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Patient-Reported Visual Disability in Fuchs' Endothelial Corneal Dystrophy Measured by the Visual Function and
Katrin Wacker1, Keith H Baratz2, William M Bourne2
1Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota; Eye Center Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Purpose:
Measuring patient-reported visual disability in Fuchs' endothelial corneal dystrophy (FECD) may be helpful in determining when to intervene and for understanding the outcomes of intervention. In this study, we aimed to validate a new patient-reported visual disability questionnaire, the Visual Function and Corneal Health Status (V-FUCHS) instrument, in FECD before and after endothelial keratoplasty (EK).
Design:
Cross-sectional study with instrument readministration at 6 weeks.
Participants:
Patients with a range of severity of FECD, including after EK, and patients with healthy corneas.
Methods:
The V-FUCHS instrument was developed based on patient interviews, expert consultations, and pretesting. Psychometric methods of classic test theory were applied to estimate reliability and validity, including testing V-FUCHS against Catquest-9SF, a cataract-specific visual disability questionnaire. Ordered polytomous Rasch-based partial credit models and item response theory diagnostics were used to define the response patterns.
Main Outcome Measures:
Reliability (primary) and validity (secondary).
Results:
The final instrument was completed by 65% of patients with a range of severity of FECD (n = 41), after undergoing EK for FECD (n = 70), and with healthy corneas (n = 28). Participants were phakic or pseudophakic. Exploratory factor analysis among FECD and patients who underwent EK showed 2 independent factors of visual disability: 7 items related to visual acuity and 8 items related to glare or diurnal variation. Retest reliability was substantial (intraclass correlation coefficient, ≥0.8, both factors). Among all patients, the visual acuity factor was correlated with Catquest-9SF scores (r = 0.65; P < 0.001; n = 96). The glare or diurnal variation factor increased with FECD severity (P < 0.001, n = 69) and was higher in FECD than healthy participants (P < 0.001). Diagnostics revealed that both factors were well calibrated and met Rasch model expectations.
Conclusions:
The V-FUCHS instrument is valid and reliable for assessing visual disability in FECD. The instrument allows for standardized, comprehensive, and rapid assessment of disease-specific visual disability and may be useful in clinical practice and research as a patient-reported outcome measure.
