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R.C. Scaffidi, D.R. Korb, J.V. Greiner, C.A. Blackie; Lipid Layer Thickness and Dry Eye Symptoms . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4444.
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Purpose: Lipid layer thickness (LLT) has been correlated to tear evaporation, tear film stability, and other ocular signs. This study was designed to determine whether symptoms indicative of dry eye states are correlated to thin lipid layers. Methods: Dry eye symptoms were graded from zero to 24 using a custom symptoms (SPEED) questionnaire (Korb et al: Eye & Contact Lens 2005). Consecutive patients presenting for examination with a symptom score > 5 were admitted. Patients with symptom scores <5 were excluded from the study. A custom designed lipid layer interferometer (Korb et al: Cornea 1994), enabling characterization of interference patterns, was used to quantify the LLT (OU) of admitted subjects. LLT was graded from 45 to 180 nm based upon the dominant colors in the interference patterns. LLT < 60 nm was classified as thin and compromised, 75 nm as marginal, and > 90 nm as adequate and thick. Results: Symptomatic subjects were divided into 2 groups: a moderate group (n=41; symptom score 5–9 points, mean = 6.8), and a severe group (n=20; symptom score > 10 points, mean =12.8). LLT of right and left eyes were averaged for a final LLT measurement for each subject. In the moderate group, 48.7% exhibited LLT < 60 nm, 36.5% LLT=75 nm, and 14.6% LLT >90 nm. In the severe group, 65.0% exhibited LLT < 60 nm, 25.0% LLT = 75 nm, and 10.0% LLT > 90 nm. In both groups the percentage of eyes with a LLT < 60 nm was significantly higher than expected if no relationship existed between LLT and dry eye symptoms (p < 0.05 for the moderate group, p < 0.005 for the severe group, chi square test df = 2). Conclusions: Patients with severe dry eye symptoms revealed a higher frequency of reduced LLT compared to patients with more moderate symptoms, with 85.2% of the moderate and 90.0% of the severe group exhibiting thin or marginal lipid layer thicknesses. However, since 14.6% of the moderate and 10.0% of the severe group exhibited LLT > 90 nm, a thick lipid layer cannot guarantee the absence of dry eye symptoms. A possible explanation is the recently reported correlation between dry eye symptoms and the sign of lid wiper epitheliopathy in the absence of any positive conventional ocular signs (Korb et al: Eye & Contact Lens 2005). This study suggests the presence of dry eye symptoms increases the likelihood of a thin or marginal lipid layer, and the need to consider the reason for the lack of an absolute correlation between dry eye symptoms and LLT.
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