Two hundred and one participants enrolled in this cross-sectional study were individuals undergoing routine ophthalmological examinations, all of whom had received a diagnosis of primary open-angle glaucoma from their attending ophthalmologist. Ethical approval for this study was obtained by the Ethics Committee at the University of Zagreb Faculty of Croatian Studies (reference number: 053-01/23-2/0001), ensuring that the research complied with all relevant ethical standards and guidelines. These participants were recruited during their visits to the ophthalmology clinic and were invited to participate in the research study. Prior to their involvement, each participant signed informed consent, indicating their understanding of the study’s purpose, procedures, and their voluntary participation.

Upon obtaining informed consent, participants were guided through the study protocol by trained research personnel. The procedure involved the completion of a comprehensive battery of questionnaires, designed to assess various psychosocial and demographic factors pertinent to the experience of glaucoma.

The battery of questionnaires administered to participants included:

Glaucoma Quality of Life Questionnaire (GQL-15) (25): The GQL-15 is a validated instrument tailored to assess the impact of glaucoma on various aspects of an individual’s QOL, covering domains such as vision-related function, mobility, and emotional well-being. The GLQ-15 consists of 15 items. Each question has scores ranging from 0 to 5, where 0 is difficulty to perform the task due to non-visual problems, 1 is no difficulty, and 5 is severe difficulty. The highest score is 75 and the lowest is 15, where higher scores indicate more difficulties with vision-related activities and are associated with lower quality of life as well. The Cronbach alpha for the current study indicates good reliability of the GQL-15 (α = 0.986).

Generalized Anxiety Disorder-7 Scale (GAD-7) (26): The GAD-7 is a widely used self-report measure consisting of 7 items designed to assess the severity of anxiety symptoms experienced by individuals over the past 2 weeks, providing valuable insights into the prevalence and intensity of anxiety. Each item has scores ranging from 0 to 3, where 0 is not at all, 1 is several days, and 3 is nearly every day. The GAD-7 total score ranges from 0 to 21. The Cronbach alpha for the current study indicates satisfactory reliability of the GAD-7 (α = 0.95).

Patient Health Questionnaire-9 (PHQ-9) (27): The PHQ-9 is a reliable and validated tool for evaluating the severity of depressive symptoms. It consists of 9 items exploring the frequency and intensity of depressive symptoms experienced by participants. Each item explores presentation of certain experiences over the course of the last 2 weeks with scores ranging from 0 to 3, where 0 is not at all, 1 is several days, and 3 is nearly every day. The PHQ-9 total score ranges from 0 to 27. The Cronbach alpha for the current study indicates satisfactory reliability of the PHQ-9 (α = 0.968).

Sociodemographic Questionnaire: A structured questionnaire was administered to collect sociodemographic information from participants, including age, gender, educational background, employment status, medical information (duration of diagnosis, visual acuity, comorbidities) and other relevant demographic variables. This information allows for the characterization of the study sample and facilitates the exploration of potential associations between sociodemographic factors and the psychosocial variables under investigation.

The administration of these questionnaires was conducted in a standardized manner, ensuring consistency and reliability across participants. Participants were encouraged to provide accurate and honest responses to each item, with the assurance of confidentiality and anonymity maintained throughout the data collection process.

Data was analyzed with IBM SPSS Statistics program (version 26). Before conducting statistical analysis, the normality of the continuous variables was tested. The results of the Shapiro–Wilk test indicated deviations from the normality for all continuous variables. However, it should be noted that all the distributions prove to be symmetrical, except the distribution of quality of life. Descriptive analyses were conducted to compute means, and standard deviation of continuous variables, as well as the median and interquartile range for the variable of quality of life. Additionally, we examined proportions of categorical variables.

In order to examine the differences in observed variables (anxiety, depression, and quality of life) regarding gender and comorbidity, an independent sample t-test were performed.

To determine the associations between glaucoma related quality of life, measures of psychological distress (anxiety and depression), and certain aspects of participants’ health, the values of the Pearson correlation coefficient were observed. Significance was set at p < 0.05.

Mediation analyses were performed to assess whether years of living with glaucoma were significant mediator of the relationship between depression and quality of life, as well as anxiety and quality of life. PROCESS module in SPSS [version 4.0., Model 4, Hayes (28)] was used to conduct the above-mentioned analysis. Significance of the indirect effect was tested with bootstrap method, where confidence interval (CI) was set at 95% and based on 5,000 bootstrap samples. The indirect effect is considered statistically significant if the 95% CI does not contain a value of 0.

This study included 201 patients with glaucoma, of which 125 (62.2%), were women, and 76 (37.8%) were men. Participants were between the ages of 42 and 94, with the average age of 70 years (M = 70.4; SD = 11.52). Most of them marked high school as the highest level of education (42.8%), are retired (64.2%), married (56.7%) and have children (82.6%). On average, our participants live more than 13 years with a diagnosis of glaucoma (M = 13.38; SD = 7.73). Regarding visual acuity, most of them have normal sight on one of the eyes based on the International Classification of Diseases 11 (ICD-11) classification for distance vision impairment (29). Sample characteristics are presented in Table 1.

The mean total score on the GQL-15 was 34.86 (SD = 18.25) indicating somewhat good quality of life of our glaucoma patients. Considering that the quality of life has a positively skewed distribution, it is necessary to consider the values of the median, which is 28 (interquartile range- iqr = 30), and deviates from the previously mentioned mean values. The mean score for depression on PHQ-9 was 13.42 (SD = 7.37), while the mean GAD-7 score was 10.64 (SD = 5.38). Using a cut-off score of ≥ 8 (30, 31), more than two thirds of the sample (68.3%) would be categorized as depressed, and approximately 63% (63.8%) would be considered anxious (30, 31).

The results of t-test (Table 2) indicated a statistically significant difference in quality of life, depression and anxiety regarding comorbidity, but not gender. Glaucoma patients with additional health problems reported greater difficulties in performing daily activities (GQL-15), and higher levels of anxiety and depression. Due to the positively skewed distribution of the quality of life, a Mann Whitney U test was performed (U = 7,143, z = 5.31, p < 0.001) which confirmed a significant difference in quality of life with respect to the comorbidity. In addition, measures of psychological distress (anxiety and depression) and quality of life differed significantly based on comorbidity, even after controlling for age. There were no statistically significant gender differences in observed variables, i.e., the GQL-15 scores, PHQ-9 scores and GAD-7 scores were similar for both groups. Additionally, observed variables did not differ significantly in regard to gender, after controlling for the age of participants.

To determine the association between certain aspects of participants’ health (visual acuity, duration of diagnosis), and quality of life, anxiety and depression, Pearson’s correlation analysis was conducted. Quality of life was significantly negatively associated with observed clinical characteristics. Visual acuity in both eyes was significantly negatively associated with GQL-15 (Pearson’s correlation coefficient of the right eye- r_R = −0.74, corresponding p-value of the right eye- p_R < 0.001; Pearson’s correlation coefficient of the left eye r_L = −0.78, corresponding p-value of the left eye- p_L < 0.001), indicating that glaucoma patients with lower visual acuity tend to experience greater difficulties in performing daily activities. Furthermore, visual acuity exhibited significant negative correlation with depression (r_R = −0.59, p_R < 0.001; r_L = −0.75, p_L < 0.001) and anxiety (r_R = −0.6, p_R < 0.001; r_L = −0.71, p_L < 0.001). Duration of glaucoma diagnosis was moderately and positively associated with GQL-15 (r = 0.56, p < 0.001), PHQ-9 (r = 0.5, p < 0.001), and GAD-7 (r = 0.48, p < 0.001), implying that longer coexistence with glaucoma is linked to greater perception of difficulties in everyday functioning and higher levels of depression and anxiety. Additionally, decrease in performance-related quality of life (GQL-15) was significantly positively correlated with depression (r = 0.83, p < 0.001) and anxiety (r = 0.8, p < 0.001).

To assess the possible mediating role of duration of diagnosis in the relationship between anxiety and quality of life, as well as depression and quality of life, simple mediation analyses were performed. Regarding the first mediation model (Figure 1), the path coefficients from depression to duration of diagnosis (b = 0.53, p < 0.001; 95% CI [0.402, 0.655]), and from depression to quality of life (path c) were significant (b = 2.06, p < 0.001, 95% CI [1.866, 2.251]). As shown in Table 3, duration of the diagnosis made a significant contribution to quality of life (b = 0.45, p < 0.001). Considering the bootstrap 95% confidence interval, the significant indirect effect from depression to quality of life through duration of diagnosis was confirmed (b = 0.24, 95% CI [0.112, 0.401]). Finally, the direct effect of depression on quality of life remained significant, but the effect value was somewhat lower (b = 1.82, p < 0.001).

Regarding the second mediation model (Table 3; Figure 2), anxiety made significant contribution to duration of the diagnosis (b = 0.69, p < 0.001, 95% CI [0.515, 0.866]), and to quality of life (path c, b = 2.72, p < 0.001, 95% CI [2.44, 3.01]). Duration of diagnosis positively predicted vision related quality of life (b = 0.54, p < 0.001). Moreover, the indirect effect of anxiety on quality of life through duration of diagnosis (b = 0.37, p < 0.001) was also significant. After accounting for duration of diagnosis as mediator, the direct effect of anxiety on quality of life remained significant (b = 2.35, p < 0.001), indicating that years living with diagnosis partially mediates the relationship between level of anxiety and vision related quality of life in glaucoma patients.

There are certain limitations related to this study. Due to the cross-sectional design, our findings have to be carefully interpreted. In order to have more generable conclusions, it would be beneficial to run longitudinal study looking at how these variables may change over time, and whether that change is related to the interplay between observed variables, or some other factors. One of the potential limitations is definitely gender ratio of our sample, and that majority of participants were older. Future research should make sure that sample is fair representative of the population in terms of gender and age. Finally, differences between various glaucoma types were not observed. Rather, we were interested if one has diagnosis of glaucoma or not. In order to see if different glaucoma types differ in the relationship with observed variables, future studies should incorporate this in the study design.