RESUMO
The limbal niche in the corneoscleral junction of the eye, habitat of the limbal epithelial stem cells (LESC), facilitates corneal epithelial regeneration by providing physical support and chemical signalling. Anatomical structures within the limbus, namely, limbal epithelial crypts and focal stromal projections, are believed to function as a putative niche for LESCs. In this study, the impact of age on the topography of this niche was investigated. Also, the relationship between niche topography and limbal epithelial cell phenotype was assessed. Ex vivo imaging of the limbus in cadaveric tissue of donors aged from infancy to 90 years was carried out using electron and confocal microscopy. The data suggested that the area occupied by the crypts was sharply reduced after the age of 60 years. The niche microstructures also became smoother with donor age. The phenotypic assessment of cultured limbal epithelial cells harvested from donors of different ages showed that the levels of putative stem cell markers as well as telomerase activity and telomere length remained unchanged, regardless of niche topography. However, the colony forming efficiency of the cultures was significantly reduced with age (p < 0.05). This is the first comprehensive study of the effect of age on the structural and phenotypic characteristics of the human limbal niche. The results have a significant biological value as they suggest a correlation of limbal architecture with decline of re-epithelialisation rate in older patients. Overall, the data also suggest that LESCs harvested from younger donors may be more suitable for cultured LESC therapy production.
Assuntos
Envelhecimento/fisiologia , Limbo da Córnea/citologia , Nicho de Células-Tronco/fisiologia , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Análise de Variância , Cadáver , Criança , Pré-Escolar , Ensaio de Imunoadsorção Enzimática , Humanos , Lactente , Recém-Nascido , Microscopia Confocal , Microscopia Eletrônica de Varredura , Pessoa de Meia-Idade , Fenótipo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Telomerase/análise , Telômero/ultraestruturaRESUMO
Pre-2000, the clinical management of keratoconus centred on rigid contact lens fitting when spectacle corrected acuity was no longer adequate, and transplantation where contact lens wear failed. Over the last decade, outcome data have accumulated for new interventions including corneal collagen crosslinking, intracorneal ring implantation, topographic phototherapeutic keratectomy, and phakic intraocular lens implantation. We review the current evidence base for these interventions and their place in new management pathways for keratoconus under two key headings: corneal shape stabilisation and visual rehabilitation.
Assuntos
Colágeno/metabolismo , Substância Própria/cirurgia , Reagentes de Ligações Cruzadas/uso terapêutico , Ceratocone/terapia , Implantação de Prótese , Terapia Combinada , Córnea/metabolismo , Substância Própria/metabolismo , Procedimentos Clínicos , Humanos , Ceratocone/fisiopatologia , Próteses e Implantes , Transtornos da Visão/reabilitaçãoRESUMO
An Asian male in his late 50s with known Marfan's syndrome (MFS) presented with sudden deterioration in vision and loss of globe structure 13 years after the placement of a silicone scleral encircling band for the management of retinal detachment. Surgical exploration revealed simultaneous intrusion and extrusion of the encircling band resulting in globe perforation and collapse. This was managed by removal of the encircling band and a scleral patch graft over the defect. This case highlights that in patients with thin sclera, such as in MFS, scleral perforation is a potential complication that should be considered in patients undergoing scleral buckling. Management of this complication is also technically difficult because of impaired healing of the sclera in these patients.
Assuntos
Síndrome de Marfan , Recurvamento da Esclera/instrumentação , Falha de Equipamento , Humanos , Masculino , Síndrome de Marfan/complicações , Pessoa de Meia-Idade , Descolamento Retiniano/etiologia , Descolamento Retiniano/cirurgiaRESUMO
Chemical and thermal burns can cause devastating injuries to the anterior segment. The consequences of alkali injuries are notoriously severe due to the rapid penetration of these agents into the ocular tissues. Denaturation of tissue, inflammation, and scarring leads to loss of function. An understanding of the pathogenesis of tissue damage has lead to a rational approach to treatment. Emergency irrigation of the eye is essential and there is a 'window of opportunity' during the first 7-10 days after injury when medical treatment can significantly limit the potentially blinding consequences. The acute injury is followed by early and late reparative phases during which the prognosis can be further improved by surgical intervention. Early surgical intervention is targeted at protecting the ocular surface and encouraging re-epithelisation. Later, surgical treatments are directed at ocular surface reconstruction and restoration of vision. However, before any attempt is made at surface reconstruction, the ocular surface environment must be optimised by division of symblepharon, and correction of lid deformity and trichiasis. If there is conjunctivalisation of the corneal surface, limbal stem cell transplantation can restore a corneal epithelial cell phenotype, and transplantation of in vitroamplified corneal epithelial stem cells has been developed as an alternative to keratolimbal transfer techniques. Keratoplasty and cataract surgery may then be necessary to clear the visual axis. Finally, keratoprosthesis is an option for the most severely damaged eyes.
Assuntos
Queimaduras Químicas/cirurgia , Queimaduras Oculares/cirurgia , Queimaduras Químicas/reabilitação , Túnica Conjuntiva/lesões , Túnica Conjuntiva/cirurgia , Córnea/cirurgia , Lesões da Córnea , Queimaduras Oculares/induzido quimicamente , Queimaduras Oculares/reabilitação , Humanos , Fatores de TempoRESUMO
Recent advances in stem cell biology have led to the exploration of stem cell-based therapies to treat a wide range of human diseases. In the ophthalmic field, much hope has been placed on the potential use of these cells to restore sight, particularly in those conditions in which other established treatments have failed and in which visual function has been irreversibly damaged by disease or injury. At present, there are many limitations for the immediate use of embryonic stem cells to treat ocular disease, and as more evidence emerges that adult stem cells are present in the adult human eye, it is clear that these cells may have advantages to develop into feasible therapeutic treatments without the problems associated with embryonic research and immune rejection. Here we discuss the current prospects for the application of various adult ocular stem cells to human therapies for restoration of vision.
Assuntos
Túnica Conjuntiva/citologia , Oftalmopatias/cirurgia , Limbo da Córnea/citologia , Retina/citologia , Transplante de Células-Tronco , Células-Tronco/citologia , Adulto , Animais , Túnica Conjuntiva/fisiologia , Células Epiteliais/fisiologia , Células Epiteliais/transplante , Humanos , Limbo da Córnea/fisiologia , Regeneração , Retina/fisiologia , Células-Tronco/fisiologiaRESUMO
BACKGROUND: Myopia (also known as short-sightedness or near-sightedness) is an ocular condition in which the refractive power of the eye is greater than is required, resulting in light from distant objects being focused in front of the retina instead of directly on it. The two most commonly used surgical techniques to permanently correct myopia are photorefractive keratectomy (PRK) and laser-assisted in-situ keratomileusis (LASIK). OBJECTIVES: The aim of this review was to compare the effectiveness and safety of PRK and LASIK for correction of myopia. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (2005, Issue 3), MEDLINE (1966 to September 2005), EMBASE (1980 to September 2005) and LILACs (1982 to 3 November 2005). We also searched the reference lists of the studies and the Science Citation Index. SELECTION CRITERIA: We included randomised controlled trials comparing PRK and LASIK for correction of any degree of myopia. We also included data on adverse events from prospective multicentre consecutive case series in the Food and Drugs Administration (FDA) trials database (http//www.fda.gov/cdrh/LASIK/lasers.htm). DATA COLLECTION AND ANALYSIS: Two authors independently assessed trial quality and extracted data. Data were summarised using odds ratio and mean difference. Odds ratios were combined using a random-effects model after testing for heterogeneity. MAIN RESULTS: This review included six randomised controlled trials involving a total of 417 eyes, of which 201 were treated with PRK and 216 with LASIK. We found that although LASIK gives a faster visual recovery than PRK, the effectiveness of these two procedures is comparable. We found some evidence that LASIK may be less likely than PRK to result in loss of best spectacle-corrected visual acuity. AUTHORS' CONCLUSIONS: LASIK gives a faster visual recovery than PRK but the effectiveness of these two procedures is comparable. Further trials using contemporary techniques are required to determine whether LASIK and PRK are equally safe.