Primary open-angle glaucoma (POAG) is the leading cause of irreversible blindness worldwide (1). POAG is a progressive neuropathy in which the optic nerve is damaged by chronically elevated pressure inside the eye (2). There is no cure for POAG. Apart from the subset of POAG patients without elevated eye pressure (normal tension glaucoma) (3), the disease is primarily managed through hypotensive eye drops that reduce pressure-induced damage (4). While ocular hypotensive therapy has been shown to delay POAG progression (5), consistent use of eye drops is a challenge for many patients. Medication adherence, which describes the degree to which patients use their eye drops as prescribed, is profoundly affected by factors such as high treatment cost (6) and complex treatment regimens (7). Research also indicates that illness perceptions may affect medication adherence (8), highlighting their important role in POAG management.

Illness perceptions have been extensively studied in chronic diseases such as diabetes and hypertension (8–12). A meta-analysis across 188 studies exploring illness perceptions revealed that accurate perceptions about the cause of disease were associated with reduced risk of hospitalization while perceptions about inability to control the course of a disease were associated with depression (11, 13, 14). However, in POAG, neither perceived cause of disease nor its relationship with other illness perceptions have been fully explored. In this study, we aimed to assess the accuracy of patients’ perceived cause of POAG and to identify associations between accuracy of perceived cause of POAG, illness perceptions, medication adherence, and quality of life (QoL).

Out of 114 patients, 97 were included in this analysis (17 patients only reported causes such as “I do not know” and were excluded from the analysis). A total of 31 patients provided three responses to the 9th BIPQ question, compared to 24 patients who provided two responses and 42 patients who provided only one response. Mean ± SD age was 69.1 ± 8.2 years and mean medication adherence was 86.0% ± 17.8. Table 1 presents patients’ baseline characteristics. Approximately 61% were female and approximately 52% were White. Sixty-six percent of patients attained a college degree or higher and approximately 36% reported a household income of $60,000 or more. Mean BIPQ total score was 29.4 ± 11.2 [maximum = 80]. Higher BIPQ total scores indicate a more daunting outlook on POAG. Mean GQL-15 total score was 24.3 ± 9.6 [54]. Higher GQL-15 total scores indicate a lower quality of life due to POAG.

Using method 1, 84 patients (86.6%) reported an accurate cause of their POAG, compared to 76 patients (78.4%) using method 2 and 77 patients (79.4%) using method 3. Regardless of the method used, a larger proportion of patients reported an accurate vs. an inaccurate cause of their POAG (χ² statistics were 51.97, 31.19, and 33.49 for methods 1, 2, and 3, respectively; all p < 0.001). Using method 1, we found that patients who reported an accurate cause of their POAG were younger (68.4 ± 8.2 years vs. 73.8 ± 6.1, p = 0.01). There were no age differences across accuracy groups when methods 2 or 3 were used. No significant differences were identified for QoL or any of the demographic variables. Figure 2 presents a summary of the accurate (A) and inaccurate (B) causal attributions. Accurate attributions included genetics/hereditary (n = 72), old age (n = 17), and diabetes (n = 9). Inaccurate attributions included lifestyle (n = 13), medical impacts/side effects (n = 15), and Quality of care (n = 14).

Table 2 presents the BIPQ illness perception scores. There were no differences between accuracy groups using method 1. Method 2 revealed that patients who identified an accurate cause of their POAG had higher scores for the Timeline perception, which reflects patients’ perceptions about how long their illness will last (8.9 ± 2.4 vs. 7.9 ± 3.1, p = 0.045). Method 3 revealed higher scores for the Timeline perception (9.0 ± 2.4 vs. 7.8 ± 3.1, p = 0.028) and lower scores for the Coherence perception (1.5 ± 2.1 vs. 1.9 ± 1.3, p = 0.048) in patients who reported an accurate vs. an inaccurate cause of their POAG. The coherence perception measures patients’ perceived level of knowledge about their illness.

The majority of patients in this study reported an accurate cause of their POAG, such as “aging,” “genetics,” and “race.” This finding suggests that most patients may be well-informed about the cause of their disease, perhaps due to POAG-specific education provided by clinicians during clinic visits or sought out by patients themselves. The most common causal attribution was genetics/hereditary factors, which is encouraging as it may translate into more frequent eye examinations among persons with a family history of POAG and their relatives. However, as many as 20% of patients attributed their POAG to inaccurate causes such as “karma,” “eating habits” and “depression.” While not recognized as risk factors for POAG, responses such as “eating habits” may be references to vascular diseases, for example diabetes, which is associated with POAG (22–25). Other responses such as “karma” and “depression” speak to a less nuanced understanding of POAG.

In this study, the accuracy of patients’ perceived cause of POAG was determined based on clinical standards established by the American Academy of Ophthalmology (AAO). Therefore, we did not acknowledge the significance of other risk factors, including vitamin D3 levels (26–28), sleep apnea (29), exercise (30), and smoking (31). As a result, responses which may have alluded to these factors (“lifestyle” [n = 2], “diet” [n = 6], “injury” [n = 8], neglect of health [n = 11]) were coded as incorrect. This potential discrepancy highlights the complex nature of POAG and the need for continued research to fully elucidate the factors that play a role in POAG development and/or progression. Similarly, the connection between diabetes and POAG remains unclear, calling the accuracy of patients’ perceived link between them into question. Notwithstanding, diabetes is recognized as a potential risk factor for POAG by clinical bodies such as the AAO and the European Glaucoma Society (32). As such, providers may discuss diabetes with patients during clinic visits, leading to patients becoming more knowledgeable about the potential connection between the two conditions.

Our finding that patients who reported an accurate cause of their POAG were younger is intuitive, as older patients tend to have lower health literacy (33), and experience more literacy barriers such as declining vision and hearing (34). Therefore, interventions for improving health knowledge and health literacy in older patients with POAG may be beneficial as they are at greater risk for disease progression (35). We also found that patients who reported an accurate cause of their POAG believed that their disease would last longer compared to patients who reported an inaccurate cause. This finding is consistent with the lifelong nature of POAG (2) and suggests that patients who are informed about the cause of their disease may also be more informed about its other aspects. Clinicians may be able to successfully ascertain patients’ disease knowledge by assessing their causal attributions. Our analysis also revealed that patients who reported an accurate cause of their POAG had lower perceived knowledge about their disease compared to patients who reported an inaccurate cause. While this finding appears to be counterintuitive, it is possible that greater awareness of the cause of POAG reflects patients’ understanding of its complex nature, resulting in less confidence in their overall knowledge level. Overall, our findings suggest that disease causality may serve as a proxy for overall disease knowledge.

To the best of our knowledge, this is the first study in POAG to analyze patients’ perceived cause of POAG and its relationship to other clinical and behavioral variables. As such, this study is an important contribution to the limited data available on perceived disease causality and its relationship to illness perceptions in POAG. Another strength of this study is that electronic monitoring was used to measure medication adherence, which is believed to be the most objective method available (25). A final strength is that as there are no standardized methods for assessing accuracy of the perceived cause of disease, we developed three different methods, which helped to minimize bias. This study is not without limitations however, which include that the BIPQ was self-administered. Despite the presence of the study coordinator who carefully described the instructions, it is possible that some patients may not have fully comprehended them, particularly for the disease causality question. Another limitation is that we did not perform Bonferroni correction. However, our finding that a larger proportion of patients reported an accurate cause of their POAG is robust and would stand even after correcting for multiple comparisons. Other significant results would likely not remain significant, but we presented these findings without correction because this is an initial assessment of causal attribution in POAG, and the results may be useful in informing future research. A final potential limitation is that not all patients provided three responses to the causal question, perhaps indicating a rushed or superficial approach to completing the questionnaire, which may have biased our findings. It is possible however, that patients who only provided one response were certain that their POAG was caused by the one factor they reported.

Despite these limitations, this study highlighted the close association between perceived cause of POAG and other illness perceptions such as knowledge level and disease duration. We found that most patients identified an accurate cause of their POAG and that an accurate cause of POAG was associated with younger age, higher perceived duration of POAG, and lower perceived understanding of POAG. Future studies should aim to assess associations between perceived cause of disease and other critical dimensions of illness perception, and to determine how these may be associated with clinical outcomes other than medication adherence, such as disease severity and disease progression.

The de-identified data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Institutional Review Board at the University of Alabama at Birmingham. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

EC: Investigation, Methodology, Writing – original draft, Writing – review & editing, Formal analysis, Data curation. SP: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing. TT: Data curation, Investigation, Writing – review & editing. LR: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review & editing.