Abstract
BackgroundDepression and anxiety are two common normal responses to a chronic disease such as glaucoma. This study analysed the measurement properties of the depression screening instrument - Patient Health Questionnaire-9 (PHQ-9) using Rasch analysis to determine if it can be used as a measure.MethodsIn this hospital-based cross-sectional study, the PHQ-9 was administered to primary glaucoma adults attending a glaucoma clinic of a tertiary eye care centre, South India. All patients underwent a comprehensive clinical evaluation. Patient demographics and sub-type of glaucoma were abstracted from the medical record. Rasch analysis was used to investigate the following properties of the PHQ-9: behaviour of the response categories, measurement precision (assessed using person separation reliability, PSR; minimum recommended value 0.80), unidimensionality (assessed using item fit [0.7–1.3] and principal components analysis of residuals), and targeting.Results198 patients (mean age ± standard deviation = 59.83±12.34 years; 67% male) were included. The native PHQ-9 did not fit the Rasch model. The response categories showed disordered thresholds which became ordered after category reorganization. Measurement precision was below acceptable limits (0.62) and targeting was sub-optimal (−1.27 logits). Four items misfit that were deleted iteratively following which a set of five items fit the Rasch model. However measurement precision failed to improve and targeting worsened further (−1.62 logits).ConclusionsThe PHQ-9, in its present form, provides suboptimal assessment of depression in patients with glaucoma in India. Therefore, there is a need to develop a new depression instrument for our glaucoma population. A superior strategy would be to use the item bank for depression but this will also need to be validated in glaucoma patients before deciding its utility.
Highlights
Glaucoma is the among the leading causes of irreversible blindness worldwide, second only to cataract as the most common cause of blindness overall, and disproportionately affects women and Asians [1,2]
Providing glaucoma patients with appropriate interventions for their depressive symptoms is essential to improving their quality of life (QoL) and compliance with treatment
The Patient Health Questionnaire-9 ( PHQ-9) was administered along with a package of other questionnaires used to assess the impact of glaucoma on visual functioning to 198 patients by trained interviewers on the day of their appointment
Summary
Glaucoma is the among the leading causes of irreversible blindness worldwide, second only to cataract as the most common cause of blindness overall, and disproportionately affects women and Asians [1,2]. Depression and anxiety have been reported as two common normal responses to a chronic disease such as glaucoma [3,4,5,6,7,8], and the patient’s mental health may result in lower treatment adherence and persistence with treatment, which in turn puts him/her at an even greater risk for complications, including impending visual loss [9,10]. Factors such as progressive visual field (VF) loss, visual impairment, the need for multiple medical treatments, and surgery may all contribute to depression in glaucoma. This study analysed the measurement properties of the depression screening instrument - Patient Health Questionnaire-9 (PHQ-9) using Rasch analysis to determine if it can be used as a measure
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