The Development of a Nystagmus-Specific Quality-of-Life Questionnaire

Abstract

Purpose: To develop a nystagmus-specific quality-of-life (QOL) questionnaire derived from patient concerns based on eudaimonic aspects of well-being.

Design: Cross-sectional study.

Participants: A total of 206 participants with nystagmus for factor analysis phase and an additional 42 participants with nystagmus for construct validity phase.

Methods: Questionnaire items were written on the basis of the 6 domains of everyday living affected by nystagmus that were elicited by previous semistructured interviews conducted with 21 people with nystagmus. After consultation with 8 nystagmus experts, 37 items were administered to 206 people with nystagmus. Factor analysis was used to identify latent factors among the items and identify items to propose new nystagmus QOL scales. Cronbach's alpha was used to assess the internal reliability of the new scales. To assess for discriminate and concurrent validity between the new nystagmus scales and an existing vision-related QOL tool, the Visual Function Questionnaire-25 (VFQ-25) was administered to 42 additional participants.

Main outcome measures: Questionnaire response scores on nystagmus-specific QOL items.

Results: The factor analysis revealed the retention of 29 items to form a measure comprising 2 distinct subscales reflecting "personal and social" and "physical and environmental" functioning as relating to nystagmus-specific QOL. The Cronbach's alpha coefficients for the "personal and social" functioning scale and "physical and environmental" functioning were 0.95 and 0.93, respectively. Tests for validity of the measure, consistent with a priori predictions, when compared with the VFQ-25, revealed the "physical and environmental" subscale showed concurrent validity (0.88), whereas the "personal and social" subscale was demonstrated to have discriminative validity (0.81).

Conclusions: We have developed a 29-item, nystagmus-specific QOL questionnaire (NYS-29) based on eudaimonic aspects of well-being with subscales that address not only physical functioning but also psycho-social issues. The NYS-29 is grounded in the perspectives and concerns of those who have nystagmus and can be used to determine the impact of nystagmus on daily living in terms of both physical and psychosocial aspects.