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Yvonne Wu, Lucia Zhu, David J Evans, Suzanne M J Fleiszig; Impact of contact lens wear on post-lens tear fluid antimicrobial activity. Invest. Ophthalmol. Vis. Sci. 2014;55(13):859.
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Contact lens-related corneal infection is most common with soft lenses, and the risk increases with extended wear. The lack of tear exchange under soft lenses might explain this, because tear fluid contains antimicrobial factors and acts upon corneal epithelial cells to make them more resistant to bacterial virulence. Here, we tested the hypothesis that tear fluid between the corneal surface and the contact lens during wear becomes less able to suppress the growth of P. aeruginosa with time.
Daily disposable lenses were worn for 1, 2, 4, 6 or 8 h immediately after removal from the blister pack, or after pre-soaking in sterile saline (2 days) to remove the packaging solution. Other lenses were not worn, but were soaked in tear fluid that had been incubated in vitro for 8 h at 35oC. After removal from the eye or tear fluid, lenses were placed front surface down into tryptic soy agar cradles with gentamicin (100 µg/ml) to suppress growth of any bacteria already on the lens. The exposed (back surface) was inoculated with ~1000 CFU of P. aeruginosa PAO1 expressing a plasmid encoding gentamicin resistance (PJNEO5) in 1μl of PBS. After 3 h at 35oC, surviving bacteria were enumerated by viable counts of lens homogenates.
Tear fluid on the back of lenses worn for 8 h was less effective at suppressing bacterial growth than lenses worn for 1 h, but only if the lens was presoaked to remove the packaging solution (median = 22,000 CFU vs 3000 CFU, P < 0.01). Maintenance of post-lens tear antimicrobial activity over time for blister pack removed lenses compared to presoaked lenses was significant for both 2 h and 4 h worn lenses (5600 vs 13650, p = 0.02; and 6775 vs 11500, p = 0.04). Importantly, much more growth occurred on the back of 8 h worn lenses than lenses soaked in tears 8 h after being collected from non lens wearing eyes (median=22000 vs 1000 [i.e no growth], p<0.01).
The data show that tear fluid can lose its antimicrobial activity under a hydrogel lens with time, and that packaging solutions can counteract this. Whether antimicrobial activity is reduced because critical tear components are degraded, excluded, or reduced in production, is not clear. Also to be established is whether the effect of packaging solution is directly on bacteria or if it acts indirectly by impacting tear fluid chemistry/physicochemistry.
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