PURPOSE. To examine the amount of bacteria that adheres to the cornea and the lenses. Clinical aspects of both lenses were also observed. METHOD. 28 subjects were examined after 1, 7, 13, 21, and 28 nights of continuous overnight, bilateral wear of lotrafilcon A or balafilcon A lenses. Lenses were removed under aseptic conditions, immersed in a solution of NaCl, Tween 80, lecithin and glass pearls, shaken for 8 hours at 39.2°F, filtered and the filters were incubated aerobically for 48 hours at 95°F. Colony counts were classified with a 5-step grading scale. 0 (no contamination), 1 (1-33 cfu), 2 (34-66 cfu), 3 (67-99), 4 (100 cfu).
RESULTS. The whole range of bacteria usually found in the eye was identified, except P. aeroginosa. Staph. epidermidis was the most common. A low amount of gram-negative bacteria were identified. Fungi such as Penicilium spp., Aspergillus spp., and Cladosporium herbarum were identified. 1.6% of the lenses showed contamination grades 2-4. 98% of all samples were classified with a score of 0 or 1. After the first night there was an average of 4.1 cfu/lens on lotrafilcon A and 3.9 cfu/lens on balafilcon A which did not significantly increase in the examinations after 7, 14, and 28 nights. The highest cfu of one lens was 103, identified as Staph. epidermidis on a balafilcon A lens after 21 nights. When observing clinical performance, a decrease of limbal redness was observed. There was also a significant difference between the two materials in movement and wettability. Lotrafilcon A showed better movement than balafilcon A. In wettability lotrafilcon A showed significantly better results the longer the wearing time was extended.
CONCLUSIONS. There was no increase of bacteria with wearing time. The amount of bacteria after 1, 7, 14, or 28 nights was nearly identical. No statistically significant differences were found. In comparison to other studies almost the same amount of bacteria was found in cases where the lenses were removed and cleaned daily. There were no significant differences in the amount of bacteria between the two lens materials. The results of this study show that silicon hydrogels could be worn safely up to one month without higher risk of bacterial contamination.