From antiquity to today, managing iris prolapse has long been a challenge for cataract surgeons everywhere, with its occurrence leading to increased risk of endophthalmitis, epithelial ingrowth, symptomatic glare, and several other postoperative complications. This article will discuss the history and mechanical theories explaining iris prolapse and an accompanying tutorial will propose ten tips to prevent and treat iris prolapse. Narrated surgical videos will be used to demonstrate these key principles.

Cataract surgery is among the oldest of surgical procedures, introduced to Europe from India by the armies of Alexander the Great around 300 BC. The ancient Greek writings of Hippocrates mention iris prolapse, and in his 1891 article, ophthalmologist H. Knapp mentioned Alexander the Great's approach to treating iris prolapse by "cutting the iris off."(1) At that time, cataract surgery was performed by extracapsular cataract extraction (ECCE), by removing the nucleus in one piece through a 9-10 mm incision, and a surgical iridectomy was often performed to prevent prolapse of the iris and uveal tissue concurrent with nucleus extraction.(2) Knapp suggested the frequency of iris prolapse to be between 4 and 8% of ECCE procedures, and proposed ten rules of preventing iris prolapse. (1) The rate of iris prolapse in the era of ECCE was suggested to be about 2%, with the highest rate found among trainees. Extracapsular cataract extraction was performed up until the mid-1980s, when small incision intracapsular cataract extraction (ICCE) and cataract phacoemulsification became the standard still used today. The transition from the 9-10 mm incision of ECCE to the 3 mm incision of ICCE improved surgical outcomes and decreased complications, including iris prolapse.(2)

In 1993, Bruce Allan, MD proposed a theoretical explanation of iris prolapse using flow mechanics. He suggested that the following two principles maintain the iris contour under normal circumstances: 1) the force generated by the difference in hydrostatic pressure between the anterior and posterior chambers, and 2) the counteracting force from the iris sphincter and dilator pupillae muscle acting on the iris root.(3) A rapid efflux of aqueous through the main corneal wound causes a relative pressure reduction anterior to the iris, effectively pulling the iris into the wound. This pressure reduction is based on Bernoulli's principle, the same principle creating the lift of an airplane in flight, whereby the pressure is lowered as a function of velocity: the faster the flow of fluid escaping the anterior chamber, the lower the pressure, creating lift on the iris and leading to iris prolapse.

Allan also used laws of fluid dynamics to suggest that at any given aqueous outflow rate, the risk of iris prolapse would increase as a function of the distance from the iris to the internal ostium of the wound. In other words, the closer the internal ostium of the wound to the iris, the greater the risk of prolapse.

In 2005, ophthalmologist John R. Campbell, observed that his patients on tamsulosin demonstrated a "floppy" iris during cataract surgery. Campbell's subsequent retrospective study was suggestive of a clinically significant association, which was then examined prospectively by his colleague, David F. Chang. Their landmark study described a newly recognized syndrome, termed "Intraoperative Floppy Iris Syndrome (IFIS)," and is among the key studies in the modern-era cataract surgery literature. IFIS is defined as a clinical triad of "fluttering and billowing of the flaccid iris stroma caused by ordinary intraocular fluid currents, a propensity for iris prolapse to the phaco and/or side-port incisions, and progressive constriction of the pupil during surgery."(4)

Despite the many advances in modern cataract surgery, iris prolapse remains a surgical challenge even today, with beginning cataract surgeons at the greatest risk. Watch the narrated video below highlighting the history of iris prolapse and the theories explaining why prolapse occurs.

 To learn how to prevent and treat iris prolapse, view the related tutorial: Ten Tips to Prevent and Treat Iris Prolapse