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Carolyn Begley, Jun Zhang, Ping Situ, Ziwei Wu, Trefford Simpson; The Ocular Surface Sensory Response to Tear Film Instability With and Without a Contact Lens. Invest. Ophthalmol. Vis. Sci. 2013;54(15):905.
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© ARVO (1962-2015); The Authors (2016-present)
Tear film instability (TFI) is a core mechanism of dry eye (DEWS, 2007), but its sensory impact on the ocular surface remains poorly understood. In this study, we test the hypothesis that TFI directly stimulates ocular surface sensory neurons and that wearing a soft contact lens (CL) partially blocks this stimulation.
Ten adapted CL wearers participated in 2 study visits. While not wearing CLs, subjects were seated behind a slit lamp biomicroscope and were asked to keep one eye open as long as possible (maximum blink interval=MBI) while fluorescein TFI was monitored and subjects simultaneously indicated the level of discomfort using a “discomfort knob” (DK) potentiometer (0-10 scale). The MBI procedure was repeated 10 times. Discomfort and burning sensations during and after each trial were rated using 0-10 visual analogue scales (VAS). The entire procedure was repeated at a second study visit while wearing CLs for a fixed 30 sec MBI with retroillumination used to view TFI over CLs.
The discomfort intensity and slope measured by the DK was significantly lower (paired t-test, p<0.004) while wearing a CL (AVG±SD; End DK=4±2; slope=0.15±0.08DK/sec) versus no CL (AVG±SD; End DK=9±2; slope=0.66±0.23DK/sec). Likewise, the VAS ratings during and after MBI trials for discomfort (AVG±SD with CL: 3.17±1.70 and 3.05±1.71; no CL: 6.38±2.11 and 4.64±2.71) and burning (AVG±SD with CL: 2.56±1.90 and 2.33±1.87; no CL: 5.90±2.63 and 4.56±2.89) were significantly lower with CLs (ANOVA p=0.013 and 0.011 for discomfort and burning, respectively).
These results support the hypotheses that TFI provides nociceptive stimulation to the cornea, perhaps due to increased osmolarity or surface drying during TFI. This effect is partially blocked and altered (less burning) by wearing a CL, which suggests that TFI over the CL surface may stimulate the ocular surface through different mechanisms.
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