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| September 2004 | Inside IOVS | Volume 45/9 |
Human Corneal Endothelial Cell Transplantation Using Collagen Sheets
Full-thickness corneal transplantation is clinically applied for bullous keratopathy. Mimura et al. (p. 2992) evaluated the function of cultured human corneal endothelial cells (CEC) in vivo and the feasibility of cultured human CEC transplantation with a collagen sheet as the substitute carrier of human CEC. They found that transplanted cultured human CEC from adult human donor cornea by means of a collagen sheet can retain their function of corneal dehydration in a rabbit model without any noticeable rejection signs. Their findings suggest the feasibility of transplantation for bullous keratopathy using cultured HCEC with a collagen sheet.
Keratocytes and Inflammatory Mediators in Contact Lens Wear
Kallinikos and Efron (p. 3011) used corneal confocal microscopy to monitor quantitative changes in keratocyte density. Keratocyte density decreased following short-term contact lens wear and direct mechanical stimulation of the cornea. Tear fluid evaluation demonstrated that the concentration of specific inflammatory mediators increased during contact lens wearing and in mechanically stimulated eyes. The authors hypothesized that the mechanical stimulation of the corneal surface, due to the physical presence of a contact lens, induces the release of inflammatory mediators which cause keratocyte dysgenesis or apoptosis. The exact mechanisms of lens-induced keratocyte loss and the identification of the large number of inflammatory mediators that could play a role in this phenomenon must still be elaborated.
Intraocular Pressure Measurement with the Contour Tonometer
The accuracy of intraocular pressure (IOP) measurements using Goldmann applanation tonometers (GAT) depends on a normal corneal thickness. The popularity of refractive surgery results in increased numbers of patients with abnormal corneal thickness and hence inaccurate IOP measurements by GAT. A tonometer suitable to replace GAT as a routine tonometer for all patients has to measure IOP as easily and quickly as the GAT but independent of ocular structures such as corneal thickness. Kaufmann et al. (p. 3118) demonstrated that the novel contour tonometer (Pascal) not only fulfills these criteria but has a lower intraobserver variability between measurements than GAT.
Re-emergence of Toxoplasma gondii in Animal Friendly Production Systems
Indoor farming and improved hygiene have decreased the number of toxoplasma cases in pigs over the past decades. However, results of the experiments described in this study by Kijlstra et al. (p. 3165) show that a growing demand for animal friendly-produced meat may lead to an increase of toxoplasma infections, although many farms still remain free of toxoplasma. In order to reduce potential infection risks, slaughterhouse monitoring combined with on-farm prevention strategies and consumer education on kitchen hygiene are necessary to ensure food safety of products from all animals raised within animal friendly production systems.
Lutein and Zeaxanthin Supplementation and Macular Pigment
Lutein and zeaxanthin make up the macular pigment (MP), which protects the macula from short-wavelength light and oxidative damage. Monkeys that never ingested these compounds have no MP and higher risk of macular defects. Neuringer et al. (p. 3234) fed such monkeys pure lutein or zeaxanthin and demonstrated rapid uptake into serum and more gradual increases in MP optical density over the first six months of supplementation. Thus both compounds were deposited in the macula, even in retinas previously devoid of MP. This finding suggests that lutein or zeaxanthin supplements can be effective in raising MP in those with chronically low levels.
Foveal RPE Changes in Xanthophyll-Free Monkeys
A distinctive feature of primate foveas is the yellow macular pigment. Leung et al. (p. 3244) studied the foveal retinal pigment epithelium (RPE) of xanthophyll-free rhesus monkeys with no macular pigment. They found that RPE cell density was reduced in the absence of macular pigment. Low levels of n–3 fatty acids induced an increase in RPE cell density both in foveal and in parafoveal regions. Supplementation with pure lutein or zeaxanthin revealed an interaction among lutein, zeaxanthin and n–3 fatty acids to produce an asymmetrical RPE density profile. These data suggest that foveal RPE may migrate in response to nutritional manipulation.
Corneal Neovascularization and Platelet-Activating Factor
Corneal neovascularization is a sight-threatening complication of corneal infections, chemical injuries, and keratoplasty. Previous studies from this laboratory showed an increase of platelet-activating factor (PAF) in corneas after alkali burn, a condition that promotes extensive neovascularization. The present report by Ma et al. (p. 2915) points to an important role of PAF in inducing corneal neovascularization by a receptor-mediated mechanism. The mechanism by which this potent inflammatory mediator exerts its action involves the expression of vascular endothelial growth factor (VEGF) and a chemotactic activity in endothelial cells. The results are promising with respect to the potential therapeutic use of PAF antagonists to prevent angiogenesis during intense corneal inflammation.
The Rabbit Retina Has No Oxygen Regulation Ability
Previous studies of intraretinal oxygen distribution in a range of mammals have consistently shown that the increase in inner retinal oxygen tension during systemic hyperoxia is considerably less than that seen in the systemic circulation. This is achieved by regulation of retinal oxygen supply and/or retinal oxygen consumption. In the present study in rabbits, Cringle and Yu
(p. 3223) have shown that the rabbit does not possess such oxygen regulation mechanisms in the retina, and consequently all retinal layers are exposed to high oxygen levels during systemic hyperoxia. This may explain the toxic effects of systemic hyperoxia on the adult rabbit retina.
Migration of Retinal Cells into a Porous Implant
One of the critical issues limiting the size and density of stimulating electrodes in a retinal prosthesis is their proximity to the target cells. Palanker et al. (p. 3266) report on a phenomenon of retinal cellular migration into a porous implant that may help to address this issue. Retinal neurons migrate within a few days into perforations larger than 5 µm in diameter in a membrane placed into the subretinal space. This may provide a means of gaining close proximity between electrodes and target cells and thus allow a greater density of stimulating elements which would subserve higher resolution.
Engineered Viruses Enhance Mammalian Protein Studies
DiCiommo et al. (p. 3320) describe a simple, enhanced genetic delivery device based on the Alphavirus genome. These engineered viruses are work horses for production of mammalian protein in mammalian cells and easy rapid purification of the correctly modified proteins, illustrated for the retinoblastoma protein. The viruses readily infect cells such as murine retinal explants and retinoblastoma, with excellent potential for short-term functional studies and identification of binding proteins.
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