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K. S. Evans, R. V. North, C. Purslow; The Relationship Between Tear Ferning, Tear Film Stability and Ocular Comfort. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4837.
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Tear ferning (TF) has shown good sensitivity and specificity in the diagnosis of dry eye, but is a relatively uncommon test, especially in contact lens wearers. The aim of this study was to investigate the relationship between TF, ocular comfort and tear film stability amongst habitual hydrogel contact lens (CL) wearers and non-contact lens (NCL) wearers.
Subjects (36 NCL, 24 CL; mean age 23.2 ± 4.8yrs) underwent assessment of non-invasive tear break up time (NIBUT), fluorescein tear break up time (FBUT) and completed the Ocular Comfort Index (OCI) questionnaire. Non-stimulated tears were collected from the inferior tear meniscus with a glass capillary. Samples of 1.5µl were air dried, observed by light microscopy (x20) and the TF pattern interpolated to 0.25 increments of Rolando’s grading scale to increase measurement sensitivity.
Using Rolando’s criteria of abnormal TF above Type 2, 14% of NCL wearers and 50% of CL wearers exhibited abnormal TF. CL wearers demonstrated significantly higher grades of TF pattern compared to NCL wearers (Mann-Whitney U Test; p<0.005), except where NCL wearers were symptomatic for ocular discomfort (Mann-Whitney U Test; p=0.374). Differences in tear film stability (NIBUT & FBUT) were insignificant between groups, and TF displayed poor correlation with tear film stability tests and OCI scores (0.267<p<0.989). TF has a sensitivity of 50% and specificity of 87.5% for the prediction of ocular discomfort in the NCL group. This reduces to 25% and 45% respectively in the CL group.
Abnormal TF appears to reflect the unfavourable ratio of salt to macromolecule concentration within the tear film. The similar TF patterns in CL wearers and symptomatic NCL wearers are likely to be caused by similar modulation of the tear film constituent ratios in each cohort. The TF technique appears to be more specific to ocular discomfort in NCL wearers compared to CL wearers.
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