Background: Primary open-angle glaucoma (POAG) is one of the most common causes of irreversible blindness. A possible association between POAG and non-communicable diseases such as hypertension and diabetes suggests that the incidence of POAG may increase. People with POAG in Nepal usually present late to hospital and have poor knowledge of glaucoma. Objectives: Anticipating a knowledge gap regarding these diseases, this study aimed to explore the knowledge of POAG, hypertension, and diabetes in the community and barriers to health care. Design: We conducted this qualitative study in the Jhaukhel-Duwakot Health Demographic Surveillance Site (JD-HDSS), a peri-urban community near Kathmandu, a capital city of Nepal. To study how disease influences knowledge, we conducted focus group discussions separately for men and women with and without pre-existing POAG, hypertension, and diabetes. Data were analyzed using the framework analysis approach. Results: Although people suffering from POAG, hypertension, and/or diabetes exhibited adequate knowledge of hypertension and diabetes, they lacked in-depth knowledge of POAG. People believed mostly in internal health locus of control. Perception of disease consequences and impact of disease on daily life was influenced by pre-existing POAG, hypertension, and/or diabetes but only in men. Gender disparity was observed regarding health literacy, health perception, and health barriers, which put women in a more difficult situation to tackle their health. We also revealed a gap between knowledge, attitude, and practice of health among women and healthy men. Conclusion: Although people in JD-HDSS exhibited adequate knowledge regarding hypertension and diabetes, they lacked in-depth knowledge about POAG. This study demonstrated gender difference in health literacy and access to health care, making women more vulnerable towards disease. We also demonstrated a gap between knowledge, attitude, and practice of health. However, tailored health literacy programs may bring changes in the health status in the community.