RESUMO
The corneal wound healing response, including the development of stromal opacity in some eyes, is a process that often leads to scarring that occurs after injury, surgery or infection to the cornea. Immediately after epithelial and stromal injury, a complex sequence of processes contributes to wound repair and regeneration of normal corneal structure and function. In some corneas, however, often depending on the type and extent of injury, the response may also lead to the development of mature vimentin+ α-smooth muscle actin+ desmin+ myofibroblasts. Myofibroblasts are specialized fibroblastic cells generated in the cornea from keratocyte-derived or bone marrow-derived precursor cells. The disorganized extracellular matrix components secreted by myofibroblasts, in addition to decreased expression of corneal crystallins in these cells, are central biological processes that result in corneal stromal fibrosis associated with opacity or "haze". Several factors are associated with myofibroblast generation and haze development after PRK surgery in rabbits, a reproducible model of scarring, including the amount of tissue ablated, which may relate to the extent of keratocyte apoptosis in the early response to injury, irregularity of stromal surface after surgery, and changes in corneal stromal proteoglycans, but normal regeneration of the epithelial basement membrane (EBM) appears to be a critical factor determining whether a cornea heals with relative transparency or vision-limiting stromal opacity. Structural and functional abnormalities of the regenerated EBM facilitate prolonged entry of epithelium-derived growth factors such as transforming growth factor ß (TGF-ß) and platelet-derived growth factor (PDGF) into the stroma that both drive development of mature myofibroblasts from precursor cells and lead to persistence of the cells in the anterior stroma. A major discovery that has contributed to our understanding of haze development is that keratocytes and corneal fibroblasts produce critical EBM components, such as nidogen-1, nidogen-2 and perlecan, that are essential for complete regeneration of a normal EBM once laminin secreted by epithelial cells self-polymerizes into a nascent EBM. Mature myofibroblasts that become established in the anterior stroma are a barrier to keratocyte/corneal fibroblast contributions to the nascent EBM. These myofibroblasts, and the opacity they produce, often persist for months or years after the injury. Transparency is subsequently restored when the EBM is completely regenerated, myofibroblasts are deprived of TGFß and undergo apoptosis, and the keratocytes re-occupy the anterior stroma and reabsorb disordered extracellular matrix. The aim of this review is to highlight factors involved in the generation of stromal haze and its subsequent removal.
Assuntos
Lesões da Córnea/patologia , Opacidade da Córnea/patologia , Substância Própria/patologia , Epitélio Corneano/patologia , Animais , Apoptose/fisiologia , Membrana Basal/patologia , Lesões da Córnea/metabolismo , Ceratócitos da Córnea/metabolismo , Opacidade da Córnea/metabolismo , Opacidade da Córnea/fisiopatologia , Proteínas da Matriz Extracelular/metabolismo , Humanos , Miofibroblastos/metabolismo , Miofibroblastos/patologia , Cicatrização/fisiologiaRESUMO
PURPOSE: To assess visual results and compare methods of measuring central corneal thickness (CCT) and corneal opacity thickness (COT) in patients with corneal opacities induced by epidemic keratoconjunctivitis (EKC) and treated with phototherapeutic keratectomy (PTK) using low-dose mitomycin C (MMC). DESIGN: Prospective consecutive case series. METHODS: Patients with chronic adenoviral corneal opacity underwent transepithelial PTK with MMC 0.002% for 1 minute. The presence of photophobia, the best spectacle-corrected visual acuity (BSCVA), and the contrast sensitivity were evaluated. CCT measurements were obtained with ultrasound pachymeter (US), ultrasound biomicroscopy (UBM), Scheimpflug tomography (Pentacam Oculus), and optical coherence tomography (OCT Visante). COT measurements were obtained with UBM, Pentacam, and OCT. RESULTS: Thirty-one eyes of 23 patients, comprising 15 women (65.2%) and 8 men (34.8%), mean age 41.8 years, were enrolled in the study. Duration of visual disturbance was 19.1 ± 14 months. The number of patients with photophobia was reduced from 100% to 29% after surgery. BSCVA improved 2 or more lines in 78% of the patients at 12 months. A hyperopic shift of 1.52 ± 0.91 diopters was achieved. Contrast sensitivity improved in both photopic and mesopic conditions. For each of the instruments, the CCT postoperative mean was significantly smaller than the preoperative measurement (P < .0001) and COT values were significantly reduced in comparison to the preoperative values (P < .001). CONCLUSION: Improvements in photophobia, BSCVA, and contrast sensitivity were observed in patients treated using excimer laser PTK with low-dose MMC for subepithelial infiltrates.
Assuntos
Infecções por Adenovirus Humanos/cirurgia , Conjuntivite Viral/cirurgia , Opacidade da Córnea/cirurgia , Lasers de Excimer/uso terapêutico , Mitomicina/administração & dosagem , Ceratectomia Fotorrefrativa , Infecções por Adenovirus Humanos/fisiopatologia , Infecções por Adenovirus Humanos/virologia , Adolescente , Adulto , Idoso , Conjuntivite Viral/fisiopatologia , Conjuntivite Viral/virologia , Sensibilidades de Contraste/fisiologia , Opacidade da Córnea/fisiopatologia , Opacidade da Córnea/virologia , Feminino , Humanos , Masculino , Microscopia Acústica , Pessoa de Meia-Idade , Fotofobia/fisiopatologia , Estudos Prospectivos , Tomografia de Coerência Óptica , Acuidade Visual/fisiologia , Adulto JovemRESUMO
BACKGROUND: The authors have developed a small portable device for the objective measurement of the transparency of corneas stored in preservative medium, for use by eye banks in evaluation prior to transplantation. METHODS: The optical system consists of a white light, lenses, and pinholes that collimate the white light beams and illuminate the cornea in its preservative medium, and an optical filter (400-700 nm) that selects the range of the wavelength of interest. A sensor detects the light that passes through the cornea, and the average corneal transparency is displayed. In order to obtain only the tissue transparency, an electronic circuit was built to detect a baseline input of the preservative medium prior to the measurement of corneal transparency. The operation of the system involves three steps: adjusting the "0 %" transmittance of the instrument, determining the "100 %" transmittance of the system, and finally measuring the transparency of the preserved cornea inside the storage medium. RESULTS: Fifty selected corneas were evaluated. Each cornea was submitted to three evaluation methods: subjective classification of transparency through a slit lamp, quantification of the transmittance of light using a corneal spectrophotometer previously developed, and measurement of transparency with the portable device. CONCLUSION: By comparing the three methods and using the expertise of eye bank trained personnel, a table for quantifying corneal transparency with the new device has been developed. The correlation factor between the corneal spectrophotometer and the new device is 0,99813, leading to a system that is able to standardize transparency measurements of preserved corneas, which is currently done subjectively.
Assuntos
Córnea/fisiologia , Topografia da Córnea/instrumentação , Bancos de Olhos/métodos , Iluminação/instrumentação , Retinoscópios , Preservação de Tecido/instrumentação , Opacidade da Córnea/diagnóstico , Opacidade da Córnea/fisiopatologia , Topografia da Córnea/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Humanos , Técnicas In Vitro , Iluminação/métodos , Reprodutibilidade dos Testes , Retinoscopia/métodos , Sensibilidade e Especificidade , Preservação de Tecido/métodosRESUMO
We have developed a spectroscopy system dedicated to eye banks in order to standardize the evaluation of the donated corneas, with respect to their transparency. The system for measuring the corneal transmission spectrum basically consists of a conventional spectroscopy single beam optical apparatus, with particularities in order to attend to the needs of the eye banks, having a linear CCD (2048 sensors) as a detector. The range of evaluation of the system is from 400 to 700 nm, which is the range of interest for these kinds of sample (corneas). Dedicated software has been developed in order to acquire the data from the system and to provide the graphical interface for the user. The software is quite easy to manipulate and provides the diagnostic with respect to the transparency of the cornea, which is based on research done in association with the clinicians of the Eye Bank of Hospital das Clínicas de Ribeirão Preto (Brazil). The system presents a resolution of 9 nm (which is good enough for this kind of measurement, that presents large bandwidths) and it is in agreement with the spectra obtained from commercial spectrophotometers (the correlation factor between our system and a Beckman DU-70 is 0.995 43 for samples of well defined bandwidths, and 0.989 73 for corneas--large bandwidth).