Development of Item Banks to Measure Refractive Error-specific Quality-of-Life Parameters

Author: Himal Kandel

Kandel, Himal, 2018 Development of Item Banks to Measure Refractive Error-specific Quality-of-Life Parameters, Flinders University, College of Nursing and Health Sciences

Terms of Use: This electronic version is (or will be) made publicly available by Flinders University in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. You may use this material for uses permitted under the Copyright Act 1968. If you are the owner of any included third party copyright material and/or you believe that any material has been made available without permission of the copyright owner please contact with the details.


Refractive error is the most common cause of visual impairment. It can be corrected with spectacles, contact lenses or surgery. Refractive error itself or its correction may have quality-of-life (QoL) implications. Impact of refractive error on QoL can be explored using qualitative studies, and measured quantitatively using patient-reported outcome (PRO) instruments. The overarching aim of this doctoral study was to develop a technologically advanced PRO instrument, in the form of item-banking to be administered through computer adaptive testing (CAT) system, to measure QoL parameters in refractive error.

Through a systematic review of literature, I found that there was no published qualitative study exploring QoL in adults with refractive error. Similarly, a need for a comprehensive and scientifically robust refractive error-specific PRO instrument was identified. The existing PRO instruments in refractive error were paper-based questionnaires. They were limited in content and psychometric properties. None of them provided a comprehensive measurement of QoL in all refractive error sub-groups. The ‘Quality of Life Impact of Refractive Correction’, the ‘Quality of Vision’ and the ‘Contact Lens Impact on Quality of life’ had comparatively better psychometric quality with some limitations compared to the other PRO instruments. The superior quality PRO instruments were developed using Rasch analysis, a modern psychometric method.

I conducted two qualitative studies to explore the impact of refractive error on QoL in adults. In Australia, 48 semi-structured in-depth interviews were conducted. Thematic analysis resulted in six themes including concerns about refractive error and its implications, inconvenience rendered in daily life and difficulties in day-to-day activities. The second study was conducted in Nepal using similar methodology to explore impact of refractive error on QoL from a low- and middle-income country perspective. A total of 101 participants were interviewed including 47 participants with uncorrected refractive error. During thematic analysis, seven major themes emerged: Activity limitation, Inconvenience, Health concerns, Psycho-social impact, Economic impact, General- and ocular-comfort symptoms, and Visual symptoms. From both studies, multidimensional impact of refractive error on people’s QoL was identified.

Content (QoL domains and items) of the refractive error-specific item banks were identified from literature (existing questionnaire and grey literature) and the qualitative studies. The content identification and refinement process consisted of systematic criteria for binning, winnowing, expert panel review and cognitive testing. This iterative process resulted into item-pool (Australia) with 443 items and item-pool (Nepal) with 392 items.

The Item-pool (Nepal) was interviewer-administered to 305 participants with refractive error. Psychometric properties of the item-pools were assessed, and optimized when required, using Rasch analysis. Rasch iterations resulted into 13 refractive error-specific item banks with 366 items. On CAT simulation, the mean number of items required for achieving high and moderate precision were 9.67 and 4.97 respectively. The final item banks were used to evaluate quality-of-life parameters across refractive error sub-groups. The item banks demonstrated good known-group validity by differentiating various sub-groups of refractive error. Overall, the findings provided promising evidence on the applicability of the refractive error-specific item banks to comprehensively and accurately evaluate quality-of-life parameters.

Keywords: Item bank, Quality of life, Refractive error, Rasch analysis, Qualitative, Patient-reported outcome

Subject: Ophthalmology thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Nursing and Health Sciences
Supervisor: Dr Paul Constable