Association between Dry Eye Parameters Depends on Tear Components

Abstract

How tear components contribute to dry-eye symptoms/signs remains less well-defined. This observational cross-sectional study enrolled 4817 (F/M = 3590/1227) patients. Subjective symptoms were evaluated with the SPEED and OSDI questionnaires. Fluorescein tear breakup time (FTBUT), superficial punctate keratitis (SPK) grading, Schirmer scores, number of expressible mei-bomian glands (MGE), lipid layer thickness (LLT), blink/partial blink rates and meibography were recorded. Patients were divided into 4 types according to their Schirmer scores and LLT, i.e., Type 1 (N = 1494): Schirmer > 5 mm, LLT > 60 nm; Type 2 (N = 698): Schirmer > 5 mm, LLT ≤ 60 nm; Type 3 (N = 1160): Schirmer ≤ 5 mm, LLT ≤ 60 nm; Type 4 (N = 1465): Schirmer ≤ 5 mm, LLT > 60 nm. Lipid deficiency (LLT ≤ 60 nm) and aqueous deficiency (Schirmer score ≤ 5 mm) were found in 38.6% and 54.5% of patients, respectively. The majority (62.4%) of lipid-deficient patients were also aqueous deficient, while 44.2% of aqueous-deficient patients were also lipid-deficient. Type 3 patients (mixed type) had the highest symptom scores (p = 0.008 and 0.007 for SPEED and OSDI, respectively), more total blinks (p < 0.001) and the shortest FTBUT (p < 0.001). Stepwise multiple regression demon-strated that LLT and Schirmer score were significant contributors to FTBUT in all 4 types. The FTBUT correlated with SPK severity in all 4 types, with Schirmer score in types 1 and 4, and with LLT in type 3 patients. SPK correlated with LLT and MGE in types 1 and 4. Age correlated with dry eye parameters more significantly than sex. Subtyping by aqueous and lipid components facilitates the understanding of dry eye pathophysiology.