Corneal Dystrophies

Corneal dystrophies have classically referred to inherited, bilateral disease without systemic findings, although there are several exceptions to this definition. Hereditary pattern is not present in most patients with epithelial basement membrane dystrophy (EBMD). Unilateral corneal changes may be found in some patients with posterior polymorphous corneal dystrophy (PPCD). TGFBI gene mutation (p.His572del) is associated with a unilateral, late-onset variant of lattice corneal dystrophy. Among all dystrophies, macular corneal dystrophy and posterior amorphous corneal dystrophy are associated with decreased corneal thickness. The International Committee for Classification of Corneal Dystrophies (IC3D) was created in 2005 to revise the corneal dystrophy nomenclature and create a current and accurate corneal dystrophy classification system. Evidential categories were created in the IC3D classification for reflecting the natural evolution of a corneal dystrophy and indicate the level of evidence supporting the existence of a given dystrophy.

Bilateral posterior lamellar corneal transplant surgery in an infant of 17 weeks old: surgical challenges and the added value of intraoperative optical coherence tomography

To describe the surgical challenges, management, and value of intra-operative optical coherence tomography in a case of a bilateral Descemet Stripping Automated Endothelial Keratoplasty corneal transplantation at 17 weeks of age for the treatment of severe posterior polymorphous corneal dystrophy resulting from a de novo mutation of the OVOL2-gene.

Non-Penetrance for Ocular Phenotype in Two Individuals Carrying Heterozygous Loss-of-Function ZEB1 Alleles

ZEB1 loss-of-function (LoF) alleles are known to cause a rare autosomal dominant disorder—posterior polymorphous corneal dystrophy type 3 (PPCD3). To date, 50 pathogenic LoF variants have been identified as disease-causing and familial studies have indicated that the PPCD3 phenotype is penetrant in approximately 95% of carriers. In this study, we interrogated in-house exomes (n = 3616) and genomes (n = 88) for the presence of putative heterozygous LoF variants in ZEB1. Next, we performed detailed phenotyping in a father and his son who carried a novel LoF c.1279C>T; p.(Glu427*) variant in ZEB1 (NM_030751.6) absent from the gnomAD v.2.1.1 dataset. Ocular examination of the two subjects did not show any abnormalities characteristic of PPCD3. GnomAD (n = 141,456 subjects) was also interrogated for LoF ZEB1 variants, notably 8 distinct heterozygous changes presumed to lead to ZEB1 haploinsufficiency, not reported to be associated with PPCD3, have been identified. The NM_030751.6 transcript has a pLI score ≥ 0.99, indicating extreme intolerance to haploinsufficiency. In conclusion, ZEB1 LoF variants are present in a general population at an extremely low frequency. As PPCD3 can be asymptomatic, the true penetrance of ZEB1 LoF variants remains currently unknown but is likely to be lower than estimated by the familial led approaches adopted to date.

Expression and Function of ZEB1 in the Cornea

ZEB1 is an important transcription factor for epithelial to mesenchymal transition (EMT) and in the regulation of cell differentiation and transformation. In the cornea, ZEB1 presents in all three layers: the epithelium, the stroma and the endothelium. Mutations of ZEB1 have been linked to multiple corneal genetic defects, particularly to the corneal dystrophies including keratoconus (KD), Fuchs endothelial corneal dystrophy (FECD), and posterior polymorphous corneal dystrophy (PPCD). Accumulating evidence indicates that dysfunction of ZEB1 may affect corneal stem cell homeostasis, and cause corneal cell apoptosis, stromal fibrosis, angiogenesis, squamous metaplasia. Understanding how ZEB1 regulates the initiation and progression of these disorders will help us in targeting ZEB1 for potential avenues to generate therapeutics to treat various ZEB1-related disorders.

Corneal cross-linking for treatment of progressive keratoconus in a patient with Alport syndrome: A case report

Purpose: Ocular features of Alport syndrome include anterior lenticonus, posterior polymorphous corneal dystrophy, and fleck-and-dot retinopathy in most cases. Keratoconus in such patients has been rarely mentioned in previous studies. To our knowledge, this is the first report of corneal cross-linking for halting the progression of keratoconus in a patient with Alport syndrome. Case report: A 22-year-old male was referred for his initial corneal topography, after he was already prescribed with rigid gas-permeable contact lenses. Alport syndrome was diagnosed in his infancy and gene COL4A5 mutation was confirmed. Ophthalmological evaluation confirmed keratoconus. One-year follow-up showed a progression on his right eye and standard corneal cross-linking was performed. Stabilization of the disease marked by normalization in visual function and corneal tomography values was noticed 1 year after the procedure. Conclusions: When diagnosing ocular clinical findings of Alport syndrome, keratoconus should be considered. Standard corneal cross-linking protocol can halt its progression.