Corneal endothelium

The corneal endothelium located on the posterior corneal surface is responsible for regulating stromal hydration. This is contributed by a monolayer of corneal endothelial cells (CECs), which are metabolically active in a continuous fluid-coupled efflux of ions from the corneal stroma into the aqueous humor, preventing stromal over-hydration and preserving the orderly arrangement of stromal collagen fibrils, which is essential for corneal transparency. Mature CECs do not have regenerative capacity and cell loss due to aging and diseases results in irreversible stromal edema and a loss of corneal clarity. The current gold standard of treatment for this worldwide blindness caused by corneal endothelial failure is the corneal transplantation using cadaveric donor corneas. The top indication is Fuchs corneal endothelial dystrophy/degeneration, which represents 39% of all corneal transplants performed. However, the global shortage of transplantable donor corneas has restricted the treatment outcomes, hence instigating a need to research for alternative therapies. One such avenue is the CEC regeneration from endothelial progenitors, which have been identified in the peripheral endothelium and the adjacent transition zone. This review examines the evidence supporting the existence of endothelial progenitors in the posterior limbus and summarizes the existing knowledge on the microanatomy of the transitional zone. We give an overview of the isolation and ex vivo propagation of human endothelial progenitors in the transition zone, and their growth and differentiation capacity to the corneal endothelium. Transplanting these bioengineered constructs into in vivo models of corneal endothelial degeneration will prove the efficacy and viability, and the long-term maintenance of functional endothelium. This will develop a novel regenerative therapy for the management of corneal endothelial diseases.

Approved by the following research ethics committee: Hospital Oftalmológico de Brasília (#17/ 2015). ABSTRACT Purpose: To investigate the effects of pterygium on corneal endothelial cell density in patients with unilateral pterygium. Methods: We performed a cross-sectional analysis of data from patients with unilateral pterygium who were selected from September 1, 2015 to July 31, 2016 at Hospital de Base do Distrito Federal to assess the corneal endothelial cell density, coefficient of variation in the cell area, hexagonality, and corneal pa chymetric results. In all patients, noncontact specular microscopy was performed in both eyes and a minimum endothelial cell count of 75 cells/mm 2 was required for inclusion in the study. The contralateral eye served as the control. Results: Sixty-one patients were included in the study. Twenty-nine (47.5%) patients were men and 32 (52.5%) were women (mean age, 50.84 ± 13.8). The percentage of pterygium that invaded the cornea ranged from 4.87% to 24.59% (median, 9.70% ± 4.99%). The mean corneal endothelial cell density (cells/mm) was lower in the pterygium eyes than in the controls (2451.83 ± 284.96 vs. 2549.95 ± 268.94, respectively; p=0.04). No differences in the mean coefficients of variation of cell size, hexagonality, and corneal pachymetric results were observed between the patients and controls. The Pearson correlation test showed a significant negative linear relationship between pterygium invasion and endothelial cell density [p<0.001, n=61, r=-0.553 (95% CI,-0.34 to-0.73)]. Conclusion: Compared with the contralateral eyes, those of patients with unilateral pterygium were associated with a decrease in corneal endothelial cell density. RESUMO Objetivo: Investigar os efeitos do pterígio na densidade de células endoteliais cor­ neanas em pacientes com pterígio unilateral. Métodos: Foi realizado um estudo do tipo transversal envolvendo pacientes com pterígio unilateral selecionados entre 1 de setembro de 2015 a 31 de julho de 2016 no Hospital de Base do Distrito Federal para avaliar a densidade de células endoteliais corneanas, coeficiente de variação da área celular, hexagonalidade, e paquimetria corneana. Em todos os pacientes foram realizadas microscopias especulares de não­contato em ambos os olhos, sendo necessário obter uma contagem endotelial mínima de 75 células/mm 2 para que o paciente fosse incluído no estudo. O olho contralateral funcionou como grupo controle. Resultados: Um total de 61 pacientes foram incluídos no estudo. Vinte e nove (47,5%) eram homens e 32 (52,5%) mulheres. A média de idade era de 50,84 ±13,8. O percentual de invasão do pterígio na córnea variou entre 4,87% a 24,59%, com uma mediana de 9,70% ± 4,99%. A media de densidade de células endoteliais corneanas foi menor nos olhos com pterígio quando comparados ao grupo controle (2451,83 ± 284,96 vs 2549,95 ± 268,94; p=0,04). Não foram encontradas diferenças entre os casos e controles em relação à média do coeficiente de variação da área celular, hexagonalidade, e paquimetria. Teste de correlação de Pearson mostrou uma relação linear negativa entre a invasão do pterígio e a densidade de células endoteliais corneanas [p<0,001, n=61, r=­0,553 (95% CI ­0,34 a ­0,73)]. Conclusão: Em pacientes com pterígio unilateral, o olho com pterígio está asso ciado a uma menor densidade de células endoteliais corneanas quando comparado ao olho contralateral.