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M. L. Flint, W. Miller, OD, PhD; Tear Film Exchange Rate in Silicone Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5640.
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Oxygen transmissibility in silicone hydrogel contact lenses provide greater oxygen levels to the corneal surface. Increased oxygen to the cornea causes corneal hypoxia to diminish. Yet, corneal inflammation and infection are still experienced with these lenses: one possible explanation may be tear stagnation under the contact lens due to insufficient tear exchange. The purpose of this study was to determine the tear exchange rate in seven different silicone hydrogel contact lens materials using an in vivo fluorophotometer on eight patients when compared to a control non-silicone hydrogel contact lens.
Lens movement was determined using biomicroscopy. Corneal surface was assessed with the Zeiss Visante OCT. Corneal astigmatism and elevation was determined using Bausch and Lomb Orbscan topographer. Blink rate was determined by monitoring eye blink in one minute. Tear exchange rate was determined by instilling high molecular weight sodium fluorescein (FITC) onto the concave portion of the lens with subsequent application to the cornea. Tear exchange rate (overall, fast, and slow decay rate) was ascertained using Kleidograph and Microsoft Excel.
Slow decay rate-Lotrafilcon A (8.471%), Lotrafilcon (5.327%), Etafilcon (4.846%), Galyfilcon (3.578%), Senofilcon (3.49%), Comfilcon (2.511%), Balafilcon (1.754%), and Enfilcon (1.105%). Average blink rate was 19 blinks per minute. Largest vertical movement was Lotrafilcon (.3mm). Smallest vertical movement was Senofilcon A (.1mm). Normal corneal astigmatism and elevations were observed.
Lens movement and tear exchange rate was not different between silicone and non-silicone hydrogel contact lenses. Slow decay rate was different between individual silicone hydrogel contact lenses ranging from 8.47% to 1.1%. Subjects showed a higher than normal blink rate of 19 blinks per minute with the average blink rate being 15 blinks per minute. Lens movement and slow decay rate showed a positive correlation resulting in a greater decay with increased movement. The results suggest that differences in individual silicone hydrogel lenses were exhibited due to the biophysical differences between lenses.Acknowledgements: NEI training grant
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