Development of a short version of the visual function questionnaire using item-response theory

Area of Science:

• Ophthalmology
• Psychometrics
• Health Outcomes Research

Background:

• Patient-reported outcomes are crucial in clinical ophthalmology but can be burdensome.
• Developing shorter, efficient measures is essential to reduce patient burden.
• The National Eye Institute's Visual Function Questionnaire (VFQ) is a comprehensive tool for assessing visual functioning.

Purpose of the Study:

• To develop and validate a short version of the VFQ using item-response theory (IRT).
• To reduce the burden on patients while maintaining the psychometric integrity of visual function assessment.
• To create a more efficient tool for measuring patient-reported visual outcomes in ophthalmology.

Main Methods:

• Analyzed VFQ data from 276 adult patients in Japan with common ophthalmic conditions (glaucoma, cataract, macular degeneration).
• Utilized a polytomous IRT model (Generalized Partial Credit Model) to select 11 items for the short version (VFQ-J11).
• Evaluated item characteristics (location, slope, missing data) and ensured representation of key domains. Assessed scale precision (test information) and conducted validation testing.

Main Results:

• Selected 11 items from the original 32 to form the VFQ-J11.
• The VFQ-J11 demonstrated good test information and well-targeted item thresholds for patients with vision impairment.
• VFQ-J11 scores showed strong correlations with visual field and visual acuity measures, and significantly improved after cataract surgery, confirming validity.

Conclusions:

• The 11-item VFQ-J11 is a reliable and valid instrument for assessing visual functioning in ophthalmic patients.
• This abbreviated questionnaire is expected to lessen patient burden.
• The VFQ-J11 maintains robust psychometric properties, making it a valuable tool for clinical and research settings.