The impact of cataract surgery questionnaire: re-evaluation using Rasch analysis

Area of Science:

• Ophthalmology
• Psychometrics
• Health Outcomes Research

Background:

• The Impact of Cataract Surgery (ICS) questionnaire was developed to evaluate outcomes post-cataract surgery.
• Assessing the psychometric properties of patient-reported outcome measures is crucial for their validity and reliability.
• The Rasch model provides a robust framework for evaluating measurement properties of questionnaires.

Purpose of the Study:

• To evaluate the psychometric performance of the Impact of Cataract Surgery (ICS) questionnaire.
• To assess the suitability of the ICS questionnaire for visual disability assessment in a cataract population using Rasch analysis.
• To determine if the ICS questionnaire exhibits unidimensionality and adequate person separation.

Main Methods:

• Ninety-one patients awaiting cataract surgery completed the four-item ICS questionnaire.
• Rasch analysis was employed to assess response category function, person separation, unidimensionality, and targeting.
• Key psychometric indicators included person separation (minimum acceptable 2.0) and item fit statistics.

Main Results:

• The ICS questionnaire demonstrated inadequate person separation (zero), failing a basic requirement for measurement.
• Response categories required collapsing for one item, and one item showed misfit, indicating it did not measure the same construct.
• Despite item misfit, deleting the item did not improve person separation. Targeting was acceptable (-0.46 logits).

Conclusions:

• The ICS questionnaire, in its current form, is unsuitable for assessing visual disability in patients awaiting cataract surgery.
• The study highlights significant psychometric limitations of the ICS questionnaire.
• Alternative, more validated visual function questionnaires are recommended for this patient population.