Development of a vision impairment score for the assessment of functional vision in dogs: Initial evidence of validity, reliability, and responsiveness

Aim: To describe the development and initial validation of a questionnaire measuring functional vision in dogs.

Methods: A 17-item survey was designed to quantify functional vision in dogs. The Vision Impairment Score (VIS) was determined by summing responses to each question. Questions were assigned to one of five subcategories: overall vision, daily activities, peripheral vision, near vision, and distance vision. Content validity was established during development phases, and construct validity via comparing results of known groups (blind vs sighted; normal vs impaired vision; surgery to improve vision vs nonrestorative surgery), and through factor analysis. Concurrent criterion validity was determined with use of a validated health-related quality-of-life (HRQL) assessment tool. Reliability and responsiveness assessments were investigated using intraclass correlation coefficient (ICC) and effect size (ES), respectively.

Results: Responses (221) from 201 dog owners were included. Compared to sighted dogs (n = 153), blind dogs (n = 48) had a higher VIS and greater impairment in all subcategories. Among sighted dogs, a higher VIS was obtained in dogs with low vision compared to those with normal vision (P < 0.001). A higher VIS was associated with poorer HRQL (P < 0.001). Perfect reliability was obtained for 6/17 questions, and excellent reliability for 11/17 questions (intraclass correlation 1.0 and >0.9, respectively), and the VIS was highly responsive to therapeutic intervention (effect size 1.46).

Conclusion: Results suggest the VIS may be clinically useful in assessing and obtaining a quantifiable measure of functional vision in dogs. Ongoing validation of the tool for clinical use is needed.