Identification and characterization of limbal stem cells

The maintenance of a healthy corneal epithelium under both normal and wound healing conditions is achieved by a population of stem cells (SC) located in the basal epithelium at the corneoscleral limbus. In the light of the development of strategies for reconstruction of the ocular surface in patients with limbal stem cell deficiency, a major challenge in corneal SC biology remains the ability to identify stem cells in situ and in vitro. Until recently, the identification of limbal stem cells mainly has been based on general properties of stem cells, e.g. lack of differentiation, prolonged label-retaining, indefinite capacity of proliferation exemplified by the clonogenic assay as well as their special role in corneal wound healing. During the last years, a number of molecular markers for the limbal SC compartment has been proposed, however, their role in distinguishing limbal SC from their early progeny is still under debate. Data reported from the literature combined with our own recent observations suggest, that the basal epithelial cells of the human limbus contain ABCG2, K19, vimentin, KGF-R, metallothionein, and integrin alpha9, but do not stain for K3/K12, Cx43, involucrin, P-cadherin, integrins alpha2, alpha6, and beta4, and nestin, when compared to the basal cells of the corneal epithelium. A relatively higher expression level in basal limbal cells was observed for p63, alpha-enolase, K5/14, and HGF-R, whereas there were no significant differences in staining intensity for beta-catenin, integrins alphav, beta1, beta2, and beta5, CD71, EGF-R, TGF-beta-RI, TGF-beta-RII, and TrkA between limbal and corneal basal epithelial cells. Therefore, a combination of differentiation-associated markers (e.g. K3/K12, Cx43, or involucrin) and putative SC-associated markers (e.g. ABCG2, K19, vimentin, or integrin alpha9) may provide a suitable tool for identification of human limbal SC. While most putative SC markers label the majority of limbal basal cells and, therefore, may not distinguish SC from progenitor cells, only ABCG2 was strictly confined to small clusters of basal cells in the limbal epithelium. At present, ABCG2 therefore appears to be the most useful cell surface marker for the identification and isolation of corneal epithelial SC. Moreover, the characteristics of the specific microenvironment of corneal SC, as provided by growth factor activity and basement membrane heterogeneity in the limbal area, could serve as additional tools for their selective enrichment and in vitro expansion for the purpose of ocular surface reconstruction.

Descemet membrane endothelial keratoplasty versus descemet stripping automated endothelial keratoplasty

PURPOSE

To evaluate visual outcome and endothelial cell survival after Descemet membrane endothelial keratoplasty (DMEK) in comparison with Descemet stripping automated endothelial keratoplasty (DSAEK).

DESIGN

Single-center, retrospective, consecutive case series.

METHODS

Thirty-eight eyes of 38 consecutive patients undergoing DMEK, who completed a 6-month follow-up, were compared with 35 eyes of 35 consecutive patients undergoing DSAEK for Fuchs endothelial dystrophy or pseudophakic bullous keratopathy. Main outcome measures included best-corrected visual acuity (in logarithm of the minimal angle of resolution [logMAR] units) and endothelial cell density within a 6-month follow-up.

RESULTS

Best-corrected visual acuity increased from 0.70 ± 0.48 logMAR and 0.75 ± 0.32 logMAR before surgery to 0.21 ± 0.14 logMAR and 0.48 ± 0.19 logMAR 3 months after DMEK and DSAEK (P < .001), respectively, and to 0.17 ± 0.12 logMAR and 0.36 ± 0.15 logMAR 6 months after DMEK and DSAEK (P < .001), respectively. Endothelial cell density decreased from 2575 ± 260 cells/mm(2) and 2502 ± 220 cells/mm(2) before surgery to 1498 ± 244 cells/mm(2) and 1778 ± 420 cells/mm(2) 3 months after DMEK and DSAEK (P < .001), respectively, and to 1520 ± 299 cells/mm(2) and 1532 ± 495 cells/mm(2) 6 months after DMEK and DSAEK (P = .483), respectively. Central corneal thickness decreased from 652 ± 92 μm before surgery to 517 ± 45 μm 6 months after DMEK, and from 698 ± 137 μm before surgery to 618 ± 66 μm 6 months after DSAEK.

CONCLUSIONS

DMEK provided faster and more complete visual rehabilitation when compared with DSAEK. However, there were no significant differences concerning endothelial cell survival within a 6-month follow-up.

Bevacizumab as a potent inhibitor of inflammatory corneal angiogenesis and lymphangiogenesis

PURPOSE

To analyze whether bevacizumab can inhibit inflammatory angiogenesis and lymphangiogenesis in the cornea. Bevacizumab (Avastin; Roche, Welwyn Garden City, UK) is a recombinant, humanized, monoclonal antibody against VEGF-A that has been approved by the U.S. Food and Drug Administration for the treatment of colon carcinomas.

METHODS

The mouse model of suture-induced corneal neovascularization was used to assess the antihemangiogenic and antilymphangiogenic effect of bevacizumab by systemic and topical application. Corneal flatmounts were stained with LYVE-1 as a specific lymphatic vascular endothelial marker and CD31 as a pan-endothelial marker, and blood and lymph vascularized areas were analyzed morphometrically. The inhibitory effect of bevacizumab on lymphatic endothelial cells (LECs) was analyzed with a colorimetric (BrdU) proliferation ELISA. The binding ability of bevacizumab to murine VEGF-A was analyzed by Western blot, ELISA, and surface plasmon resonance.

RESULTS

The systemic and topical applications of bevacizumab significantly inhibited the outgrowth of blood (P < 0.006 and P < 0.0001, respectively) and lymphatic (P < 0.002 and P < 0.0001, respectively) vessels. Inhibition of the proliferation of LECs was also significant (P < 0.0001). Western blot analysis, ELISA, and the surface plasmon resonance assay showed that bevacizumab binds murine VEGF-A.

CONCLUSIONS

Topical or systemic application of bevacizumab inhibits both inflammation-induced angiogenesis and lymphangiogenesis in the cornea. This finding suggests an important role of VEGF-A in corneal lymphangiogenesis. Bevacizumab may be useful in preventing immune rejections after penetrating keratoplasty or tumor metastasis via lymphatic vessels.

Inhibition of Hemangiogenesis and LymphangiogenesisafterNormal-Risk Corneal Transplantation by Neutralizing VEGF Promotes Graft Survival

PURPOSE

To evaluate the occurrence and time course of hem- and lymphangiogenesis after normal-risk corneal transplantation in the mouse model and to test whether pharmacologic strategies inhibiting both processes improve long-term graft survival.

METHODS

Normal-risk allogeneic (C57BL/6 to BALB/c) and syngeneic (BALB/c to BALB/c) corneal transplantations were performed and occurrence and time course of hem- and lymphangiogenesis after keratoplasty was observed, by using double immunofluorescence of corneal flatmounts (with CD31 as a panendothelial and LYVE-1 as a lymphatic vascular endothelium-specific marker). A molecular trap designed to eliminate VEGF-A (VEGF Trap(R1R2); 12.5 mg/kg) was tested for its ability to inhibit both processes after keratoplasty and to promote long-term graft survival (intraperitoneal injections on the day of surgery and 3, 7, and 14 days later).

RESULTS

No blood or lymph vessels were detectable immediately after normal-risk transplantation in either donor or host cornea, but hem- and lymphangiogenesis were clearly visible at day 3 after transplantation. Both vessel types reached donor tissue at 1 week after allografting and similarly after syngeneic grafting. Early postoperative trapping of VEGF-A significantly reduced both hem- and lymphangiogenesis and significantly improved long-term graft survival (78% vs. 40%; P < 0.05).

CONCLUSIONS

There is concurrent, VEGF-A-dependent hem- and lymphangiogenesis after normal-risk keratoplasty within the preoperatively avascular recipient bed. Inhibition of hem- and lymphangiogenesis (afferent and efferent arm of an immune response) after normal-risk corneal transplantation improves long-term graft survival, establishing early postoperative hem- and lymphangiogenesis as novel risk factors for graft rejection even in low-risk eyes.

Multilayer amniotic membrane transplantation for reconstruction of deep corneal ulcers

PURPOSE

To evaluate the efficacy of multilayer amniotic membrane transplantation for reconstruction of corneal epithelium and stroma in the context of deep corneal ulcers.

DESIGN

Prospective, noncomparative, interventional case series.

PARTICIPANTS

Eleven consecutive patients with deep corneal ulcers refractory to conventional treatment; six patients had herpetic keratitis and five had other forms of neurotrophic keratitis.

INTERVENTION

Multilayer amniotic membrane transplantation with kryopreserved human amniotic membrane.

MAIN OUTCOME MEASURES

Integrity of corneal epithelium and stroma, opacification, and appearance of grafted membrane during 12 months follow-up.

RESULTS

Amniotic membrane transplantation markedly reduced ocular inflammation in all patients. Epithelium healed above all corneal ulcers within 4 weeks and remained stable in 9 of 11 patients for 1 year. Two patients with recurrent epithelial defect suffered from severe neurotrophic keratitis. Following transplantation the amniotic membranes gradually dissolved over a period of 12 months, but stromal thickness remained stable.

CONCLUSION

Amniotic membrane transplantation allows corneal surface reconstruction in patients with persistent epithelial defects. The multilayer technique is useful for treating deep corneal ulcers and even descemetoceles. Because the procedure results in stability of the ocular surface over a period of more than 12 months in most patients, it may be considered an alternative to conventional surgical techniques for ocular surface reconstruction.

Global Consensus on Definition, Classification, Diagnosis, and Staging of Limbal Stem Cell Deficiency

PURPOSE

Despite extensive knowledge gained over the last 3 decades regarding limbal stem cell deficiency (LSCD), the disease is not clearly defined, and there is lack of agreement on the diagnostic criteria, staging, and classification system among treating physicians and research scientists working on this field. There is therefore an unmet need to obtain global consensus on the definition, classification, diagnosis, and staging of LSCD.

METHODS

A Limbal Stem Cell Working Group was first established by The Cornea Society in 2012. The Working Group was divided into subcommittees. Four face-to-face meetings, frequent email discussions, and teleconferences were conducted since then to obtain agreement on a strategic plan and methodology from all participants after a comprehensive literature search, and final agreement was reached on the definition, classification, diagnosis, and staging of LSCD. A writing group was formed to draft the current manuscript, which has been extensively revised to reflect the consensus of the Working Group.

RESULTS

A consensus was reached on the definition, classification, diagnosis, and staging of LSCD. The clinical presentation and diagnostic criteria of LSCD were clarified, and a staging system of LSCD based on clinical presentation was established.

CONCLUSIONS

This global consensus provides a comprehensive framework for the definition, classification, diagnosis, and staging of LSCD. The newly established criteria will aid in the correct diagnosis and formulation of an appropriate treatment for different stages of LSCD, which will facilitate a better understanding of the condition and help with clinical management, research, and clinical trials in this area.

Corneal higher-order aberrations after Descemet's membrane endothelial keratoplasty

PURPOSE

We compared corneal higher-order aberrations (HOAs) in eyes after Descemet's membrane endothelial keratoplasty (DMEK), Descemet's stripping automated endothelial keratoplasty (DSAEK), and penetrating keratoplasty (PK), and in a control group that had not undergone surgery.

DESIGN

Retrospective analysis of clinical data.

PARTICIPANTS

Thirty eyes of 30 patients who had undergone standard DMEK, 20 eyes of 20 patients after DSAEK, 20 eyes of 20 patients after PK, and 20 eyes of 20 controls were analyzed.

METHODS

In addition to standard postoperative examinations, each participant was analyzed with the Pentacam high-resolution rotating Scheimpflug imaging system (Pentacam HR, Oculus, Wetzlar, Germany). Data were compared between groups.

MAIN OUTCOME MEASURES

Visual acuity and HOAs.

RESULTS

The mean follow-up was 6.5 ± 1.2 months after DMEK, 22.6 ± 11.8 months after DSAEK, and 103.1 ± 74.2 months after PK. There were no statistically significant differences for the anterior 4.0-mm zones between the DMEK group and the controls or between the DMEK and DSAEK groups. The DMEK procedure compared with PK showed statistically significant differences in all terms for the 4.0-mm zones. All combined Zernike terms for mean posterior aberrations of the central 4.0-mm zones showed statistically significant higher aberrations for DMEK compared with controls. The DMEK procedure compared with DSAEK showed statistically significant lower mean values for all combined Zernike terms, except for coma and coma-like terms in the central 4.0-mm zones of the posterior corneal surface. Compared with PK, DMEK showed statistically significant lower mean values for all combined Zernike terms for the central 4.0-mm zones of the posterior corneal surface, except for spherical aberration (SA) and SA-like terms. Best spectacle-corrected visual acuity (BSCVA) after DMEK was statistically significantly better than after DSAEK (P=0.001) and PK (P=0.005). There was no statistically significant difference when BSCVA was compared with controls (P=0.998).

CONCLUSIONS

Both DSAEK and PK exhibit increased posterior corneal HOAs even years after surgery. Patients receiving DMEK display only slight changes in posterior corneal HOAs.

Reproducibility of the optic nerve head topography with a new laser tomographic scanning device

BACKGROUND

Laser scanning tomography has been shown to be an accurate and reliable method for the assessment of the three-dimensional optic disc topography. The authors investigate the reliability of morphometric measurements with the Heidelberg retina tomograph, a new instrument which was designed based on this technology, which simplifies handling and is much smaller than the laser tomographic scanner.

METHODS

Three independent measurements of the optic disc were performed in 39 eyes of 39 patients which were equally divided into the following three groups: glaucoma, glaucoma suspects, and controls.

RESULTS

The mean coefficient of variation for measurement in the glaucoma, glaucoma suspect, and control groups was 2.9%, 5.0%, and 3.4%, respectively, for cup area; 4.9%, 4.6%, and 4.6%, respectively, for cup volume; 5.2%, 3.8% and 3.3%, respectively, for mean cup depth; and 5.2%, 4.1%, and 4.0%, respectively, for maximal cup depth. The mean standard deviation for one pixel of the total image was 30 +/- 6 microns, 28 +/- 7 microns, and 22 +/- 6 microns for the three groups, respectively.

CONCLUSION

The Heidelberg retina tomograph enables fast and reliable measurement of the optic disc topography and therefore may allow exact follow-up of patients.

Characterization of extracellular matrix components in the limbal epithelial stem cell compartment

A specialized microenvironment or niche, which regulates maintenance, self-renewal, activation, and proliferation of stem cells by external signals, is one of the key prerequisites for stem cell function. However, the parameters determining the limbal stem cell niche are not yet defined. In order to characterize the role of basement membrane (BM) and extracellular matrix components in the generation of a microenvironmental niche for limbal stem and progenitor cells, we extensively analyzed the topographical variations of the BM zone of human ocular surface epithelia using immunohistochemistry and a large panel of antibodies to most of the presently described intrinsic and associated BM components. Apart from BM components uniformly expressed throughout all ocular surface epithelia (e.g. type IV collagen alpha5 and alpha6 chains, collagen types VII, XV, XVII, and XVIII, laminin-111, laminin-332, laminin chains alpha3, beta3,and gamma2, fibronectin, matrilin-2 and -4, and perlecan), the BM of the limbal epithelium shared many similarities with that of the conjunctival epithelium, including positive labelling for type IV collagen alpha1 and alpha2 chains, laminin alpha5, beta2, and gamma1 chains, nidogen-1 and -2, and thrombospondin-4, whereas type IV collagen alpha3, type V collagen, fibrillin-1 and -2, thrombospondin-1, and endostatin were present in the corneal BM, but lacking or more weakly expressed in the limbal and conjunctival BMs. As compared to both the corneal and conjunctival BMs, the limbal BM showed a markedly increased immunoreactivity for laminin alpha1, alpha2, beta1 chains, and agrin, and a specific but patchy immunoreactivity for laminin gamma3 chain, BM40/SPARC, and tenascin-C, which co-localized with ABCG2/p63/K19-positive and K3/Cx43/desmoglein/integrin-alpha2-negative cell clusters comprising putative stem and early progenitor cells in the basal epithelium of the limbal palisades. Components that were particularly expressed in the corneal-limbal transition zone included type XVI collagen, fibulin-2, tenascin-C/R, vitronectin, bamacan, chondroitin sulfate, and versican, all of which co-localized with vimentin-positive cell clusters comprising putative late progenitor cells in the basal epithelium. This pronounced heterogeneity of the BM in the limbal area, both in the region of limbal palisades and the corneal-limbal transition zone, appears to be involved in providing unique microenvironments for corneal epithelial stem and late progenitor cells. Identification of specific niche parameters might not only help to understand limbal stem cell regulation, but also to improve their selective enrichment and in vitro expansion for therapeutic strategies.

Time course of angiogenesis and lymphangiogenesis after brief corneal inflammation

PURPOSE

To study the time course of angiogenesis and lymphangiogenesis in the cornea after a short inflammatory insult. This might be helpful for the timing of corneal transplantation in high-risk eyes.

METHODS

The mouse model of suture-induced inflammatory corneal neovascularization was used. After placement of 3 interrupted 11-0 sutures into the corneal stroma of BALB/c mice (left in place for 14 days), corneas were excised 2, 3, 5, 7, 14, and 21 days as well as 1, 2, 3, 6, and 8 months after surgery. Hem- and lymphangiogenesis were evaluated using double immunohistochemistry of corneas with CD31/PECAM1 as panendothelial and LYVE-1 as lymphatic endothelial marker.

RESULTS

Both blood and lymphatic vessels grew into the cornea as early as day 2 after suture placement. The outgrowth was initially parallel. Hem- and lymphangiogenesis peaked around day 14. Thereafter, both vessel types started to regress. Regression of lymphatic vessels started earlier and was more pronounced than that of blood vessels. Whereas at 6 and 8 months (partly) perfused CD31+++/LYVE-1(-) blood vessels and (nonperfused) ghost vessels could still be observed, there were no CD31+/LYVE-1+++ lymphatic vessels detectable beyond 6 months after this short inflammation.

CONCLUSIONS

After a temporary inflammatory insult to the cornea, there is initially parallel outgrowth of both blood and lymphatic vessels. But thereafter, lymphatic vessels regress earlier than blood vessels and are completely regressed by 6 months. Earlier regression of pathologic corneal lymph versus blood vessels suggests that corneal graft survival in high-risk eyes might best be delayed for a prolonged interval following an inflammatory insult.

Cryopreserved human amniotic membrane for ocular surface reconstruction

BACKGROUND

Amniotic membrane transplantation is used for the reconstruction of the ocular surface in the context of, for example, corneal ulcers or conjunctival scarring. The mechanisms by which preserved amniotic membrane grafts promote reepithelialization are unknown. As a first step the viability and proliferative capacity of amnion cells following cryopreservation of membranes in glycerol is investigated.

METHODS

Fresh and cryopreserved (in 50% glycerol) amniotic membranes were investigated histologically and by vital stains. Following enzymatic digestion, amniotic cells were stained for viability and cultured in DMEM+10% FBS. In addition, explant cultures were established from fresh and cryopreserved membranes.

RESULTS

Histological examination showed no significant morphological alteration following cryopreservation. While fresh membranes contained predominantly vital cells, no such cells were detected following cryopreservation. Also, cells removed enzymatically from cryopreserved membranes were not viable and did not grow in culture. While both epithelial and fibroblastic cells grew from fresh membranes, no growth was seen from cryopreserved membranes.

CONCLUSION

The results suggest that the technique for preservation which is most widely used for ophthalmological amniotic membrane transplantation significantly impairs viability and proliferative capacity. This supports the clinical finding that neither immunological reactions nor signs of ingrowth of amniotic cells are observed in patients. Furthermore amniotic membrane grafts seem to function primarily as matrix and not by virtue of transplanted functional cells.

Reproducibility of topographic measurements of the optic nerve head with laser tomographic scanning

Topographic analysis and measurement of the optic nerve head is important for the diagnosis and follow-up of glaucoma. To quantify structures of the optic nerve head the new technique of laser tomographic scanning was used. A laser beam was focused onto the surface of the optic nerve head and the reflected light was detected in a confocal detection unit. The consequent change of focus produced a tomographic scanning series and allowed measurement of three-dimensional structures. To analyze the reproducibility of optic cup measurements the authors did ten recordings of one eye of eight normal volunteers. The mean standard deviation of the measurements was +/- 0.015 mm3 and the mean coefficient of variation was 9.5%. Confocal laser tomographic scanning is a safe, effective, convenient method to measure and document the topography of the optic nerve head and should be a valuable technique for follow-up of glaucoma patients.

Corneal limbal microenvironment can induce transdifferentiation of hair follicle stem cells into corneal epithelial-like cells

The aim of this study was to investigate the transdifferentiation potential of murine vibrissa hair follicle (HF) stem cells into corneal epithelial-like cells through modulation by corneal- or limbus-specific microenvironmental factors. Adult epithelial stem cells were isolated from the HF bulge region by mechanical dissection or fluorescence-activated cell sorting using antibodies to alpha6 integrin, enriched by clonal expansion, and subcultivated on various extracellular matrices (type IV collagen, laminin-1, laminin-5, fibronectin) and in different conditioned media derived from central and peripheral corneal fibroblasts, limbal stromal fibroblasts, and 3T3 fibroblasts. Cellular phenotype and differentiation were evaluated by light and electron microscopy, real-time reverse transcription-polymerase chain reaction, immunocytochemistry, and Western blotting, using antibodies against putative stem cell markers (K15, alpha6 integrin) and differentiation markers characteristic for corneal epithelium (K12, Pax6) or epidermis (K10). Using laminin-5, a major component of the corneo-limbal basement membrane zone, and conditioned medium from limbal stromal fibroblasts, clonally enriched HF stem and progenitor cells adhered rapidly and formed regularly arranged stratified cell sheets. Conditioned medium derived from limbal fibroblasts markedly upregulated expression of cornea-specific K12 and Pax6 on the mRNA and protein level, whereas expression of the epidermal keratinocyte marker K10 was strongly downregulated. These findings suggest that adult HF epithelial stem cells are capable of differentiating into corneal epithelial-like cells in vitro when exposed to a limbus-specific microenvironment. Therefore, the HF may be an easily accessible alternative therapeutic source of autologous adult stem cells for replacement of the corneal epithelium and restoration of visual function in patients with ocular surface disorders.

Proinflammatory cytokines are involved in the initiation of the abnormal matrix process in pseudoexfoliation syndrome/glaucoma

Pseudoexfoliation (PEX) syndrome, which is an age-related, generalized elastotic matrix process, currently represents the most common identifiable risk factor for open-angle glaucoma. Dysregulated expression of proinflammatory cytokines has been implicated in the initiation of various fibrotic disorders and in the pathophysiology of glaucoma. Here we investigated the presence, expression, regulation, and functional significance of proinflammatory cytokines in eyes with early and late stages of PEX syndrome/glaucoma in comparison with normal and glaucomatous control eyes using multiplex bead analysis, immunoassays, real-time PCR, Western blotting, immunohistochemistry, and cell culture models. Early stages of PEX syndrome were characterized by approximately threefold (P < 0.005) elevated interleukin (IL)-6 and IL-8 levels in the aqueous humor and a concomitant approximately twofold (P < 0.001) increase in mRNA expression levels in anterior segment tissues as compared with controls. In contrast, late stages of PEX syndrome/glaucoma did not differ significantly from controls. IL-6, IL-6 receptor, and phospho-signal transducer and activator of transcription 3 could be mainly localized to walls of iris vessels and to the nonpigmented epithelium of ciliary processes. IL-6 and IL-8 were significantly up-regulated by ciliary epithelial cells in response to hypoxia or oxidative stress in vitro, whereas IL-6, but not IL-8, induced the expression of transforming growth factor-beta1 and elastic fiber proteins. These findings support a role for a stress-induced, spatially, and temporally restricted subclinical inflammation in the onset of the fibrotic matrix process characteristic of PEX syndrome/glaucoma.

Descemet membrane endothelial keratoplasty combined with phacoemulsification and intraocular lens implantation: advanced triple procedure

PURPOSE

To evaluate the functional and morphologic outcome of Descemet membrane endothelial keratoplasty (DMEK) combined with phacoemulsification and intraocular lens implantation in patients suffering from endothelial dysfunction and cataract.

DESIGN

Retrospective, single-center, consecutive case series.

METHODS

Triple-DMEK (DMEK with simultaneous cataract surgery) was performed in 61 consecutive eyes of 56 patients using corneal donor tissue pre-stored in either short-term culture (Optisol-GS) at 4 C or organ culture (Dulbecco's modified Eagle's medium, CorneaMax medium) at 34 C. Main outcome measures included the number of air injections necessary for graft attachment as well as best-corrected visual acuity (BCVA [logMAR]), central corneal thickness (CCT), endothelial cell density (ECD), refractive spherical equivalent, refractive cylinder, and topographic cylinder at 1, 3, and 6 months postoperatively.

RESULTS

BCVA increased from 0.6 ± 0.23 logMAR preoperatively (n = 54) to 0.19 ± 0.22 logMAR at 6 months (n = 27) after surgery (P ≤ .05). ECD of donor corneas decreased from 2573 ± 235 cells/mm(2) (n = 61) to 1550 ± 326 cells/mm(2) (n = 29) after 6 months (P ≤ .05). CCT decreased from 651 ± 69 μm (n = 54) preoperatively to 521 ± 65 μm (n = 27) after 6 months (P ≤ .05). Refractive spherical equivalent was -0.3 ± 2.8 D (n = 27) preoperatively and 0.9 ± 1.5 D 6 months (n = 27) after surgery. A total of 54.5% of eyes were within 1 D of emmetropia (n = 12) and 77.3% were within 2 D of emmetropia (n = 17) 6 months (n = 22) after surgery. Refractive cylinder was -0.9 ± 1.0 D preoperatively (n = 49) and -1.5 ± 1.0 D 6 months (n = 23) after surgery. The change in refractive cylinder within the first month was statistically significant (P ≤ .05; Wilcoxon test). Topographic cylinder was 2.1 ± 1.7 D preoperatively (n = 58) and 1.7 ± 1.1 D 6 months (n = 28) after surgery. Between 3 and 6 months a significant change in topographic cylinder towards lower values was measured (P ≤ 0.05; Wilcoxon test). Optimized spherical results were achieved by selecting intraocular lenses based on a hyperopic shift of -0.75 D.

CONCLUSION

DMEK combined with cataract surgery (triple procedure) can routinely be performed in cases of endothelial dystrophy and cataract. The addition of cataract surgery to DMEK had no adverse effect on endothelial function or graft adhesion and did not increase the likelihood of postoperative complications.

Split cornea transplantation for 2 recipients: a new strategy to reduce corneal tissue cost and shortage

PURPOSE

To evaluate the feasibility of using a single donor cornea for 2 recipients by combining deep anterior lamellar keratoplasty (DALK) and Descemet's membrane endothelial keratoplasty (DMEK) surgeries on the same day.

DESIGN

Single-center, nonrandomized, prospective, interventional case series.

PARTICIPANTS

Twelve consecutive donor corneas were scheduled for split cornea transplantation combining DALK for a keratoconus patient and DMEK for a Fuchs' endothelial dystrophy patient on the same surgery day.

METHODS

First, a big-bubble DALK procedure was performed for the keratoconus eye. When bare Descemet's membrane was prepared successfully requiring no conversion to penetrating keratoplasty (PK), then during surgery the donor, endothelium-Descemet's membrane layer was removed and stored for subsequent DMEK in a second patient, and the remaining anterior lamella of the donor cornea was used to complete the DALK surgery. Afterward, a DMEK procedure was performed on the second patient with Fuchs' endothelial dystrophy, grafting the stored endothelium-Descemet's membrane layer of the original donor button.

MAIN OUTCOME MEASURES

Success of using a single donor cornea for 2 recipient eyes, best spectacle-corrected visual acuity (BSCVA), and complication rates within 6 months follow-up.

RESULTS

A single donor cornea could be used for 2 recipients in 10 of 12 donor buttons (83%). In 2 cases (17%), the DALK procedure had to be converted to PK requiring a full-thickness corneal graft. Therefore, 10 donor corneas (45%) could be saved. Six months after surgery, mean BSCVA was 20/35 (range, 20/50-20/25) in 10 eyes that underwent successful DALK, 20/50 (range, 20/63-20/40) in 2 eyes that underwent conversion from DALK to PK, and 20/31 (range, 20/50-20/16) in 10 eyes that underwent DMEK. Postoperative complications after DALK included Descemet's folds in 3 eyes (30%) and epitheliopathy in 2 eyes (20%). After DMEK, partial graft detachment occurred in 5 eyes (50%) and was managed successfully with intracameral air reinjection. All corneas remained clear up to 6 months after surgery.

CONCLUSIONS

Split use of donor corneal tissue for combined DALK and DMEK procedures in 2 recipients on the same surgery day is a promising strategy to reduce donor shortage and cost in corneal transplantation surgery in the future.

Heterozygous NTF4 mutations impairing neurotrophin-4 signaling in patients with primary open-angle glaucoma

Glaucoma, a main cause of blindness in the developed world, is characterized by progressive degeneration of retinal ganglion cells (RGCs), resulting in irreversible loss of vision. Although members of the neurotrophin gene family in various species are known to support the survival of numerous neuronal populations, including RGCs, it is less clear whether they are also required for survival and maintenance of adult neurons in humans. Here, we report seven different heterozygous mutations in the Neurotrophin-4 (NTF4) gene accounting for about 1.7% of primary open-angle glaucoma patients of European origin. Molecular modeling predicted a decreased affinity of neurotrophin 4 protein (NT-4) mutants with its specific tyrosine kinase receptor B (TrkB). Expression of recombinant NT-4 carrying the most frequent mutation was demonstrated to lead to decreased activation of TrkB. These findings suggest a pathway in the pathophysiology of glaucoma through loss of neurotrophic function and may eventually open the possibility of using ligands activating TrkB to prevent the progression of the disease.

Genetic association study of exfoliation syndrome identifies a protective rare variant at LOXL1 and five new susceptibility loci

Exfoliation syndrome (XFS) is the most common known risk factor for secondary glaucoma and a major cause of blindness worldwide. Variants in two genes, LOXL1 and CACNA1A, have previously been associated with XFS. To further elucidate the genetic basis of XFS, we collected a global sample of XFS cases to refine the association at LOXL1, which previously showed inconsistent results across populations, and to identify new variants associated with XFS. We identified a rare protective allele at LOXL1 (p.Phe407, odds ratio (OR) = 25, P = 2.9 × 10^-14) through deep resequencing of XFS cases and controls from nine countries. A genome-wide association study (GWAS) of XFS cases and controls from 24 countries followed by replication in 18 countries identified seven genome-wide significant loci (P < 5 × 10^-8). We identified association signals at 13q12 (POMP), 11q23.3 (TMEM136), 6p21 (AGPAT1), 3p24 (RBMS3) and 5q23 (near SEMA6A). These findings provide biological insights into the pathology of XFS and highlight a potential role for naturally occurring rare LOXL1 variants in disease biology.

Thalidomide inhibits corneal angiogenesis induced by vascular endothelial growth factor

BACKGROUND

Ocular diseases caused by neovascularization are among the leading causes of blindness. No specific pharmacological treatment is available. Among potential drugs, thalidomide deserves special interest since a wide body of clinical experience exists. However, its antiangiogenic effect is controversial. We therefore investigated the effect of thalidomide on corneal angiogenesis induced by vascular endothelial growth factor (VEGF), which has a special role among angiogenic growth factors.

METHODS

Corneal neovascularization was induced in NZW rabbits by an intrastromal pellet loaded with 500 or 750 ng VEGF. Animals received two daily feedings of 200 mg/kg thalidomide.

RESULTS

Significant inhibition of corneal angiogenesis (P < 0.0001) was caused by the teratogenic dose of thalidomide after the 5th day of treatment and persisted for more than 16 days. No obvious side effects were recorded.

CONCLUSIONS

Thalidomide has a significant antiangiogenic effect against VEGF-induced neovasclar growth. Together with earlier findings this observation indicates that the drug inhibits two angiogenic pathways which are mediated through integrin adhesion molecules.

The Pathogenesis of Floppy Eyelid SyndromeInvolvement of matrix metalloproteinases in elastic fiber degradation

OBJECTIVE

To investigate histopathologic alterations of eyelid biopsy specimens from patients with floppy eyelid syndrome (FES) with special regard to elastic fiber content and ultrastructure as well as to the expression of elastin-degrading enzymes to elucidate the pathogenesis of this disorder.

DESIGN

Retrospective, interventional case series.

PARTICIPANTS AND CONTROLS

Eleven consecutive patients with FES and 10 age-matched control patients with basal cell carcinoma of the eyelid.

METHODS

Horizontal pentagonal eyelid resections of 16 upper lids were performed in 11 patients with FES. Full-thickness eyelid biopsy specimens from study and control patients were examined by light and transmission electron microscopy, semiquantitative morphometry, and immunohistochemistry using antibodies against matrix metalloproteinase (MMP)-2, MMP-7, MMP-9, and MMP-12 and neutrophil elastase.

RESULTS

All patients treated with surgical horizontal eyelid shortening were asymptomatic at follow-up. Histopathologic analysis of the surgical specimens showed, apart from unspecific signs of chronic inflammation, a significant decrease in the amount of elastin within the tarsal plate and eyelid skin as compared with controls. Residual elastic fibers revealed an abnormal ultrastructure with a diminished elastin core. Immunohistochemistry demonstrated an increased immunoreactivity for elastolytic proteases, particularly MMP-7 and MMP-9, in areas of elastin depletion in FES specimens as compared with controls.

CONCLUSIONS

The findings indicate that upregulation of elastolytic enzymes, most probably induced by repeated mechanical stress, participates in elastic fiber degradation and subsequent tarsal laxity and eyelash ptosis in FES.

Genotype-correlated expression of lysyl oxidase-like 1 in ocular tissues of patients with pseudoexfoliation syndrome/glaucoma and normal patients

Pseudoexfoliation (PEX) syndrome is a generalized disease of the extracellular matrix and the most common identifiable cause of open-angle glaucoma. Two single nucleotide polymorphisms in the lysyl oxidase-like 1 (LOXL1) gene (rs1048661 and rs3825942) have been recently identified as strong genetic risk factors for both PEX syndrome and PEX glaucoma. Here we investigated the expression and localization of LOXL1, LOXL2, and lysyl oxidase (LOX) in tissues of PEX syndrome/glaucoma patients and controls in correlation with their individual single nucleotide polymorphism genotypes and stages of disease. LOXL1 ocular expression was reduced by approximately 20% per risk allele of rs1048661, whereas risk alleles of rs3825942, which were highly overrepresented in PEX cases, did not affect LOXL1 expression levels. Irrespective of the individual genotype, LOXL1 expression was significantly increased in early PEX stages but was decreased in advanced stages both with and without glaucoma compared with controls, whereas LOX and LOXL2 showed no differences between groups. LOXL1 was also found to be a major component of fibrillar PEX aggregates in both intra- and extraocular locations and to co-localize with various elastic fiber components. These findings provide evidence for LOXL1 involvement in the initial stages of abnormal fibrogenesis in PEX tissues. Alterations of LOXL1 activation, processing, and/or substrate specificity may contribute to the abnormal aggregation of elastic fiber components into characteristic PEX fibrils.

From hair to cornea: toward the therapeutic use of hair follicle-derived stem cells in the treatment of limbal stem cell deficiency

Limbal stem cell deficiency (LSCD) leads to severe ocular surface abnormalities that can result in the loss of vision. The most successful therapy currently being used is transplantation of limbal epithelial cell sheets cultivated from a limbal biopsy obtained from the patient's healthy, contralateral eye or cadaveric tissue. In this study, we investigated the therapeutic potential of murine vibrissae hair follicle bulge-derived stem cells (HFSCs) as an autologous stem cell (SC) source for ocular surface reconstruction in patients bilaterally affected by LSCD. This study is an expansion of our previously published work showing transdifferentiation of HFSCs into cells of a corneal epithelial phenotype in an in vitro system. In this study, we used a transgenic mouse model, K12(rtTA/rtTA) /tetO-cre/ROSA(mTmG) , which allows for HFSCs to change color, from red to green, once differentiation to corneal epithelial cells occurs and Krt12, the corneal epithelial-specific differentiation marker, is expressed. HFSCs were isolated from transgenic mice, amplified by clonal expansion on a 3T3 feeder layer, and transplanted on a fibrin carrier to the eye of LSCD wild-type mice (n = 31). The HFSC transplant was able to reconstruct the ocular surface in 80% of the transplanted animals; differentiating into cells with a corneal epithelial phenotype, expressing Krt12, and repopulating the corneal SC pool while suppressing vascularization and conjunctival ingrowth. These data highlight the therapeutic properties of using HFSC to treat LSCD in a mouse model while demonstrating a strong translational potential and points to the niche as a key factor for determining stem cell differentiation.

Promotion of graft survival by vascular endothelial growth factor a neutralization after high-risk corneal transplantation

OBJECTIVE

To evaluate whether hemangiogenesis, lymphangiogenesis, and concomitant invasion of mononuclear phagocytes occurring after high-risk corneal transplantation in already vascularized high-risk recipient corneal beds increase the risk for subsequent immune rejection.

METHODS

Three intrastromal sutures were left in place for 6 weeks in the corneas of BALB/c mice, causing neovascularization. Three weeks after suture removal, keratoplasty was performed (donors C57BL/6 mice). The treatment group received a vascular endothelial growth factor A (VEGF-A)-neutralizing cytokine trap at 0, 4, 7, and 14 days postoperatively (Fc protein was used as the control treatment). Morphometry was performed in corneal flat mounts using lymphatic endothelial hyaluronan receptor-1 (a specific lymphatic endothelial marker), CD31 (a panendothelial marker), and F4/80 (a marker for mononuclear phagocytes).

RESULTS

After corneal transplantation, significant additional hemangiogenesis (mean area covered by vessels [SD], 68% [18%] postoperatively vs 40% [18%] preoperatively; P = .03) and lymphangiogenesis (12% [1.3%] postoperatively vs 9% [2.8%] preoperatively; P = .03) were observed. Postoperative neutralization of VEGF-A inhibited operation-induced hemangiogenesis (35% [8%]; P = .007) and lymphangiogenesis (6% [1.6%]; P = .03) and decreased the recruitment of mononuclear phagocytes into the graft (mean [SD], 501 cells/mm(2) [152] in treated mice vs 684 cells/mm(2) [35] in Fc controls; P = .03). After 8 weeks, 23% of the treated corneas were not rejected, whereas all control corneas were rejected after 21 days (P = .007).

CONCLUSIONS

Neutralization of VEGF-A after high-risk corneal transplantation effectively inhibits postoperative hemangiogenesis, lymphangiogenesis, and recruitment of antigen-presenting cells and improves corneal graft survival.

CLINICAL RELEVANCE

Blocking of VEGF-A after high-risk corneal transplantation may be a novel approach to improve graft survival.

Stem cells and corneal epithelial regeneration

Self-renewing tissues such as the corneal epithelium contain stem cells which represent the proliferative reserve. Studies of cellular differentiation and proliferation suggest that corneal epithelial stem cells are localised exclusively in the basal limbal epithelium. Although regulatory factors for the amplification of corneal stem cells are unknown, serum factors such as retinoic acid might induce differentiation of stem cells to transient amplifying cells which are responsible for cell amplification. These cells are regulated by various polypeptide growth factors and extracellular calcium. Loss or malfunction of stem cells does not permit maintenance or regeneration of the corneal epithelial mass but leads to conjunctivalisation of the corneal surface. Clinically, several ocular surface disorders such as chemical burns can cause limbal damage and consecutive limbal insufficiency. Treatment for these disorders is available only by transplantation of healthy stem cells, which can be performed as both autograft and allograft.

Evaluation of lamina cribrosa and peripapillary sclera stiffness in pseudoexfoliation and normal eyes by atomic force microscopy

PURPOSE

Pseudoexfoliation (PEX) syndrome is a systemic disorder of the elastic fiber system that can lead to PEX glaucoma. Elastotic alterations in the lamina cribrosa (LC) of PEX eyes suggested biomechanical implications predisposing to pressure-induced optic nerve damage. In this pilot study, the stiffness of LC and peripapillary sclera (ppSC) in eyes with and without PEX syndrome were analyzed by atomic force microscopy (AFM) nanoindentation.

METHODS

Unfixed cryosections (5-μm thick) were prepared from the optic nerve heads (ONH) of three donor eyes with PEX syndrome and three age-matched control eyes. AFM force mapping was performed in selected regions of the central, midperipheral, and peripheral LC and the ppSC using a spherical cantilever tip. To determine the local Young's modulus of elasticity (YME) as a measure of tissue stiffness, force curves were acquired and analyzed using the spherical Hertz model.

RESULTS

For the LC, the median YME values calculated from single stiffness maps averaged 17.2 (±2.7) kPa in normal eyes and 10.1 (±1.4) kPa in PEX eyes, indicating a significant PEX-related decrease in stiffness by over 40% (P < 0.01). The corresponding YME values for the ppSC, which revealed a 9-fold higher tissue stiffness than in the LC, averaged 158.3 (±59.8) kPa for control and 85.8 (±16.9) kPa for PEX samples.

CONCLUSIONS

AFM was proven suitable for determining the stiffness of ONH tissues, encouraging further large-scale analyses. The marked decrease in stiffness, implying an increased deformability of the ONH in PEX eyes, may reflect an inherent tissue weakness rendering these eyes more vulnerable to glaucomatous damage.