Doerte Luensmann, PhD, Dipl Ing (AO) is a clinical scientist at the Centre for Contact Lens Research, University of Waterloo School of Optometry, Canada.Between 39%[1] and 50%[2] of all contact lens wearers have a prevalence of contact lens related complications at some point. Although most events are considered non-significant and may be asymptomatic, others require suspending lens wear or necessitate treatment before lens wear can be continued. In this month’s editorial, Mark Willcox references a recent study conducted by Zhao and colleagues, which investigated whether the amount of protein and cholesterol that accumulates on silicone hydrogel lenses is associated with clinical parameters and the occurrence of adverse events.
Zhao Z, Naduvilath T, Flanagan JL, Carnt NA, Wei X, Diec J, et al. Contact lens deposits, adverse responses, and clinical ocular surface parameters. Optom Vis Sci. 2010;87:669-74
In this study, participants wore contact lenses on a daily basis, following a biweekly or monthly replacement schedule. Different types of silicone hydrogel lenses (senofilcon A, balafilcon A, galyfilcon A, lotrafilcon B ) and care regimens (ClearCare, Aquify, Opti-Free Express, Opti-Free RepleniSH) were included in this study. A total of 583 worn lenses were collected so that half could be analysed for total protein content and the other half could be analysed for cholesterol. Univariate and multivariate analysis determined the association between deposition rates and clinical parameters.
The authors found a significant association between the occurrence of solution-induced corneal staining (SICS) and the amount of protein (p=0.0008) and cholesterol (p=0.01) deposited on the lens. Out of the 278 lenses that were analysed for protein content, 37 eyes presented with SICS and the amount of protein found on these lenses was significantly higher compared to the non-staining group. A similar trend was seen for the 305 lenses that were analysed for cholesterol deposition. The 45 eyes that presented with significant amounts of SICS had more cholesterol deposits on their lenses compared to the non-stainers. The authors suggested that the solution is more likely to be responsible for the occurrence of SICS and the association with protein and lipid deposition is probably correlative rather than causative.
Protein deposition rates also correlated weakly with overall corneal and conjunctival staining, lens surface wettability and lens fit tightness (r ≤ I0.23I). In other words, higher amounts of protein deposition were associated with higher levels of corneal staining and a better wetting lens surface, but it was also associated with lower levels of conjunctival staining and a tighter lens fit. Cholesterol deposition rates had a slightly weaker correlation with ocular parameters: Corneal vascularisation and the grade of front surface deposition on the lenses were the only two parameters that showed a weak positive correlation with the amount of cholesterol per lens (r ≤ 0.19).
Parameters that did not seem to be associated with protein or cholesterol accumulation rates were the grades of blepharitis, meibomian gland blockage, bulbar and limbal or palpebral conjunctival redness. The fact that redness, which is typically a sign of inflammation, was not associated with amount of protein deposition has been shown in previous studies and the authors concluded that an inflammatory response might not be driven by the total amount of protein deposited but instead by individual proteins (4). Other studies have suggested that the conformational state of the deposited proteins could be a triggering factor for an immune response and not necessarily the total amount deposited (5).
Infiltrative or mechanical adverse events had no association with the level of tear film deposition rates. The authors concluded from the study that the amount of protein deposition had a stronger impact on lens performance than the amount of deposited cholesterol. They further pointed out that the level of deposition on silicone hydrogel lenses does most likely not indicate any causative relevant physiological response.
REFERENCES
1. Keech PM, Ichikawa L, Barlow W. A prospective study of contact lens complications in a managed care setting. Optom Vis Sci, 1996;73(10):653-8.
2. Forister JF, et al. Prevalence of contact lens-related complications: UCLA contact lens study. Eye Contact Lens, 2009;35(4):176-80.
3. Zhao Z, et al.. Contact lens deposits, adverse responses, and clinical ocular surface parameters. Optom Vis Sci87, 2010;(9):669-74
4. Richard NR., et al.. Evaluation of tear protein deposits on contact lenses from patients with and without giant papillary conjunctivitis. CLAO J, 1992. 18(3):143-7.
5. Donshik PC, Ehlers WH, Ballow M. Giant papillary conjunctivitis. Immunol Allergy Clin North Am, 2008; 28(1): 83-103.
