Tear film parameters in challenging environments

Purpose: Despite advances in materials, discomfort and dryness symptoms are still frequently reported as reasons for dissatisfaction with or discontinuation of soft contact lens wear. Such symptoms are frequently reported in lens wearers and non-wearers in challenging environments. The effect over time of two challenging environments on tear film stability and quantity was tested.
Method: Tear film parameters were assessed over a 60 min period in a custom built walk-in environmental chamber (Weiss Gallenkamp, UK) which controls temperature (°C) and relative humidity (%RH) independently. Environments tested were: (i) ‘indoor office’ at 21C and 30% RH; (ii) ‘aircraft cabin’ at 21C and 10%RH. Tear film stability was assessed using non-invasive reflected grid observation scored in seconds as time to first distortion of the grid pattern. Tear film quantity was assessed by tear meniscus height measured in mm using on-screen callipers (Ionico) from captured digital slit lamp images. Phenol red threads were scored in mm of wetted strip in 15 s. Ten subjects participated with the two environments tested on different days.
Results: Tear film stability significantly reduced following 55 min in ‘indoor office’ (p = .018) but not for ‘aircraft cabin’ (p = .110). Tear meniscus height decreased significantly following 15 min in ‘aircraft cabin’ (p = .028) but no significant change was found for ‘indoor office’. Phenol red thread tests gave no significant change in results for either environment.
Conclusions: Both tear film stability and quantity were progressively adversely affected over time by low humidity environments. Strategies to increase humidity or reduce evaporation are required to offset effects on the tear film.