Content Validity of Two Generic Preference-Based Measures in Retinitis Pigmentosa, Including X-Linked Retinitis...

Retinitis pigmentosa (RP) is a group of retinal diseases characterized by night blindness and impairment in visual field and acuity. The most severe form of RP is X-linked RP (XLRP). The relevance of common generic preference-based measures (GPBMs) in visual conditions like XLRP is often questioned. The purpose of this study was to assess content validity of the EQ-5D-5L and Health Utilities Index (HUI) in patients with XLRP or other types of RP, collectively abbreviated as (XL)RP.

People with (XL)RP in the US participated in qualitative interviews conducted via telephone/videoconference. Interviews began with concept elicitation to identify the impact of (XL)RP on quality of life. Participants then completed the instruments and answered questions about their clarity, relevance, and comprehensiveness.

The sample included 23 participants with RP, including 12 with XLRP (73.9% male; mean age 50.2 y). Participants reported a variety of impacts of (XL)RP, some of which overlap with the EQ-5D-5L and HUI (e.g., emotional impact, usual activities). Participants stated that both instruments were clear and easy to understand (n = 21, 91.3% for EQ-5D-5L and n = 18, 78.3% for the HUI), but also identified important concepts that were not assessed by the questionnaires. Eighteen participants (78.2%) identified at least one important concept missing from the EQ-5D-5L and 20 participants (87.0%) identified at least one concept missing from the HUI. Missing concepts included visual symptoms, driving, impact of light/darkness, and ability to do things they used to enjoy.

While the EQ-5D-5L and HUI include some content relevant to people with (XL)RP, both instruments appear to be missing concepts that are specifically relevant to this patient population, which could limit content validity and sensitivity to disease severity. Therefore, it may be useful to consider alternative methods for estimating utilities associated with (XL)RP.