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Development of a Keratoconus-Specific Questionnaire Using Rasch Analysis
Jyoti Khadka1, Paul G Schoneveld, Konrad Pesudovs
1*PhD †MSc ‡PhD, FAAO Discipline of Optometry and Vision Science, Flinders University of South Australia, Adelaide, South Australia, Australia (all authors).
Summary
A new 29-item questionnaire, the Keratoconus Outcomes Research Questionnaire (KORQ), effectively measures quality of life for keratoconus patients, assessing activity limitations and symptoms.
Area of Science:
- Ophthalmology
- Patient-Reported Outcomes
- Psychometrics
Background:
- Keratoconus significantly impacts patients' quality of life.
- Existing measures may not adequately capture the specific QoL aspects related to keratoconus.
- Development of a validated, disease-specific questionnaire is needed.
Purpose of the Study:
- To develop and validate the Keratoconus Outcomes Research Questionnaire (KORQ).
- To create a reliable and valid instrument for assessing keratoconus impact on QoL.
Main Methods:
- Multi-phase study: literature review, patient surveys, expert consultation, pilot testing with Rasch analysis, and psychometric validation.
- Iterative item reduction and scale refinement based on Rasch analysis.
- Final validation involved 169 keratoconus patients using a 4-option rating scale.
Main Results:
- Initial 44-item questionnaire refined to a 29-item KORQ (18 activity limitation, 11 symptoms).
- Convenience subscale was discarded due to inadequate measurement precision.
- The final KORQ demonstrated good psychometric properties and strong correlation with visual acuity and contrast sensitivity.
Conclusions:
- The 29-item KORQ is a psychometrically sound and valid tool.
- It reliably assesses activity limitations and symptoms in keratoconus patients.
- KORQ provides valuable insights into the functional impact of keratoconus.
