PEER REVIEWED

Does Microincisional Vitrectomy Surgery Increase the Risk for Endophthalmitis?

SURAJIT SAHA, AB • BRYAN PROPES, MD • KATHERINE A. FALLANO, BA • DIANA V. DO, MD

Endophthalmitis remains the most serious postoperative complication of ophthalmic surgery. As the popularity of sutureless microincisional vitrectomy grows, the concern for postoperative endophthalmitis likewise increases. Although endophthalmitis remains a rare complication, it can be associated with a poor prognosis and is visually and mentally devastating to the patient. Determining which surgical practices best reduce the risk of endoph thalmitis is therefore of critical importance, but the rarity of this condition makes obtaining accurate data difficult.

Several retrospective studies have suggested an increased risk of endophthalmitis in sutureless 25-g vitrectomy.^1-3 Although these retrospective studies do not provide level 1 medical evidence for an increased risk of endophthalmitis after sutureless microincisional surgery, it remains critical to take appropriate measures to minimize the chance of infection. With this effort in mind, various recent publications have proposed intraoperative safety guidelines for small-gauge sutureless vitrectomy.^4,5 In this review, we examine possible risk factors for endophthalmitis, review surgical techniques, and discuss prophylactic measures that may reduce the risk of endophthalmitis.

RISK FACTORS FOR ENDOPHTHALMITIS IN MICROINCISIONAL VITRECTOMY

In the medical literature, sutureless ophthalmic surgery has been associated with an increased incidence of endophthalmitis. While the majority of the available data pertain to endophthalmitis risk after clear corneal cataract surgery, some of the same risk factors clearly apply to microincisional vitrectomy as well.^6-8

Certain preoperative risk factors may increase the risk for endophthalmitis. However, only a few studies discuss these possible preoperative risk factors, which include chronic blepharitis, ocular surface disorders, lacrimal drainage abnormalities, or immunosuppression.⁶ It is difficult to control for these confounding risk factors in retrospective studies; therefore, it is unclear whether cases of postoperative endophthalmitis are more likely in patients with blepharitis or other ocular-surface disorders. Certainly, it is recommended to treat active ocular-surface disorders or infections before proceeding with elective vitrectomy surgery if possible.

Some of the techniques used in microincisional vitrectomy surgery may potentially increase the risk of endophthalmitis. Stewart and colleagues have investigated ocular-surface fluid contamination of sutureless 25-g vitrectomy incisions.⁹ They hypothesize that excessive scleral manipulation may increase the risk of endophthalmitis. When depressing the sclera near the site of a 25-g cannula, the cannula is redirected anteriorly. If the cannula is plugged, the sclerotomy may not be disrupted. However, if the cannula contains an instrument, such as a lightpipe, the manipulation of this instrument could oppose the anterior displacement of the cannula, thereby distorting the wound architecture and enlarging the sclerotomy wound. Distorting the sclerotomy site may allow fluid from the surface of the eye to contaminate the vitreous cavity. Additionally, scleral depression can tear the conjunctiva by pulling it posteriorly while a segment remains anchored at the 25-g cannula. The conjunctival tear may possibly encourage subclinical wound leakage, thereby raising the risk of ocular infection.⁹ When performing scleral depression, it may be helpful to plug the cannula rather than leave an instrument within it to decrease the risk of wound distortion.

Hypotony is a potential complication of sutureless microincisional vitrectomy surgery that may increase the risk of endophthalmitis. Hypotony may occur from a leaking sclerotomy site, which could allow bacteria and ocular surface fluid to enter the eye. To decrease the possibility of hypotony, Shah and colleagues recommend removing the superior cannulas while maintaining the infusion in order to create high pressure inside the vitreous cavity This promotes vitreal occlusion of the sclerotomy, thereby potentially reducing the risk of postoperative hypotony.¹⁰

Air-fluid exchange at the end of surgery is another possible method of reducing the risk of hypotony. An air-fluid exchange at the conclusion of the surgery may help maintain early postoperative intraocular pressure, limit fluid leakage from the sclerotomy sites, and reduce the chance of bacterial entry from the incisions.¹¹

The lack of sutures in microincisional vitrectomy surgery may also contribute to an increased risk of endophthalmitis due to ocular surface fluid contamination. Singh and colleagues performed 3-port vitrectomy on cadaver eyes, varying the needle gauge (23-g or 25-g), whether conjunctival displacement was used, and whether the sclerotomy was sutured.⁹ India ink was subsequently applied to the ocular surface of all eyes to simulate bacteria, and intraocular pressure was varied to imitate postoperative IOP changes.

Upon histological examination of the incisions, India ink particles were identified in the wound in over two-thirds of eyes that underwent 25-g sutureless vitrectomy. Conjunctival displacement had no effect on whether ink entered the wound or not. Meanwhile, sutured incisions, regardless of whether they were 20- or 25-g, did not have ink particles in the wound. The authors concluded that sutureless vitrectomy techniques may increase the risk of bacterial wound contamination and that suturing may protect against the ingress of ocular surface fluid.¹¹

Additional potential risk factors for endophthalmitis after microincisional vitrectomy include patient-induced wound distortion in the acute postoperative period, such as eye rubbing, and the nonuse of subconjunctival antibiotics at the conclusion of surgery.¹²

Mason and colleagues have proposed specific techniques to reduce the risk of infection. They attribute their low and almost equal rates of endophthalmitis in 20-g and 25-g vitrectomy to the following practices: meticulous wound construction using 30-degree angled entry; examination and removal of vitreous wicks from sclerotomies; and close inspection for a water-tight sclerotomy following cannula removal with utilization of suture closure if needed.¹²

WOUND CONSTRUCTION AND HANDLING

Wound construction is a key area where proper surgical technique can help decrease the risk of wound leaks and postoperative hypotony, which may be risk factors for endophthalmitis. Since the success of sutureless vitrectomy is highly dependent on wound construction, the sclerotomy incisions should have a configuration that promotes self-sealing. Creating a self-sealing wound can involve two techniques: conjunctival displacement prior to wound creation and construction of an oblique wound.

Endophthalmitis affecting the cornea (above) and the anterior chamber (below).

Displacing the conjunctiva while introducing the trocar and cannula at the start of surgery creates a misaligned wound between the conjunctiva and sclera. In theory, when the cannula is removed, the conjunctiva moves back to cover the sclerotomy, thereby precluding a continuous tract that could otherwise allow fluid circulation and bacterial influx.

Constructing an oblique wound creates a self-sealing, valve-like effect, similar to the clear corneal wounds used for phacoemulsification. Most surgeons use a sharp troca with an overlying cannula to construct the sclerotomy sites.

Many surgeons first enter the sclera at a 30-degree angle until the bevel of the trocar blade is no longer visible; they then redirect the trocar/cannula toward the center of the vitreous cavity (aiming towards the optic disc) to further angle the incision. This type of wound construction creates a long, angled tract through the sclera that is more likely to be self-sealing.

ANTIMICROBIAL PROPHYLAXIS

The core principle of reducing the incidence of endophthalmitis is to avoid the introduction of a microbial pathogen, mostly from the patient's own extraocular tissues, into the eye either during or after surgery. The use of topical antibiotic eyedrops prior to the microincisional vitrectomy procedure is controversial; furthermore, no study has demonstrated any benefit for preoperative topical antibiotic eyedrops. Therefore, we do not recommend using preoperative antibiotics as this method is unproven.

Currently, the best method to reduce the risk of endophthalmitis is the use of povidone-iodine solution to clean the ocular surface of the eye before surgery. Speaker and Menikoff demonstrated a reduction in the incidence of postoperative endophthalmitis from 0.24% to 0.06% by applying 2 drops of 5% povidone-iodine into the conjunctival fornix during surgical preparation.^13,14

Perioperative prophylaxis has also been investigated. The European Society of Cataract and Refractive Surgery study group conducted a multicenter, prospective, random ized, partially masked cataract-surgery study to compare intracameral cefuroxime and topical perioperative levofloxacin for endophthalmitis prophylaxis. Among 16,603 recruited patients, 20 eyes developed infectious endophthalmitis. Eyes that did not receive intracameral cefuroxime (1 mg in 0.1 mL normal saline) were associated with a 4.92-fold increased (95% confidence interval, 1.87-12.9) risk for postoperative endophthalmitis. The study group also noted that there were additional risk factors: The use of clear corneal incisions, less experienced surgeons, placement of silicone intraocular lenses, and intraoperative complications all increased the risk for endophthalmitis.¹⁵ Therefore, further studies will need to be performed before intracameral antibiotics can be recommended for cataract (or vitrectomy) surgery.

Postoperative topical antibiotic drops are routinely used after retina surgery. Retrospective studies have suggested that topical antibiotic drops may reduce the risk of postoperative endophthalmitis in cataract surgery.^16,17 Although there is no conclusive evidence that demonstrates the effectiveness of postoperative topical antibiotics after vitreoretinal surgery, the use of topical drops is considered standard of care.

ENDOPHTHALMITIS TREATMENT

As soon as a case of endophthalmitis is suspected, treatment with intravitreal antibiotics should be initiated immediately and samples should be taken concurrently for strain identification.¹⁸¹⁹

Intravitreal antimicrobial pharmacotherapeutic intervention requires sufficient dosages to completely eradicate the pathogens that are present, as well as to prevent the formation of resistant strains. Since infections such as endophthalmitis are usually associated with extensive leukocyte and monocyte tissue infiltration, Jensen and colleagues recommend additional anti-inflammatory treatment with corticosteroids to combat the inflam matory reaction.¹⁷

Based on the results of the 1995 Endophthalmitis Vitrectomy Study, the current guidelines for the treatment of endophthalmitis generally recommend intravitreal antibiotics for patients with hand motions visual acuity or better, and pars plana vitrectomy when the vision is light perception.¹⁹ Some recent publications, however, dispute these practices.^17,20,21 Kuhn and Gini claim that complete vitrectomy yields far better outcomes for the treatment of postoperative endophthalmitis than those published in the Endophthalmitis Vitrectomy Study.²¹ Behrens-Baumann has proposed immediate pars plana vitrectomy as a potential treatment for acute postoperative endophthalmitis.¹⁹

CONCLUSION

Although several published studies have suggested that sutureless microincisional vitrectomy may be associated with a higher risk of endophthalmitis compared to traditional 20-g surgery, these studies are limited by their retrospective nature and contain inherent biases that do not provide the strongest level of medical evidence. Indeed, an article in the July 2009 issue of Ophthalmology strongly suggests that there is no greater risk to 25-g surgery at all.²² There is currently no conclusive evidence that the rate of postoperative endophthalmitis is increased following transconjunctival sutureless vitrectomy. A sufficiently powered prospective study to definitively resolve this issue is challenging, as it would involve tens of thousands of patients in order to detect a small difference in the rates of endophthalmitis between 20-, 23-, and 25-g surgery.

Surgeons should be aware of the potential risks associated with sutureless microincisional surgery. The Micro-Surgical Safety Task Force has published guidelines advising surgeons on recommended microincisional techniques.^4,5 Understanding proper preop preparation, wound construction, and surgical techniques may reduce the risk of endophthalmitis and other postop complications. RP

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