the ophthalmologist and the internist will facilitate a more precise diagnosis of ocular involvement in amyloidosis and allow the multidisciplinary management of these patients.Abbreviations: CD: corneal dystrophy; CLA: corneal lattice amyloidosis; CNS: central nervous system; CT: computed tomography; FAP: familial amyloidotic polyneuropathy; GDLCD: gelatinous drop-like corneal dystrophy; GLN: gelsolin; LCD: lattice corneal dystrophy; MRI: magnetic resonance imaging; OLT: orthotopic liver transplantation; TEM: transmission electron microscopy; TGFBI: transforming growth factor β induced; TTR: transthyretin.

[Corneal dystrophies in optical coherence tomography]

BACKGROUND

Corneal optical coherence tomography (anterior segment OCT, AS-OCT) is described in the current IC3D classification of corneal dystrophies to be a method for improvement of clinical diagnostics and treatment.

OBJECTIVE

In this case series AS-OCT images of corneal dystrophies were analyzed with respect to morphological changes.

MATERIAL AND METHODS

This was a retrospective imaging and morphological case series with 38 eyes. For image acquisition the corneal module of the high-resolution spectral-domain OCT Zeiss Cirrus HD-5000 platform (Oberkochen, Germany) was employed. The following corneal dystrophies were analyzed: epithelial basement membrane dystrophy, Meesmann corneal dystrophy, Reis-Bücklers corneal dystrophy, granular corneal dystrophy type 1, granular corneal dystrophy type 2 and macular corneal dystrophy.

RESULTS

The AS-OCT images showed the typical changes of the dystrophies through hyperreflectivity and hyporeflectivity in the individual corneal layers. The findings in the AS-OCT images correlated well with the histological descriptions in the literature and provided additional information to the slit lamp examination, especially with respect to the exact location of the alterations.

CONCLUSION

Corneal AS-OCT imaging seems to be a helpful tool for determination of morphological changes in patients with corneal dystrophies and can facilitate both the diagnostics and surgical treatment decisions.

Granular type I corneal dystrophy in a large consanguineous Tunisian family with homozygous p.R124S mutation in the TGFBI gene

Purpose: We report the clinical features and the mutational analysis in a large Tunisian family with granular corneal dystrophy type I (GCD1). Patients and Methods: Thirty-three members of the Tunisian family underwent a complete ophthalmologic examination. DNA extraction and direct Sanger sequencing of the exons 4 and 12 of transforming growth factor β Induced (TGFBI) gene was performed for 42 members. For the molecular modeling of TGFBI protein, we used pGenTHREADER method to identify templates, 3D-EXPRESSO program to align sequences, MODELLER to get a homology model for the FAS1 (fasciclin-like) domains and finally NOMAD-ref web server for the energy minimization. Results: The diagnosis of GCD1 was clinically and genetically confirmed. Sequencing of exon 4 of TGFBI gene revealed the p.[R124S] mutation at heterozygous and homozygous states in patients with different clinical severities. Visual acuity was severely affected in the homozygous patients leading to a first penetrating keratoplasty. Recurrence occurred rapidly, began in the seat of the corneal stitches and remained superficial up to 40 years after the graft. For heterozygous cases, visual acuity ranged from 6/10 to 10/10. Corneal opacities were deeper and predominating in the stromal center. According to bioinformatic analysis, this mutation likely perturbs the protein physicochemical properties and reduces its solubility without structural modification. Conclusions: Our study describes for the first time phenotype-genotype correlation in a large Tunisian family with GCDI and illustrates for the first time clinical and histopathological presentation of homozygous p.[R124S] mutation. These results help to understand pathophysiology of the disease.

REVIEW: Current understanding of the pathogenesis of Fuchs' endothelial corneal dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is the most prominent reason for corneal-endothelial transplantations across the globe. The disease pathophysiology manifests through a combination of various genetic and non-heritable factors. This review provides a comprehensive list of known genetic players that cause FECD, and discusses the prominent pathological features that participate in disease progression, such as channel dysfunction, abnormal extracellular matrix deposition, RNA toxicity, oxidative stress, and apoptosis. Although current practices to correct visual acuity involve surgical intervention, this review also discusses the scope of various non-surgical therapeutics to remedy FECD.

Clinical diversity in macular corneal dystrophy: an optical coherence tomography study

PURPOSE

To characterise the corneal deposits of macular corneal dystrophy and correlate with high-resolution optical coherence tomography (OCT).

METHODS

A total of 23 eyes of 15 patients were evaluated for clinical features on slit lamp biomicroscopy, and high-resolution OCT was performed to correlate the clinical findings. The deposits were characterised based upon their location and level in the corneal layers.

RESULTS

Mean age was 31.5 (Range 20-67) years. The stromal deposits were restricted to central 8 mm in 9 eyes; in the rest of the 14 eyes, the deposits were seen in both central and peripheral cornea. In one patient, no such distinction could be made due to diffuse nature of the deposits throughout the cornea with sparing of 1-2 mm of the cornea internal to the limbus. The central deposits were in the anterior stromal layers, while the peripheral deposits were in the deep stromal corneal layers and non-contiguous with the anterior stromal deposits. In one patient aged 67 years, the peripheral deposits in deep corneal layers were more prominent than the central anterior stromal deposits and were associated with a significant thickening of Descemet membrane.

CONCLUSIONS

MCD exhibits a clinically diverse presentation as revealed on the clinical and optical coherence tomography study. Immunophenotype and genotype-phenotype correlation may further help in understanding various clinical presentations of MCD.

Mutation update: TGFBI pathogenic and likely pathogenic variants in corneal dystrophies

Human transforming growth factor β-induced (TGFBI), is a gene responsible for various corneal dystrophies. TGFBI produces a protein called TGFBI, which is involved in cell adhesion and serves as a recognition sequence for integrins. An alteration in cell surface interactions could be the underlying cause for the progressive accumulation of extracellular deposits in different layers of the cornea with the resulting changes of refractive index and transparency. To this date, 69 different pathogenic or likely pathogenic variants in TGFBI have been identified in a heterozygous or homozygous state in various corneal dystrophies, including a novel variant reported here. All disease-associated variants were inherited as autosomal-dominant traits but one; this latter was inherited as an autosomal recessive trait. Most corneal dystrophy-associated variants are located at amino acids Arg124 and Arg555. To keep the list of corneal dystrophy-associated variant current, we generated a locus-specific database for TGFBI (http://databases.lovd.nl/shared/variants/TGFBI) containing all pathogenic and likely pathogenic variants reported so far. Non-disease-associated variants are described in specific databases, like gnomAD and ExAC but are not listed here. This article presents the most recent up-to-date list of disease-associated variants.

Evaluation of TGFBI corneal dystrophy and molecular diagnostic testing

To date, 70 different TGFBI mutations that cause epithelial-stromal corneal dystrophies have been described. At present one commercially available test examines for the five most common of these mutations: R124H, R124C, R124L, R555W, and R555Q. To expand the capability of identifying the causative mutation in the remaining cases, 57 mutations would need to be added. The aim of this study was to obtain a better understanding of the worldwide distribution and population differences of TGFBI mutations and to assess which mutations could be included or excluded from any potential assay. A total of 184 published papers in Human Gene Mutation Database (HGMD) and PubMed from 34 countries worldwide reporting over 1600 corneal dystrophy cases were reviewed. Global data from 600,000 samples using the commercially available test were analyzed. Case studies by University College of London (UCL), Moorfield’s Corneal Dystrophy Study data and 19 samples from patients with clinical abnormality or uncertainty for which the current test detected no mutation were used to predict an achievable detection rate. Data from the literature search showed no difference in the spectrum and frequency of each mutation in different populations or geographical locations. According to our analysis, an increase to the worldwide detection rate in all populations from 75 to 90% could be achieved by the addition of six mutations—H626R, A546D, H572R, G623D, R124S, and M502V—to the currently available test and that may be beneficial for LASIK pre-screening worldwide.