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Vertical movement of epithelial basal cells toward the corneal surface during use of extended-wear contact lenses." Invest Ophthalmol Vis Sci 44(3

PURPOSE. To study the effects of extended contact lens wear (EW) on the movement of basal epithelial cells toward the corneal surface. METHODS. Rabbits (n ϭ 32) were injected with 5-bromo-2-deoxyuridine (BrdU) to label a group of proliferating basal epithelial cells, and, 24 hours later, one randomly chosen eye was fitted with a low-or medium-oxygen-transmissible (Dk/t) rigid gas permeable (RGP) contact lens, while the other eye served as the control (n ϭ 28). Four rabbits were not fitted with any contact lens. Rabbits were euthanatized at different time points and the corneal epithelium was immunocytochemically stained for BrdU and/or Ki-67 and counterstained with propidium iodide or Syto 59. Corneal flatmount tissues were examined three dimensionally under a laser confocal microscope and the location of each BrdU-labeled cell in the corneal epithelium (basal or suprabasal) was determined. RESULTS. Four days after injection of BrdU, both low-(P Ͻ 0.001) and medium-Dk/t RGP (P Ͻ 0.001) lens groups showed significantly more BrdU-labeled cells in the basal cell layer than in the control eyes. Six days after injection of BrdU, a small percentage of BrdU-labeled cells (Ͻ0.5%) were Ki-67 positive. CONCLUSIONS. Within 6 days, the majority (80%) of BrdU-labeled basal cells became terminally differentiated and rarely divided secondarily in the central epithelium. Short-term use of lowand medium-Dk/t RGP EW contact lenses slows the normal movement of basal epithelial cells toward the surface in the central cornea. This is consistent with known EW-lens-induced decreases in corneal epithelial basal cell proliferation and surface cell exfoliation. Overall, the data suggest that EW lenses significantly inhibit the normal homeostatic turnover rate of the corneal epithelium. (Invest Ophthalmol Vis Sci. 2003;44:1056 -1063) DOI:10.1167/iovs.02-0725 E xtended-wear (EW) contact lens users are exposed to a significantly higher risk of development of an infectious corneal ulcer than daytime lens wearers and non-contact lens users. 1,2 One of the important components of the ocular surface's defense against infection is the intact corneal epithelium, which forms a strong barrier against the penetration of infectious organisms. Increasing evidence in humans and rabbits suggests that EW contact lens use produces a decrease in basal cell proliferation and surface cell exfoliation of the corneal epithelium, causing an apparent stagnant ocular surface. There are, however, currently no reports on the effect(s) of contact lens wear on the movement of epithelial basal cells toward the surface of the cornea. Based on previous studies, we have proposed that in the central corneal epithelium, continuous contact lens wear slows down the movement of basal epithelial cells toward the corneal surface. Epithelial cells in the cornea are continuously in motion. There are two principal directions for the migration of epithelial cells: centripetal and vertical. Early observations with pigment and ink tracers have revealed the existence of centripetal movement in the corneal epithelium from the periphery to the center. 6 By contrast, vertical or upward cell movement occurs when basal cells leave the basal lamina and move toward the surface of the corneal epithelium, ultimately ending in apoptotic exfoliation. 7-10 Using tritiated thymidine labeling to track the movement of basal cells toward the corneal surface, Hanna and O'Brien 11 estimated the turnover rate of the epithelium to be 3.5 to 4 days in the rat and 6 to 7 days in the mouse. Beebe and Masters 12 demonstrated that after a single-pulse injection of 5-bromo-2-deoxyuridine (BrdU), the first BrdU-labeled cells reach the rat corneal epithelial surface by days 3 to 4; however, some BrdUlabeled cells remain in the basal cell layer for up to 14 days. Overall, these findings suggest that the complete homeostatic turnover rate of the normal epithelium may be longer than previously suspected. In this study, the proliferation marker BrdU was selected to label a group of basal epithelial cells in both corneas of each rabbit before application of a contact lens. Once a cell takes up BrdU, the label remains detectable in the nucleus over time, even if the cell exits the cell cycle or is not actively undergoing cell division. BrdU-labeled cells can then be monitored over time as they move upward toward the surface of the corneal epithelium

A DETAILED STUDY OF STRANGE PARTICLE PRODUCTION IN e+ e- ANNIHILATION AT HIGH-ENERGY

Results onK0 and Λ production ine+e− annihilation at c.m. energies of 14, 22 and 34 GeV are presented. The shape of theK0 and Λ differential cross sections are very similar to each other and to those of π±,K± and$p(\bar p)$. Scaling violations are observed forK0 production. We obtain a value for the probability to produce strange quark-antiquark pairs relative to that to produce up or down quark-antiquark pairs of 0.35±0.02±0.05. The value ofRh=σ(e+e-→hX)/σµµ is shown to rise steadily with c.m. energy for all particle species. At 34 GeV we find 1.48±0.05K0 and 0.31±0.03 Λ per event. We have searched for possible Λ polarization. The production ofK0's and Λ's in jets is examined as a function ofpT2 and rapidity and compared to that of all charged particles; the yields in two and three jets are also investigated. Results are presented from events with two baryons$(\Lambda ,\bar \Lambda ,por\bar p)$ observed