Purpose: To evaluate a novel method to measure the osmolality of worn contact lenses and assess the impact of contact lens and tear film osmolality on comfort during short-term wear.
Methods: A new method to measure contact lens osmolality was validated by testing for repeatability and by evaluating independence of lens material, power, and osmolality value of the lens. This method was then used in a clinical study. Nine different lens types were each worn by 15 subjects. Osmolality, tear film, and ocular surface parameters were tested for their association to comfort using linear mixed model.
Results: The method to measure contact lens osmolality was independent of lens material (p = 0.911), power (p = 0.826), and osmolality value of the lens (p = 0.858). No differences in contact lens osmolalities between two different days were observed (p > 0.05). Comfort after 6 h of lens wear was associated with the osmolality of the worn lens (p = 0.006, r = -0.41) but not with tear osmolality after lens wear (p = 0.993). Comfort was associated with conjunctival indentation (p = 0.002, r = -0.37). Osmolality of worn lenses significantly correlated with tear film break-up time (p = 0.003, r = -0.22), lens water content (p < 0.001, r = -0.58), conjunctival indentation (p < 0.001, r = 0.45), and ocular sensitivity (p < 0.05) after 6 h lens wear.
Conclusion: This newly developed method to measure contact lens osmolality was repeatable and independent of lens material, power, and osmolality value of the contact lens. Although no association between tear film osmolality and ocular comfort after 6 h of lens wear could be demonstrated, contact lens osmolality was associated with comfort and ocular surface characteristics, and may provide the link between symptoms and clinical observations.