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M. Guillon, C. Maissa; Tear Film Evaporation - Large Population Study. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5412.
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The incidence of dry eye symptoms is significantly higher in contact lens wearers than in age matched non wearers. The aetiology of contact lens related dry eyes is thought to be of evaporative nature. It was postulated that the presence of a contact lens is associated with intrinsic increased tear film evaporation, even in the absence of symptoms. The hypothesis is tested in the current study through the comparative evaluation of large contact lens and non contact lens wearing populations.
Tear film evaporation was measured with the Oregon Health Sciences University Evaporimeter and dry eye symptomatology was quantified with the McMonnies questionnaires.
A total of 166 non contact lens wearers (NCLW) (332 eyes) aged 32.5 ± 12.5 years and 107 soft contact lens wearers (CLW) (214 eyes) aged 31.4±10.3 years form the two test populations. The McMonnies questionnaires revealed 39 NCLW and 49 CLW were symptomatic.The principal findings were: i) the incidence of dry eye was higher (p<0.05) for CLW (46%) than NCLW (23%); ii) for each population the rate of evaporation was higher for the symptomatic than the asymptomatic groups (p<0.05) ; iii) the rate of evaporation was significantly higher (p<0.05) for asymptomatic CLW than NCLW at both 30% (22.4±7.0 vs 14.2 ± 6.3 10 -7 g/cm2/s) and 40% (18.0 ± 6.4 vs 10.2± 5.3 10 -7 g/cm2/s) hygrometries; iv). the rate of evaporation was also significantly (p<0.05) higher for the symptomatic CLW than NCLW at both 30% (24.4±5.9 vs 18.1 ± 8.7 10 -7 g/cm2/s) and 40% (19.9 ± 6.0 vs 14.2± 6.3 10 -7 g/cm2/s) hygrometries.
The intrinsically higher rate of evaporation with contact lenses confirms the aetiology of the problem and is the determinant contributing factor in producing a higher incidence of dry eyes amongst contact lens wearers than non wearers.
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