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.

We uncover the significance of a previously unappreciated structural feature in corneal stroma, important to its biomechanics. Vogt striae are a known clinical indicator of keratoconus, and consist of dark, vertical lines crossing the corneal depth. However we detected stromal striae in most corneas, not only keratoconus. We observed striae with multiple imaging modalities in 82% of 118 human corneas, with pathology-specific differences. Striae generally depart from anchor points at Descemet’s membrane in the posterior stroma obliquely in a V-shape, whereas in keratoconus, striae depart vertically from posterior toward anterior stroma. Optical coherence tomography shear wave elastography showed discontinuity of rigidity, and second harmonic generation and scanning electron microscopies showed undulation of lamellae at striae locations. Striae visibility decreased beyond physiological pressure and increased beyond physiological hydration. Immunohistology revealed striae to predominantly contain collagen VI, lumican and keratocan. The role of these regions of collagen VI linking sets of lamellae may be to absorb increases in intraocular pressure and external shocks.

AimTo assess the influence of graft thickness and regularity on visual recovery and postoperative wavefront aberrations after endothelial keratoplasty (EK).Methods150 EKs performed in eyes with corneal endothelial disorders and no other ocular comorbidities, preoperative and postoperative assessment with spectral domain optical coherence tomography and postoperative assessment with whole eye wavefront aberrometry were retrospectively analysed. Eyes were classified into five groups: Descemet Membrane Endothelial Keratoplasty (DMEK), nanothin Descemet Stripping Automated Endothelial Keratoplasty (DSAEK) (15–49 µm), ultrathin DSAEK (50–99 µm), thin DSAEK (100–149 µm) and conventional DSAEK (150–250 µm).ResultsThe preoperative diagnosis was Fuchs dystrophy in 139 eyes (92.7%). The graft thickness measured after graft deswelling was in average 74 µm with a mean coefficient of variation of 17%. The average follow-up time was 32 months. The mean spectacle-corrected logarithm of minimum angle of resolution visual acuity improved from 0.76 (20/116) before surgery to 0.14 (20/27) at last follow-up visit. No significant differences in final visual acuity were found between the five groups. The time to reach 20/40 vision was significantly shorter in the DMEK and nanothin DSAEK groups compared with the remaining three DSAEK groups. No significant differences in postoperative aberrometry measurements were found between the five groups. Shorter time to reach 20/40 visual acuity was associated with better preoperative visual acuity and thinner graft. Higher final vision improvement was associated with poorer preoperative visual acuity. Higher postoperative high-order aberrations were associated with poorer preoperative visual acuity.ConclusionThe main advantage of DMEK and nanothin DSAEK over thicker DSAEKs was the rapidity of visual recovery. Final quality of vision was not influenced by graft thickness and regularity.

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