Allergies and contact lenses

More recently, Wolffsohn & Emberlin examined the potential barrier effects of DD lenses against airborne antigens. Ten patients, with skin prick and ocular conjunctival provocation-confirmed allergic sensitivity to grass pollen were recruited. Each had their ocular symptoms and appearance of bulbar and limbal conjunctival redness, palpebral conjunctival redness and roughness, and corneal and conjunctival fluorescein staining graded before and five minutes after exposure to grass pollen for two minutes, in a purpose-designed exposure chamber to simulate the conditions of a ‘very high’ pollen-count day. This was repeated on three occasions when wearing two differing types of hydrogel DD lenses and no contact lenses. The results demonstrated that DD contact lenses offered a barrier to the airborne antigen.

Thus, evidence exists to suggest that contact lens wearers who suffer from mild ocular allergy can be advised that wearing hydrogel DD lenses may be protective and should be more comfortable than wearing reusable contact lenses. However, most CL wearers today are fit with silicone hydrogel (SiHy) lenses. But interestingly, to-date, no peer-reviewed publications have investigated the use of these with allergy-prone sufferers. Indeed, a quick search shows a number of patient and, sadly, also practitioner blogs express the opinion that patients may actually be ‘allergic’ to their SiHy lenses.

To determine whether allergy to silicone within the SiHy lenses is possible, an understanding of how allergic reactions occur is needed. The underlying mechanism is outside the scope of this article, but ultimately involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to the allergen that the person has been exposed to and then to a receptor on mast cells or basophils, where it triggers the release of inflammatory chemicals such as histamine, resulting in the classical symptoms and signs seen in allergic responses. This immune response is triggered as a defense mechanism. The immune system is ‘wired’ to only recognise molecules that have a carbon-based chemistry (such as proteins, sugars, nucleic acids), as that may signal attack by microorganisms. Silicones, also known as polysiloxanes, are synthetic polymers made up of repeating units of siloxane, which is a chain of alternating silicon and oxygen atoms. Thus, silicone has none of the properties that would elicit a true allergic response and cannot produce an allergic event in isolation.

The concept of a “silicone allergy” stems from interactions of silicone-based biomaterial applications in body sites other than the eye, notably silicone breast implants. There have been a small number of case reports in the literature pertaining to silicone “allergic” responses, however, these invariably turn out to be either not a true allergic reaction (as there are no IgE antibodies involved) or are due to other types of hypersensitivity reactions, often attributable to impurities in the silicone such as metals or silicone-protein complexes. Thus, a careful literature review would suggest that “allergy to silicone hydrogel lenses” is a myth. The silicone moieties within silicone hydrogel lenses remain tightly bound within the polymeric structure of lenses and do not leach or leak from the lenses and, even if they did, do not possess the necessary characteristics to elicit an allergic response.

So why do practitioners misdiagnose symptoms of patients wearing SiHy lenses as being linked to an allergy to silicone? What responses to contact lenses mimic those seen in allergic eye disease? Many eye care practitioners have indeed had the experience of seeing a patient respond less than ideally to SiHy CLs. The wearing of SiHy lenses has been linked to a number of inflammatory complications that may mimic allergic eye disease, including itching, infiltrative keratitis, CL-associated papillary conjunctivitis and acute red eye.

So, if not due to “silicone allergy”, what precipitates these observed responses? As outlined in recent reviews, many of these complications are due to the surface and bulk properties of SiHy materials being different to that of hydrogels. The incorporation of siloxane groups increases the modulus and stiffness of SiHys, resulting in a number of mechanical complications. SiHy materials are more hydrophobic than hydrogels. Deposition profiles also differ between SiHy and hydrogel materials, with SiHy lenses exhibiting increased amounts of lipid and lower amounts of protein (which is often denatured) compared with hydrogel lenses. With regards to infiltrative keratitis (IK), several reports have demonstrated that wearing SiHy materials on a reusable basis results in an almost two-fold increase in the relative risk for IK. The reasons behind this increase in infiltrates for reusable SiHy lenses remains a subject of intense debate, but factors under consideration include the increased modulus, reduced wettability, altered deposition patterns and interactions with both solutions and bacterial exotoxins.

So how can practitioners overcome these potential issues with SiHy materials? The argument for using DD SiHy lenses is growing. Published data show comparable performance to DD hydrogel lenses. along with excellent physiological responses and comfort levels. Of note is the fact that levels of IK are no different between SiHy and hydrogel materials when used on a DD modality.

This article has reviewed the use of contact lenses in patients with mild to moderate ocular allergies and the literature would suggest that using DD lenses, whether hydrogel or SiHy, would be a useful modality. By adopting this approach, wearers would potentially suffer from fewer symptoms and would avoid the misleading symptoms that mimic “silicone allergy”.

*For more on the latest research into dry eye disease, see our Dry Eye special.

References

Wolffsohn JS, Emberlin JC: Role of contact lenses in relieving ocular allergy. Cont Lens Anterior Eye 2011; 34;4: 169-72.

Kumar P, Elston R, et al.: Allergic rhinoconjunctivitis and contact lens intolerance. Clao J 1991; 17;1: 31-4.

Mastrota K: Unmasking the dry eye masqueraders. Review of Cornea & Contact Lenses 2015; March 14-17.

Gomes JAP, Azar DT, et al.: TFOS DEWS II iatrogenic report. Ocul Surf 2017; 15;3: 511-538.

Wolffsohn JS, Arita R, et al.: TFOS DEWS II Diagnostic Methodology report. Ocul Surf 2017; 15;3: 539-574.

Hayes VY, Schnider CM, et al.: An evaluation of 1-day disposable contact lens wear in a population of allergy sufferers. Cont Lens Anterior Eye 2003; 26;2: 85-93.

Hall BJ, Jones LW, et al.: Silicone allergies and the eye: fact or fiction? Eye Contact Lens 2014; 40;1: 51-7.

Jones L: Doc, I think I’m allergic to these new lenses. Contact Lens Spectrum 2018; 33;5: 44-51.

Jones L, Walsh K: The evolution of silicone hydrogel daily disposables: Two decades of material and design innovation. Optician 2018; 252;May 4: 25-32.

Lin MC, Yeh TN: Mechanical complications induced by silicone hydrogel contact lenses. Eye Contact Lens 2013; 39;1: 115-24.

Nichols JJ: Deposition on silicone hydrogel lenses. Eye Contact Lens 2013; 39;1: 19-22.

Chalmers RL, Keay L, et al.: Multicenter case-control study of the role of lens materials and care products on the development of corneal infiltrates. Optom Vis Sci 2012; 89;3: 316-25.

Chalmers RL, Wagner H, et al.: Age and other risk factors for corneal infiltrative and inflammatory events in young soft contact lens wearers from the Contact Lens Assessment in Youth (CLAY) study. Invest Ophthalmol Vis Sci 2011; 52;9: 6690-6.

Szczotka-Flynn L, Diaz M: Risk of corneal inflammatory events with silicone hydrogel and low dk hydrogel extended contact lens wear: a meta-analysis. Optom Vis Sci 2007; 84;4: 247-56.

Diec J, Tilia D, et al.: Comparison of Silicone Hydrogel and Hydrogel Daily Disposable Contact Lenses. Eye Contact Lens 2018; In press.

Chalmers RL, Hickson-Curran SB, et al.: Rates of adverse events with hydrogel and silicone hydrogel daily disposable lenses in a large postmarket surveillance registry: The TEMPO Registry. Invest Ophthalmol Vis Sci 2015; 56;1: 654-63.

About the author

Professor Lyndon Jones is director of Centre for Ocular Research and education (CORE) at the University of Waterloo, while Annie Berg is based at the Department of Kinesiology at Brock University, both in Ontario, Canada.