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Evaluation of the vitreous microbial contamination rate in office-based three-port microincision vitrectomy surgery using Retrector technology
© Rezende et al.; licensee BioMed Central Ltd. 2014
Received: 26 July 2013
Accepted: 28 February 2014
Published: 1 May 2014
To perform a microbiological contamination analysis of the vitreous during office-based micro-incision vitrectomy surgery (MIVS) assessing whether the bacteria detected correlated with patient's ocular conjunctival flora.
This is a prospective, interventional, nonrandomized case series of patients undergoing office-based MIVS, anti-VEGF, and dexamethasone intravitreal injections (triple therapy) for the treatment of wet age-related macular degeneration (AMD) and diabetic macular edema (DME).
All patients were operated at a small procedure room in an ambulatory clinic of the Department of Ophthalmology, University of Montreal, Quebec, Canada. Conjunctival samples were done before placing the sclerotomies. The MIVS was done with a 23-gauge retractable vitrector, a 27-gauge infusion line, and a 29-gauge chandelier. Undiluted and diluted vitreous were collected for aerobic, anaerobic and fungal cultures. Outcomes measured were bacterial species identification within samples collected from the conjunctiva and the vitreous.
Thirty-seven patients (37 eyes) were recruited and completed over 17 months of follow-up. Twenty-eight had wet AMD and nine had DME. There were 13 men and 24 women, with a mean age of 78 years. Eighteen patients (46%) had culture positive conjunctival flora. Twenty-six bacterial colonies were tabulated in total from the conjunctival swabs. All bacteria detected were gram-positive bacteria (100%), most commonly: Staphylococcus epidermitis in 11 (42%) and Corynebacterium sp. in 6 (23%). Only 1/18 patients had more than 3 species isolated, 6/18 patients had 2 species and 11/18 patients had 1 species identified on the conjunctival swab. Only 1 of the 37 undiluted midvitreous samples was culture positive, equating to a contamination rate of 2.7%. None of the diluted vitreous samples were culture positive. All cultures were negative for fungus. No serious postoperative complications occurred, including bacterial endophthalmitis, choroidal detachment, and retinal detachment.
This preliminary study of office-based MIVS gives us insights on the ocular surface microbial profile and vitreous contamination rate of performing such procedures outside the OR-controlled environment. Our initial results seem to indicate that there is little risk of bacterial translocation and contamination from the conjunctiva into the vitreous. Therefore, if endophthalmitis occurs post-operatively, the source may likely arise after the procedure. Larger studies are needed to confirm our data.
The recent technological innovations in continually refining and decreasing gauge size for vitreoretinal surgeries have further ignited interest in the development of office-based, portable microincision vitrectomy surgery (MIVS). Indeed, the concept of bringing vitrectomy surgery out of the operating room (OR) is not new. Starting in the early 1980s, case series on the successful use of portable vitrectors in rural, non-OR settings have been reported [1, 2]. One of the latest commercial models is a cannula-less 23-ga needle with an incorporated 25-ga vitrector called the Retrector whose indications have evolved from a simple tap and inject to numerous diagnostic and therapeutic functions [3–5].
With the introduction of a new surgical technique, increased risks of complications and endophthalmitis are always a major concern [6, 7]. One of the main suspected routes of contamination is through the transconjunctival pathway, in which insertion of surgical instruments directly through conjunctiva may inadvertently track ocular surface organisms into the vitreous [6–9].
In this prospective study, we sought to assess the rate of conjunctival bacterial translocation and vitreous contamination following office-based three-port vitrectomies performed using the Retrector portable vitrector. We also evaluated whether the vitreous isolates correlated to the species identified from the same patients’ conjunctiva.
Surgical method and sample collection
Initial conjunctival sampling
After written informed consent was obtained, the first conjunctival specimen sampling was performed prior to any anaesthetic or topical drops. Calcium alginate swabs were passed several times over the bulbar conjunctiva and then plated unto anaerobic and aerobic sleep blood agar, chocolate agar, Sabouraud agar and an enriched brain-heart infusion broth. The fornix was not sampled. Care was also taken not to let the swab come in contact with the lashes or conjunctival areas other than those that would lie directly over where the 3 ports were placed. The patients then received topical anaesthetic drops followed by a peribulbar injection of 2% lidocaine without epinephrine.
Two other specimens were obtained from the vitreous cavity at the beginning and the end of vitrectomy. The first undiluted sample was aspirated using a sterile 1.0 ml syringe connected to the aspiration line of the portable vitrector. A minimum of 0.5 ml of undiluted vitreous fluid was cut and removed from the mid-vitreous through controlled manual aspiration, all the while visually monitoring for and avoiding globe collapse.
At the end of the vitrectomy, a second 10 ml sample of vitreous diluted through continuous BSS infusion was again manually collected in through the vitrector aspiration line. Both vitreous samples were promptly capped after collection and sent to the microbiology department at the end of the case. 0.8 mg (0.2 ml) of preservative-free dexamethasone and 2.5 mg (0.1 ml) of bevacizumab were then delivered on separate 30-ga needles into the eye through the 29-ga trocar after chandelier removal. The intraocular pressure (IOP) was digitally assessed and, if necessary, the remaining volume deficit was compensated by BSS. The integrity of the sutureless wounds was verified. If a leak or vitreous wick was noted, vitreous was removed with the vitrector and thermocauterization was applied to coapt the conjunctiva overlying the sclerotomy site. None of the sclerotomies needed to be sutured. All patients were seen at 24 hours, 1 week and 1 month postoperatively for follow-up.
Conjunctival samples and both undiluted and dilute vitreous samples were directly transported after collection to the Department of Microbiology of the same institution for further analysis with a delay <1 h after collection. The unplated vitreous samples were cultured under aseptic techniques unto anaerobic and aerobic agars. Incubation was performed at 37°C for 48 hours aerobically in an atmosphere of 7% CO2 and then anaerobically. Sabouraud agar at 25°C was used to enhance fungal isolation. Bacterial samples were kept for at least 1 week while fungal cultures were held for 1 month. Quantitative data were expressed as mean ± SD. Associations between microbial data and clinical findings that may predispose to bacterial presence was expressed as an odds-ratio. (SPSS for Mac; SPSS, Inc, Chicago, IL). Statistical significance was defined as P < .05.
- Left eyes
- Right eyes
- Mean ± SD
77.9 ± 7.4 years
- Mean ± SD
16.8 ± 2.0 months
- Exudative AMD
Most commonly isolated bacterial species from conjunctival surface
Conjunctival flora N (%)
Only 1 of the 37 undiluted midvitreous samples was culture positive, equating to a contamination rate of 2.7%. The bacterium isolated was Propionibacterium sp. This patient’s conjunctiva also grew Propionibacterium sp. The dilute vitreous sample from this patient was culture negative. None of the 37 dilute midvitreous samples were culture positive and there was no fungal growth in any sample.
Although there was a slightly higher rate of male gender (OR 1.01, 95% CI 0.26-3.92, P = 0.99), diabetes mellitus (OR 1.30, 95% CI 0.34-4.93, P = 0.39) and hypertension (OR 1.92, 95% CI 0.52-7.00, P = 0.32) amongst those with detection of positive conjunctival flora cultures, the values were not statistically significant.
All patients did well after samples collection. Only one patient in the cohort experienced asymptomatic hypotony with an intraocular pressure of 6 on post-operative day 1. This transient phenomenon self-resolved completely on the next follow-up one week later. None developed serious postoperative complications, including bacterial endophthalmitis, choroidal detachment, and retinal detachment.
The use of modern office-based vitrectomy has greatly evolved since it was first introduced [3–5, 10–12, 14]. Newer models have allowed for better visualization and more precise surgical maneuvers to be performed within the clinic or minor procedure room. While not a replacement for in-OR 3-port pars-plana vitrectomy, the potential of the office-based vitrector now seems expansive [3, 4, 10–12, 14]. The incidence of reported complications and endophthalmitis following office-based vitrectomy remains largely unknown. The largest combined study to date of 4509 single-port procedures performed using the Intrector places endophthalmitis rates at around 0.17% (62.9% in an office setting, 37.1% in an OR setting) . This data differs from our study’s surgical model where all procedures were three-port and performed in the office setting. Comparatively, modern endophthalmitis rates for standard 23-ga and 25-ga MIVS are reported at around 0.02-0.10%, although values ranging from 0.02%-0.80% have been described throughout the years [9, 15–23].
Our study is the first to detail microbial colonization of the ocular surface and corresponding vitreous contamination for office-based portable MIVS. Our preliminary survey suggests that this is a well-tolerated procedure with little long-term complications. Our conjunctival flora culture positivity is slightly lower than that previously reported in vitrectomy literature (46% instead of 61-98%) . This may be due to the difference in our sampling method. To reduce lid contamination, we only cultured the bulbar conjunctiva where the instruments would be introduced. Based on prior literature, we also chose not to administer prophylactic topical antibiotics to patients prior to sampling [6, 8]. Despite the lack of topical antibacterial prophylaxis, only 1/68 vitreous samples were culture positive. It is likely that the 5% povidone-iodine preparation left on the surgical field for 5 minutes prior to the start of the case is in part responsible for this finding [6, 7, 9]. Shimada et al. have even advocated for the repeated irrigation of 0.25% povidone-iodine unto the surgical field during a procedure to reduce vitreous contamination. However, as per the authors, the safety and efficacy of such a practice needs further statistical confirmation from a larger scale study necessitating enrollment of over 50,000 eyes .
Several studies postulated that compared to the 20-ga vitrector, the smaller lumen of a 25-ga instrument reduces the infusion rate of BSS, hence slowing the “flushing” of the vitreous cavity, making the exit of bacteria more difficult [8, 16, 17, 23]. In the case series presented by Tominaga et al. on the microbiological study comparing 20-ga to 25-ga vitrectomies, 22.5% (9/40) of patients undergoing 25-ga MIVS had vitreous contamination at the beginning of the vitrectomy surgery. This number decreased to 0% at the end of the vitrectomy, with the authors hypothesizing that the constant infusion of BSS during surgery might possibly play a “cleansing” role [8, 16, 23]. Our own results did not demonstrate such a dramatic decrease in vitreous bacterial load since there was already little bacterial contamination at the beginning of vitrectomy. Perhaps this may be due to the reduced surgical time (on average 10 minutes) and the sturdy hypodermic, needle-type build of the Retrector, manufacturing sharper and cleaner wounds .
While the conclusions of our study are thought provoking, some inherent limitations to experimental design include the single surgeon, prospective nature of the current study, limiting extrapolations as to the external validity of this study. In addition, the patient cohort is small, with a relatively low bacterial detection rate within both undiluted and diluted vitreous. It is possible that to increase the sensitivity of bacterial detection and to further prove that the same genetic strain of bacteria within the vitreous cavity came from the conjunctival flora, quantitative PCR could be used in addition to conventional culture in future cases [27–30]. Currently, such techniques have only been advocated for cases when minute quantities of bacteria are present, especially once antibacterial or antiviral therapies have been initiated [24, 28–31].
The observed microbiological profiles indicate that although the ocular surface is well inhabited by gram-positive flora, the risks of vitreous bacterial contamination is low during the set-up and process of the surgery. Hence, the usefulness of BSS infusion in vitreous cleansing remains to be further elucidated. We hope that increased experience and attention paid in future large-scale studies to the possible routes of post-operative contamination will streamline approaches and further mitigate the current rates of endophthalmitis in office-based vitrectomies. We hope to witness this evolution make its use easier and more accessible in the future as a safe alternative to conventional vitrectomy for simple and short vitreoretinal surgical cases.
Flavio A Rezende and Cynthia X Qian are joint first authors.
We would like to thank Dr. Mohamed Haji, Aouatef Benlemmouden and Manon Lambert for their invaluable help in the set-up of the procedures. We are also grateful to the Department of Microbiology at the Maisonneuve Rosemont Hospital affiliated with the University of Montreal for their collaboration in the culture and analysis of our samples.
Supported in part by a research grant from the Fonds de Recherche en Ophtalmologie de l’Université de Montréal (FROUM), University of Montreal, (Montreal, Quebec, Canada), a research grant from Retina Foundation of Canada (clinical research grant to Dr. Rezende); and an instrument grant from Novartis Canada. The sponsors or funding organizations had no role in the design or conduct of this research. The authors report no financial conflict of interest.
Dr. Rezende received a Retina Foundation of Canada clinical research grant. Dr. Sapieha is an Alcon Research Institute New Investigator Award recipient and has operating grants from the Canadian Institute of Health Research (CIHR), the Canadian National Institute for the Blind (CNIB), and the Canadian Diabetes Association.
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