Objective To determine whether patients attending the ophthalmology department underestimate their glaucoma risks. Method We conducted a cross-sectional survey with a final study population of 1203 individuals from two medical centers in Taiwan during January 1-June 30, 2019. The "High concern"group was defined as the set of patients who rated themselves as having low risk but who had been rated by physicians as having medium or high risk of developing glaucoma over the next year. Results Approximately 12% of the respondents belonged to the "High concern"group. For those with education at the college level or higher, the interaction term was estimated to be 0.294 (95% CI = 0.136-0.634). Marginal effect calculations revealed significant sex-based differences in the effect of knowledge at specific age intervals. Conclusions A considerable proportion of patients attending the ophthalmology department underestimate their glaucoma risks. Misjudgment of glaucoma risks can lead to delays in seeking of medical attention. Glaucoma education should be designed according to each patient's education level and sex, as its effect is not consistent across different education and sex clusters.