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We appreciate the comments of Dr Safran. Indeed, the work he cites may provide a scientific basis for one of our findings that we had not previously considered.The vision-related portion of our questionnaire was intended to assess (1) the limitations in activities requiring vision, (2) a self-evaluation of vision, and (3) visual symptoms in patients with cytomegalovirus retinitis. In designing this instrument, we assembled indicators of the commonly experienced range of each of these concepts. For visual symptoms, qualitative patient interviews suggested that blind spots and floaters were prevalent and bothersome and that each should be represented in our questionnaire. In a preliminary version, an item about "blind spots or blurry spots" was intended to assess scotomata and an item about "spots floating in front of your eyes" was intended to assess vitreous cells.Questionnaire items are valid if they measure what they purport to measure in
Wu AW, Holbrook J, Jabs DA. Unperceived Visual Field Defects-Reply. Arch Ophthalmol. 1997;115(5):687. doi:10.1001/archopht.1997.01100150688034