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A.J. Shortt, G.A. Secker, P.M. Munro, P.T. Khaw, S.J. Tuft; Identification of Novel Limbal Structural Processes and Evidence of Regional Variation in Limbal Stem Cell Niche Architecture . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1112.
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© ARVO (1962-2015); The Authors (2016-present)
To employ novel imaging techniques to investigate the structural characteristics of the corneal epithelial stem cell niche & to evaluate the effect of age on these characteristics.
Confocal microscopy was used to collect z–stack image series of the corneal limbus in normal cadaveric human corneal whole mounts. Images collected at the level of the basal epithelial layer were merged to create 360 degree montages of the corneal limbal niche. Scanning laser confocal ophthalmoscopy was used to collect corresponding z–stack image series from healthy normal subjects in–vivo. Scanning electron microscopy of decellularised normal cadaveric human corneas was performed to reveal novel structural characteristics of the stromal component of the corneal limbal niche.
Confocal microscopy of 10 cadaveric human corneal wholemounts & in–vivo confocal ophthalmoscopy of 10 normal subjects revealed previously unrecognised structures and a regional variation in limbal architecture. Limbal epithelial cell crypts & newly identified stromal projections located at the corneal periphery are not uniform in distribution, rather there is a superior and inferior predominance suggesting a specialised niche environment. Scanning electron microscopy of 18 decellularised corneas confirmed that the variation in limbal stromal architecture correlates with the distribution of epithelial crypts. Quantification of the area of limbus occupied by crypts & stromal projections was performed for each corneal quadrant (superior, inferior, nasal and temporal).This was expressed as a percentage of the total area of each corneal segment (n=18). Mean values (±SEM) for superior (20.5±1.8%), inferior (13.4±1.4%), nasal (5.9±1.1%) & temporal (5.0±3.7%) segments confirmed the above observations. Donor & subject age were associated with significant changes in limbal morphology. The number of limbal crypts decreases with age. In a proportion of older donors there was a complete absence of crypts but stromal projections were found to persist.
Transplantation of ex–vivo cultured limbal stem cells is a novel cellular therapy for corneal stem cell failure. This new finding of a regional variation in niche structure suggests a non uniform distribution of corneal epithelial stem cells. This is clinically important when performing biopsy of stem cells for ex–vivo culture. The effect of age on niche structure may imply an age related reduction in limbal stem cell numbers.
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