Equalizing the pressure gradient is the key.

By Uday Devgan, M.D., F.A.C.S.

We�ve all been there before: the delicate iris prolapses out of our phaco incision during cataract surgery, making everything more difficult. Why does this happen? And how can iris prolapse be effectively managed? This article will answer those two key questions.
Risk Factors for Iris Prolapse

Figure 1. Iris prolapse during cataract surgery.

Cataract incisions can also play an important role in iris prolapse. Clear corneal incisions that are too posterior, situated too close to the iris root, may contribute to issues of prolapse. In addition, excessively leaky incisions are a significant contributor as creation of large currents of fluid flow will likely cause the iris to billow out of the eye as well. Eyes where the papillary dilation is weak are also more prone to iris prolapse because there is more iris tissue accessible to the incisions.
Extraocular forces can also contribute to iris prolapse, such as the case with an overly voluminous retrobulbar injector or a forceful lid speculum. These can both cause posterior pressure on the globe, thereby increasing the pressure behind the cataract. When incisions are made in the anterior chamber, dropping the anterior chamber pressure dramatically, this posterior pressure creates a gradient.

Pressure Gradients are Key
All cases of iris prolapse can be explained with the concept of a pressure gradient. The iris will tend to move from the area of high pressure to the area of low pressure. This mismatched pressure gradient causes the iris to prolapse. Therefore, the best way to correct the problem is to equalize the pressure gradient (Figure 2a-c).

Figures 2a-c. Iris prolapse is caused by a pressure gradient, with high pressure behind the iris and low pressure in front of it (2a). This pressure gradient can be equalized by lowering the pressure behind the iris (2b), or by increasing the pressure in front of the iris (2c).

Causes of high pressure behind the iris include:
Intraocular causes

Figures 3a-b. During nucleus removal the posterior pressure from the inflow irrigation can cause iris prolapse (3a). By placing a plug of Healon 5 over the subincisional iris (3b), the pressure over the iris can be increased to equalize the pressure gradient, thereby solving the problem of iris prolapse.

- capsule block syndrome during hydrodissection
- broken posterior capsule with hydrated vitreous during hydrodissection
- trapped viscoelastic or saline behind the iris
- choroidal hemorrhage
- relative high vitreous pressure in nanophthalmic eyes
Extraocular causes
- excessive retrobulbar anesthetic injection
- tight lid speculum
- patient squeezing/valsalva maneuver
The iris does not naturally prolapse out of the eye, but when the pressure gradient is such that the posterior pressure is much higher than the anterior pressure, the iris is forced to flow out of the incision. The techniques that we have been taught to rectify this problem are all methods to equalize the pressure gradient.

Figures 4a-b. At the end of the case, with no viscoelastic in the eye, the iris may tend to prolapse again due to the pressure gradient (4a). By lowering the pressure behind the iris (4b), the pressure gradient can be equalized and the iris will return to the eye.

For extreme cases, giving the patient intravenous mannitol or even performing a partial pars plana anterior vitrectomy to decrease the posterior pressure may be appropriate options. However, for most cases of iris prolapse, simple techniques can be employed to restore the iris to its anatomic position and successfully complete the cataract surgery.
Managing Iris Prolapse: Nucleus Removal

During nucleus removal via the phaco probe, it is common to have the inflow irrigation flow behind the iris, which further contributes to the pressure gradient and the iris prolapse (Figure 3a). In this situation, it is easier to increase the pressure in front of the iris to equalize the pressure gradient. This can be achieved by placing a plug of a super-cohesive viscoelastic on top of the subincisional iris (Figure 3b). Here, a traditional cohesive viscoelastic would work, however a viscoelastic such as Healon 5 (Advanced Medical Optics [AMO], Santa Ana, Calif.) is a better choice. Currently, Healon 5 and Healon GV (AMO) are the only viscoelastics in the category of super-cohesive or visco-adaptive.

Videos of Robert Osher, M.D., using Healon 5 for floppy iris syndrome, show the viscoelastic is

highly effective for this use. However, my surgical skills are not as stellar as Dr. Osher�s and I find it difficult to use just Healon 5 for the entire case. Instead, I prefer to use my traditional dispersive viscoelastic, which I have used in thousands of cases, as my main viscoelastic, with a plug of Healon 5 over the subincisional iris. This allows me to continue with my normal technique of cataract surgery while the plug of Healon 5 keeps the iris in position while I finish the case.

Steps After Viscoelastic Removal
The Healon 5 plug can be used effectively during most of the surgery: apply a plug during phaco, apply another plug during cortex removal, then apply a final plug before IOL insertion. However, at the end of the case, when the IOL is safely within the capsular bag and we want to remove the viscoelastic, how do we solve the iris prolapse?
In this situation, there is fluid behind the iris, causing it to billow and prolapse outside of the eye (Figure 4a). The first step is to use the Osher technique of hydrating the clear corneal incision prior to removing the viscoelastic. After removal of the viscoelastic, the iris will tend to prolapse. At this point, use the cannula or a second instrument to flatten the anterior chamber and release the fluid that is trapped behind the nucleus (Figure 4b).

Now, with a flat anterior chamber, there should be no pressure gradient and the iris should automatically return to its normal position within the eye. Use balanced salt solution on a cannula to re-inflate the anterior chamber via the paracentesis. As you re-inflate the anterior chamber, you can direct your stream of balanced salt solution on top of the iris to prevent prolapse.
In summary, the management of iris prolapse involves equalizing the pressure gradient. Determine the cause of the increased posterior pressure and then either increase the pressure in front of the iris by applying a plug of Healon 5 or decrease the pressure behind the iris by releasing trapped fluid. Once the pressures are equalized, the iris will naturally return to its normal position. OM

Uday Devgan, M.D., F.A.C.S., is in private practice at the Maloney Vision Institute and is acting chief of ophthalmology at the Olive View - UCLA Medical Center, and assistant clinical professor at the UCLA Jules Stein Eye Institute in Los Angeles. He serves as a consultant to Advanced Medical Optics and Bausch & Lomb, however he has no financial interests in any of the products or companies mentioned. Dr Devgan can be reached at: 10921 Wilshire Blvd #900, Los Angeles, CA 90024, by phone at 310-208-3937, via fax at 310-208-0169, or by e-mail at
devgan@ucla.edu. Web site is www.maloneyvision.com.