![]() Surgical trauma to the iris caused by the trephine or scissors can also result in a fixed dilated pupil. These angiographic findings are compatible with severe iris ischemia. The vessels are also tortuous, and at a late stage the iris vessels leak. Patients who had a fixed dilated pupil after PKP reveals delayed and segmental filling of the iris vessels. The cause for iris ischemia could be an acute post-operative increase in IOP, compression of iris vessels against the incision edge of the host cornea as the lens-iris diaphragm moves forwards during surgery, and visco-elastic material left in the anterior chamber angle. The leading explanation for the development of UZS is ischemic atrophy of the sphincter muscle secondary to iris strangulation with resultant pupil dilatation. Iris abnormalities, which may be more common in keratoconus, the instillation of strong mydriatics, and bringing the iris into contact with the peripheral cornea to produce peripheral anterior synechiae may also be triggers. ![]() The most widely accepted theories are ischemia of the iris and acute rise in IOP. The mechanism of UZS has not been fully determined and is probably multifactorial. ![]() Possible risk factors for UZS are increase intraocular pres-sure (IOP) during or after surgery, the use of atropine or other mydriatic agents, the presence of keratoconus,viscoelastic material left in the eye,and anterior chamber inflammatory reaction in the postoperative period. UZS usually occurs unilaterally despite bilateral surgery. The reported incidence of UZS after PKP varies widely, ranging from 0 % to 17.7%. Historically, Urets-Zavalia Syndrome (UZS) has been defined as a fixed and dilated pupil following penetrating keratoplasty (PKP) for keratoconus in patients who receive mydriatics. In 1963, Alberto Urrets-Zavalia described six patients with wide and rigid pupils, multiple posterior synechiae, and iris atrophy after undergoing PKP. 2.3 Associations with Ophthalmic Surgeries.
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