alpha(1)-Adrenergic receptor antagonists and the iris: new mechanistic insights into floppy iris syndrome

Understanding the role of adrenergic receptors in iris biology has gained widespread interest due to the recently described intraoperative floppy iris syndrome sometimes encountered during cataract surgery. alpha(1)AR-mediated iris dilator smooth muscle contraction occurs via alpha(1a)ARs whereas alpha(1b)ARs mediate iris arteriolar contraction. Because alpha(1)AR antagonists are first-line therapy for benign prostatic hyperplasia and lower urinary tract symptoms, more elderly patients requiring cataract surgery now receive these drugs. After reviewing intraoperative floppy iris syndrome, strengths/weaknesses of supporting data, and reviewing iris biology, a case is made that rather than being drug specific (alpha(1)AR antagonists), intraoperative floppy iris syndrome may represent the "tip of the iceberg." Relaxed iris dilator muscle resistant to adrenergic agonists should be expected with clinical drugs shown to relax the iris dilator (e.g., antagonists at alpha(1)AR, endothelin-A, angiotensin receptors, nitric oxide donors such as nitrates), and/or diseases associated with endothelial dysregulation (e.g., congestive heart failure, diabetes, hypertension). Rather than a rare, unexpected, unpredictable syndrome due to one drug, a careful medical history should elucidate intraoperative floppy iris syndrome predisposition. Just as anticoagulants are discontinued prior to elective surgery, conservative management of elderly patients suggests discontinuation of drugs that relax iris dilator muscle, in consultation with the patient's primary physician, should be considered prior to cataract surgery.