PARS PLANA ANTERIOR VITRECTOMY FOR THE ANTERIOR SEGMENT SURGEON
Lisa Brothers Arbisser, MD
Every cataract surgeon encounters unplanned vitreous loss. Eyes respond differently, and surgeons are not automatons. It behooves us to have a plan in mind, tools with which to execute the plan at the ready, and to be prepared for every contingency for every case. The earlier a complication is recognized and limited, the better the result. Rarely do we breach the posterior capsule without rupturing the anterior hyaloid. If it is intact, however, optimal outcomes result, assuming implant stability is achieved. Rupture of the anterior hyaloid membrane with prolapse of vitreous into the anterior segment changes the risk of late complications. Once vitreous is lost through incisions, there is a greater likelihood of retinal tear or detachment, and another set of actions is indicated. Depending upon the timing, this may be associated with residual lens remnants.
An ounce of prevention is worth a pound of cure. When optimally managed, outcomes can rival uncomplicated surgery. This chapter, based on both experience and laboratory exploration, details the tools and techniques based upon a set of cardinal principles. Anterior segment surgeons are most comfortable with anterior incisions. Regardless of the incision site, there are universal principles for success. Although this chapter is intended to fully describe the pars plana approach to anterior vitrectomy, skills transfer wetlabs, apprenticing for a day with a vitreoretinal surgeon, or other hands-on experience is recommended prior to attempting a new technique in the setting of a complicated cataract case.
Guiding Principles
- First of all, avoid intra- and postoperative vitreous traction. Vitrectomy itself need not result in significant visual disability. Visual function is impaired by sequelae resulting from suboptimal vitreous management, such as retinal detachment, hemorrhage, and macular edema. Strictly embracing proper technique almost always avoids impaired visual outcomes.
- Maintain a normotensive globe. Employ tight incisions for anterior vitrectomy. Complications prolong surgery, and hypotony invites hemorrhage, choroidal effusion, and subsequent edema. Alternating high and low intraocular pressure (IOP) can cause shearing where choroidal vessels are tethered by anatomy; sudden hemorrhage may result. Phacoemulsification can fail without a controlled and stable environment, and our vitreoretinal colleagues would not dream of using leaky incisions. The anterior segment surgeon must follow suit in handling complications.
- Vitreous always follows a gradient from high to low pressure. Once a complication is recognized, maintenance of the anterior chamber and avoiding collapse is essential. Think of vitreous like egg white in a bowl—tilt the bowl and it will come streaming out, running downhill. Vitreous follows an instrument withdrawn from an incision and may convert vitreous prolapse into vitreous loss. Infusion may easily displace vitreous. This is the logic for a biaxial approach to vitrectomy for any incision. Always separate the irrigation sleeve from the vitrector shaft, and always discontinue infusion before exiting the eye. Incisions exceeding the diameter of the vitrector facilitate vitreous’s preferential egress through the leaky incision rather than into the vitrector port.
- Never fish around the complex and wondrous structure of vitreous. Not typically visible in vivo, the vitreous body is composed of solid parts: cortex, septa, and cisternal walls. These surround and separate more liquid parts: canals, cisterns, and spaces. The equator-parallel and sagittal septae follow an incomplete spiral that is a mirror image in the left and right eye. The vitreous body resembles a snail shell in this way, as septae radiate between the 12 petal-like cisterns that surround the bursa premacularis and the cistern preoptica. In the equator-parallel section, the vitreous body resembles a cut orange. Collagen fibrils and fibers interact with hyaluronic acid as formed vitreous, and the lamellae are interconnected by a loose mesh of fibers. The high water/low protein content is unique in the body. This complex structure we are manipulating acts like a toy Slinky attached to wallpaper (the retina). It functions as both a filter and a barrier.1 Cataract surgeons must respect the vitreous. In the setting of unplanned loss, remove only the prolapsed vitreous that may adhere to anterior structures or incisions; disturb the unoffending structure as minimally as possible. Placing instruments other than a vitrector into the vitreous body to retrieve lens fragments courts disaster. Robert Machemer irrigated into the vitreous to create an animal model for retinal detachment research. Although others teach levitation of a descended nucleus with either a spatula or ophthalmic viscosurgical device (OVD) cannula through the pars plana, I disagree with this practice (Figure 63-1).
- Protect other tissues from collateral damage. Although we must deal with vitreous, we should avoid losing needed capsule support, chewing up iris, or causing corneal edema by failing to protect endothelium. The thinnest part of the retina and most likely to tear is located anteriorly near the vitreous base. This attachment must be respected. The anterior segment surgeon must leave a clean anterior segment with a stable implant whenever appropriate, a clean bag, and a clear visual axis for rapid visual rehabilitation or to allow further timely management. Surgeons should avoid vitreous incarceration in the pars plana sclerotomy just as they would an anterior incision to prevent postoperative traction. Visualization of the incision site with indentation ophthalmoscopy is mandatory within the early postoperative period.
- Endophthalmitis prophylaxis is critical. The incidence of infection is a multiple of that of a standard case.
- Be prepared. Code red and code blue alerts are accepted random routine preparation in the medical environment. Consider establishing and practicing Code V at the end of a random surgical day. Have a reusable clean vitrectomy kit for practice available. Make sure the surgeon and staff know where equipment is kept, know how to set up, establish parameters to check, and verify that instruments, medications, and devices are at the ready. The higher the volume of cataract surgery, the lower the complication rate and the less prepared for contingency a center may be without this Code V practice routine (Table 63-1).
- Never fish around the complex and wondrous structure of vitreous. Not typically visible in vivo, the vitreous body is composed of solid parts: cortex, septa, and cisternal walls. These surround and separate more liquid parts: canals, cisterns, and spaces. The equator-parallel and sagittal septae follow an incomplete spiral that is a mirror image in the left and right eye. The vitreous body resembles a snail shell in this way, as septae radiate between the 12 petal-like cisterns that surround the bursa premacularis and the cistern preoptica. In the equator-parallel section, the vitreous body resembles a cut orange. Collagen fibrils and fibers interact with hyaluronic acid as formed vitreous, and the lamellae are interconnected by a loose mesh of fibers. The high water/low protein content is unique in the body. This complex structure we are manipulating acts like a toy Slinky attached to wallpaper (the retina). It functions as both a filter and a barrier.1 Cataract surgeons must respect the vitreous. In the setting of unplanned loss, remove only the prolapsed vitreous that may adhere to anterior structures or incisions; disturb the unoffending structure as minimally as possible. Placing instruments other than a vitrector into the vitreous body to retrieve lens fragments courts disaster. Robert Machemer irrigated into the vitreous to create an animal model for retinal detachment research. Although others teach levitation of a descended nucleus with either a spatula or ophthalmic viscosurgical device (OVD) cannula through the pars plana, I disagree with this practice (Figure 63-1).
Figure 63-1. Do not fish around in the vitreous. (Reprinted with permission from Steve Charles, MD.)
First Signs of Complication
A rupture in the posterior capsule and, in particular, the anterior hyaloid changes the pressure relationship between the anterior and posterior chambers and the posterior segment. This change in the distribution of fluid will in turn affect the anterior chamber’s depth and, often, the pupil’s size. The pupil may suddenly bounce or snap (Video 63-1). An increase or decrease in the anterior chamber’s depth during phacoemulsification or irrigation/aspiration (I/A) is a warning sign, so unless there is a good explanation for the change, stabilize and explore.
A momentary spider of the posterior capsule is likely associated with a tear and must be inspected after stabilizing the chamber and protecting the hyaloid with OVD. An unusually clear appearance of the posterior capsule is usually a rent or hole (Video 63-2).
Because vitreous follows a gradient from high to low pressure, it will always preferentially seek the flow into the phaco or I/A tip and obstruct its action. If lenticular material suddenly stops coming to the phaco tip, there is likely vitreous in the way. Vitreous cannot be refluxed out of an I/A tip but must be sharply cut to avoid traction.
The classic later signs of vitreous loss are an asymmetrically enlarged pupil and remote movement of the iris when touching the incision. Another ominous sign of vitreous loss is tilting of the nucleus’ equator or loss of mobility in a previously rotatable nucleus. Seeing clear space beyond the equator or having the equator come into view after removing the nucleus are sure signs of zonular loss with possible vitreous prolapse through the defect. A subtle sign of the presence of a forward strand of vitreous may be the inability to seal a properly constructed incision.
Figure 63-2. Biaxial incisions with new anterior paracentesis to fit the vitrector. The simplest choice for minimal vitreous presentation and the only choice when the view behind pupil is obscured.
Vitrectomy Options
To avoid vitreous traction, consider the best approach based on the particular condition of the eye. We need not always use an automated vitrector. If a small wisp of vitreous presents around zonules, it can be amputated with scissors and reposited to the posterior segment with OVD.
A simple wisp that can be controlled is rare when vitreous prolapses through a broken posterior capsule. In the face of prolapse, automated vitrectomy is almost universally needed. In all cases, the clear corneal paracentesis will be used for the irrigation cannula. When there is a small amount of prolapse without vitreous loss through incisions, vitrectomy can be nicely handled with the vitrector inserted through a clear corneal incision sized to fit the bare vitrector shaft. This is also always the right choice when there is no view through the pupil or there is extreme or abnormal dimensional anatomy.
In the presence of copious vitreous prolapse, vitreous loss through incisions, or significant herniation around the bag equator, a pars plana sclerotomy approach to anterior vitrectomy is most efficient and preferable in my experience. The irrigating cannula is still placed through the clear corneal paracentesis. A direct entry sclerotomy is created under a fornix-based conjunctival flap with a microvitreoretinal blade. At the end of the case, this sclerotomy should be sutured whatever the vitrector gauge. Alternatively, a trocar system that allows a transconjunctival sutureless entry is theoretically the best option as long as the globe can withstand the pressure required to make the sclerotomy. Trocars have the advantage of allowing repeated entry without trauma to the sclera or choroid. They are less likely to have incarceration at the incision site, which can result in vitreous traction. Any incision, anterior or posterior, should be closed when not in use. Sclerotomies can be closed with a temporarily tied suture (preferably 8-0 polyglactin), a scleral plug, or with a valved trocar (Figure 63-2).
Figure 63-3. (A) Pars plana incision for anterior vitrectomy. Irrigation through the side port with vitrector through pars plana 3.0 to 3.5 mm posterior to limbus. (B) Irrigation through side port anteriorly, bare vitrector needle through pars plana sclerotomy, and viewed through the pupil.
Rationale for Pars Plana Approach to Anterior Vitrectomy
Because vitreous follows a pressure gradient from high to low, ideally the lowest pressure will always be in the posterior segment relative to the anterior segment once the hyaloid is ruptured and during the remainder of a case after vitreous presentation. The best way to accomplish this is with a pars plana vitrectomy. We also want to minimize traction by removing the vitreous close to its base. As instruments exit the eye, vitreous will tend to follow. If any vitreous follows the instrument to the incision, it will be right near the vitreous base rather than up at the corneal incision when employing a limbal approach.
This technique is more efficient because it amputates anterior-posterior attachments to prolapsed vitreous immediately, relieving traction without increasing the size of the posterior capsule rent. It is less likely to encourage more vitreous prolapse and removes only the offending vitreous, sparing the general vitreous body structure.
With a limbal incision and a downward angled vitrector through a rent in the posterior capsule, the view can be compromised. Also, there is a tendency to remove vitreous that has not prolapsed forward, which encourages more to come forward, potentially enlarging the posterior capsular rent. It is also very challenging to clear sheets of vitreous in intimate contact with posterior capsule or iris without damaging those structures from the anterior approach. The sheet tends to be broad, thin, and tightly adherent to these structures. The pars plana approach keeps a higher pressure in the anterior chamber. In vitro studies by Liliana Werner et al have confirmed the superiority of placing the vitrector through the pars plana.2
Subsequent manipulation to remove cortex and implant a lens is less likely to result in representation of the vitreous as long as the anterior chamber is maintained. Finally, the pars plana approach facilitates amputation of the vitreous within incisions (Video 63-3). Although classically taught, using a sweep from the side-port incision to drag entrapped vitreous from the incision creates more traction on the connection, so I strongly discourage this (Figure 63-3 and Video 63-4).
Nomenclature: Vitrectomy Mode (Irrigation/Cut/Aspiration) vs Cortex Mode (Irrigation/Aspiration/Cut)
The best machine parameters for performing vitrectomy are the same regardless of what incision location is used for the vitrector. Employ the settings that most effectively reduce vitreoretinal traction and prevent followability. For the majority of phacoemulsification machines, bear in mind foot position 1 is irrigation only, foot position 2 engages both irrigation and cutting by activating the guillotine, and aspiration ensues only as foot position 3 is entered, resulting in irrigating, cutting, and vacuum simultaneously. This ensures that no vacuum is applied to the vitreous without chopping it off in tiny bites, minimizing traction in any part of the foot position sequence. (The Alcon Centurion employs only foot positions 1 and 2, in which cutting speed and vacuum magnitude is linear.)
All machines have an alternate setting that is not the default. In this case, foot position 1 initiates irrigation as before, but foot position 2 allows vacuum, and cutting mode only activates on foot position 3. This setting, I/A/Cut (vs the default I/Cut/A) goes by different names on different platforms and is useful when followability is desired during removal of the residual cortex after prolapsed vitreous has been dispatched. This useful setting allows the surgeon to remain in foot position 2 while removing lens material where followability is desirable but can allow near instant activation of the cutter in the event vitreous presents.
Always employ the default setting when there is any likelihood that vitreous will be encountered.
Machine Settings
CUTTING RATE AND FLOW
Dr. Steve Charles has coined the term port-based flow limiting. This describes the goal of achieving the highest cut rate possible, the lowest effective flow rate, and the lowest vacuum that generates the removal of vitreous. As the vitreous is engaged, the faster the guillotine opens and closes, the more traction is reduced because a lesser volume of vitreous enters with less followability. The highest cut rate possible on some older phaco machines is 400 cuts/min. Newer models achieve up to 16,000 cuts/min. Faster cutting leads to less traction and a smoother removal of vitreous. Always use the fastest cut rate available for vitrectomy on the available machine. The higher rates are one of the reasons that 3-port total planned vitrectomy has become safer over time. When close to the retinal surface the higher rates are critical. For anterior vitrectomy, where we remain within the pupillary aperture, this speed is less critical and still acceptable with any phaco machine for the cataract surgeon’s purpose. The technique, however, will vary slightly depending upon the cut rate. At lower rates, the episodic pull of the vitreous is almost visible, as is the opening and closing of the guillotine. With these lower cut rates, it is very important not to drag vitreous around and critical to keep the vitrector handpiece steady in one place until the accessible prolapsed vitreous has been removed. The needle can then be moved to a new location in foot position 2 to be certain no vitreous is dragged along by the flow, then foot position 3 is reengaged to remove prolapsed vitreous in this new location. Waving the needle around and rapidly moving its position is discouraged. With the higher cut rates, the action of the guillotine is such a blur that really only the sound provides the feedback of activity. The effect is more like erasing than aspirating vitreous, and the activity at the vitrector tip can be more efficient and dynamic without causing traction. This simultaneously promotes safer and quicker surgery. The aspiration flow rate (for peristaltic pump platforms) is generally set at 15 to 20 cc/min depending on vitrector gauge. The logic is simply to make things happen but not too fast.
LINEAR VS FIXED VACUUM SETTING
Vitreoretinal surgeons who work in the posterior segment every day prefer to use linear vacuum for vitrectomy, and therefore, this is usually the default for phaco machines as well. Familiarity leads to facility. Surgeons may adjust the vacuum on the fly based on how vitreous is behaving. They may wish to be more or less aggressive with vacuum, and the nuance of where they are in foot position 3 is intuitively controllable.
Anterior segment surgeons who rarely perform vitrectomy are not usually as adept at these maneuvers and often get nowhere due to a light foot that may not even venture into foot position 3. Staying in foot position 2 accomplishes nothing because there will be continuous cutting without suction. For those with a heavy foot, the nuance of applying more or less vacuum during vitreous removal is lost, and they may use more vacuum than necessary and may cause more traction. Anterior segment surgeons can consider a panel/fixed setting for vacuum instead of a linear vacuum setting for vitrectomy. Find and maintain the lowest level of vacuum that moves the vitreous; there is no reason to use higher or lower vacuum once vitreous removal is evident.
A panel setting allows us to either go pedal-to-the-metal in foot position 3 with suction or come up into foot position 2 without suction. The vacuum default settings on today’s phaco machines are usually set at 150 mm Hg, ideal perhaps for primary 3-port total vitrectomy. In unplanned vitrectomy, however, the anterior segment surgeon is almost always removing vitreous in a sea of dispersive viscoelastic, causing an effective level to be closer to 250 mm Hg for 20-gauge and 350 mm Hg for 23-gauge vitrectomy on average.
ADJUSTING IRRIGATION INFLOW
The irrigation bottle must be kept moderately high in order to maintain a normotensive eye. If there is forced infusion, then a normotensive setting in the range of 25 mm Hg should be chosen. Most phaco machines’ default settings place the bottle low. The appropriate bottle height depends on the size of cannula as well as the vacuum level. Most anterior segment surgeons opt for a 23-gauge cannula. The port of the irrigation cannula should be held sideways, neither irrigating down into the vitreous nor directly up toward the endothelium. To control the IOP, have the scrub nurse stand with one hand on the bottle’s button, ready to raise it as needed, and one hand on the vacuum button. Start the vacuum for 20-gauge vitrectomy at around 200 mm Hg, and ask the scrub nurse to progress by 10-mm increments to 250 mm Hg or stop once the vitreous begins to move.
As soon as movement toward the vitrector port is seen, with a finger on the globe from the nondominant hand holding the irrigation cannula, the surgeon can instruct the scrub nurse to raise the bottle until homeostatic normotension is achieved. Ideally, just prior to removing the vitrector at the endpoint, the bottle would once again be lowered to reduce the IOP when not aspirating any longer. Finally, irrigation is turned off and the vitrector removed from the incision.
Visualization: Particulate Staining
Though slit or tangential illumination with a light pipe can help to see the clear vitreous, nothing compares to triamcinolone acetonide as a tool to particulate stain the vitreous (Figure 63-4). This technique was originally devised by Gholam Peyman,3 then popularized in the anterior segment by Scott Burke (Video 63-5).4,5 Surgeons can use rinsed preserved Kenalog off-label, but the commercially available non-preserved Triesence preparation is approved by the US Food and Drug Administration. When instilled intracamerally, the suspended particles are individually trapped in the vitreous matrix but will rinse out of aqueous. It will not adhere to OVD but can be blocked by it. Triesence is best diluted 10 to 1 with balanced salt solution to prevent a white-out effect within the anterior chamber obscuring intraocular structures. The dilution also provides enough volume for repeated use during the case. The suspension can settle out of its diluent in the syringe because there is no chemical to keep it suspended, but an air bubble in the syringe can facilitate shaking up and resuspending the particles. The air should then be expelled before use in the eye. In the best of all worlds, triamcinolone would be sitting on the back table, prepared to be used immediately upon suspicion of a complication to be followed by OVD. However, as OVD is always at hand, it is preferentially used immediately to stabilize the environment when a complication is suspected. The triamcinolone then is usually used after initial vitrectomy, once the OVD is also removed, to provide a critical visual endpoint for vitrectomy. Triamcinolone instillation into the anterior chamber should also be one of the last maneuvers in a complicated case to rule out any unsuspected vitreous prolapse. As an added benefit, the drug has the therapeutic effect of reducing postoperative inflammation.
Figure 63-4. (A) Triamcinolone preferentially adheres to vitreous, like “throwing a sheet over the ghost.” (B) Dilute triamcinolone particulate identifies vitreous in this cadaver eye.
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