F. Majo

The Effect of Standard and High-Fluence Corneal Cross-Linking (CXL) on Cornea and Limbus

PURPOSE When treating peripheral ectatic disease-like pellucid marginal degeneration (PMD), corneal cross-linking with UV-A and riboflavin (CXL) must be applied eccentrically to the periphery of the lower cornea, partly irradiating the corneal limbus. Here, we investigated the effect of standard and double-standard fluence corneal cross-linking with riboflavin and UV-A (CXL) on cornea and corneal limbus in the rabbit eye in vivo. METHODS Epithelium-off CXL was performed in male New Zealand White rabbits with two irradiation diameters (7 mm central cornea, 13 mm cornea and limbus), using standard fluence (5.4 J/cm(2)) and double-standard fluence (10.8 J/cm(2)) settings. Controls were subjected to epithelial removal and riboflavin instillation, but were not irradiated with UV-A. Following CXL, animals were examined daily until complete closure of the epithelium, and at 7, 14, 21, and 28 days. Animals were killed and a corneoscleral button was excised and processed for light microscopy and immunohistochemistry. RESULTS For both irradiation diameters and fluences tested, no signs of endothelial damage or limbal vessel thrombosis were observed, and time to re-epithelialization was similar to untreated controls. Histological and immunohistochemical analysis revealed no differences in the p63 putative stem cell marker expression pattern. CONCLUSIONS Even when using fluence twice as high as the one used in current clinical CXL settings, circumferential UV-A irradiation of the corneal limbus does not alter the regenerative capacity of the limbal epithelial cells, and the expression pattern of the putative stem cell marker p63 remains unchanged. This suggests that eccentric CXL may be performed safely in PMD.

Pathologies épithéliales cornéennes et insuffisance en cellules souches limbiques

Treatment of corneal epithelial diseases induced by limbal stem cell deficiency is an important challenge in ocular surface reconstruction. Since the 1990s, corneal stem cells have been localized in the limbus. This new concept completely changed the way we consider ocular surface reconstruction, with new diseases now found to be isolated in the ocular surface. Limbus insufficiency syndromes are specific depending on their origin (congenital or acquired), their expression (unilateral or bilateral, partial or total), their progression (acute or chronic), and the mechanism involved (burn, infection, chronic inflammation, etc.). Some of these diseases are local diseases and others are systemic diseases. Clinically, limbus insufficiency is a switch of the normal corneal epithelial phenotype (expression of a specific keratin, avascularity, and transparency of the corneal matrix) in an opaque and fibrovascularized cornea. In terms of cellular biology, a phenotype is a terminal expression of a cell differentiation process. This process is the outcome of the interaction between the genome of a cell or a group of cells with their microenvironment. In limbus insufficiency, epithelial cells and corneal matrix are destroyed, and it is the destruction of these two components that leads to limbus insufficiency syndrome.Le traitement des pathologies epitheliales par insuffisance en cellules souches limbiques (ICSL) represente un defi therapeutique important de la chirurgie reconstructrice du segment anterieur. Depuis les annees 1990, la mise en evidence dans le limbe de cellules a fort potentiel de division a permis une approche therapeutique nouvelle. Les cellules souches limbiques sont responsables du renouvellement de l’epithelium corneen en physiologie et lors d’un processus cicatriciel. Ces nouvelles donnees de biologie cellulaire ont permis d’identifier des pathologies secondaires a la destruction de ces cellules souches. Les syndromes d’ICSL regroupent des maladies tres diverses dans leur origine (congenitale ou acquise), dans leur expression (partielle, totale, uni ou bilaterale), dans leur evolutivite (aigue ou chronique) et dans leur etiopathogenie (brulure, infection, inflammation chroniqueh). Certaines de ces pathologies sont des atteintes locales strictement limitees a la surface oculaire alors que d’autres sont l’expression de maladies systemiques. En clinique, la destruction du limbe et de ses cellules souches aboutit a une perte du phenotype corneen normal (tissu avasculaire, transparent, exprimant une keratine specifique). Dans un tissu, le phenotype est l’expression terminale des processus de differenciation cellulaire. Ces processus sont regis par l’interaction du genome d’une cellule (ou d’un groupe cellulaire) avec son micro environnement. Dans le cas d’une ICSL, l’epithelium et le stroma corneen sont touches et c’est la conjonction de leur destruction avec une atteinte de la region limbique qui conduit au syndrome d’ICSL.

Majo et al. reply

Replying to: T.-T. Sun, S. C. Tseng & R. M. Lavker 463, 10.1038/nature08805 (2010)Our claim is not that there are no stem cells in the limbus, but that there is more to corneal renewal than the limbus and that the double-dome-shaped structure of the cornea and physical constraints have a crucial impact on cell dynamics.

12-Year Outcomes of Microkeratome-Assisted Anterior Lamellar Therapeutic Keratoplasty (ALTK) for Disorders of the Anterior Part of the Corneal Stroma – A Comparative Review of Adult and Children

PURPOSE To report the visual outcomes and complications of automated anterior lamellar therapeutic keratoplasty (ALTK) in adults and children, and to examine these outcomes as a function of age and etiology. METHODS A consecutive series of cases undergoing automated ALTK procedures performed at the Jules-Gonin Eye Hospital Lausanne, Switzerland, between June 2003 and January 2015. Only patients with at least 3 months of follow-up were included. RESULTS There were 53 eyes (24 right) of 51 patients (17 female, 16 juvenile), with a mean age of 34.8 years (range from 3 months to 88 years), analyzed. The mean follow-up was 35 (± 26) months. Diagnosis in the adult (n = 37) vs. juvenile (n = 16) eyes was different: opacity following surgical complication 8 vs. 0, congenital 1 vs. 1, dystrophy 5 vs. 2, infection 12 vs. 5, keratectasia 3 vs. 0, trauma 7 vs. 0, tumor 1 vs. 3, and allergy 0 vs. 5. Visual impairment as a consequence of corneal scarring was the principle indication for surgery in both adult (70%; 26) and juvenile eyes (63%; 10); other indications were choristoma, dermoid, other tumors, astigmatism, and congenital opacity. In adult vs. juvenile eyes, the mean visual acuity (spectacle and contact lenses) was, at last visit, 0.55 vs. 0.45 LogMAR (p = 0.78), with a range of 100% to hand movements. Failure occurred in 6 (16%) vs. 2 (13%) cases and complications were observed in 14 (38%) vs. 9 (56%) cases, however, more surgical revision was required in juvenile eyes, 4 (11%) vs. 7 (43%) (p = 0.01, Fisher test). CONCLUSIONS This study shows that anterior lamellar keratoplasty in children retains good visual function when combined with adequate amblyopic therapy. However, the rate of complications is higher in juveniles and requires more intensive interdisciplinary follow-up.

[Darwin or Lamarck? Understanding the ocular surface and its normal or abnormal differentiation in order to cure ocular surface destruction with corneal opacification].

According to the World Health Organization, 5.1% of blindnesses or visual impairments are related to corneal opacification. Cornea is a transparent tissue placed in front of the color of the eye. Its transparency is mandatory for vision. The ocular surface is a functional unit including the cornea and all the elements involved in maintaining its transparency i.e., the eyelids, the conjunctiva, the lymphoid tissue of the conjunctiva, the limbus, the lacrymal glands and the tear film. The destruction of the ocular surface is a disease caused by : traumatisms, infections, chronic inflammations, cancers, toxics, unknown causes or congenital abnormalities. The treatment of the ocular surface destruction requires a global strategy including all the elements that are involved in its physiology. The microenvironnement of the ocular surface must first be restored, i.e., the lids, the conjunctiva, the limbus and the structures that secrete the different layers of the tear film. In a second step, the transparency of the cornea can be reconstructed. A corneal graft performed in a healthy ocular surface microenvironnement will have a better survival rate. To achieve these goals, a thorough understanding of the renewal of the epitheliums and the role of the epithelial stem cells are mandatory.

329 Greffes lamellaires antérieures automatisées dans les maladies du stroma antérieur de la cornée : 4 années d’expérience

Objectif Nous presentons nos resultats cliniques concernant l’utilisation de greffes lamellaires anterieures automatisees dans le traitement des maladies du stroma de la cornee. Materiels et Methodes Vingt-quatre greffes lamellaires anterieures automatisees realisees entre 2003 et 2006 ont ete analysees prospectivement sans groupe temoin. La serie de cas comprenait 7 femmes et 17 hommes avec un âge moyen de 34,3 ans (3,25 a 55,5 ans). Les indications etaient : des complications de chirurgie refractive (n = 6), des keratocones (n = 5), des leucomes (n = 11) et des indications diverses (n = 2). L’evaluation clinique comprenait : la meilleure acuite visuelle corrigee pre et post-operatoire, la keratometrie pre et post-operatoire, la qualite de l’interface, la survenue de complications per et post-operatoires et la capacite a retirer l’opacification corneenne en fonction de l’evaluation clinique pre-operatoire. Resultats Le suivi moyen etait de 14,8 mois (0.3 a 29 mois). L’acuite visuelle pre-operatoire moyenne etait de 0,3 (0,005 a 0,6). L’acuite visuelle post-operatoire moyenne etait de 0,5 (0,1 a 1,0). Les greffons etaient transparents et l’interface Claire dans tous les cas. Les complications per operatoires etaient : une perforation corneenne et une predictibilite de la decoupe de la lamelle du donneur insuffisante avec le microkeratome des greffes lamellaires anterieures automatisees. Le suivi post-operatoire a permis d’observer 1 deplacement de la greffe, 1 reprise de sutures, 13 astigmatismes superieurs a 3D, 1 pli du greffon en regard d’un fil, une infection fongique, 3 rejets epitheliaux et 1 opacite dans le stroma residuel. Discussion Deux types de chirurgies peuvent etre realises dans la prise en charge des maladies du stroma de la cornee : la greffe lamellaire anterieure automatisee ou manuelle et la greffe lamellaire anterieure profonde. La greffe lamellaire anterieure automatisee a l’avantage d’utiliser un microkeratome qui a fait sa preuve en chirurgie refractive, tant sur le plan de son efficacite et de sa precision, que sur la qualite de l’interface qu’il cree lors de la decoupe. Conclusion La greffe lamellaire anterieure automatisee est une technique simple et fiable permettant de traiter efficacement les atteintes du stroma moyen et superficial de la cornee tout en preservant l’endothelium du receveur. Il s’agit d’un avantage decisif par rapport a la greffe transfixiante dans la prise en charge de ce type de pathologies.