Objective: The purpose of this study was to compare the discriminative properties of two generic health-related quality of life (QoL) instruments (SF-36 and EQ-5D) and a newly developed disease-specific patient-reported outcomes instrument (Impact of Dry Eye on Everyday Life (IDEEL)) to distinguish between different levels of dry eye severity.
Methods: Assessment of 210 people: 130 with non-Sjogren's Keratoconjunctivitis Sicca (non-SS KCS), 32 with Sjögren's Syndrome (SS) and 48 controls; comparison of SF-36, EQ-5D, and IDEEL age-adjusted data by dry eye severity levels. Severity was assessed based on diagnosis (non-SS KCS, SS, control), patient-report (none, very mild, mild, moderate, severe, extremely severe) and clinician-report (none, mild, moderate, severe).
Results: Discriminative validity results were consistent for all instruments. Significant differences between severity levels were found with most SF-36 scales (P < 0.05), all EQ-5D scales (P < 0.05), and all IDEEL scales (P < 0.0001), except for Treatment Satisfaction. IDEEL scales consistently outperformed the generic QoL measures regardless of the severity criterion used. Most SF-36 scales outperformed the EQ-5D QoL scale, but the EQ-5D visual analog scale outperformed the SF-36 scales, except for General Health Perceptions.
Conclusions: The disease-specific IDEEL scales are better able to discriminate between severity levels than the majority of the generic QoL scales. Preliminary evidence demonstrates that the IDEEL will be sensitive to QoL changes over time, although further testing in controlled longitudinal studies is needed.