For many years, contact lens packaging solution contained nothing more than buffered saline. However, as materials and modalities evolved, surfactant and humectant agents were added to the packaging to increase initial comfort and improve wearing time.
Contact lens attributes, such as water content, surface treatments, the polymer matrix and additive functional groups, can affect the uptake and release of soaking solution components.1
Now, understanding what is in the blister pack is more important that ever, in light of the increasing popularity of daily disposable contact lenses, where packaging solution is applied to the eye everyday.
The normal pH range for tears is 6.5 to 7.6, with a mean value of 7.0.2 Buffers are used to keep the solution’s pH within that normal range. Packaging solutions are buffered with either borate or phosphate. These buffers have been used extensively in ophthalmic solutions for many years. Borate, in particular, has several antimicrobial properties, which seemingly make it an ideal additive to eye drops and contact lens solution preparations. However, borate is known to alter tight junctions on corneal epithelial cells and has been reported to exhibit both cytotoxic and anti-inflammatory effects.3 Interestingly, a recent study examined the biological effect of these buffers on corneal epithelial cells and concluded that borate-buffered packaging solutions adversely affect the viability of human corneal epithelial cells in vitro to such an extent that the cytotoxic effects may outweigh the antimicrobial properties.1
Wettability describes how a fluid spreads and interacts with a solid surface, and is believed to affect contact lens comfort; the more wettable the lens, the lower the wetting angle and, in theory, the better the comfort.4,5
Surfactants and humectants, such as polyvinyl alcohol (PVA), hydroxypropyl methylcellulose (HPMC) or block copolymers, have been added to packaging solutions in an effort to deliver increased wettability, improved comfort and decreased surface tension on the lens upon removal from the blister pack.
The polymer matrix of the contact lens surface will become hydrophobic or hydrophilic, depending on the surrounding environment. When exposed to air during interblink intervals, hydrophobic groups in the polymer will migrate toward the lens surface. Exposure to wetting agents promotes the formation of hydrophilic groups on the lens and results in a more “wettable” surface.6 An ideal wetting agent would stay on the surface of the lens throughout the wearing period.
A study recently examined the effect of blister pack wetting agents on daily disposable contact lenses.6 It found that currently marketed daily disposable contact lenses have significantly different in vitro wettabilities, due, in part, to the components of the packaging solution. While these agents lowered the wetting angles of the in vitro contact lens, other reports have yielded conflicting information on how this specific finding could translate into improved in-eye comfort.7,8
Uptake and release patterns of contact lens solution components are well reported in the literature. In some instances, these patterns can adversely affect contact lens wear. Practitioners should be aware that packaging solution components will demonstrate similar uptake and release patterns, which could affect corneal health and comfort––even in daily disposable lens wearers.
1. Gorbet MB, Tanti NC, Jones L, Sheardown H. Corneal epithelial cell biocompatibility to silicone hydrogel and conventional hydrogel contact lens packaging solutions. Mol Vis. 2010 Feb 19;16:272-82.
2. Abelson MB, Udell IJ, Weston JH. Normal human tear pH by direct measurement. Arch Ophthalmol. 1981 Feb;99(2):301.
3. Imayasu M, Shiraishi A, Ohashi Y, et al. Effects of multipurpose solutions on corneal epithelial tight junctions. Eye Contact Lens. 2008 Jan;34(1):50-5.
4. Read ML, Morgan PB, Kelly JM, Maldonado-Codina C. Dynamic contact angle analysis of silicone hydrogel contact lenses. J Biomater Appl. 2010 Mar 10. [Epub ahead of print]
5. Maldonado-Codina C, Morgan PB. In vitro water wettability of silicone hydrogel contact lenses determined using the sessile drop and captive bubble techniques. J Biomed Mater Res A. 2007 Nov;83(2):496-502.
6. Menzies K, Rogers R, Jones L. In vitro contact angle analysis and physical properties of blister pack solutions of daily disposable contact lenses. Eye Contact Lens. 2010 Jan;36(1):10-8.
7. Scott WL, Rein MJ, Pack LD. Subjective comparison of 2 daily disposable contact lenses: Focus Dailies with AquaRelease and Proclear 1-Day. Optometry. 2010 Jan;81(1):40-6.
8. Walker J, Young G, Hunt C, Henderson T. Multi-centre evaluation of two daily disposable contact lenses. Cont Lens Anterior Eye. 2007 May;30(2):125-33.