Development of an instrument to measure glaucoma medication self-efficacy and outcome expectations

The purpose of this study was to develop and evaluate the psychometric properties of (a) a glaucoma medication self-efficacy scale and (b) a glaucoma outcome expectations scale.

Two instruments were developed: a glaucoma medication self-efficacy scale and a glaucoma outcome expectations scale. Packets containing (a) the instruments and patient demographic questions and (b) a letter explaining the study were distributed to 225 glaucoma patients from three ophthalmology practices between August and December 2007. The instrument was completed by 191 patients for a response rate of 85%. Principal components factor analysis with a varimax rotation and Cronbach's alpha reliability were used to analyse the data. To assess discriminant validity, we administered the scales and two self-reported measures of adherence in a separate sample of 43 glaucoma patients who were currently using at least one glaucoma medication.

Our results yielded a 21-item self-efficacy in overcoming barriers that might interfere with the use of glaucoma medications scale, a 14-item self-efficacy in carrying out specific tasks required to use eye drops correctly scale, and a four-item glaucoma outcome expectations scale. Results of the Cronbach's alpha reliability indicated that the scales are internally consistent. The self-efficacy scales were both significantly associated with two patient self-reported measures of glaucoma medication adherence, which show discriminant validity.

Eye care providers and researchers can use these scales to identify patients with low self-efficacy in using their glaucoma medications and patients who do not believe that following their eye care providers' advice can help their vision.