The cornea is the clear front of the eye and its surface is composed of an epithelium. This is renewed by stem cells located at the limbus, which encircles the periphery of the cornea. These limbal stem cells become lost or deficient in the blinding disease of limbal stem cell deficiency. In this review article, we discuss the historical perspective in managing limbal stem cell deficiency as well as describing the more contemporary treatment options, and in particular the culture and transplantation of human limbal stem cells. This treatment was first proposed 13 years ago and many case series have been presented to date showing promising outcomes of this technique. However, challenges still remain in treating the debilitating disease of limbal stem cell deficiency. Here we discuss some of the questions, which remain to be answered in this field.
Fuchs endothelial corneal dystrophy (FECD) is a progressive, blinding disease characterized by corneal endothelial (CE) cell apoptosis. Corneal transplantation is the only measure currently available to restore vision in these patients. Despite the identification of some genetic factors, the pathophysiology of FECD remains unclear. In this study, we observed a decrease in the antioxidant response element-driven antioxidants in FECD corneal endothelium. We further demonstrated that nuclear factor erythroid 2-related factor 2, a transcription factor known to bind the antioxidant response element and activate antioxidant defense, is down-regulated in FECD endothelium. Importantly, we detected significantly higher levels of oxidative DNA damage and apoptosis in FECD endothelium compared with normal controls and pseudophakic bullous keratopathy (iatrogenic CE cell loss) specimens. A marker of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine, colocalized to mitochondria, indicating that the mitochondrial genome is the specific target of oxidative stress in FECD. Oxidative DNA damage was not detected in pseudophakic bullous keratopathy corneas, whereas it colocalized with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells in FECD samples. Ex vivo, oxidative stress caused characteristic morphological changes and apoptosis of CE, suggestive of findings that characterize FECD in vivo. Together, these data suggest that suboptimal nuclear factor erythroid 2-related factor 2-regulated defenses may account for oxidant-antioxidant imbalance in FECD, which in turn leads to oxidative DNA damage and apoptosis. This study provides evidence that oxidative stress plays a key role in FECD pathogenesis.
Fuchs endothelial corneal dystrophy (FECD) is characterized by progressive loss of corneal endothelial cells, thickening of Descement's membrane and deposition of extracellular matrix in the form of guttae. When the number of endothelial cells becomes critically low, the cornea swells and causes loss of vision. The clinical course of FECD usually spans 10-20 years. Corneal transplantation is currently the only modality used to restore vision. Over the last several decades genetic studies have detected several genes, as well as areas of chromosomal loci associated with the disease. Proteomic studies have given rise to several hypotheses regarding the pathogenesis of FECD. This review expands upon the recent findings from proteomic and genetic studies and builds upon recent advances in understanding the causes of this common corneal disorder.
PURPOSE: To report an unusual presentation of posterior polymorphous corneal dystrophy (PPCD) associated with band keratopathy, iridocorneal adhesions, heterochromia, keratoconus, and confocal microscopic findings suggestive of iridocorneal endothelial syndrome.
METHODS: Confocal microscopy, corneal topography, electroretinography, and genetic analysis were performed in the proband and his siblings.
RESULTS: A 23-year-old man presented with decreased vision in both eyes over 9 months. Examination revealed bilateral alterations in corneal endothelial mosaic with corneal edema and beaten metal appearance in the right eye and cystoid endothelial opacities in the left eye. Marked heterochromia, band keratopathy, and broad peripheral anterior synechiae were present in both eyes. Topographic features of keratoconus were noted. Electroretinography did not detect abnormal retinal function, as has been described with PPCD associated with VSX1 mutations. Diagnosis of PPCD was postulated on the basis of the examination of 3 of proband's brothers by confocal microscopy. Genetic analysis of 3 known PPCD genes, VSX1, COL8A2, and TCF8, did not detect any mutations.
CONCLUSIONS: In severe cases, PPCD can resemble iridocorneal endothelial syndromes in both clinical appearance and imaging studies (confocal microscopy). There was a strong genetic phenotypic penetrance in the family, which was essential in the diagnostic decision making. A yet undetermined genotype is contributing to this unusual PPCD phenotype.