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Editors Selection IGR 9-4

Quality of life: Validity of questionnaires

Comment by John Walt on:

19353 Are standard instruments valid for the assessment of quality of life and symptoms in glaucoma?, Lamoureux EL; Ferraro JG; Pallant JF et al., Optometry and Vision Science, 2007; 84: 789-796

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Lamoureux et al. (826) report on a well designed and methodological study, to test the hypothesis if two older QoL instruments (the GSS and IVI) are currently valid instruments to assess patient reported outcomes of daily living and symptoms, in a glaucoma population. However, the authors' conclusion that there may be a need to develop a glaucoma-specific instrument to assess Quality of Life in this population would have actually been found with a more detailed current literature search. Patricia Nelson and colleagues published the Glaucoma Quality of Life fifteen item instrument (GQL-15) in a paper called Quality of Life in Glaucoma and its Relationship with Visual Function (Journal of Glaucoma 2003; 12: 139-150). Nelson and team realized in their pilot study published in 1999 that further research was needed on the subject of quality of life and glaucoma. The short-comings of previous instrument used to measure QoL in glaucoma were greatly improved with the GQL-15's sensitivity to listening to patient reported outcomes in their methodological development. Examining the face validity of the items in the GSS one could speculate nearly half the items are measuring side-effects of older treatments more than patient reported symptoms of actual disease progression. The author's methods of using a Rasch analysis of the item responses from actual glaucoma patients is strong. However, their findings of "both scales displayed ineffective person-item targeting as a large number of participants demonstrated little difficulty with the most difficult items" is most likely due to the items in the two instrument they tested rather than the disease. The next logical step in building the knowledge base in this interesting growing area of research in glaucoma would be to replicate the current presented test methodology with the GQL-15 glaucoma instrument, rather than develop another disease specific glaucoma instrument as the authors suggest in their conclusion.

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