June 2020
Volume 61, Issue 7
ARVO Annual Meeting Abstract  |   June 2020
Residual Intraocular Bacterial Load as a Function of Vitrectomy Fluidics
Author Affiliations & Notes
  • Ryan A Shields
    Associated Retinal Consultants P.C., Royal Oak, Michigan, United States
    Byers Eye Institute, Stanford Hospital, California, United States
  • Ira Schachar
    Byers Eye Institute, Stanford Hospital, California, United States
  • Footnotes
    Commercial Relationships   Ryan Shields, None; Ira Schachar, None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science June 2020, Vol.61, 2310. doi:
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      Ryan A Shields, Ira Schachar; Residual Intraocular Bacterial Load as a Function of Vitrectomy Fluidics. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2310.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose : Endophthalmitis is one of the most devasting complications following pars plana vitrectomy (PPV). Though, retrospective clinical studies have not shown a difference in the rate of endophthalmitis following PPV between 23, 25, and 27-gauge vitrectors, case reports appear to demonstrate a high rate of endophthalmitis following short cases such as floaterectomies. We hypothesize that this observation is due to higher residual bacterial load which occurs after smaller gauge and shorter surgical times.

Methods : Freshly enucleated porcine eyes underwent a pars plana inoculation with 50 microliters of concentrated Escherichia coli. Following the inoculation, the eye underwent a core PPV with either 23, 25, or 27-gauge instruments for either 1 or 5 minutes. Immediately after the vitrectomy an intravitreal tap was performed, and the fluid plated to calculate the residual bacterial load if any. The number of colony forming units (CFUs) were quantified by serial dilutions on agar plates at 48 hours post-vitreous tap. Wilcoxon signed rank testing was performed to determine statistical significance.

Results : The initial E. Coli inoculum contained 1.6 x 10^9 CFUs. Following vitrectomy > 99.9% of bacteria was removed from the vitreous cavity regardless of vitrectomy gauge size and time of vitrectomy. All combinations of gauge size and vitrectomy time demonstrated a statistically significant reduction in CFU’s other than a 1 minute 27-gauge PPV (p = 0.109) when compared to non-vitrectomized eyes (Figure 1)(Table 1). A one minute PPV was associated with a higher residual bacterial count as compared to a five minute PPV when pooling all gauges (p = 0.025). There was no statistical difference between 25 and 27-gauge (p = 0.268) and 23 and 25 gauge (p = 0.119). However, 23-gauge was more effective in clearing the vitreous cavity as compared to 27-gauge (p = 0.008). A post-vitrectomy injection of 0.1 mL of moxifloxacin was effective in preventing the growth of all recovered bacteria.

Conclusions : Vitrectomy surgery regardless of length and gauge size is effective in debulking the vitreous cavity of an infectious burden. Nevertheless, 27-gauge instrumentation appears to be the least efficient in reducing the bacterial burden following a pre-vitrectomy inoculation. Ultimately, 27-gauge instrumentation may carry a higher risk of post-vitrectomy endophthalmitis, albeit a small risk.

This is a 2020 ARVO Annual Meeting abstract.




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