More complex artificial tear fluids have also been developed [8, 16, 19, 30] consisting of for example, a mixture of turkey egg white lysozyme, immunoglobulin A from human colostrum, bovine lactoferrin, serum albumin and mucin [16]. Since natural tear fluid and human blood serum show marked similarities in pH value, osmolarity, ionic strength, and protein composition [6, 50–52], the artificial tear fluid used in the current investigation offers a relatively high degree of realism. Because of their similarities, human blood serum has been previously used clinically as a replacement for human tear fluid [52–54]. Although human blood serum represents
a useful analogue of human tear fluid, serum has a higher protein concentration, lower quantities of antimicrobial substances, and lacks tear-specific proteins. In the current investigation selleck kinase inhibitor therefore, the protein concentration of serum was reduced to a physiologically relevant value by diluting 1:5 with the click here ocular irrigation solution BSS® and the tear-specific protein lysozyme was added at a physiological concentration. The serum used
was pooled and aliquotted from 50 different patient samples and thus avoids in-vivo variation between single serum samples. To prevent the deformation of the flexible CL caused by floating loosely in a suspension that presumably is a common feature of previously reported models, supportive coupons incorporating convex contact surfaces were machined from polycarbonate. The check details resulting support
of the CLs resulted in a stable, solid surface with a high surface tension incident to the convex shape of the CL. Additionally, intermittent contact with air for the central section of the CL was achieved by the use of continuous rotational mixing, combined with adjustment of the volume of artificial tear fluid so that the top of the CL surface was in contact with air in a manner similar to that which occurs very in-vivo through the movement of the eyelid (Figure 1). Continuous agitation also effectively avoided dehydration of CLs. The effect of the third phase, forming a solid:air interface, and eyelid movements on bacterial adhesion to CLs has infrequently been reported in literature [21, 24, 30, 55]. Vermeltfoort et al. [21] passed air bubbles over the CL to mimic the natural shear action of blinking of the eyelid. Borazjani et al. [24] proposed that the effect of tear flow and the shear force of blinking may limit bacterial development on worn CLs. In the current study, viable bacterial numbers on the silicone CLs decreased within the first few hours, an observation that contrasts with some previous studies [19, 25, 26, 33, 56], which have generally reported a continuous increase of initial bacterial adherence.
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