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Samuel D Hanlon, Karen Dionne, Shyam Panthi, Tawnya Wilson, Jason J Nichols; A rabbit model for in vivo imaging of pre-clinical signs of corneal inflammation. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3210.
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Infiltration of the cornea by extravascular leukocytes is commonly observed in response to inflammatory stimuli. Prior to extravasation, leukocytes are known to marginate in the post capillary venules, transiently bind to (“rolling”) and firmly adhere to inflamed vascular endothelium before transmigration. In vivo confocal microscopy provides the means to observe this process and has been observed in human patients. This methodology holds the potential for use in animal models where early signs of inflammation are being investigated. The purpose of this study was to show the feasibility of using in vivo confocal microscopy by observing and quantifying the extent of leukocyte rolling and adhesion in the corneal limbus in a rabbit model.
Five normal adult rabbits (8 eyes) were anesthetized with isoflurane and limbal venules imaged with an HRTIII-RCM. Image sequences were captured at 30 frames per second. The number of rolling or adherent leukocytes per millimeter (mm) of venule length and the blood flow velocity were determined from stabilized image sequences. The effect of inflammation was confirmed with a corneal epithelial abrasion in one eye of one otherwise normal adult rabbit; the corneal limbus was imaged two hours later using the aforementioned approach, well before the peak leukocyte response typically seen.
In all rabbit eyes, including the wounded cornea, the average velocity of blood flow was 342µm/sec. In normal rabbit eyes, 28.8 ±12 rolling or adherent leukocytes per mm of vessel length per minute were observed using the in vivo confocal imaging. However, for the rabbit that underwent corneal epithelial wounding, 304.2 ± 94 rolling or adherent leukocytes per mm of vessel length per minute were observed. Corneal epithelial wounding resulted in nearly a 10 fold increase in rolling or adherent leukocytes present in the limbal region indicating an increase in the inflammatory response.
This work has demonstrated that in vivo confocal microscopy may be used for observing blood flow characteristics non-invasively in the corneal limbus and detecting early signs of corneal/ocular sub-clinical inflammation using a rabbit model. Data obtained from non-inflamed rabbit eyes will serve as a base for comparison when using this methodology for detecting early signs of inflammation in vivo under a variety of other potential inflammatory responses.
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