The introduction of several recent techniques for secondary intraocular lenses (IOLs) has renewed interest in anterior-segment manipulation for the vitreoretinal (VR) surgeon.^1-4 Be it ensuring adequate pupillary diameter or operating in eyes with complex anatomy, several concepts can be kept in mind to help achieve surgical goals while maintaining corneal and iris health.

CHOICE OF OPHTHALMIC VISCOSURGICAL DEVICES

Ophthalmic viscosurgical devices (OVDs), or viscoelastics, were critical to the evolution of phacoemulsification cataract surgery and remain a mainstay of anterior-segment surgery.⁵ Ophthalmic viscosurgical devices are capable of stabilizing and pressurizing the anterior chamber, protecting the corneal endothelium, and creating space within the globe. Vitreoretinal surgeons often use OVD to coat the surface of the cornea prior to pars plana vitrectomy (PPV), to coat the posterior surface of an IOL to prevent “fogging,” or to prevent prolapse of air or gas into the anterior chamber when operating in unicameral eyes.

Ophthalmic viscosurgical devices are comprised of biopolymers, such as sodium hyaluronate, chondroitin sulfate, or hydroxypropyl methylcellulose, with varying molecular weights that determine their functional properties.⁵ Ophthalmic viscosurgical devices are typically described as cohesive, dispersive, or a combination of cohesive and dispersive products. Cohesive OVDs (high viscosity, high molecular weight) are known for deepening the anterior chamber, flattening iris and capsule, pressurizing the globe, and being relatively easy to remove from the eye. Dispersive OVDs (low viscosity, low molecular weight), on the other hand, are known for coating and protecting the corneal endothelium and being relatively difficult to remove from the eye.

Arshinoff previously described the “soft-shell technique” for use of a cohesive and dispersive OVD during phacoemulsification cataract extraction: a dispersive OVD to coat the endothelium, and a cohesive OVD to form the anterior chamber and flatten the capsule and iris.⁶ The soft-shell technique can similarly be used during vitreoretinal cases with anterior-chamber manipulation to maximize the strengths of both OVD subtypes.

Pearls for Working With OVD

• Be familiar with OVD trade names (Table 1). This will aid operating room staff in obtaining the desired type of OVD (cohesive, dispersive, or both) for your case.
• Be mindful of the infusion line. Cohesive OVD in particular can be easily prolapsed via corneal or scleral wounds or lost to the posterior segment in aphakic eyes. To avoid unintentional loss of OVD after placement, clamp the infusion line when performing anterior-segment maneuvers.
• When protection of the corneal endothelium is of particular interest (eg, IOL exchange surgery, prior history of endothelial keratoplasty), use of dispersive OVD either alone or in combination with cohesive OVD in a soft-shell technique is recommended.
• Take care to remove residual anterior chamber OVD. Retained OVD in the posterior chamber is unlikely to cause an intraocular pressure (IOP) spike. Retained OVD in the angle or anterior chamber, however, may cause significant IOP spike in the early postoperative period, particularly if cohesive OVD is used.

PUPIL AND IRIS MANAGEMENT

Pupil management is imperative during procedures requiring both posterior-segment and anterior-segment work. Trauma, prior surgery, or uveitis may lead to abnormal iris anatomy affecting the pupil, diagnosed easily on slit lamp examination preoperatively. Ensuring adequate pupillary dilation for PPV may require removal of prepupillary membranes, lysis of adhesions, and pharmacologic and/or manual pupillary dilation. In addition, miosis may be desired to avoid prolapse of a posterior chamber IOL in eyes with gas tamponade, to confirm adequate placement of an anterior chamber IOL, or prior to creation of a peripheral iridotomy (PI).

Manual Dilation

Both flexible iris hooks and a Malyugin ring (Microsurgical Technology) can effectively be used for manual pupillary dilation.⁷ Iris hooks can form a diamond or pentagon shaped iris (Figure 1) using 4 or 5 hooks, respectively, while a Malyugin ring forms a more circular pupil with 8 separate points of contact. While the amount of stretch applied to each hook can vary the size of pupillary opening with iris hooks, a Malyugin ring allows for either a 6.25-mm or 7-mm pupillary opening. Malyugin rings may be applied via a single clear corneal incision and thus do not require separate paracenteses for use. If using a contact-lens-based viewing system, a Malyugin ring may be preferred to avoid interference of iris hooks with contact lens positioning.

Viscomydriasis and Lysis of Adhesions

Use of OVD, particularly cohesive OVD, can result in adequate mydriasis by physically expanding the iris margin. Similarly, viscodissection is an effective method for lysis of adhesions. The OVD is provided in a syringe, which typically has a bent cannula. This cannula is useful in mechanically lysing adhesions (posterior synechiae, iridocorneal adhesions) while the OVD is simultaneously injected to create potential space.

Intracameral Agents

Intracameral short-acting acetylcholine (Miochol-E; Bausch + Lomb) or longer acting carbochol (Miostat; Alcon) are effective pharmacologic agents to cause pupillary miosis. Similarly, epi-Shugarcaine (epinephrine 0.025% and lidocaine 0.75% in balanced salt solution), developed by Joel Shugar, MD, for management of intraoperative floppy iris syndrome,^8,9 is effective in providing pupillary dilation intraoperatively. Intracameral epi-Shugarcaine is especially helpful in cases were lysis of adhesions must be performed first, because more rapid pharmacologic dilation can be achieved shortly thereafter.

Pearls for Dealing With a “Difficult” Iris

• A careful preoperative exam can help identify potential pupillary issues prior to surgery. Having a plan prior to starting the case will save time in terms of retrieval of instruments and use of intracameral agents.
• Several issues can occur, including iris prolapse, which may occur intraoperatively with a short corneal wound. To help re-posit the iris, try creating a paracentesis 90° to 180° away from the prolapse. Using an iris sweep through this paracentesis to sweep iris back into the anterior chamber is often effective. Subsequent placement of a small amount of OVD overlying the iris in the prior area of prolapse can then help stabilize iris position. This is also helpful to avoid iris incarceration when placing sutures to close corneal incisions.
• Using acetylcholine or carbochol to cause miosis prior to creation of a PI can help avoid an oversized iridotomy. Using a momentary vitrectomy mode to first engage iris in the cutter mouth prior to cutting is also an effective method to create a properly sized PI using the vitreous cutter.
• Most VR surgeons cringe when thinking of iris defect repair. When necessary or planned, use of a Seipser sliding knot is a common method for repair.

WOUND CHOICE AND CONSTRUCTION

Careful construction of corneal or scleral tunnel wounds is critical to minimize complications related to would incompetence. As with anterior-segment surgery, goals of wound construction are anterior-chamber stability, short-term and long-term wound sealing, minimizing induced astigmatism, and a wound size adequate to achieve surgical access to the anterior chamber.

Corneal Incisions

Clear or “near-clear” (inclusive of limbal vasculature) corneal incisions are commonly used for the implantation, removal, or exchange of foldable IOLs. Common phacokeratome blades are available in 2.4-mm, 2.75-mm, and 3.0-mm sizes. A square or rectangular incision of even depth (equal width of roof and floor of incision) radial to the limbus is the preferred construction. Chevron-shaped incisions are indicative of unequal roof or floor depth.

When possible, a temporal corneal incision, as opposed to a superior incision, is preferred to reduce surgically induced astigmatism. A temporal corneal incision may be most preferred in older patients who have against-the-rule astigmatism at baseline.

Scleral Tunnel Incisions

Scleral tunnel incisions are required when implanting or explanting a rigid posterior-chamber or anterior-chamber IOL. Scleral tunnel incisions are less likely to induce astigmatism, and they may be preferred in eyes with pre-existing endothelial keratoplasty grafts of larger diameter.

After conjunctival peritomy and dissection of Tenon’s capsule, most scleral tunnels are initiated 1.0 mm to 3.0 mm posterior to the limbus with a scleral groove of desired width. Similar to corneal incisions, adequate depth (equal width of roof and floor) is important to prevent complications. Shallow scleral depth leads to buttonholes within the sclera, and deep scleral depth may lead to entering the anterior chamber near the iris root with risk of hemorrhage.

Pearls for Wound Construction

• Be mindful of wound length for corneal incisions. Short wounds lead to iris prolapse and poor sealing, while long wounds make removal and entry of instruments and IOLs more difficult. A wound length of approximately 2 mm to 2.5 mm is often desired.
• Check wound closure carefully at the close of the case with the infusion clamped. This will give you a better assessment of potential leakage in the postoperative period.
• Anterior-segment manipulation or IOL explantation may require extension of corneal wounds beyond 3 mm, and thus closure of wounds with 10-0 Nylon suture is recommended.
• Hydrating the roof corneal wounds with BSS prior to more definitive closure is helpful. Prior to creation of a scleral tunnel incision, careful hemostasis helps maintain good visualization of tunnel depth. Also, using a caliper to measure corneal or scleral tunnel width is helpful to ensure proper sizing prior to attempting IOL placement or removal.

MAKING LIFE EASIER

Surgical cases with significant anterior-segment and posterior-segment work are often challenging, particularly when a surgeon is out of practice with anterior-segment manipulation. Adding surgical time to accommodate an anticipated learning curve, or perhaps seeking the advice or assistance of an anterior-segment colleague, may be helpful in particularly complex cases. In addition to the above pearls, the following tips are helpful to keep in mind:

• Sommering’s ring: A thick Sommering’s ring is difficult to fragment with a vitreous cutter. Removal of the ring en bloc via the anterior chamber, if possible, is preferred. Otherwise, use of a fragmatome may be necessary for efficient removal.
• Hemostasis: Maintaining meticulous external hemostasis prior to creation of scleral tunnels or additional sclerotomy sites (fragmatome) is advised to maintain adequate visualization.
• Use of a fragmatome: When planning a sclerotomy to accommodate a fragmatome, consider creating a limited conjunctival peritomy away from a trocar cannula site. Use external cautery to maintain hemostasis and close the fragmatome sclerotomy prior to resuming vitrectomy or anterior-segment work.
• Facial anatomy: Consider orbital and facial anatomy when planning incision and paracentesis sites. A high nasal bridge may make angles of entry difficult with instrumentation.
• Helpful instruments: Several instruments not commonly found in posterior segment surgical trays may be helpful in anterior segment manipulation. MST sets (Microsurgical Technology) with micrograspers and IOL cutting forceps are particularly helpful in secondary IOL cases (Figure 2). When closing corneal incisions, Colibri forceps may make grasping of corneal tissue easier than typical 0.12 forceps. An 18-gauge eraser-tip wet-field cautery is a good tool for external hemostasis.
• Know your operating room capability: Vitreoretinal surgeons will undoubtedly be familiar with vitrectomy equipment. However, knowing what anterior-segment tools are also available beforehand (instrumentation, OVD, and so on) will make for a smoother operating experience.

CONCLUSION

Vitreoretinal surgeons are expanding surgical techniques and capabilities, particularly in IOL-related work, making anterior-segment manipulation more commonplace. Attention to detail, be it wound construction, choice of OVD, or preoperative planning of incision sites, can help maximize visual and anatomic outcomes in both the anterior and posterior chambers. RP

REFERENCES

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