Optimal cutoff value of the dry eye-related quality-of-life score for diagnosing dry eye disease

**Background:** Dry eye disease (DED) is a common ocular surface disorder that impairs vision, quality of life, and work productivity. Diagnosis relies on subjective symptom assessment and tear film breakup time (TFBUT). The Dry Eye-Related Quality-of-Life Score (DEQS) questionnaire, developed in Japan, evaluates both ocular symptoms and health-related quality of life, but lacks validated cutoff values for DED diagnosis and severity classification. This study aimed to determine optimal DEQS cutoff values for DED detection and severity grading using a hospital-based, cross-sectional, observational design.

**Methods:** A total of 427 outpatients (296 DED, 131 non-DED) from Juntendo University Hospital (Tokyo, Japan) were enrolled between September 2017 and September 2021. DED was diagnosed per the 2016 Asia Dry Eye Society criteria: DED symptoms (J-OSDI ≥13 points) and TFBUT ≤5 seconds. Participants completed the DEQS and J-OSDI questionnaires and underwent dry eye examinations including TFBUT, corneal and conjunctival fluorescein staining (CFS), Schirmer I test (SIT), and maximum blink interval (MBI). Receiver operating characteristic (ROC) analysis was used to determine optimal DEQS cutoff values for DED diagnosis and severity classification (mild, moderate, severe) based on J-OSDI severity categories (13–22, 23–32, ≥33 points). The Youden index maximized sensitivity and specificity.

**Key Results:** Among 427 participants, 296 (69.3%) had DED and 131 (30.7%) were non-DED. The DED group had significantly higher DEQS and J-OSDI scores, and lower TFBUT and MBI (all P<0.001). DEQS summary score was strongly positively correlated with J-OSDI (r=0.874, P<0.001) and negatively correlated with MBI (r=−0.236, P<0.001). ROC analysis for DED diagnosis yielded an AUC of 0.915, with an optimal DEQS cutoff of 15.0 points (sensitivity 83.5%, specificity 87.0%). Positive predictive value was 93.6% (247/264) and negative predictive value was 69.9% (114/163). For severity classification, DEQS cutoff values were 15.0 points for mild DED (AUC 0.937, sensitivity 83.6%, specificity 91.9%), 20.0 points for moderate DED (AUC 0.946, sensitivity 80.8%, specificity 94.5%), and 26.8 points for severe DED (AUC 0.940, sensitivity 88.7%, specificity 86.0%). MBI showed a gradual downward trend across severity groups (13.3±7.4, 10.6±6.8, 10.3±6.6, 10.0±6.5 seconds for DEQS <15, ≥15 to <20, ≥20 to <26.8, ≥26.8, respectively; all P<0.001 vs. non-DED). TFBUT did not differ significantly between groups (all ~1.7 seconds).

**Clinical Implications:** The DEQS questionnaire with an optimal cutoff of 15.0 points provides a valid, sensitive, and specific tool for DED diagnosis when combined with TFBUT ≤5 seconds. The proposed severity cutoffs (15.0, 20.0, 26.8 points) enable standardized classification of subjective symptom severity, facilitating patient self-management and efficient clinical decision-making. The DEQS offers advantages over the OSDI by including health-related quality-of-life items, making it suitable for broader use in clinical practice, health check-up screening, and online services. Early diagnosis and severity grading can improve treatment outcomes and reduce the socioeconomic burden of DED. Limitations include single-center design in Japan, older predominantly female population, and lack of significant differences in objective dry eye tests (TFBUT, SIT, CFS) between groups, possibly due to inclusion of patients with improved symptoms. Nonetheless, MBI differences support the validity of the DEQS cutoff values.