摘要:

Excimer laser photorefractive keratectomy (PRK) procedures photoablate the central optical zone, potentially altering the corneal vertex normal and thus the corneal topography (CT) system reference axis. Anterior corneal surface coordinates (x, y, and z) were computer generated to simulate spherical and PRK-ablated corneal surfaces. Power maps were reconstructed by using surface tangents relative to various assumed CT reference axes, the original and displaced vertex normals. The simulation process eliminated focus, alignment, and surface-reconstruction errors. A simulated 5.00-D myopic PRK decentered 1 mm from the vertex produced a new corneal vertex 0.13 mm from the original position. Axial power-map generation by using this new reference axis produced a spherical keratectomy with astigmatic untreated periphery. This computer simulation demonstrates that reference axis changes are significant for even modest PRK decentration and can explain apparent steepening in untreated corneal areas. CT users should be aware that pre-and postoperative CT power maps may not be directly comparable

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The high bioavailability and low toxicity of fluconazole, a stable, water-soluble, low-molecular-weight bis-triazole antifungal, makes it a good candidate for consideration as a topical ocular agent. The penetration of fluconazole (0.2%) into the corneas and aqueous humors of New Zealand white rabbits was assayed by gas liquid chromatography (GLC). Peak corneal levels occurred essentially immediately at 5 min in the corneas [debrided, 8.2 ± 1.2 (μg/g; nondebrided, 1.6 ± 0.6 μg/g; (mean ± SEM)] and at 15 min after application in the aqueous [debrided, 9.4 ± 2.3 μg/ml; nondebrided, 1.6 ± 0.6 μg/ml; (mean ± SEM)]. Estimating from semilogarithmic plots of the data, the half-life in the debrided eyes was 15 min; in the nondebrided eyes, t½, was 30 min. A loading dose of a 20-μl drop per min for 5 min yielded levels of 59.9 ± 11.3 μg/g (mean ± SEM) in the debrided corneas and 32.4 ± 1.9 μg/ml (mean ± SEM) in the corresponding aqueous humor. A regimen consisting of this loading dose followed by one 20 μl drop/h for 6 h showed 45.9 ± 3.5 μg/g (mean ± SEM) in the debrided corneas and 8.8 ± 1.7 μg/ml (mean ± SEM) in the corresponding aqueous. The same regimen yielded values of 3.1 ± 0.2 μg/g in the nondebrided corneas and 1.3 ± 0.2 μg/ml (mean ± SEM) in the aqueous. Minimal inhibitory concentrations (MIC) at 24 h for yeasts ranged from <1.25 to 20 μg/ml, for hyaline molds from 2.5 to >20 μg/ml, and dematiaceous molds from <1.25 to >20 μg/ml. Topical fluconazole exhibits pharmacokinetics and selective MICs that merit further evaluation for its ophthalmic use as a topical antifungal agent

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The process of corneal wound healing involves the transformation of adjacent corneal keratocytes to myofibro-blast-like cells characterized by the development of prominent microfilament bundles containing α-smooth muscle-specific actin (α-SM), a contractile protein thought to be important in mediating wound contraction. Recent studies have shown that the expression of α-SM in cultured corneal keratocytes can be induced by serum and TGFβ1. To study the cellular and molecular mechanisms underlying this transformation process and to begin to identify the role of α-SM in wound contractile events, we generated immortalized rabbit corneal cell strains with extended life by using SV40 transfection. Two unique strains were isolated (TRK-36 and TRK-43). TRK-36, which appears similar to normal corneal keratocytes, maintains a stellate, keratocyte morphology when grown in the absence of serum and transforms to a myofibro-blast-like cell when treated with TGFβ1(1 ng/ml), as indicated by the induced expression of α-SM actin. TRK-43 exhibits features characteristic of myofibroblasts in that it constitutively expresses α-SM actin under serum-free conditions. Both strains show in vitro contraction of collagen gels ≥80% in 24 h in serum-containing medium. Interestingly, under serum-free conditions, TRK-43 cells showed significantly greater contraction of collagen gels compared with those of TRK-36. Overall, the establishment and further study of these cell strains may provide important insights into the molecular mechanisms underlying myofibroblast transformation

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

The Tampa Trephine (Martin Marietta Speciality Components, Largo, FL, U.S.A.) penetrating keratoplasty technique uses a 7.0-mm corneal donor button with six rectangular 1 x2-mm tabs of Bowman's layer, 75 μm in thickness, which are inserted into the recipient stroma beneath Bowman's layer. We evaluated the safety of the Tampa Trephine tissue-trephination method on the cat corneal endothelium combining vital staining and scanning electron microscopy, comparing it with the standard Week trephination technique. The Tampa Trephine tissue trephination produces a donor button with a 6.7-mm diameter central area of normal endothelium. Localized peripheral areas of cellular loss, endothelial and Descemet's tears, endothelial detachment, and folding along the border of the trephination were observed with the Tampa Trephine method, all located in an area of ≤150 μm, adjacent to the edge of the button. Standard trephination induced a localized peripheral area of endothelial damage <50 μm in extension from the donor edge. A theoretic maximal 8.4% peripheral endothelial cell loss is induced with the Tampa Trephine trephination method, compared with a 2.8% loss with the standard procedure. The peripheral location of the alterations after the Tampa Trephine does not hinder the viability of the corneal endothelium, as it has been clinically observed

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Replacement of the entire anterior segment of the eye is a very ambitious and complex endeavor and it is not known whether the retina remains functional when the anterior structures have been removed. We used routine histopathologic evaluation and electroretinographic measurements to determine the structural and functional status of rabbit retinas following surgical removal of the internal anterior structures (iris, ciliary body, and lens) and replacement of the vitreous with silicone oil. In some cases, we were able to record both a scotopic and a photopic electroretinographic response as long as 15 weeks after complete removal of the internal anterior segment structures. Although many hurdles remain and more efficacious surgical techniques and biomaterials need to be developed, our results suggest that, in the rabbit, the retina may continue to function in the absence of critical anterior segment structures

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Effective chemotherapy forAcanthamoebakeratitis has been hampered because of the marked resistance of the parasites to a variety of antimicrobial agents. In view of the fact that topical Brolene (propamidine isethionate) and neosporin are currently considered to be the medical treatment of choice in Europe, we sought to determine whether pentamidine may be equally effective, because the drug is more readily available to ophthalmologists in the United States. In this study, we compared the amoebicidal activity of the Brolene (commercial product), propamidine isethionate and pentamidine isethionate (Pentam) in vitro against three different species ofAcanthamoeba, and the drugs' corresponding biocompatibility with rabbit corneal epithelial and endothelial cell cultures. The results indicated that there were significant species differences in drug sensitivity. Propamidine (> 1,000 μg/ml) was clearly less effective than pentamidine (>125 μg/ml) againstA. castellanii, although equivalent potency (>250 μg/ml) was observed againstA. polyphaga.On the other hand, propamidine (>31.25 μg/ml) was slightly more effective than pentamidine (>62.5 μg/ml) againstA. hatchetti.Both drugs were also relatively nontoxic after short-term contact with cell cultures, even though the highest concentration of pentamidine caused low-grade injury to the superficial epithelium and reversible membrane damage to the endothelium. Steady-state levels of propamidine at effective amoebicidal concentrations, however, were much more toxic than pentamidine, which indicated that the drug has a much lower therapeutic index. Our data suggest that pentamidine may be an effective therapeutic option because of its potency and low toxicity

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Synthetic peptides, ranging from 12 to 18 residues, containing partial sequences from natural cecropin A and melittin were tested for activity in an experimental pseudomonas keratitis model in rabbits. In separate experiments, twoPseudomonas aeruginosastrains: (a) a clinical isolated strain, and (b) an American Type Culture Collection (ATCC) strain, were inoculated into the stroma of one cornea of each rabbit. Peptides were topically applied at 0.1% in phosphate-buffered saline (PBS) and compared with PBS alone and 0.3% gentamicin eye drops. Clinical evaluation, based on the McDonald-Shadduck scale, was performed during a <48-h period after the bacterial inoculation. The peptide-treated animals showed significantly lower (p< 0.05) inflammatory signs and lower anterior-segment bacterial damage compared with PBS-treated animals, after the first 6 h. The antiinflammatory/antimicrobial activity was non significantly different (p< 0.05) from that in animals treated with gentamicin. We conclude that peptides keeping the sequence KWKLFKK from cecropin A and at least the sequence VLKVL from melittin show promise as novel agents in topical ocular therapy of bacterial keratitis

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Recent reports have demonstrated the expression of intercellular adhesion molecule-1 (ICAM-1; CD54) on the epithelium in various allergic diseases and inflammatory conditions, including the bronchial epithelium of patients with allergic asthma, conjunctival epithelium of allergic patients after allergen-specific challenge, and corneal epithelium of rejected corneal allografts. We investigated the presence of ICAM-1 expression on the corneal epithelium from a patient with vernal keratoconjunctivitis (VKC). Immunohistochemical staining of the diseased cornea demonstrated abundant ICAM-1 expression on the corneal epithelium. Immunoreactive ICAM-1 appeared to localize primarily to the cells of the basal and middle layers of the corneal epithelium. No staining was detected on the ocular surface epithelium. The normal, healthy cornea demonstrated no significant ICAM-1 expression on any of the epithelial layers, similar to that previously reported. To the best of our knowledge, this is the first report of ICAM-1 expression on the corneal epithelium from a patient with VKC

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

A 22-year-old female college student from the southwestern United States was first seen with progressive fluffy white growths over both corneas nasally and a history of chronic allergies and extensive sun, wind, and chlorine exposure as a competitive swimmer. The lesions were superficial, elevated, crescent-shaped, vascularized, and extended from the limbal conjunctiva onto the peripheral cornea nasally. The lesions were composed of an unencapsulated thick fibrovascular pannus with numerous fibrocytes, chronic inflammatory cells and mast cells, and abundant linear and wavy elastinophilic profiles, but no adipose tissue. Ultrastructurally, the elastinophilic structures were immature elastic fibers arranged in globules and bundles within a thick collagenous matrix. No mature elastic fibers were found. A few areas of elastotic degeneration were also found. This lesion resembled elastofibromas that have been reported more commonly in the subcapsular region and only once in the ocular region. Previous reports debated whether the elastic material in elastofibromas is derived from excessive production of elastic fibers by activated fibrocytes or from elastotic degeneration of collagen. In our case, both processes occur and are presumed to result from excessive ultraviolet radiation, wind and chlorine exposure, and perhaps, chronic inflammation; features that have been ascribed to the pathogenesis of pingueculae and pterygia

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0277-3740    

出版商:OVID    

年代:1997

数据来源: OVID