[In vivo confocal microscopy and optical coherence tomography as innovative tools for the diagnosis of limbal stem cell deficiency (French translation of the article)]. / Progrès dans les méthodes diagnostiques du déficit en cellules souches limbiques. Apport de la microscopie confocale et de la tomographie en cohérence optique.

The limbus is the anatomical and functional barrier between corneal and conjunctival epithelia. It is characterized by presence of the limbal stem cell niche which allows corneal homeostasis to be maintained. Limbal stem cell deficiency is characterized by a dual process: insufficient regeneration of corneal epithelium, which cannot therefore assure its function of physiological support, associated with corneal invasion by conjunctival proliferation. Diagnosis is currently made via routine clinical examination, corneal impression cytology and in vivo confocal microscopy (IVCM). Slit lamp examination shows abnormal limbal anatomy, thin and irregular epithelium with late fluorescein staining, and superficial vascularization. With its high resolution, IVCM allows identification of limbal and corneal epithelial changes at a cellular level in en face views, parallel to the corneal surface, but with a restricted viewing field of the corneal surface. It shows a poor transition between the corneal and conjunctival epithelia, associated with a loss of the normal corneal epithelial stratification, low basal cell and sub-basal nerve plexus densities, even with sub-epithelial fibrosis. Optical coherence tomography in central cornea and at the limbus, with scans in different orientations, allows a quick, global and non-invasive analysis of normal eyes and those with limbal stem cell deficiency. It shows a thin limbal epithelium, lacking normal thickening, featuring absence of stromal undulations and limbal crypts in cross-sections and sections parallel to the limbus, lack of visible limbal crypts in en face sections, loss of clear transition between the hyporeflective corneal epithelium and the hyperreflective conjunctival epithelium, and hyperreflective sub-epithelial fibrosis.

In vivo confocal microscopy and optical coherence tomography as innovative tools for the diagnosis of limbal stem cell deficiency.

The limbus is the anatomical and functional barrier between the corneal and conjunctival epithelia. It is characterized by the presence of the limbal stem cell niche, which allows corneal homeostasis to be maintained. Limbal stem cell deficiency is characterized by a dual process: insufficient regeneration of corneal epithelium, which cannot therefore assure its function of physiological support, associated with corneal invasion by conjunctival proliferation. Diagnosis is currently made via routine clinical examination, corneal impression cytology and in vivo confocal microscopy (IVCM). Slit lamp examination shows abnormal limbal anatomy, thin and irregular epithelium with late fluorescein staining, and superficial vascularization. With its high resolution, IVCM allows identification of limbal and corneal epithelial changes at a cellular level in en face views parallel to the corneal surface, but with a restricted viewing field of the corneal surface. It shows a poor transition between the corneal and conjunctival epithelia, associated with a loss of the normal corneal epithelial stratification, low basal cell and sub-basal nerve plexus densities, and subepithelial fibrosis. Spectral domain optical coherence tomography of the central cornea and limbus, with scans in variable orientations, allows a quick, global and non-invasive analysis of normal eyes and those with limbal stem cell deficiency. It shows a thin limbal epithelium, lacking normal thickening, featuring absence of stromal undulations and limbal crypts in cross-sections and sections parallel to the limbus, lack of visible limbal crypts in en face sections, loss of clear transition between the hyporeflective corneal epithelium and the hyperreflective conjunctival epithelium, and hyperreflective subepithelial fibrosis. The limbus is the anatomical and functional barrier between the corneal and conjunctival epithelia. It is characterized by the presence of the limbal stem cell niche, which allows corneal homeostasis to be maintained. Limbal stem cell deficiency (LSCD) is characterized by a dual process: insufficient regeneration of corneal epithelium, which cannot therefore assure its function of physiological support, associated with corneal invasion by conjunctival proliferation.

Three-dimensional structure of the mammalian limbal stem cell niche.

Although the existence of the limbal stem cell (LSC) niche is accepted, precise knowledge of its three-dimensional (3D) architecture remains incomplete. The LSC niche was explored on freshly excised and organ-cultured corneoscleral rims from human donors (n = 47), pigs (n = 15) and mice (n = 27) with full-field optical coherence microscopy (FFOCM). Limbal crypt features were detected in 90% of organ-cultured human corneoscleral rims, extending between the palisades of Vogt as radially oriented rectangular (74% of eyes) and/or rounded (23% of eyes) forms, often branching off to, or becoming interconnected by, sub-scleral radially or circumferentially oriented crypts (in 56% of eyes). Mean crypt volume represented 16% of sampled limbal volume on the vertical axis and 8% on the horizontal axis. In pigs, palisades were finer and crypts wider with relatively uniform distribution around the eye, and radial orientation, connecting to numerous narrow criss-crossing invaginations beneath the scleral surface. In mice, only a circumferential limbal trough was detected. Mean crypt volume represented 13% of sampled limbal volume in humans and 9% in pigs. FFOCM combined with fluorescence, and confocal fluorescence microscopy, showed presence of p63-α+ cells and cytokeratin-3+ cells in the limbal crypts. To assess colony forming efficiency (CFE), limbal epithelial cells were cultured at low density with mitomycin-arrested 3T3 feeders. CFE increased with limbal crypt volume and was not significantly decreased in organ-cultured cornea, despite degradation of the epithelial roof, suggesting that stem cells remain protected at the base of crypts during organ culture. CFE in human samples was significantly greater than in pig, and CFE in mouse was zero. Crypt architecture in the three species appears associated with eye exposure to light. LSC density increased with percentage limbal volume occupied by crypts.