Konrad Pesudovs is Foundation Professor and Chair of Discipline of Optometry and Vision Science at Flinders University. His main research interest is ophthalmology outcomes research; incorporating optical, visual and patient-centred measurement into the holistic measurement of outcomes in ophthalmology.
(Spanish Council of Optometry, 2009) Gothwal, Vijaya; Wright, Thomas; Lamoureux, Ecosse L; Pesudovs, Konrad
Purpose: The Adaptation to Age-related Vision Loss (AVL) scale was
developed to measure the adjustment of older adults who are adapting
to late-life vision loss. The purpose of this study was to assess whether
the AVL scale satisfies the Rasch model in a cataract population.
Methods: The 24-item AVL scale (18 negatively and 6 positively
coded) was mailed to 436 cataract patients for self-administration
whilst they were on the waiting list for cataract surgery at the
Flinders Eye Centre, Adelaide, South Australia. Rasch analysis was
performed to determine whether the items were measuring a single
construct (unidimensionality) as examined with fit statistics and
principal components analysis (PCA) of the residuals. The ability
of the scale to distinguish between the levels of adaptation of the
participants (person separation) was investigated, with a value ≥ 2.0
established as the minimum acceptable.
Results: The AVL scale was unable to differentiate sufficiently between
participants’ levels of adaptation, indicating poor person separation.
One item did not fit the construct, causing misfit. Furthermore,
the five positively worded items did not appear either to measure the
same construct as other items, resulting in lack of unidimensionality
evidenced by PCA. Following the deletion of these items, the AVL
scale was one-dimensional but a single item continued to misfit, so
it had to be deleted, resulting in an 18-item AVL scale. Even so, the
discriminating abilities of the scale continued to be poor.
Conclusions: The AVL scale is not an appropriate measure of
adaptation to vision loss in a cataract population.