Contact Lens Care Solutions

There are a number of anatomical and physiological differences between Asian and Caucasian eyes. Anatomical characteristics specific to the Asian eye include an oblique angle of the palpebral fissure, a smaller vertical palpebral aperture, a smaller horizontal visible iris diameter, a flatter cornea and greater corneal toricity.1-4 Asian eyelids have greater herniation of the orbital fat in the upper and lower eyelids, combined with a narrower palpebral aperture, possibly resulting in higher lid tension.5-7 The physiology of the Asian eye differs from that of the Caucasian eye in having a shorter tear breakup time, smaller tear meniscus volume, and reduced pre-corneal tear film stability.8,9 (Yeh TN, Tran N, Graham AD, Green HM, Lin MC. Relationships among tear film stability, tear osmolarity, corneal staining history, and dryness symptoms. Invest Ophthalmol Vis Sci. 2013;54. ARVO E-Abstract 4332.) Adverse responses to contact lens wear have been documented more frequently in Asian eyes than in Caucasian eyes. In controlled experimental settings, Hamano, et al. reported a higher incidence of endothelial bleb formation under hypoxic conditions in Asians compared to Caucasians and African Americans.10 Other studies have shown that Asians are more susceptible to micro-trauma during rigid gas-permeable contact lens extended wear, as well as after eight hours of closed-eye soft contact lens wear.4,11 In a clinical setting, Asian eyes exhibit a higher incidence of observable biomicroscopic signs, including limbal and conjunctival injection, corneal and conjunctival staining, and neovascularization.12,13 (Sanders TL, French HM, Yeh TN, Tran N, Green HM, Graham AD, Lin MC. Effects of irrigation on adverse events during continuous contact lens wear. 2010. AAO E-Abstract 105123.) In recent years, researchers have focused on the relationship between solution toxicity and adverse ocular events during lens wear.14-19 Carnt, et al. found that eyes with solution-related staining are three times more likely to experience a corneal infiltrative event, suggesting that solution-related corneal staining could be a potential risk factor for developing low-level corneal inflammation. Although solution-related corneal staining has been well documented, the type of corneal staining reported has been mostly diffuse, superficial, and micropunctate in presentation, which is generally transient and asymptomatic. Lebow, et al. found that differences exist between different MPS with respect to the type, extent, and depth of solution-related corneal staining; however, the severity of staining, on average, was considered clinically insignificant. Although several authors have examined the ocular response of the Asian eye to contact lens wear, none to date has studied racial differences in the ocular response to the use of lens care solutions. Of particular interest in the present study is the moderate-to-severe level of corneal staining that would prompt practitioners to recommend discontinuation of lens wear and possibly to implement clinical treatment. The degree to which this level of corneal staining occurs in response to contact lens solution toxicity has not been fully documented, nor is it known whether such solution-related staining is more common in Asian eyes. In addition, there have been differing reports of the relationships between lens care solutions and biomicroscopic signs other than corneal staining, depending on the type of solution investigated.14,20-22 Finally, racial differences in symptoms of discomfort or dryness are known to exist,23-25 but have not been investigated with respect to the use of lens care solutions. In the present study, we address these questions by examining the Asian and Caucasian ocular surface response and subject symptomatology with two biguanide-preserved contact lens care solutions used with daily silicone hydrogel contact lens wear.