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National Eye Institute Visual Function Questionnaire or Indian Vision Function Questionnaire for visually impaired: a
Vijaya K Gothwal1, Shailaja P Reddy, Rebecca Sumalini
1Meera and L B Deshpande Centre for Sight Enhancement, Vision Rehabilitation Centres, L V Prasad Eye Institute, Hyderabad, India. vijayagothwal@gmail.com
Investigative Ophthalmology & Visual Science
|June 16, 2012
Summary
The long form visual functioning scale (LFVFS(39)) and the visual functioning scale (VFS) of the Indian vision function questionnaire (IND-VFQ) both accurately measure visual functioning in visually impaired Indian adults. These instruments can be calibrated together for comparable results.
Area of Science:
- Ophthalmology
- Psychometrics
- Public Health
Background:
- Visual functioning (VF) assessment is crucial for visually impaired (VI) individuals.
- The NEI-VFQ(39) and IND-VFQ are established questionnaires for measuring VF.
- Rasch scaling provides a robust method for analyzing psychometric data.
Purpose of the Study:
- To evaluate if the 15-item LFVFS(39) and 13-item VFS from the IND-VFQ meet Rasch model assumptions.
- To determine if both instruments measure the same construct (VF) in an Indian VI population.
- To assess the cocalibration potential of these two VF measures.
Main Methods:
- 120 visually impaired adults completed both the LFVFS(39) and IND-VFQ concurrently.
- Data were analyzed using the Rasch measurement model to assess unidimensionality and item fit.
- Principal components analysis was used to confirm unidimensionality.
Main Results:
- Both LFVFS(39) and IND-VFQ's VFS required category reorganization for optimal functioning.
- Both instruments demonstrated high measurement precision (person separation = 2.76).
- Separate and pooled analyses confirmed adherence to Rasch model assumptions, including unidimensionality, with all items fitting.
Conclusions:
- The LFVFS(39) and VFS of the IND-VFQ are valid measures of visual functioning in the Indian VI population.
- Both instruments exhibit equal measurement precision and can be calibrated onto a single metric.
- This allows for direct comparison of their measurement ranges and facilitates cross-instrument analysis.
