Adult rat pupils were dilated with a mixture of 5% phenylephrine hydrochloride and 0·5% cyclopentolate, or constricted with 0·125% echothiophate iodide. The eyes were removed and fixed in glutaraldehyde. They were prepared for scanning electron microscopy by the camphene and critical point drying methods and coated with a thin layer of gold. In pupillary dilation the posterior surface of the iris is deeply circumferentially grooved. The ridges, separated by grooves, probably represent rows of posterior epithelial cells. The ridges divide and merge with neighbouring ridges. The height of the ridges, and the width and depth of the intervening grooves vary with the degree of dilation. An amorphous layer, most likely the basement membrane, covers all of the posterior surface obscuring the boundaries between the individual epithelial cells. In pupillary constriction the posterior surface of the iris is smooth and flat or there may be hints of bulging outwards of the posterior epithelial cells. In extreme pupillary constriction where the pupillary diameter is very small, the posterior surface of the iris is smooth except for a small zone around the pupillary margin. The posterior epithelial cells around the pupillary margin are arranged in radial ridges. These ridges are high around the pupillary margin but they become lower and eventually disappear peripherally. Large bulbous structures, formed probably as a result of eversions of the posterior epithelial cells, are often seen in amongst the radial epithelial ridges. A series of overlapping humps around the pupillary margin are probably due to the underlying sphincter muscle bundles. Two new features of the iris are revealed by scanning electron microscopy. Ciliary-iris processes are found all along the periphery of the iris anchoring the highly mobile iris to the ciliary body. Varying numbers of blood vessels lie superficial to the posterior surface of the iris. They appear to come from the iris stroma, turn around at the pupillary margin to traverse the whole extent of the posterior surface of the iris. These blood vessels may play a small role in the nutrition of the adult lens. In pupillary dilation the anterior surface of the iris is made up of a mass of circumferentially-oriented blood vessels bulging prominently into the anterior chamber. In pupillary constriction the blood vessels are stretched out. They zig-zag from the periphery of the iris towards the pupillary margin. Branches are often given off at the external bend of the parent blood vessel. These then go deep into the iris tissue. The larger blood vessels appear to be arranged much like the pleats of an accordion. The cells of the anterior border layer are variously polygonal in shape with a centrally located oval nucleus. Iris pores are formed as a result of gaps in between the individual epithelial cells spanned by cytoplasmic cell processes. Iridic crypts are generally large, irregularly round or oval in shape and possess well-defined borders. Cytoplasmic prolongations of the underlying cells and a fibrillar connective tissue network normally fills the openings of the iridic crypts.

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{{Explor lien
   |wiki=    Eau
   |area=    LotaV3
   |flux=    Main
   |étape=   Exploration
   |type=    RBID
   |clé=     ISTEX:0CEACA249203C5776B4E890A4B60C16BB6BDEA00
   |texte=   A scanning electron-microscopic study of the posterior and anterior surfaces of the rat iris in pupillary dilation and constriction
}}