Water exposure and other risk behaviours in contact lens wearers

Abstract

This thesis aimed to assess risk factors for contact lens-related disease with contemporary lens types, investigate associations between water exposure during contact lens wear and storage case contamination, and evaluate the impact of education in the form of a no water sticker on changing water contact behaviour. A prospective case-control study found that poor lens hygiene and water exposure during lens wear were independent risk factors for contact lens-related disease including infiltrative and infectious events (p<0.05). Higher storage case contamination carried 2.12x (95% CI 1.34-3.36) increased risk of contact lens-related disease. To determine associations between water exposure and storage case contamination, a reliable, efficient and cost-effective alternative method for standard plate count was required. The ATP assay was found to be a rapid and scalable storage case quantification technique, based on its lowest detection limit and maximum repeatability, compared with the MTT and Resazurin reduction assays. The LAL assay for endotoxin was used as a surrogate for Gram-negative bacterial contamination of cases. Water exposure during contact lens wear such as showering with lenses was independently associated with increased overall storage case contamination (p<0.001), while swimming with lenses and using wet hands to handle lenses were independently associated with high endotoxin levels, as a surrogate for Gram-negative bacterial contamination (p<0.05). A randomised controlled trial to investigate behaviour changes when a no water sticker was added to the contact lens storage cases found that after 6 weeks, participants assigned to receive the no water sticker had an overall reduced water exposure score and a greater proportion had low endotoxin levels in their storage case, compared to those who did not receive the sticker (p<0.05). However, no significant impact was observed on the individual water contact behaviours and overall storage case contamination. In conclusion, water contact behaviours including showering and swimming while wearing lenses are associated with increased risk of contact lens-related disease and increased storage case contamination. By educating contact lens wearers using the no water stickers, the overall water exposure behaviour was reduced. However, further research on no water stickers to determine the long-term behaviour change and to refine the messaging about avoiding individual water contact behaviours is required.