Endophthalmitis following pars plana vitrectomy: a literature review of incidence, causative organisms, and treatment outcomes.

Endophthalmitis following pars plana vitrectomy is a very uncommon cause of endophthalmitis. Cases reported over the last decade show a decrease in incidence over time. To optimize visual outcome, early diagnosis and treatment are essential. In this review we report a summary of the incidence of endophthalmitis following vitrectomy, various risk factors for their occurrence, the microbiological profile and the visual outcomes post treatment.

Introduction

Endophthalmitis is characterized by severe inflammation of the ocular tissues and fluids. Acute-onset postoperative infectious endophthalmitis is the most frequent category and may be associated with severe visual loss. The incidence of endophthalmitis varies with the surgical procedure performed. The most reported categories of endophthalmitis are following cataract surgery/intraocular lens implantation and following intravitreal injections. A review of the literature indicates the incidence in these scenarios to vary from 0.07% to 0.4% for cataract surgery and from 0.038% to 0.065% for intravitreal injections.1–5 Endophthalmitis following pars plana vitrectomy (PPV) is an uncommon cause of endophthalmitis (Figure 1). The reported rates of post-PPV endophthalmitis have been decreasing over the last decade. In this review, the incidence of post-PPV endophthalmitis, risk factors for occurrence, microbiological profile, and treatment outcomes in the sutureless PPV era are reported.

Figure 1

Anterior segment photograph of a patient with endophthalmitis following pars plana vitrectomy operated for rhegmatogenous retinal detachment. Cultures were positive for Bacillus cereus. Visual acuity was light perception after treatment.

Incidence

Endophthalmitis following PPV is relatively uncommon. Over the years, there have been various studies which reported incidences of endophthalmitis after PPV (Table 1).6–13 The incidence ranges between 0.03% and 0.14% for 20 G PPV. None of the cases had additional concurrent surgery.

Table 1

Incidence of endophthalmitis following pars plana vitrectomy in 20 G surgery

Reference	Year	Case occurrence	Incidence
Ho and Tolentino6	1984	4/2,817	0.14%
Cohen et al8	1995	18/12,216	0.15%
Aaberg et al7	1998	3/6,557	0.04%
Zhang et al9	2003	3/7,000	0.04%
Eifrig et al10	2004	6/15,326	0.03%
Sakamoto et al45	2004	1/1,886	0.05%
Joondeph et al11	2005	5/10,397	0.04%
Mollan et al12	2009	2/5,278	0.03%
Chen et al17	2009	1/3,046	0.03%
Scott et al21	2011	1/4,403	0.02%

Incidence in transconjunctival sutureless vitrectomy

The first reported case of endophthalmitis in transconjunctival sutureless vitrectomy (TSV) surgery was in 2005 following a 25 G PPV (Table 2).14 The vitreous sample was negative on Gram stain and culture. After intravitreal and oral antibiotics, vision increased from hand motion close to face to 6/6 at the 3-week follow-up visit.

Table 2

Incidence of endophthalmitis in transconjunctival sutureless vitrectomy

Reference	Year	Case occurrence	Incidence
Shaikh et al16	2007	2/129	1.55%
Kunimoto and Kaiser15	2007	1/443	0.22%
Scott et al18	2008	1/119	0.84%
Shimada et al19	2008	1/3,343	0.03%
Chen et al17	2009	1/431	0.23%
Hu et al20	2009	1/1,424	0.07%
Scott et al21	2011	2/4,151	0.04%
Mutoh et al46	2012	4/502	0.79%

Older studies comparing 25 G with 20 G PPV generally reported higher rates in the 25 G group. Kunimoto and Kaiser compared endophthalmitis rates after 20 G and 25 G PPV in 2007 and reported 0.23% in 25 G cases as compared with 0.018% in 20 G cases, which was statistically significant.15 Both the groups had final median visual acuity of counting fingers. Shaikh et al reviewed 129 consecutive cases of 20 G and 129 consecutive cases of 25G PPV in 2007 and reported two cases (1.55%) of endophthalmitis in the 25 G group and none in the 20 G group.16 Chen et al in 2009 reported a nonsignificantly higher rate of endophthalmitis in 25 G (0.23%) compared with 20 G (0.03%) PPV.17 Scott et al in a multicenter study 2008 reported a significantly higher rate of endophthalmitis in 25G TSV (0.84%) versus 20 G PPV (0.03%).18 Of these, most cases (9/11) in the TSV group that developed endophthalmitis had straight incisions which may have been a possible risk factor.

However, other studies, and especially newer studies, have reported no significant difference in endophthalmitis rates between the two groups, perhaps reflecting advances in wound construction and improvements in surgical technique.19–21 There are also reports which show very rare occurrence of endophthalmitis post TSV.22,23

In a 2-year, prospective, nationwide surveillance study from the UK, the rate of endophthalmitis after PPV was 28 per 48,433 (0.058%). There were no statistically significant differences in the rates between small gauge TSV and 20 G PPV.24 Culture positivity was reported in 60.7% of cases. Outcomes were generally poor, with 29.6% of eyes having final visual outcomes of light perception, no light perception, or evisceration.25

Predisposing factors

There are certain factors that may increase the incidence of post-PPV endophthalmitis (Table 3). These include inadequate wound closure, postoperative hypotony, vitreous incarceration at a sclerotomy site, aqueous intraocular tamponade, additional concomitant intraocular procedures, and surgeon learning curve.

Table 3

Risk factors associated with endophthalmitis after pars plana vitrectomy

Surgery-related risk factors	Patient-related risk factors
Inadequate wound closure	Diabetes mellitus or other causes of immune compromise
Hypotony	Trauma or excessive eye rubbing
Vitreous incarceration	Noncompliance with treatment
Endotamponade agent (air, gas, or silicone oil)
Subconjunctival and intravitreal injections
Surgeon learning curve (non-beveled sclerotomies)

Inadequate wound closure and hypotony

In the first reported case of endophthalmitis following TSV, the authors speculated lack of adequate wound closure and wound leak to be possible contributory factors.14 The hypotony from a sclerotomy leak may allow ingress of microorganisms into the vitreous cavity from the ocular surface.26–28 An optical coherence tomography study reported the benefits of a sutured sclerotomy over an unsutured one with respect to wound closure.29 Other studies have reported ingress of India ink across unsutured sclerotomies while no ink was shown to enter the globe in cases of sutured sclerotomies.30–34

Sclerotomy site vitreous incarceration (vitreous wick)

Another potential risk factor for endophthalmitis may be vitreous incarceration at a sclerotomy site. Endoscopic evaluation of autopsied vitrectomized eyes have reported vitreous incarceration at the port sites.34,35 In an unsutured wound, this can allow communication of ocular surface bacteria to the inside of the globe by a “vitreous wick” phenomenon wherein microorganisms can migrate from the exterior into the vitreous cavity along a strand of vitreous prolapsing out of the unsutured sclerotomy wound.36

Type of intraocular tamponade

In earlier reports,15,18 no intraocular gas or oil tamponade following PPV was used. It was hypothesized that balanced salt solution is likely to provide poorer wound integrity at the sclerotomy site compared with tamponade agents due to different surface tension properties. Higher surface tension properties of air, gas, and silicone oil may prevent fluid from egressing across the sclerotomy.37 It is also suspected that air, gas, and silicone oil do not support bacterial growth as well as balanced salt solution.

Contamination of the vitreous cavity

Vitreous contamination rates by microorganisms are reported to be significantly higher during TSV than during 20 G surgery (22% versus 2.4%).38,39 Although the penetrating instruments in their study were not cultured, the most common organism isolated in their study was Propionibacterium acnes which is consistent with residual ocular surface flora. The lower incidences of bacterial contamination during 20 G surgery may be associated with less risk of surgical instruments directly contacting the conjunctiva.

Associated pharmacotherapy

Subconjunctival antibiotics are sometimes used at the conclusion of intraocular procedures. With emergence of TSV, many centers have done away with this practice. In addition, some surgeons use intravitreal triamcinolone, dexamethasone, or bevacizumab injections at the end of surgery. These additional injections, along with the practice of eliminating subconjunctival antibiotics, could potentially increase the risk of endophthalmitis.18

Surgeon learning curve

As in any other ophthalmic surgery, vitrectomy also has a learning curve. In one study, surgeons beginning to transition from 20 G to TSV surgeries were reported to face higher rates of hypotony and wound leakage, which are potential risk factors for endophthalmitis.27 A common challenge during the learning curve is a poorly constructed incision, which may lead to postoperative wound leakage.

Diabetes mellitus

There is a theoretical association between diabetes mellitus and an increased risk of endophthalmitis following PPV. As diabetics are relatively immunologically compromised, there is a potential for an increased rate of procedure-related infections. Diabetics are relatively more likely to have longer surgeries for proliferative diabetic retinopathy and associated complications such as traction retinal detachment. These surgeries may have multiple insertions and removal of instruments and may be combined with cataract surgery, increasing the risk of endophthalmitis. In most studies describing endophthalmitis, a substantial proportion of the patients were diabetic.6,8,10–12,15,17–19,40

Microbiological spectrum

Multiple studies have implicated a variety of microorganisms. The reported bacteria include coagulase-negative staphylococci, Pseudomonas species, Propionibacterium, enterococci, and Bacillus species. Most studies report that coagulase-negative staphylococci is the most common organism.40–44

Clinical features

Clinical features of endophthalmitis following PPV are similar to those of endophthalmitis following cataract surgery. Typically patients present acutely with a hypopyon and dense vitritis. Some cases, however, may demonstrate a delayed presentation, perhaps due to the lack of vitreous and consequent lack of severe posterior segment inflammation until later in the course of the disease. Possibly because of coexisting advanced vitreoretinal diseases, the visual outcomes after treatment of endophthalmitis following PPV are often poor.

Prophylaxis

As in any case of endophthalmitis, early detection and prompt treatment are important elements in having a successful clinical outcome. The following preoperative, intraoperative, and postoperative measures can be taken to theoretically reduce the incidence of post-PPV endophthalmitis.34

Preoperative preparation

Preoperative preparation of lids and lashes with povidone-iodine 10% solution is highly recommended as it has been shown to reduce ocular flora in these areas. In patients with reported iodine allergy, chlorhexidine gluconate can be considered for the eye lids.25 However, povidone-iodine 5% should be used directly on the ocular surface.

Usage of lid speculum and adhesive surgical drape should ensure that no eye lashes are exposed in the surgical field. If a few lashes stay exposed after draping, consider redraping or removing the exposed lashes. In patients with active ipsilateral eye lid infection (stye or severe blepharitis), elective vitreous surgery can be postponed until the inflammation is treated.

Intraoperative care

Some centers use antibiotics in the infusion fluid, but this is a controversial practice. At this time, there have been no reported studies comparing the incidence of post-PPV endophthalmitis in eyes with or without antibiotics in the infusion fluid.

During small-gauge TSV, it is recommended to displace the conjunctiva before making a trocar entry. After entry, the conjunctiva can be released to its original position. This ensures that the conjunctival entry and the scleral entry wound are not in the same line, which may reduce risks of bacterial entry into the vitreous cavity.

During small-gauge TSV, scleral incisions should be beveled and not perpendicular to the scleral surface. A beveled incision offers better wound closure, reducing risks of sclerotomy leak.

After small-gauge TSV cannula removal, it is important to check for wound leak or vitreous wicking. If the eye goes soft or there is egress of air bubbles, the sclerotomy should be sutured. One may consider suturing the conjunctiva and the sclerotomy separately in such cases.

Postoperative care

Complaints of pain and blurred vision should alert the surgeon to look for subtle signs of endophthalmitis. The Endophthalmitis Vitrectomy Study did not enroll patients with post-PPV endophthalmitis, so its results do not directly apply to these cases. Nevertheless, certain principles apply. Vitreous tap and inject is quick, inexpensive, and does not require access to an operating room or specialized vitrectomy equipment. Prior to antibiotic injection, a vitreous cavity sample should be obtained for culture and sensitivity. If the vitreous cavity is filled with gas or silicone oil, a sample from the anterior chamber can be taken. A negative microbiology report does not rule out endophthalmitis. In case of doubt, one can repeat the sampling and treat with a broad-spectrum intravitreal antibiotic combination.

Culture positivity

Various studies have demonstrated culture positivity rates in cases of post-PPV endophthalmitis (Table 4). Culture positivity is very varied across studies. On average, about 70% of all samples across studies have shown a positive microbiology culture report. In a large multicenter study, Cohen et al8 had 16 culture-positive cases out of 18 cases (89%) of endophthalmitis post vitrectomy. Abi-Ayad et al have shown the lowest incidence of 29% (4/14 cases).

Table 4

Culture positivity rates in endophthalmitis after pars plana vitrectomy

Reference	Year	Culture positivity rate	Culture-positive cases (n)	Predominant organism
Cohen et al8	1995	89%	16/18	CNS
Aaberg et al7	1998	100%	3/3	CNS
Eifrig et al10	2004	83%	5/6	Staphylococcus aureus
Joondeph et al11	2005	100%	5/5	CNS
Abi-Ayad et al40	2007	29%	4/14	CNS
Scott et al18	2008	100%	1/1	CNS
Shimada et al19	2008	100%	2/2	MRSA, Enterococcus faecalis
Chen et al17	2009	50%	1/2	Staphylococcus aureus
Mollan et al12	2009	0%	–	None
Scott et al21	2011	50%	2/3	CNS
Mutoh et al46	2012	0%	–	None

Abbreviations: CNS, coagulase-negative staphylococci; MRSA, methicillin-resistant Staphylococcus aureus.

Visual outcomes

Visual outcomes after treatment of post-PPV endophthalmitis are varied in the literature. In general, the outcomes are worse than that after cataract surgery, perhaps due to the underlying retinal pathology and associated poor visual potential. Although good visual outcomes have been reported in a few patients, most large studies show poor post-treatment visual gain (Table 5).

Table 5

Visual acuity outcomes in reported series of post-pars plana vitrectomy endophthalmitis after treatment

Reference	Diagnosis at time of PPV	Year	Cases (n)	Visual outcome at last visit
Cohen et al8	ERM, MH, PDR	1995	18/12,216	3 EV, 6 NLP, 1 HM, 1 LP, 2 20/400, 1 20/50, 1 20/30, 1 20/25 and 2 20/20
Aaberg et al7	–	1998	3/6,557	All eyes NLP
Eifrig et al10	PDR, macular pucker, recurrent RD	2004	6/15,326	3 NLP, 1 LP, 1 2/200 and 1 20/200
Joondeph et al11	VH, MH, ERM, RD	2005	5/10,397	2 NLP, 1 HM, 1 20/200 and 1 20/50
Shaikh et al16	ERM	2007	2/129	One 20/400, one 20/40
Scott et al18	ERM, PDR, CRVO, disc pit	2008	13/7,682	1 LP, 1 HM, 1 20/400, 1 5/200, 2 20/150, 1 20/100, 2 20/20, 2 20/40, 2 20/30
Shimada et al19	ERM	2008	2/6,935	Both cases NLP
Chen et al17	VH, TRD with VH	2009	2/3,477	One 20/200, one 20/125
Mollan et al12	MH, PDR	2009	2/5,278	One 1/60, one 6/12
Scott et al21	RD, MH, ERM	2011	3/8,554	One HM, one 20/100, one 20/40
Mutoh et al46	CME, ERM	2012	4/502	One 20/30, one 20/100, one 20/20, one 20/25

Abbreviations: PPV, pars plana vitrectomy; NLP, no light perception; LP, light perception; HM, hand motion vision; ERM, epiretinal membrane; RD, retinal detachment; VH, vitreous hemorrhage; CRVO, central retinal vein occlusion; PDR, proliferative diabetic retinopathy; CME, cystoid macular edema; MH, macular hole; TRD, traction retinal detachment; EV, eviscerated.

Conclusion

Endophthalmitis after PPV is a rare but potentially very serious event. The outcomes are often poor despite prompt and appropriate treatment. The risk was potentially higher in the initial years of TSV surgeries, which could be hypothesized to be due to leaking sclerotomies. However, most recent studies have reported very low rates.