Development of an 18-Item Measure of Symptom Burden in Patients With Glaucoma From the Collaborative Initial Glaucoma Treatment Study’s Symptom and Health Problem Checklist

Abstract

Administration of a brief questionnaire to evaluate glaucoma symptoms would lend useful information for patient care. To develop a shortened glaucoma symptom measure based on the Collaborative Initial Glaucoma Treatment Study (CIGTS) Symptom and Health Problem Checklist (SHPC) and evaluate its psychometric properties. This measure development study evaluated the factor structure of the 43-item SHPC that was obtained from CIGTS participants at baseline and every 6 months thereafter. These 607 participants were enrolled at 14 clinical centers in the United States and had newly diagnosed open-angle glaucoma. Their mean deviation (SD) from visual field testing was −5.5 (4.3) dB. Data were collected from October 1993 through April 1997. The factor structure of the SHPC, confirmatory factor analysis of the resulting 18-item questionnaire (SHPC-18), the reliability of the SHPC-18, and associations of the 2 symptom subscales (Local Eye and Visual Function) of the SHPC-18 with visual field severity and 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ25) subscales. Among the 607 participants (mean [SD] age at enrollment, 57.5 [10.9] years), 334 (55.0%) were men and 273 (45.0%) were women; 231 (38.1%) were African American. Exploratory factor analysis and longitudinal growth modeling documented Local Eye and Visual Function symptom subscales. Cronbach α values for mean weighted internal consistency were 0.83 and 0.89 for the Local Eye and Visual Function subscales, respectively, and remained stable over time. Scores on each subscale significantly correlated with the NEI-VFQ25 total score (r = −0.41 and r = −0.59, respectively) and with all subscale scores (P < .01). Participants with more severe glaucoma had higher (worse) mean (SD) scores than those with mild glaucoma at baseline on the Local Eye (4.68 [6.62] vs 3.07 [5.60]) and Visual Function (8.44 [11.45] vs 4.42 [8.94]; P < .05) SHPC-18 subscales. Participants who underwent trabeculectomy reported a higher frequency of any Local Eye symptoms than those treated with topical medications (eg, at 12 months, 153 of 269 [56.9%] vs 11 of 276 [40.9%]; P < .001). These results suggest that the SHPC-18 is a reliable, responsive, and psychometrically sound measure of patient-reported, glaucoma-related symptoms. The measure is responsive to treatment and discriminates the severity of glaucoma. This shorter version of the original SHPC measure may be useful in clinical and research settings to better understand the influence of glaucoma symptoms on patients’ daily life.