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Jun Zhang, Carolyn G Begley, Larry N Thibos, Ping Situ, Trefford L Simpson, Ziwei Wu; Visual Disturbance and Ocular Irritation in an Experimentally Induced Tear Film Instability Model. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1989.
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Tear film instability (TFI) is a core mechanism of dry eye (DEWS, 2007), but its connection to dry eye symptoms of ocular irritation and visual disturbance remains poorly understood. In this experimental TFI model, we test the hypothesis that TFI over the pupil decreases optical quality, visual acuity (VA) and stresses the ocular surface, leading to dry eye-like symptoms, and that wearing a soft contact lens (CL) partially alters this relationship.
10 adapted soft contact lens (CL) wearers participated in 2 study visits, with and without CL. TFI by retroillumination (RI), VA and RMS fit error (RMSFE), an optical marker for TFI over the pupil (Liu et al, 2010) were measured simultaneously by a 3-channel optical system. Subjects were asked to keep one eye open for up to 30 sec, if possible, while TFI was monitored and subjects simultaneously turned a knob to adjust the letter size of the VA. The procedure was repeated 10 times. Discomfort and blurry vision during and after each trial were rated using 0-100 visual analogue scales (VAS). The current symptom questionnaire (CSQ) was filled in before and just after all testing.
TFI occurred in 69% of trials of eye opening trials. There was a statistically significant (paired t-test, p<0.05) in increase in RMSFE between CL and no CL trials, with an average of 1394±832 (CL) and 594±104 (noCL). The increase in average logMAR VA was 0.54±0.24 (CL) and 0.44±0.14 (noCL), with no significant difference between groups. The median CSQ sum score (total=50) was 11 with CLs and 5 without CLs before testing and showed a statistically significant increase to 26 and 34, respectively, just after testing (Wilcoxon Signed-RankTest, p<0.03). The median CSQ symptom of discomfort (total 5) increased from 1 to 4 in both groups and blurry vision increased from 1 to 4 (CL) and 1 to 3 (no CL) before and after testing.
These results support the hypothesis that TFI leads to decreased VA and optical quality and increased discomfort, and that CL wear at least partially ameliorates the discomfort reported during TFI. After repeated TFI trials, both groups reported increased discomfort and blurry vision, suggesting cumulative effects in both groups and supporting the idea that TFI can lead to both classes of symptoms.
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