The repeatability of subjective and objective tear ferning assessment and its association with lipid layer thickness, non-invasive tear break-up time and comfort

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PurposeTo determine the repeatability of tear ferning (TF) grading analysed by subjective and objective techniques, and its correlation with lipid layer thickness (LLT), non-invasive keratograph break-up time (NIKBUT), and ocular surface disease index (OSDI) comfort scores with and without ocular lubricants. MethodsA prospective, randomised, controlled clinical study was conducted. Eighteen healthy non-contact lens wearers aged between 18 to 45 years attended a total of three visits. They were randomly allocated to receive no drops on two occasions to examine method repeatability (visits A and B) or a 60 μL drop of Refresh® (visit C). At each visit, LLT and NIKBUT were assessed followed by basal tear collection. The TF pattern was established by pipetting one μL volume of tears onto a glass slide that was allowed to air-dry and imaged under a microscope. The resulting tear ferning pattern was determined using subjective grading and a novel computerized objective analysis technique that measured the local contrast of ferning contours. ResultsPaired t-tests found that all measurements collected between eyes, on different days for visit A and B were not significantly different (p >0.05). Eyes and days were averaged and compared to visit C. Paired t-tests between the averaged baseline visits and visit C for LLT, NIKBUT including subjective and objective TF scores showed no significant difference (p>0.05). No significant correlation was shown between the TF scoring and OSDI, LLT or NITBUT (p>0.05). There was however a high significant correlation and agreement between the subjective and objective analysis techniques for TF grading. ConclusionsTF grade, LLT and NITBUT are repeatable. As with other ocular surface assessments, subjective and objective TF gradings did not significantly correlate with the measures of tear film stability or comfort. Lubricants had no effect on TF grade, LLT or NITBUT. The novel objective analysis technique is a promising candidate for a repeatable and unbiased assessment of tear ferning.