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.

wound too long

Making the wound too long can lead to several problems.

As is so often true in eye surgery, early problems can compound and lead to even bigger problems. A long wound can make it difficult to properly center the capsulorhexis as it can be hard to control the tear in the subincisional area. A decentered rhexis can lead to trouble with cortex removal and IOL placement. A long wound can make movement of instruments in the eye very difficult as they can distort the cornea clouding the view. The phacoemulsification needle in the long wound will meet more resistance and can get hotter which can lead to wound burn. One of the most common and difficult problems with the long wound is corneal edema that comes from irrigating into the corneal stroma rather than the anterior chamber with a long wound.   All of these issues decentered rhexis, corneal disotortion, and corneal clouding can make subincisional cortex removal nearly impossible.

Eccentric rhexis. the long wound can make it difficult to maintain the proper diameter in the subincisional area which leads to a decentered rhexis. You can help prevent this by using a paracentesis with a smaller instrument like a needle or Duet micro-forceps to create the rhexis under the wound. The ecentric rhexis can lead to several problems as the case proceeds. the subincisional cortical material can be very difficult to remove. occasionally a decentered rhexis can lead to IOL decentration as the more peripheral capsule can catch the edge of the optic and with contraction decenter the IOL. also the eccentric rhexis can lead to poor placement of the IOL with one haptic in the bag and one in the bag which is the most common cause of IOL decentration.

Corneal distortion. The long wound can make lateral movement of instruments very difficult as the cornea gets striae and loses clarity. One solution is to use smaller instruments such as the needle for the rhexis or smaller diameter forceps (such as the MST Duet forceps). another simple solution is to funnel the inside portion of the corneal wound which allows for lateral movement with less striae. sometimes placing ocucoat or cornea coat on the surface will lessen the striae and corneal distortion but not always. be careful of phaco burn from the longer wound.

Corneal edema. the long wound can force the irrigation port to hydrate the wound. Keep the phaco needle as central as possible to avoid irrigating into the wound. Move the irrigation sleave toward the needle tip during coaxial phaco to place the irrigation port closer to the needle tip and farther from the corneal wound. if the corneal is beginning to cloud in the subincisonal area then remove the subinicional cortex first in case you lose your view. consider using a bimanual system to better keep the irrigation out of the wound. rarely you may have to finish the case later.

Difficulty with subincisional cortex. the long wound alone can make removal of the subincisional cortex tricky. however the long wound with subsequent eccentric rhexis and corneal edema can be really tricky. Use 90 degree tip to the remove sub-incisional cortex first. consider a bimaual approach if available. consider repeat hydrodissection of the subincisional cortex through a paracentesis. often you can simply push the material toward the periphery of the bag with a Drysdale or viscoelastic, place the IOL, then remove the cortex with the safety of the IOL to hold the posterior capsule away. poor visibility of during sub incisional cortical removal is a time of risk for capsular tear.

Consider moving to another site. Some times the best approach is to simply abandon the original incision and move to another site with a proper incision. Often this is difficult as the brow or handedness get in the way of this solution. make sure the alternative incision is not long too!

Here is a video highlighting some of these points.

anterior vitrectomy

Vitreous can be very difficult for the anterior segment surgeon. when it presents we can be tempted to take short cuts which can lessen the safety of our surgery. being prepared is your best defense and here i will present a few tips based on my experience with the vitreous.

The cause of vitreous prolapse in your case is important as it may guide your surgical reatment and IOL location. A capsular tear can cause vitreous prolapse with an anterior tear extending posteriorly probably being most common. Primary posterior tears from the phaco needle being too deep or from a strike from the I/A device or another instrument are also common. It is best to find a cause which does not involve the surgeon such as a tear extending from a preexisting weakness from a posterior polar cataract, iatrogenic (different surgeon) from pars plana vitrectomy, or from penetrating lens trauma. Besides tears zonular dialysis can lead to vitreous prolapse and can come from your surgery with forceful rotation or pulling on the capsule with the I/A or from pre-existing conditions such as trauma, PXF, or Marfan’s.

For me the first sign of vitreous prolapse is denial. I begin to think that something is not right but and find lots of reasons why everything is really OK. denial is a powerful force for me. More objective signs of vitreous loss are the chamber suddenly deepens, the pupil widens, the residaul lens lens material is no longer centered or doesnt spin, lens particles no longer come to the phaco needle, and a big sign would be lens particles sink to the back of the eye.

3 basic principles of vitrectomy are to 1) go bimanual with separate irrigation and cutting devices, 2) close the chamber, and 3) cut low and irrigate high. if you follow these 3 principles you can keep most of the vitreous out of the front of the eye and away from the wound, iris, cornea where it can cause so much trouble. most importantly you can help to limit the amout of vitreous expression and its risk of retinal detachment.

go bimanual with separate device for irrigation and cutting is fairly easy now as most machines will allow this or assume this from the start. some machines such as the alcon 10,000 had a coaxial device and you had to remove a sleeve to make it bimanaul. i like to use a 23 gauge cortex extractor cannula to irrigate with the cutter usually in my dominant hand.

close the chamber so that no fluid can get out with the vitrectomy instruments in the eye. this will require you typically to close your main incision and add a paracentesis if you are doing traditional coaxial phaco. through one paracentesis you will place your irrigation cannula and through another larger paracentesis you will place your vitreous cutter/aspirator. if you use a 3.0 mm or similar phaco wound for the vitreous cutter apsirator the chamber will not be controlled and fluid and vitreous will stream through this wound around the cutter. you need to make the area of least resistance for any fluid or vitreous to leave the eye be the aspiration/cutter device. see the video showing the importance of closing the chamber to control the flow of vtreous.

With control of the chamber and bimanual instruments you can cut low and irrigate high. You will want to have the cutter/aspirator low to get at the root of the vitreous while irrigating high in the closed chamber to create a fluid pressure differential to push the vitreous toward the cutter. if you irrigate in the area of the cutter/aspirator you may push the vitreous away from the cutter and even worse more anterior toward the wound. in this video you can see the use of the 3 principles to remove the vitreous and some residual cortical material.

there are 3 basic phases in the case when vitreous presents: early in the case with most of the crystalline lens in the eye, with only some cortical material left (most common), and while placing the IOL.

When vitreous presents early during nucleus removal clean up is the most difficult. the vitreous is often entwined in the nuclear pieces. it can be very difficult to get posterior enough with the cutter to cut off the vitreous at its source with all of the nuclear pieces in the way. and most importatnly it is hard to not bump the pieces through the capsular tear to fall south into the back of the eye. you have a big decision to make right up front: convert to ECCE or not. if the nucleus is hard and mostly in one piece i would strongly consider converting the a large incision ECCE. the video below outlines the issue with conversion to ECCE and ther steps are listed below:

• If topical do subtenons injection
• Close temporal incision and create standard ECCE superiorly (or extend existing wound)
• Have Wescott scissors ready when looping out lens to cut vitreous
• Close with 2 vicryl safety sutures
• Anterior vitrectomy, Weck cell vitrectomy
• Dry removal of residual cortical material with syringe on 27 gauge cannula
• Use J-cannula if needed for subincisional material
• Consider staining with preservative free dilute kenalog
• Place IOL if possible in sulcus or AC (if AC, don’t forget peripheral iridotomy)
• Miochol to bring pupil down—seats sulcus IOL, peaked pupil helps to detect vitreous

Sometimes even with early loss of vitreous with nuclear material left you can carefully proceed with phacoemulsification. the key is to provide some separation between the space with vitreous and the area of phacoemulsification. the pace is slowed down with a low bottle height and low vacuum (Osher slow motion phaco). here are the steps.

• Seal off capsular hole with liberal use of viscoat (cohesive OVD will not work)
• Keep phaco occluded in the lens as much as possible to avoid pulling on the vitreous
• Lower the vacuum and bottle height
• Consider using a sheets glide to seal off hole -- trap nucleus in AC
• Work with one or two large pieces (rather than chopping into many small bits that can more easily fall south

The most common time for vitreous is while removing the last bit of nuclear material or during cortical removal. The main emphasis during this phase is to remove any residual cortical material following vitrectomy. loss of small amounts of cortical material to the back of the eye or leaving small amounts in the anterior segment will often present no difficulty. Preserving capsule for lens placement in the sulcus is important also. the steps when vitreous comes in this phase are:

• Place viscoat in area of tear or dialysis before removing instruments
• as always split into irrigating cannula (eg. 23g. cortex extractor) and the vit cutter (w/o sleeve)
• Suture wound and use two paracenteses one for the cutter and one for irrigating cannula
• Irrigate high and cut/suck low – creates a pressure gradient to push the V back
• Settings low vacuum 100 range, low bottle height 50 range, max cut rate
• Dry removal of residual cortical material with syringe on 27 gauge cannula
• Use J-cannula if needed for subincisional material
• Consider staining with kenalog (see below)
• Place IOL if possible in sulcus (see video below) or AC (if AC don’t forget peripheral iridotomy)
• Miochol to bring pupil down

The least common time for vitreous is while placing or just after placing the IOL. Usually in this phase very little vitreous comes forward. the main issues surround the IOL. will it be stable in the bag or should the IOL (or often an appropriate IOL) be placed in the sulcus. here are the steps for dealing with vitreous in this phase and a video showing this situation.

• Stabilize the IOL by placing one haptic out of the wound or in the AC
• Anterior vitrectomy as described above – attempt to get the cutter below the IOL
• Place both haptics in the sulcus if possible (cannot use SA60 in sulcus consider alt fixation)
• Use weck cell sponge to ensure wound is clear
• Consider stain
• Miochol to check pupil

Most patients who have an anterior vitrectomy do very well. it is important to be honest with the patient about what happened. i usually tell them:

"the thin membrane that surrounds the cataract tore during surgery. I had to take some extra time to remove the gel from the back of the eye. I was able to remove all of the cataract and place the artifical lens. i think everything is going to be great but i will have to watch you a little more closely for a while"

In summary the most important thing to remember with anterior vitrectomy is to control the chamber and use bimanual instrumentation.

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.

Pearls for Small Pupils

I use three techniques to manage small pupils:  stretching, iris hooks, and the Malyugin ring.

Pupil stretching used to be one of the main ways that I would force mydriasis.  This is really a good technique if you have posterior synechiae or if the patient has been on Pilocarpine chronically.  However, more and more I am avoiding using pupil stretching techniques because it is contraindicated in patients that are on Flomax (or other alpha blockers) as it can lead to even more problems with iris prolapse.  Compounding this problem is the reality that so often patients cannot remember having been on Flomax (or their other medications).  Because my practice is concentrated at our VA Hospital here in Iowa City, I have a lot of patients who have been on either Flomax or junior varsity versions of this alpha blocker in the past (Hytrin, Cardura, saw palmetto…) and so if they have a small pupil I just assume that have had Flomax.  I also think pupil stretching should be avoided in patients with shallow chambers, as there is a tendency for iris prolapse in those patients as well.  

The technique that I use for pupil stretching is to use two Kuglen hooks -- one through the paracentesis and the other through the main wound.  The hook through the paracentesis grabs the pupil and pulls it towards the paracentesis and then the other hook pushes 180 degrees across from the paracentesis to stretch the pupil.  The stretch is held for a few seconds and it is not uncommon that you will notice some hemorrhage along the pupil.  This is a good thing as it shows that there has been some change in the pupillary sphincter.  Following stretching of the pupil, you need to use a dispersive viscoelastic which is highly viscous to help push the pupil open.  There is really only one highly cohesive dispersing viscoelastic for me -- Viscoat; although others, such as Healon D and Vitrax, may be available in your area.  I like to place the Viscoat in a circular pattern, around and around, to gently push the pupil out.  You often find that at first you didn’t think there was much effect from the pupil stretch, and then after adding the Viscoat in this fashion, you gain enough mydriasis to safely proceed with surgery.    

I will also caution you that during hydrodissection, the fluid wave can catch the dispersive viscoelastic, pulling the iris with it out of the eye, producing prolapse of the iris.  As such, I recommend that you remove the viscoelastic over the lens, before hydrodissection, either using the automated irrigation/aspiration unit or use a syringe with BSS to wash out some Viscoat.  This will reduce the likelihood of iris prolapse during hydrodissection.  However, you just need to be careful during hydrodissection to avoid iris prolapse. 

 

Iris hooks are a great technique for the small pupil and I use them often, although I don’t use them as often as I used to as I am transitioning some to the Malyugin ring, which I will discuss below.  Iris hooks are great for shallow chambers, they are great for complex cases where you might have to convert to a large incision extracapsular procedure or if you have to use complicated suturing of IOLs or Cionni rings during the case which would make an internal device such as a Malyugin ring more difficult.  I usually avoid iris hooks if there is a bleb present, because it is sometimes hard to work around the bleb and you have to be very careful not to damage the bleb.  They are also harder when there are narrow lid fissures because the hooks get in the way of the lids, and so I tend to avoid them in that situation.  

The way I like to use iris hooks, I described in a paper with Louis Omphroy.¹ In this technique, we use a diamond configuration of the hooks such that there is one hook under the main incision, one across, and then one hook 90 degrees to either side of the wound.  This creates, relative to the incision, a diamond configuration of the iris.  I like to use a 27 gauge needle, a Grieshaber knife, or a 75 blade to make the four paracenteses for the iris hooks.  You want to make these as posterior as possible and you want to make them short and angled slightly down, such that the hook, when it is placed in the eye, is aimed towards the iris.  I like to place the hooks before I add viscoelastic so that the chamber is not so deep that it makes it very difficult to grab a hold of the iris.  After placing the hooks, then I add viscoelastic and make the incision just anterior to one of the hooks.  I tend to use a Kelman McPherson and a straight tie to place the hooks as shown in the video below.

 

I like the Malyugin ring and use it most of the time now for small pupils.  The Malyugin ring comes in two sizes; one with an internal diameter of 6.2 mm and the other with an internal diameter of about 7 mm.  The Malyugin ring is great in patients that are on alpha blockers such as Flomax².  It is great in patients that have narrow lid fissures because it does not involve any external manipulation to the eye and so you don’t have to have proptosis or great exposure.  I would recommend avoiding the Malyugin ring if you think you are going to convert to an extracap as this is very difficult with the ring as opposed to being relatively easy when using iris hooks.  I would avoid the Malyugin ring when using other intraocular hardware such as Cionni rings or suturing inside the eye, as the Malyugin ring can get in the way (relative to iris hooks) when doing these complex procedures.   

The Malyugin ring is placed with a special inserter into the eye and the leading eyelet is engaged onto the iris and then one toes down a bit as the ring is pushed further in, trying to engage the lateral eyelets as well.  Very often, only one of the two lateral eyelets is also engaged in the initial insertion process.  The trailing eyelet often is very difficult to disengage from the inserter without introducing a hook through the paracentesis to push the ring slightly to the side to allow the inserter to exit the eye.  I tend to use a Kuglen hook to subsequently place the eyelets that were not initially engaged with the inserter; a Lester hook can also be used or Sinskey hook.  

Retraction of the Malyugin ring is probably the trickiest thing.  You want to first disengage the leading eyelet which is across from the wound and then you want to disengage the leading eyelet and T it up slightly to the side and anterior.  Use plenty of viscoelastic so that you don’t engage the IOL during this process and that so that the cornea is safe.  The inserter is then placed in the eye slightly to the side of the eyelet, but over the ring, and then is turned such that the hook is over the entire eyelet and then pulled back and engaged onto the eyelet and pulled back into the inserter.  It is most important that you not completely retract the ring into the inserter, as funny things happen when you do this.  As shown in the video below, odd things will happen if you try to totally retract the ring, so just pull it back so that it is just thin enough to come back through the wound and pull it out of the eye. 

There are two choices for the Malyugin ring; one which is 6.2 mm in internal diameter which is useful for most cases, but if the pupil starts off big or if you are going to use a particularly large IOL, then I would recommend using the 7.0 mm Malyugin ring.  We tend to stock both in the operating room here, and use the smallest ring that you can to get the job done.  The advantage of the smaller ring is that it is easier to insert and easier to retract, and the advantage of the larger ring is that you can use it when the pupil starts off bigger.  

 

References: 

1.  Oetting TA, Omphroy LC.  Modified technique using flexible iris retractors in clear corneal cataract surgery, Cataract Refract Surg 2002;28(4):596-8.

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

 

operating microscope basics

It is very important to learn how to operate the microscope before your first day in the OR.   while ther are some subtle variations among models and manufacturers the basics of the footpedal and operation of the scope are similar.  The scope has a starting XY position which is established at the start of the case and small variation in this are made using the foot pedal.  The scope has a starting focal point (i suppose this is the Z position) and small variations from this are made during the case using the foot pedal.  often the intensity of the light can be controlled with the foot pedal.  

during cataract surgery each of your extremities will be busy.  usually the non dominant foot is left for the microscope pedal.  unless you are a soccer player your left fot is probably not that coordinated.  as such you should practice using the pedal way before your first case.  most people take off their shoes so that they can feel the microscope pedal better.   

The typical positions of the microscopes foot switch controls are shown below.  the foot pedal is designed so that the foot can sit on a foot rest.  A rocker swith in front of the foot rest is most important and moves the scope up and down to make small changes in focus.    a rocker switch behind the foot rest controls the zoom or magnification.  the magnification is typically low during the wound and is increased during steps such as capsulorhexis.  several inches in front of the foot rest is a joy stick which controls the XY position of the scope.  both the XY position and the focus shuold be centered prior to the case (usually a switch on the scope) and manually put into optimal initial position to allow maximal excursion of these functions during the case.    

  

When you arive in the OR ask yourself: “where will I be sitting?

·       Are you operating from a superior approach -- Superior approach is preferred when you may have a large incision with lots of sutures (eg. ICCE, ECCE, tough phaco when you may convert) and/or when you may have iris trauma (tolerated better under the lid) and when you are doing a trabeculectomy and want the bleb under the lid.   

·       Typical phaco is from a temporal approach to avoid the brow.  i usually do rights eyes a bit inferior/temporal like at 8 oclock and left eyes superior/temporal like at about 2 oclock.  some surgeons like the chief cataract surgeons like Dr Tim Johnson are always true temporal whether operating on the right or left eye.   

Proper Sequence to adjust Equipment to your body

1.     Place retrobulbar block first (give it time to work while setting up scope)

2.     Put assistant’s eyepiece and camera on proper side of microscope

3.     Push center focus and center XY position buttons on microscope (may be same button)

4.     Adjust ocular inter-pupillary distance and zero both objectives

5.     Lower surgeons chair

6.     Raise bed height to just allow both feet under bed onto both pedals

a.     Dominant foot – phaco pedal

b.     Non dominant foot microscope footswitch

c.     Take off shoes (wear white Nike crew length socks)

7.     Manually move entire microscope (not footswitch) so that you are in focus

8.     Raise surgeon chair height enough to allow surgeon to see comfortably into oculars

9.     Prep and Drape

This video goes over these issues with the microscope pedal: