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L. Panagis, M. Basile, A. H. Friedman, J. Danias; Histopathologic Findings in Intraoperative Floppy Iris Syndrome (IFIS). Invest. Ophthalmol. Vis. Sci. 2009;50(13):5580.
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To understand the pathophysiology of IFIS and the specific role of alpha 1A adrenoceptors (a-1A AR’s) in this condition.
Trabeculectomy was performed in the superonasal quadrant of an 83-year-old Hispanic male with advanced open angle glaucoma on chronic therapy with Tamsulosin for benign prostatic hypertrophy. Intraoperatively, the iris was noted to be floppy and prolapsed through the sclerotomy. Iris specimens from the patient were studied using histological methods (H&E, Trichrome and Periodic Acid Schiff (PAS) and immunohistochemistry for actin, myoglobulin, a-1A AR’s and myosin. Additional samples were processed for ultrastructural studies using transmission electron microscopy (TEM).
Light microscopy revealed normal anatomy with normal appearing dilator muscle fibers, arteriols, stroma and pigment epithelium. Actin, myosin and myoglobulin distribution and intensities by immunohistochemistry were similar between IFIS and non-IFIS tissue. A-1A AR’s immunoreactivity was detected in both IFIS and control irides. The staining pattern suggested that a-1A AR’s are present in iris arteriolar smooth muscle cells in addition to the dilator muscle. Co-localization of myosin with a-1A AR’s staining confirmed the presence of these receptors on smooth muscle cells of iris arterioles. Evaluation of the ulrastructure of the iris in IFIS using TEM showed the presence of abundant melanosomes in melanocytes and blood vessels as observed in normal iris. The iris arterioles seen in the stroma possessed a thick endothelial basement membrane, a semilongitudinally oriented muscularis and an abundant perivascular collagen coat.
The presence of a-1A AR’s in human iris was confirmed immunohistochemically. A-1A AR’s were localized in the muscularis of iris arterioles in addition to their presence in the iris dilator muscle. The presence of a1A adrenoceptors on iris vessels suggests that IFIS may develop because of iris vascular dysfunction and that the iris vasculature may serve a structural in addition to a nutritive function.
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