Patients and sample size

This cross-sectional study was conducted from August to November 2016. One hundred ninety eligible patients with glaucoma, who were being routinely followed at the Glaucoma Clinic of the Ophthalmology Department at Shiraz University of Medical Sciences, Iran, were enrolled. Sample size was calculated based on empirical rules widely used by experts in this field and on earlier methods which have been mentioned in the literature.19, 20 Based on a rule of thumb (10-fold number of questionnaire items), a minimum sample of 150 subjects was required. To achieve the required sample size we used a convenience sampling method.

The eligibility criteria were ability to speak and understand Persian, an age older than 18 years, and being followed more than 6 months in the glaucoma clinic prior to enrollment. All patients were re-evaluated again on the day of the study by a glaucoma specialist for confirmation of the diagnosis and staging the glaucoma severity. Patients with primary open-angle glaucoma (POAG), primary angle-closure glaucoma (PACG), and secondary glaucoma were included.

The exclusion criteria were severe psychiatric problems, cognitive impairments (Dementia and Alzheimer), and other eye diseases with vision impairment secondary to other causes (cataract, corneal opacities, and age-related macular degeneration).

The study protocol complied with the tenets of the Declaration of Helsinki, and was approved by the local Ethics Committee at Shiraz University of Medical Sciences. Written informed consent was obtained from all eligible patients after they were informed about the study objectives.