Estimating minimally important differences for two vision-specific quality of life measures

Area of Science:

• Ophthalmology
• Clinical Research
• Patient-Reported Outcomes

Background:

• Open-angle glaucoma (OAG) affects visual function and quality of life.
• Assessing changes in visual function is crucial for managing OAG.
• The Visual Activities Questionnaire (VAQ) and National Eye Institute-Visual Function Questionnaire (NEI-VFQ) are used to measure visual function.

Purpose of the Study:

• To estimate minimally important differences (MIDs) for the VAQ and NEI-VFQ.
• To provide clinically meaningful benchmarks for interpreting changes in visual function scores.

Main Methods:

• 607 subjects with newly-diagnosed OAG were enrolled in the CIGTS study.
• Participants were randomized to medication or surgery.
• Anchor-based and distribution-based methods were used to estimate MIDs using visual acuity (VA) and mean deviation (MD) as anchors.

Main Results:

• Anchor-based analyses showed MIDs for VAQ ranged from 2.6 to 5.2 units and for NEI-VFQ from 2.3 to 3.8 units.
• A 10-letter increase in better eye VA corresponded to MIDs of 5.2 for VAQ and 3.8 for NEI-VFQ.
• A 3-dB increase in better eye MD corresponded to MIDs of 2.6 for VAQ and 2.3 for NEI-VFQ.

Conclusions:

• A range of MIDs was established for both VAQ and NEI-VFQ.
• MIDs were sensitive to the estimation method, anchor, and questionnaire.
• These MIDs can aid in interpreting the clinical significance of visual function changes in glaucoma patients.