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TR Karkkainen, MK Smith, JR Wood; The Effect Contact Lens Solution Osmolarity Has on Tear Film Tonicity . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3090.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:. Contact lens wear can increase tear film osmolarity, which may produce adverse corneal effects as well as be associated with dry eye symptoms. Previous studies in our laboratory revealed the solution contained within a contact lens material is hypertonic and may be responsible for increases in tear film osmolarity seen with contact lens wear. In this study we examined what effect storing lenses in hypotonic solutions has on tear film tonicity during wear. If there is a significant effect on lowering tear film osmolarity this may be useful in decreasing corneal complications encountered with lens wear and improving lens induced dry eye symtoms. Methods:Twenty soft daily wear contact lenses were used in this study. Each lens was randomly assigned to soak in either a hypotonic (100 mmol/kg) solution or the lenses original storage solution, which was nearly isotonic (285 mmol/kg). The lenses were soaked for 30 minutes and then randomly applied to either the right or left eye of the subject. Tear film tonicity was measured by collecting a 2-uL sample from the inferior tear prism and measuring the osmolarity on a Wescor-5520 vapor pressure osmometer. Tear samples were collected prior to lens insertion and at 5 min., 30 min, 1 hr and 2 hr after insertion. The measurements were repeated three times for each of the five time intervals for a total of 300 measurements. The results were statistically analyzed for significant differences between the means using an ANOVA. Results:The mean tear film osmolarity prior to lens wear for the eyes wearing hypotonic and isotonic solutions was 294.77 mmol/kg and 302.83 mmol/kg respectively, and was not significantly different (p≷0.05). The overall mean tear film osmolarity during lens wear was 307.15 mmol/kg and 319.10 mmol/kg for eyes wearing lenses stored in 100 mmol/kg and 285 mmol/kg solutions respectively. An ANOVA revealed the relative decrease in tear film osmolarity for the eyes wearing lenses containing hypotonic solutions was statistically significant (p<0.05). In addition a t-test showed that the increase in tear film osmolarity for the eyes wearing hypotonic solutions was not significant from the baseline non-lens wearing condition. Conclusion:Contact lenses soaked in hypotonic solutions result in a significantly lower tear film osmolarity during wear. The lower osmolarity is closer to normal physiologic values, which may help prevent adverse corneal events and be beneficial for patients who experience symptoms relating to contact lens induced dry eye. Future studies should be performed measuring the efficacy and safety of such solutions on a large population of patients and with various lens materials.
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