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D.A. Samuelson, S. Gilbert, P.A. Lewis, M. Chisholm, I.H. Horowitz, R. Ofri; Morphological and Histochemical Characterization of the Iridocorneal Angle of the Thompson Gazelle . Invest. Ophthalmol. Vis. Sci. 2003;44(13):652.
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Purpose:Recently, the normal IOP of the Thomson gazelle (Gazella thomsoni) has been reported to be one of the lowest recorded among mammals, being less than 8 mm Hg. This study examines for the first time the morphology of the gazelle's ciliary body and associated outflow apparatus. Special attention was paid to features of the iridocorneal angle and their possible relationship with the ciliary body musculature (CBM) with the aim of understanding the anatomical basis for the low IOP measured in this species. To this end, the presence of smooth muscle actin (smA) was examined immunohistochemically. Methods:Sagittal sections of seven globes from 2 young and 2 adult animals were cut. The sections were stained with either H&E;, PAS or Masson trichrome. For the presence of smA, additional sections were incubated with primary antibody (mouse anti-human sm actin) overnight at 50 degrees C and treated sequentially with secondary antibody (rabbit anti-mouse immunoglobulin), peroxidase labeled streptavidin, and substrate chromagen solution (AEC) and appropriate washes. Results:The anterior margin of the ICA was supported by a well developed pectinate ligament. The uveal trabecular meshwork (UTM) posterior to the pectinate ligament comprised most of the volume of the ICA. The corneoscleral trabecular meshwork (CSTM) was small and compact and lied in a distinctly formed sulcus, bordered posteriorly by a scleral spur. The CSTM was lined externally by large veins that comprised the angular aqueous plexus (AAP), often joined into a single sinus. Labeling of smA revealed the presence of myofibroblasts along the margin of the AAP. The CBM extended anteriorly toward the base of the iris. Muscle fibers were oriented radially and circularly as well as longitudinally. Conclusions:The outflow apparatus of the T. gazelle shares anatomical similarities with those of other large herbivorous spp, especially the pig and the water buffalo. However, the combined ICA-CBM association appears to be a unique arrangement among mammalian ciliary bodies that is especially well designed for aqueous humor removal.
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