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K.C. Kligman, K. Desai, P.A. Lewis, D.A. Samuelson; MORPHOLOGY OF THE UVEOSCLERAL PATHWAY IN DOMESTIC SPECIES . Invest. Ophthalmol. Vis. Sci. 2004;45(13):43.
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Purpose:Our understanding of the uveoscleral (US) pathway in the mammalian eye is limited to the rate of aqueous humor outflow in a few animals, principally the dog, cat, rabbit, and primates. Knowledge of the structure of the US pathway and the role that this pathway plays in aqueous humor dynamics in the eyes of different animals is very limited. To that end, we have begun to investigate the US pathway in the normal eyes of 4 domestic spp, the cat, pig, cow and horse. The present study examined the comparative structure of anterior US pathway, using sagittal and tangential sections. Methods:Formalin–preserved specimens from anterior uveas of two or more individuals of the cat, pig, cow and horse were embedded and serially sectioned sagittally and then tangentially. Every 10th section was treated with a particular stain that included: H&E, Masson’s trichrome, smooth muscle actin immunolabel, and elastin stain. Results:Within feline, bovine and equine specimens the outer anterior ciliary body musculature (CBM) formed longitudinal and circumferential attachments to trabeculae of the iridocorneal angle (ICA). Spaces between the endings of the CBM formed avenues for the beginning of the US pathway and varied in the amount of extracellular matrix (ECM) material being most developed in the pig. In the cow, other anterior muscle bundles attached the CBM to the sclera concomitant with the presence of an anterior elastic sheath. In the horse, these muscle bundles were connected to branching connective tissue trabeculae within the US pathway that were attached radially to the sclera. In the cat, muscle bundles were more abundant and formed a fine meshwork of trabecular associations with the posterior ICA. Other species variations involving the posterior attachment of the CBM to the sclera were observed. Conclusions:It is evident that the US pathway is relevant for aqueous humor dynamics. Each species possessed a clearly developed US pathway being most developed in the horse and least developed in the pig. The outermost bundles of muscle associated with the CBM appeared to have close interaction with the US pathway and the degree of these muscle associations differed with species. The species specific anatomical variations within the US pathway could play a pivotal role in the variability of aqueous outflow along this pathway that is known to occur among mammals.
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