IOL placement with a posterior capsular tear

Loss of the posterior capsule and its potential support for the IOL is one of the most difficult challenges we face as cataract surgeons. Efficient management of this complication is important for the long term health of the operative eye. Here I will present a few suggestions on IOL placement in this situation and a few videos that may be helpful for the beginning surgeon.

The initial challenge is to adequately remove the residual lens material and vitreous while leaving as much capsule as possible to assist in supporting the IOL. It is very important that the vitreous has been completely removed from that the anterior segment as outlined in other sections of this blog. Then you must face the often tough decision of whether to place the IOL in the bag, sulcus, a combination of the bag and sulcus, or in the anterior chamber. You should also be ready to place sutures to secure the IOL to the iris if the sulcus placement is not stable.

Bag placement. Sometimes even with a posterior capsular tear an IOL can be gently placed in the bag most commonly when the tear is round or converted to a round tear. It is very important that the posterior capsular tear is stable as the force of placing the IOL can extend the tear further, releasing more vitreous, and could lead to placement of the IOL onto the retina. Here is a video of a planned posterior capsular rhexis and the gentle placement of a single piece acrylic into the bag.

Sulcus Placement. Usually when you have a posterior capsular tear the IOL is placed in the sulcus. The most important thing is to have a proper IOL for the sulcus ready to go in your OR at all times. The best IOL for the sulcus has a large optic that allows for mild decentration and a better view of the retina. The best IOL for the sulcus has long haptics that will center the IOL even in large eyes. The best IOL for the sulcus has smooth thin haptics to reduce chaffing of the posterior leaf of the iris^{3, 4}. I prefer acrylic over silicon IOLs for sulcus implantation as patients with capsule trauma are at increased risk for retinal detachment and the possible use of silicon oil. I like the Alcon MA50 3 piece IOL as it has wide haptics, a large yet injectable 6.5 mm optic and it is acrylic. Others advocate for the large Starr silicon IOL (AQ2010V) as they feel that the larger haptics and rounded optic edge out weigh the advantage of the acrylic material. Please remember to always use a large 3 piece IOL for this job and not a single piece acrylic (SPA). SPA IOLs are not designed for the sulcus and the large square edge haptic can cause uveitis, hyphema, vitreous hemorrhage, and glaucoma.

The second most important thing is to place the IOL with both haptics in the sulcus. If you place one haptic in the sulcus and the other in the bag the IOL will be unstable and often decentered. One reason that it is hard to get both haptics in the sulcus is that the most common area of damage to the capsule is directly across from the wound. This area is vulnerable to radial tears as OVD is often running low as the capsulorhexis passes this point and this area is vulnerable as the phaco tip and chopper are active in this region. Unfortunately this is the same area where the leading haptic naturally flows during IOL insertion. If the capsule is damaged in this area then the sulcus is poorly defined and the leading haptic can end up posterior to the anterior capsule rather than in the sulcus as intended. Defining the sulcus with a viscous dispersive viscoelastic (e.g. Viscoat) will greatly ease placement of the haptics.

Combination of Sulcus and Bag. . When you have a posterior capsular tear with a nicely centered and intact anterior capsulotomy you have more options. One of the nicest options is to first place the IOL in the sulcus and then prolapse the optic posteriorly capturing it by the anterior capsule while leaving the haptics securely in the sulcus [1]. This technique allows coverage of most of the IOL edge with capsule, allows the centered anterior capsulotomy to keep the IOL centered, and still allows suture fixation of the sulcus based haptics to the iris if needed. Here is a nice video showing this technique:

Rarely, you will encounter the situation with a late tear of the posterior capsule when a SPA IOL is already placed in the bag. In this situation you should strongly consider simply exchanging the SPA IOL for a 3 piece IOL designed for the sulcus. However another option with a perfectly centered intact anterior capsulotomy is to anteriorly displace the optic from the bag such that the optic is captured by the anterior capsulotomy and the haptics remain in the bag which protects the iris from the square edge. Here is a video showing this technique which will rarely present.

AC IOL. When the IOL cannot be adequately supported by the sulcus, surgeons have several options: place an AC IOL, suture the IOL to the iris, or suture the IOL to the sclera. Another option which is often not available in an emergent setting is to use an iris clip IOL such as the Artisan but this IOL has not been approved for this indication by the US FDA [2]. None of these approaches is clearly superior. Wagoner as part of an American Academy of Ophthalmology study reported that there is no significant difference in results when comparing AC IOLs, iris sutured IOLs, or scleral sutured IOLs when capsular support is insufficient [3]. As such practical concerns such as availability of devices, ease of the procedure, and surgeon preference drive this decision. I have outlined the placement of AC IOL in this blog.

Iris sutured IOLs offer some practical advantages over scleral sutured IOLs in the emergent situation of a posterior capsular tear (I almost never place scleral sutured IOLs in this situation). One advantage is that you can place a 3 piece IOL in the sulcus and then asses if the residual capsule alone will support the IOL. If the 3 piece IOL does not center or seems unstable, the IOL can be readily sutured to the iris without changing the IOL or explanting haptics to tie scleral based suture. The IOL optic is moved anteriorly and captured by the pupil with the addition of acetylcholine (Miochol-E Novartis). The haptics are sutured to the peripheral iris using modifications of McCannel’s technique [4] with either an external knot [5,6] or with a sliding internal knot as described by Chang [7]. Typically 10-O prolene suture is used with a long curved needle such as a CTC-6 needle (Ethicon # 9090G-SD) to secure the haptics to the iris. Here is a video where the zonlues were severly damaged and after placing the IOL in the sulcus the IOL was sutured to the iris.

Suturing IOLs to the sclera especially in an emergent setting is probably the most difficult option. Techniques to suture IOLs to the sclera often employ special IOLs with haptic eyelets [8], require more robust suture material such as 9-O prolene, and may require a scleral flap or tutoplast to cover the external suture material [9]. The routine use of 10-O prolene suture material has been reconsidered as many of these sutures eroded and broke over time. Additionally, suturing an IOL to the sclera after placing the IOL is difficult as the haptics would have to be externalized to set the suture which is more complicated than the iris suture technique.

In summary if the sulcus seems sufficient to support the IOL then the surgeon should place a large 3 piece IOL in the cililary sulcus. If after placement in the sulcus, the IOL does not seem stable, then the surgeon can supplement the capsule support with iris fixation sutures and the long term results seem excellent [10]. If it is clear that the sulcus will not support an IOL, then i tend to place an AC IOL as it is a simpler procedure and offers at least similar results to scleral or iris sutured IOLs [3].

References

1. Gimbel HV, Sun R, Ferensowicz M, Anderson Penno E, Kama, Intraoperative management of posterior capsule tears in phacoemulsification and intraocular lens implantation, Ophthalmology, 2001 Dec;108(12):2186-9; discussion 2190-2.
2. Oetting TA, Newsom T, Bilateral Artisan lens for aphakia and megalocornea: Long-term follow-up, J Cataract Refract Surg. 2006 Mar;32(3):526-8.
3. Wagoner MD, Cox TA, Ariyasu RG, Jacobs DS, Karp CL; Intraocular lens implantation in the absence of capsular support: a report by the American Academy of Ophthalmology, Ophthalmology. 2003 Apr;110(4):840-59.
4. McCannel MA. A retrievable suture idea for anterior uveal problems. Ophthalmic Surg 1976; 7(2):98–103.
5. Stutzman RD, Stark WJ, Surgical technique for suture fixation of an acrylic intraocular lens in the absence of capsule support J Cataract Refract Surg. 2003 Sep;29(9):1658-62.
6. Condon GP., Simplified small-incision peripheral iris fixation of an AcrySof intraocular lens in the absence of capsule support, J Cataract Refract Surg. 2003 Sep;29(9):1663
7. Chang DF, Siepser slipknot for McCannel iris-suture fixation of subluxated intraocular lenses, J Cataract Refract Surg. 2004 Jun;30(6):1170-6.
8. Buckley EG, Safety of transscleral-sutured intraocular lenses in children, J AAPOS. 2008 Oct;12(5):431-9. Epub 2008 Aug 15
9. Oetting TA, Johnson AT, Tisseel and Tutoplast cover, J Cataract Refract Surg. 2007 Dec;33(12):2153, Comment: J Cataract Refract Surg. 2008 Jun;34(6):881-2; author reply 882.
10. Condon GP, Masket S, Kranemann C, Crandall AS, Ahmed II, Small-incision iris fixation of foldable intraocular lenses in the absence of capsule support, Ophthalmology, 2007 Jul;114(7):1311-8.

Phaco Machine Basics

Phacoemusification machines can be overwhelming at first. Here i will try to simplify them as best i can to help those that are just getting started using them. I think it is important to have a good understanding of how they operate and not simply rely on past settings, equipment representatives, and/or the circulating nurses to run these devices critical to your success as a cataract surgeon.

These machines have four main components and software that ties the components together. First a system of irrigation which is typically just a bottle that is hung at variable heights above the surgical eye. Second the foot pedal which allows the surgeon to control the machine. Third an ultrasound hand piece which typically has crystals which vibrate the phaco needle with various power waveforms controlled by the phaco machine. And finally and most importantly, the pump, which is classically either a flow based or vacuum based device.

The irrigation system on phaco machines is typically is just an adjustable bottle held higher than eye to allow infusion of fluid. The machine can adjust the bottle height for various phases of the surgery. For example when the vacuum goes up during segment removal the bottle height typically will need to be higher to maintain the anterior chamber. similarly when you are doing anterior vitrectomy the bottle height should go way down. The machine can also turn the fluid on and off. When the foot pedal goes from position 0 to 1 the fluid is typically turned on by the phaco machine. Some phaco machines can detect when the irrigating fluid bottle is getting near empty but most cannot.

The foot pedal is typically controlled with the dominant foot (w/o shoes w/socks). although some such as the famous surgeon Jim Davidson (marshaltown iowa) suggests that the phaco foot pedal is simpler than the microscope pedal and uses his non-dominant foot for the phaco machine saving the dominant foot for the microscope. The most basic function of the accelerator like portion of the foot pedal is common across all brands with 4 positions: Position 0 – everything is off; Position 1 – irrigation is on, no pump, no U/S; Position 2 – irrigation is on, pump is on, no U/S; Position 3 – irrigation is on, pump is on, U/S is on. some of the foot pedals are wireless now such (eg. Stellaris) but most have a cable that connects to the phaco machine

The ultrasound (U/S) hand piece vibrates the phaco needle at a set rate in the 20,000 to 40,000 HZ range. The vibration is typically delivered by electrically stimulating crystals with a resonate frequency and the crystals are connected to the phaconeedle. many of the modern hand pieces have as many a 4 crystals to allow the needle to handle more load from a hard cataract. Increasing the U/S power typically increases the excursion of the needle but not the frequency which usually remains stable. With increasing load, such as a very hard cataract, the frequency and excursion may not keep up. when setting up the pahco machine for the case one must "tune" the handpiece. the machine sends pulse to the handpiece and sees how much power must be delivered to move the needle. this "tuning" helps to adjust for subtle variations from different needles and handpieces.

The phaco machine can set up a variety of ultrasound modes. In continuous mode the ultrasound energy is on on when the pedal is in position 3 and increases in excursion or power the deeper the surgeon is into position 3 up to a set maximum. In pulse mode the ultrasound contains pulses of ultrasound where it is on (set %) and then off (set %) for a set frequency. the deeper the pedal is into position 3 the more power each pulse will have up to a set maximum. The typical pulse will have a 50% duty cycle with an on time equal to the off time. the classic pulse setting is the howard fine "choo choo chop" setting with a low frequency of about 4 Hz and 50% duty cycle that is useful to acquire a piece for chopping and kind of sounds like a choo choo train. another common setting is to increase the frquency to about 100 Hz and have an on time which is less than off time creating hyperpulses which seem to run more cool to protect against wound burn. finally most machines feature a burst mode where stepping further into position 3 decreases the time between bursts of phaco such that when the pedal is fully engaged the power is continuous.

Recently some machine handpieces have featured an oscillatory component in addition to the classic longitudinal ultrasound. AMO features a figure 8 motion of the phaco needle in it latest phaco machine. Alcon in the infinity Ozil machine has a rotational feature in addition to the longitudinal ultrasound. as this rotational energy does not directly push away the nucleus pieces like the longitudinal ultrasound does the nuclear bits seem to come more readily to the tip in these modes.

The phaco pump is the most important and complex part of the phaco machine. The pump comes in two basic varieties: vacuum based (eg venturi) and flow based (eg peristaltic). A vacuum based pump creates more vacuum (mmHg) when the pump works harder. A flow based pump creates more flow (cc of fluid/min) when the pump works harder. In a real world it is hard to separate flow from vacuum as the resisitance in the tubing keeps the two related. the parameters of the pump will depend on the phase of the surgery. you will want very little fluid flow during sculpting and you will want alot of vacuum when removing the segments or when holding onto the nucleus during chopping. You might want to look over the classic definitive text in this area by Barry S. Seibel, Phacodynamics.

In pumps the vacuum, flow rate and resistance to flow in the tubing are related. I find it useful (maybe because i used to be an electrical engineer) to compare the fluid relationship to Ohm's law (E=IR) where the relationship between current I (analgous to flow rate) , voltage E(analogous to vacuum) and resistance R (analogous to resistance to flow in tubing) are related. just like it is impossible to have a pure current source or voltage source it impossible to create a pure vacuum or flow based pump. but these pumps do behave differently in practice and so it is important to understand how to operate them to your specifications.

Vacuum Pumps. The most common of these are Venturi pumps (Stellaris, Millennium, Accurus) where compressed air passes over a column of air creating a vacuum proportional to the flow of air over the column (this is similar to the way a wing creates lift). Increasing pump power increases vacuum directly; flow rate indirectly based on the amount of resistance to flow. Typically a Venturi pump requires an external source of compressed air (Millennium) or an internal compressor (Accuris or Stelaris) which has limited acceptance of this pump. The compressed gas flows over the open top of a rigid column or cassette attached to tubing creating vacuum. Flow rate for a particular amount of vacuum is then dependant on the resistance of flow to the fluid. This is roughly analogous to electric current voltage relationship (Ohm’s. This law) i=e/r where e = voltage (analogous to vacuum); i = current (analogous to flow rate); r = resistance (analogous to tubing and occlusion). As such with a given vacuum setting of the pump when you have less resistance in the tubing the flow rate will increase and conversely when you have more resistance you will get less flow through the tubing.

Controlling the vacuum based pump is very simple as you only have to set the vacuum and have no setting for flow rate. Typically you would use a fixed vacuum (ie. no matter how deep you are into position 2 or 3 the vacuum stays the same) for sculpting and to hold while chopping. You would typically use a variable vacuum (ie. the deeper into position 2 the more vacuum and faster the pump) to remove epinuclear material and for I/A of the cortex.

Flow based pumps. The most common flow based pump is the peristaltic pump (Infinity, Sovereign, and Legacy). With peristaltic pumps the faster the pump goes the more cc/min of fluid passes through the tubing or the more flow. This is often refered to as the aspiratiion flow rate (AFR). Increasing the power of the pump increases the flow rate directly and vacuum indirectly through the resistance of the tubing. So the vacuum is just dependant on the amount of fluid flow and this relationship is roughly analogous to electric current voltage relationship (Ohm’s law): e=ir where e = voltage (analogous to vacuum); i = current (analogous to flow rate); r = resistance (analogous to tubing resistance). As such you will only get some vacuum if there is some resistance to flow (or some occlusion).

These flow based machines typically have a setting for the flow rate but also have a vacuum cut off. the vacuum cut off is the point at which the pump will stop if a certain vacuum is reached. so you set the flow rate and pump humms along until the vacuum rises (due to increased resistance) to the vacuum cut off point and then the pump simply stops. so even though with peristaltic machines you have a vacuum and a flow rate setting you can only make the pump work harder by increasing the flow rate. setting the vacuum higher only sets the point higher at which the pump stops when this vacuum is reached.

With modern peristaltic pumps (eg. Infiniti) for each foot position 2 you can have fixed or variable flow; fixed or variable vacuum cut off. if you want the pump to be responsive to pressing harder on the pedal (eg for I/A) you would use a variable setting such that the aspiration flow rate or at least the vacuum cut off increases as you step down into position 2. when you set both the flow rate and the vacuum cut off to be variable so that it increases as you step into position 2 the peristaltic pump begines to feel more like a venturi pump. you typically would set the pump low and fixed for sculpting (80 mmHg vacuum cut off: 20 cc/min flow rate); higher but still fixed for chopping and segment removal (300 mm Hg and 30 cc/min); and high and vairable for I/A where you need more control (500 mmHg and 50 cc/min flow rate). i usually use roughly a 10:1 ratio of vacuum cut off:flow rate with the infinity and legacy for segment removal, chopping and I/A.

Which pump is better?. There is no clear favorite for every situation. For certain parts of the procedure the flow based pumps seem better like sculpting the groove as you can set the vacuum low with a reasonble flow rate. For other parts of the procedure like I/A and anterior vitrectomy vacuum based pumps are better as the vacuum is not related as much to occlusion (resistance to flow). for years the flow based pumps were most popular in part at least because the early vacuum based pumps required an external compressed gas line and as the peristalitic were cleverly marketed as "safer" for divide and conquer. recently, as the phaco procedure has moved more toward higher vacuum for chopping and away from scupting the vacuum based pumps are getting more popular.

Vacuum based pumps seem to have less post occlusion surge during segment removal and material seems to come to the tip better for irrigation aspiration. vacuum based pumps are clearly better for vitrectomy as the vitreous comes to the tip even without occlusion from the guillotine which can be frustrating with flow based pumps. The disadvantage of the venturi pump which is the most common vacuum based pump is the need for compressed gas and the need for a rigid cassette.

Flow based pumps seem to be better for low vacuum jobs like sculpting. With modifications such as setting the vacuum and the flow to increase with increasing position 2 on the foot pedal the flow based pumps can be more responsive for I/A like the vacum based pumps. The flow based pumps do not require compressed gas.

Phaco for soft lenses

Alot is written about phaco on hard lenses; but, in many ways the soft lenses are the most dangerous.  Soft lenses tend to jump to the phaco needle which can lead to capsule rupture.  soft lenses are hard to crack which can make the divide and conquer very difficult.  Here i discuss 2 strategies for soft lenses to increase safety for these tricky lenses.

Prolapse.  The simplest strategy for very soft lenses is to simply prolapse the soft lens into the anterior chamber.  even better is to prolapse just the nucleus.  First i like to hydrodissect, careful to keep the cannula over the lens, to avoid prolapse.  then spin the lens.  Then perform hydrodelineation and allow the nucleus to prolapse into the anterior chamber.  in a perfect world you can just prolapse the nucleus (sometimes soft lenses have a denser central core) and leave the epinuclear material in the bag.  Then remove the nucleus with the phaco needle with epinuclear settings (linear control of vacuum 0-350, asp at like 30-35 fixed, little power or ozil).   remove the epinuclear material with the phaco needle and a shizzle manuever or with the I/A tip.

Soft Chop.   The technique I like best for the soft lens is to use a soft chop with no vacuum.  avoiding vacuum is very important as the phaco needle can rapidly move through the soft lens material into the capsule.  The idea is to use the phaco needle to hold and support the soft lens while slicing through the lens with the chopper.  as you can see in the video below, you will not be able to use the usual chop where you embed and hold the nucleus and cannot use a vertical chop.   instead the phaco needle simply supports the lens and the chopper goes deep (I like the Siebel chopper) and moves in a horizontal fashion just to the left of the phaco needle moving to the left when reaching the needle to split the lens.  the lens does not always dramatically break into pieces.  however after you slice the lens into pieces (i usually use 6) you will find that the lens will come into the anterior chamber with epinuclear setting (similar to those above).  often the nucleus comes first leaving the epinuclear material which comes in a separate step using a shizzle or the I/A tip.

Tips for lefty learners of cataract surgery

Introduction.  Learning cataract surgery is hard enough when you are right handed like your mentor.  However when you are left handed and your teacher is right handed it can be tough.    Everything seems backwards for both teacher and student.  Here I will outline some tips on how to learn and teach cataract surgery when the lefty student meets the righty teacher.   I think there are 4 main issues:

Incision Location.  Often surgeons will cheat a little bit superior or inferior of temporal toward their dominant hand.   However this can be a big issue when the dominant hands of teacher and student don't match.  If the lefty student makes the incision at about 4 oclock for a left eye it may be convenient for the student but will be very hard for the right handed teacher if he/she needs to take over the case.   There are a couple of solutions to this issue.  One is to make the incision exactly temporal at 3 (left eye) or 9 (right eye) oclock so that it is equal for student and teacher.  Another solution is to make all of the incisions superior temporal.  For the right eye the left handed learner operates superior  temporal convenient for his/her left hand.  Then the teacher if he/she needs to take over can sit at the head (superior) and the incision will be convenient for the teachers right hand.  For the left eye the learner can sit at the head (superior) and make the incison superior temporal with his/her left hand.  The teacher on these left eyes can take over by sitting on the side (temporal) and the incision will be in a good location for their right dominant hand.  So if the learner sits temporal on right  eyes and superior for left eyes taking over the case by a righty will not be an issue.

Some instruments are handed.   Yes this is an issue!.   While scissors and clamps can be harder for lefties the big issue in ophthalmology is that some of the choppers are made for either right or left handed surgeons.     Very confusing as a right handed chopper is held in the righy's left hand.  Getting a chopper for a left handed surgeon (to hold in his right hand) can be a problem as the student often has no control over the OR.  Play the fairness card.  lefty bigots!  However dont wait too long as it will take time to get equipment orders approved and in the OR at most large institutions.   So i suggest that lefties plan ahead.    One of our residents developed some interesting strategies to use right handed choppers despite being a lefty for example see what we called the side saddle chop.



Mirror Image.  Just like it is convenient for right handed surgeons to rotate the lens or tear the rhexis in a certain direction the same is true for lefties.  But in the other direction.  This obvious point took me a while to figure out as a teacher.  I like to take the rhexis around clockwise (i am a righty) and it did not occur to me until i had mentored several lefties that they may prefer the mirror of what i was doing and go in the other direction.  The same is true for the direction of spinning the lens especially when chopping. 

The IOL is made for the right hander.    The IOL haptic insertion into the optic is optimized for right handed surgeons.  The IOL is designed so that it is very easy to insert when a right handed surgeon pushes the haptic/optic junction with a hook from the right side (with the right hand).  As such lefties have to recognize this issue and simply use their non dominant hand right hand for this step.  The good news is that while the IOL is optimized for right handed surgeon insertion; the IOL is easier for lefties to remove for the same reason (unfortunately this almost never comes up).

Summary.  Lefties should consider sittikng temporal on right eyes and sit superior on left eyes so the right handed attending can easily take over.  get a few left handed choppers.  Lefties should go clockwise for the rhexis and spin the lens counter clockwise while you chop.    Finally,  lefties will have to use their right hand to hold the Kuglen or other hook to insert the IOL.

Iris Prolapse

Iris prolapse can create problems during surgery and can lead to iris damage which can be dysfunctional.

Iris prolapse typically comes from a wound which is too short or from an iris which is floppy and/or poorly dilated.  The actual prolapse of the iris usually occurs during hydrodissection and can create transillumination defects, loss of iris tissue, iridodialysis, and hyphema.   It is important for eye surgeons to know how to preserve the iris when prolapse occurs and i suppose, more importantly, to prevent it from occuring in the first place.


     

Wound too short.  When the wound is too short one of the best options to prevent iris prolapse is to simply close the short wound and move to another site.  Often however moving to another site is difficult as the brow, a bleb, or the surgeons handedness get in the way of this solution.   A nice simple solution is to place a single iris hook under the incision to pull the iris under the incision preventing prolapse.  If the pupil is also small it can be useful to place 4 hooks in a diamond configuration with one hook under the wound to both prevent iris prolapse and to open the small pupil.  Iris rings such as the Malyugin ring can be used also but if the wound is very short the iris can still prolapse with the ring. 

Floppy iris.  When the patient is at risk for a floppy iris (intraoperative floppy iris syndrome) from an alpha blocker (especially Flomax or tamsulosin) or some other cause (eg ischemia ) it may be best to prevent iris prolapse with iris hooks or a Malyugin ring especially if the pupil is small.  The most common time for iris prolapse is during hydrodissection when the fluid wave passes around the lens and out the eye taking the iris out too.  Excessive and especially dispersive viscoelastic can make hydrodissection more risky for iris prolapse.  I like to remove viscoelastic above the lens prior to hydrodissection to help prevent this complication.   Gentle rocking of the lens will help to release trapped fluid behind the lens which will lower the pressure and deepen the anterior chamber.

Repositing the iris.  When iris prolapse occurs the emphasis should be on preserving the iris and preventing further prolapse.  The first step following prolapse is to use the paracentesis to remove fluid pressure from within in the eye which is pushing the iris out.  Then using a viscoelastic cannula gently reposit the iris.  After the iris is back into position consider placing an iris hook under the wound to keep the iris from further prolapse.   below you will find a video showing these techniques  Rarely, iris prolapse willl occur when you face posterior pressure from a choroidal hemorrhage, choroidal effusion, or misdirection of aqueous.

References:

Chang DF, Braga-Mele R, Mamalis N, Masket S, Miller KM, Nichamin LD, Packard
RB, Packer M; ASCRS Cataract Clinical Committee. ASCRS White Paper: clinical
review of intraoperative floppy-iris syndrome. J Cataract Refract Surg. 2008
Dec;34(12):2153-62. 

Chang DF. Use of Malyugin pupil expansion device for intraoperative
floppy-iris syndrome: results in 30 consecutive cases. J Cataract Refract Surg.
2008 May;34(5):835-41.

Chang DF, Campbell JR. Intraoperative floppy iris syndrome associated with
tamsulosin. J Cataract Refract Surg. 2005 Apr;31(4):664-73.