AIM: To evaluate the clinical significance of outer zona pellucid in tear ferning image in dry eye patients and explore a new method for evaluation tear lipid layer.

METHODS:Forty-seven patients were randomly selected from the outpatient department of ophthalmology, He Eye hospital, Shenyang from May 2018 to July 2019. The right eye was selected as the study object. All patients were investigated by the ocular surface disease index(OSDI)questionnaire and performed lipid layer classification by DR-1 tear interferometry, NIBUT and tear meniscus height examination by OCULUS Keratograph. Then tears were collected and tear ferning tests was performed. The whole tear crystallization images were observed and photographed by microscopy, then measured by Digimizer software and the area ratios of outer transparent belt were calculated. Pearson correlation analysis were performed between area ratios of outer transparent belt and OSDI scores, lipid layer levels, tear meniscus height values, NIBUT values.

RESULTS: The area ratios of outer transparent belt were negatively correlated with OSDI scores(r=-0.764, P<0.05), negatively correlated with lipid layer levels(r=-0.838, P<0.05), positively correlated with NIBUT values(r=0.575, P<0.05)and the correlation between tear meniscus height values was not significantly(r=-0.237, P=0.112).

CONCLUSION: The outer transparent belt in tear crystallization image can be used to evaluate the lipid layer of tear film; the larger area ratios of outer transparent belt, the thicker the lipid layer. This method has the advantages of quantified results, good repeatability, low requirement on equipment, and is worth popularizing.