Stefan Schrader

In sickness and in health: Corneal epithelial stem cell biology, pathology and therapy

Our window to the world is provided by the cornea on the front surface of the eye. The integrity and functionality of the outermost corneal epithelium is essential for vision. A population of limbal epithelial stem cells (LESCs) are responsible for maintaining the epithelium throughout life by providing a constant supply of daughter cells that replenish those constantly lost from the ocular surface during normal wear and tear and following injury. LESC deficiency leads to corneal opacification, inflammation, vascularization and discomfort (Daniels et al., 2001, 2007). Cultured LESC delivery is one of several examples of successful adult stem cell therapy in patients. The clinical precedence for use of stem cell therapy and the accessibility of the transparent stem cell niche make the cornea a unique model for the study of adult stem cells in physiological conditions as well as in disease.

Evaluation of lipid layer thickness measurement of the tear film as a diagnostic tool for Meibomian gland dysfunction.

Purpose: The LipiView interferometer (TearScience Inc, Morrisville, NC) is capable of delivering quantitative values of the tear-film lipid layer thickness (LLT). The purpose of this study was to investigate whether there is a correlation between the LLT and other diagnostic criteria for Meibomian gland dysfunction (MGD). Methods: We performed a retrospective analysis of 110 patients (199 eyes) from our dry eye clinic. Subjective symptoms, break-up time (BUT), expressible Meibomian glands, and LLT were measured. Results: There was a significant correlation between expressible Meibomian glands and LLT (r = 0.36, P < 0.0001). Also, a possible trend of inverse correlation between subjective symptoms (standard patient evaluation of eye dryness) and the LLT was observed; however, this was not significant (r = −0.13, P < 0.08). Analysis of the whole study collective revealed no correlation between the BUT and the LLT (r = 0.003, P = 0.97). A subgroup analysis of the patients with an LLT ⩽ 60 showed a better correlation between the LLT and the BUT, which was marginally not significant (r = 0.21; P = 0.059). For a cut-off value of ⩽75-nm LLT, we found a sensitivity of 65.8% and a specificity of 63.4% for the detection of an MGD. For a cut-off value of ⩽60, the sensitivity was 47.9%, and the specificity was 90.2%. Conclusions: The positive correlation between the LLT and expressible meibomian glands found in this study suggests a higher probability of MGD in patients with a low LLT. This automated assessment of the LLT might be a suitable screening test for detecting MGD. However, further prospective studies are needed to confirm these results and to identify potential confounders.

Animal Models of Dry Eye

BACKGROUND The causes of dry eye include lacrimal gland insufficiency, meibomian gland dysfunction, impairment of the neuronal innervation and environmental stress - all leading to irritation of the ocular surface. Several animal models have been developed to imitate different pathophysiologic mechanisms in the development of dry eye. Understanding the characteristics and limitations of these models will help researchers choose the right models to address specific problems and develop new treatment modalities in dry eye. METHODS Medline searches were performed to identify English language articles relating to different animal models of dry eye. Manual cross-referencing was also performed and some historical articles were included. RESULTS AND CONCLUSION A huge variety of animal models exists, mimicking different pathophysiologic mechanisms which can cause dry eye. The mouse is the model most commonly used to study autoimmune mechanisms, because of the diversity of different knockout and transgenic strains and good availability of antibodies. For studying dry eye signs, rabbit or dog models are more suitable, because they present decreased tear secretion and ocular surface changes, have longer lifespans, and offer better accessibility of the ocular surface. For studying special causes of dry eye, such as defects of neuronal reflex loops, environmental changes, or evaporative dry eye, the model of choice should recapitulate the underlying pathophysiologic mechanism.

Evaluation of an automated thermodynamic treatment (LipiFlow®) system for meibomian gland dysfunction: a prospective, randomized, observer-masked trial.

PURPOSE To compare the effectiveness of a single LipiFlow(®) treatment with combined lid warming and massage in patients with meibomian gland dysfunction (MGD). METHODS In this prospective, randomized, crossover, observer-masked clinical trial, subjects were randomized to receive either a single 12-min LipiFlow-LipiFlow Thermal Pulsation (LTP) system treatment or to perform combined twice-daily lid warming and massage for 3 months. All subjects were examined before, and 1 and 3 months after initiation of treatments. Investigated parameters included subjective symptoms, lipid layer thickness, meibomian gland assessment, tear break-up time, tear osmolarity, corneal and conjunctival staining, Schirmer test values, and tear meniscus height. RESULTS A total of 31 subjects completed the 3-month follow-up. At 1 and 3 months, patients in the LipiFlow treatment group had a significant reduction in Ocular Surface Disease Index (OSDI) scores compared with those in the lid-margin hygiene group. Both treatments produced a significant improvement in expressible meibomian glands compared to the baseline parameters, but no significant difference was noted between the two groups. The other investigated objective parameters did not show a significant difference. CONCLUSION Results of our study show that a single LipiFlow treatment is as least as effective as a 3-month, twice-daily lid margin hygiene regimen for MGD. However, the present study was observer-masked only, and therefore a placebo effect may have confounded any improvements in subjective symptoms and other parameters in both groups.

Review of Alternative Carrier Materials for Ocular Surface Reconstruction

Abstract Severe ocular surface disorders can result in deficiency of limbal stem cells that is potentially associated with chronic inflammation, impaired vision and even blindness. Advanced stem cells deficiency requires reconstruction of the OS with autologous or allogeneic limbal stem cells. To address such deficiency, a limbal tissue biopsy is taken and limbal cells are expanded on a carrier, which then can be used for OS reconstruction. Human amniotic membrane – currently the most common carrier for transplantation of limbal epithelial stem cells – has the downsides of carrying the risk of disease transmission, limited transparency, variable and unstable quality and low mechanical strength. This article reviews the advantages and disadvantages of the established carrier materials for limbal stem cell transplantation, as well as discussing emerging alternatives, including carriers based on collagen, fibrin, siloxane hydrogel contact lenses, poly(ε-caprolactone), gelatin–chitosan, silk fibroin, human anterior lens capsule, keratin, poly(lactide-co-glycolide), polymethacrylate, hydroxyethylmethacrylate and poly(ethylene glycol) for their potential use in the treatment of limbal stem cell deficiency.

Tissue Engineering for Conjunctival Reconstruction: Established Methods and Future Outlooks

Reconstruction of the conjunctiva is an essential part of ocular surface regeneration, especially if an extensive area or the whole ocular surface is affected, such as in patients with ocular cicatricial pemphigoid, Stevens-Johnson syndrome, toxic epidermal necrolysis, or chemical/thermal burns. In these situations, corneal reconstruction almost inevitably fails unless the conjunctival surface is first repaired and a deep fornix is restored. The growing field of tissue engineering and advances in stem cell research offer promising new alternatives for these challenges. This article reviews the present approaches for reconstruction of the conjunctival surface, considering the established strategies and new potential methodologies.

Six-month effects of a thermodynamic treatment for MGD and implications of meibomian gland atrophy.

Purpose: The aim of this study was to evaluate the 6-month effect of a single automated thermodynamic treatment (LipiFlow) and implications of meibomian gland atrophy on treatment efficacy 6 months after application. Methods: We analyzed the data of 26 subjects with meibomian gland dysfunction before and 6 months after treatment. Investigated parameters included subjective symptoms, lipid layer thickness, meibomian gland assessment, tear osmolarity, corneal and conjunctival staining, lid margin parallel conjunctival folds, Schirmer test values, bulbar redness, tear meniscus height, meibomian gland atrophy, and noninvasive tear break-up time. Results: Subjective symptoms (mean Ocular Surface Disease Index, 42 ± 19 to 33 ± 21; P = 0.004, mean Standard Patient Evaluation of Eye Dryness 16 ± 7 to 12 ± 7; P = 0.0001), lipid layer thickness (44.0 ± 15.6 to 51.3 ± 20.4; P = 0.014), number of expressible glands (2.9 ± 1.6 to 6.4 ± 4.6; P < 0.0001), lid margin parallel conjunctival folds (2.3 ± 1.0 to 2.0 ± 0.9; P = 0.04), and bulbar redness (1.4 ± 0.5 to 1.2 ± 0.5; P = 0.0001) were all improved 6 months after treatment. Symptomatic improvement was higher in patients with less severe meibomian gland atrophy compared with patients with more dropout at treatment. There was no change of meibomian gland atrophy 6 months after treatment. Conclusions: In summary, the results showed that a single thermodynamic treatment is effective in the treatment of meibomian gland dysfunction and that the effects last for at least 6 months. We suggest performing meibography in every patient before treatment for better prediction of therapeutic effects.

Keratin films for ocular surface reconstruction: evaluation of biocompatibility in an in-vivo model.

Amniotic membrane (AM) transplantation is the clinical standard for ocular surface reconstruction, however recently keratin film (KF) has been proposed as an alternative material. Aim of the current study was to evaluate corneal biocompatibility of KF in a rabbit model. Forty-six New Zealand white rabbits underwent dissection of a corneal intrastromal pocket in which an AM or KF implant was inserted and observed for 10 days and for 4 weeks. Half of animals received topical steroids, while the other half were left without. At the end of the follow-up clinical and histology examinations were performed to evaluate transparency, inflammation and degradation. After 10 days the clinical and the histology results appeared to be comparable in KF implanted eyes treated with and without steroids. After 4 weeks, comparable clinical results were observed in all KF implanted eyes, while the inflammation score was lower in non-steroid compared to steroid treated eyes along with a higher degradation rate of the keratin films. In conclusion, keratin films from human hair show a good biocompatibility and transparency in vivo. The administration of topical steroids seems to slow down implant degradation which might be important for the modulation of tissue integration and matrix regeneration.

Evaluation of Meibomian Gland Dysfunction and Local Distribution of Meibomian Gland Atrophy by Non-contact Infrared Meibography

Abstract Aims: The main purpose of this study was to investigate the relationship between Meibomian gland atrophy (meiboscore) and Meibomian gland expressibility. In addition, the local distribution of Meibomian gland loss was analyzed. Methods: A retrospective analysis of 128 patients (92 women and 36 men, 57 ± 17 years) from our dry eye clinic was performed. Infrared meibography was performed using the Keratograph 5 M (Oculus, Wetzlar, Germany) and evaluated with a scoring system introduced by Arita et al. Results: A significant inverse correlation between Meibomian gland atrophy measured by meibography and expressible Meibomian glands (r = −0.197, p = 0.003) as well as between meiboscore and TBUT (r = −0.1615, p = 0.012) was found. There also was a significant correlation between the total meiboscore and the age (r = 0.33, p < 0.0001). We could find a strong and highly significant correlation between the total meiboscore and the individual meiboscore of the upper eyelid (r = 0.905, p < 0.0001) and the lower eyelid (r = 0.892, p < 0.0001). There was no significant difference of Meibomian gland atrophy between the individual thirds of the upper eyelid, but for the lower eyelid, we could find a higher degree of Meibomian gland atrophy in the nasal third compared with the middle and the temporal third (Dunns post hoc test, p < 0.0001). Conclusions: Meibomian gland atrophy seems to be not constant over the tarsal plate but the examination of the lower tarsus might be sufficient in most of the cases. The correlation of the meiboscore with functional dry eye parameters suggest that in patients with detectable Meibomian gland atrophy there is also an impaired Meibomian gland function. However, meibography seems not to be sufficient as a single test for the diagnosis of MGD. For the future larger, prospective studies are needed to confirm these results and further evaluate the potential of meibography in the diagnosis of MGD.

In vitro characterization and ex vivo surgical evaluation of human hair keratin films in ocular surface reconstruction after sterilization processing

The disadvantages of human amniotic membrane (hAM), used for ocular surface reconstruction, necessitate the development of standardized alternatives. Keratin-derived-films (KF) have been indicated as transferable substrate for cell cultivation and tissue engineering. The impact of different sterilization procedures on KF and surgical feasibility were investigated. Human hair KF were prepared and sterilized; optical, biomechanical properties, in vitro cell seeding efficiency and proliferation of human corneal epithelial cells were studied and compared with hAM. Surgical feasibility was tested on enucleated porcine eye. Sterilized KF showed higher light transmission and significantly higher E-modulus than hAM; cell-seeding-efficiency and proliferation rate were not affected. Although KF could be surgically handled, suture placement was more difficult compared to hAM. Plasma treatment seems the best sterilization method for KF; it does not affect cell biology or optical and biomechanical properties. However material modifications are requested before KF may represent a feasible alternative for ocular surface reconstruction.