This was the first study to investigate the relationship between illness perceptions and VRQoL in a Chinese glaucoma population. The hierarchical linear regression model explained up to 70.1% of the variance in VRQoL, and the clinical variables accounted for the greatest variance in the model. Chronic comorbidities, type of glaucoma, BCVA and MD in the better eye, and identity (symptoms) of illness perceptions are the critical predictors of VRQoL. These findings suggest that primary glaucoma patients without chronic disease have better BCVA and fewer VF defects in their better eye, while those who perceive fewer symptoms attributable to glaucoma are likely to experience higher VRQoL.
Our study highlights the specific contributions of illness perceptions to glaucoma patients' VRQoL after controlling for demographic and clinical variables. Illness perception has been considered an important psychological factor affecting adherence and QoL in patients with some chronic diseases, such as cancer, chronic kidney disease, diabetes, cardiovascular disease and chronic obstructive pulmonary disease (COPD). Specifically, previous studies have reported that higher identity was a strong predictor of outcomes, predicting lower QoL in coronary heart disease (CHD) patients, which is consistent with our findings. However, existing studies in the field of glaucoma have tended to analyse the relationship between illness perceptions and adherence or between adherence and QoL; thus, their results only briefly mention a univariate association between illness perceptions and QoL without further exploration[32–34]. Given that these studies have suggested that identity has a significant impact on medication adherence and that glaucoma patients with better adherence tend to report a better perceived QoL, combined with the results of this study, we speculate that interventions targeted at identity may improve QoL. A randomized controlled trial (RCT) revealed a reduction in identity scores, corresponding to significantly fewer complaints of symptoms in the cognitive behavioural therapy (CBT) intervention group. Another RCT that used psychological family-based interventions for patients with type 2 diabetes also reported statistically significant improvements in health outcomes, including glycaemic control (a decrease in glycated haemoglobin) and diabetes identity (a reduction in perceived symptom burdens). These examples imply that identity, as one of the core cognitive dimensions in CSM, is modifiable through psychological interventions such as CBT. Therefore, subsequent studies could try to examine whether cognitive interventions are equally effective in glaucoma patients.
The total BIPQ score in our sample population was higher than that among patients with diabetes and COPD[38–40]. Glaucoma patients are more likely to perceive the threat of illness, possibly because the impairment of visual function caused by disease progression can severely affect the patient's mobility and cause them to lose independence. In contrast, we obtained higher scores in our sample than in patients with glaucoma in Turkey, the United States and Australia in terms of BIPQ consequence, identity, concern and emotions. On the other hand, the scores of BIPQ timeline and treatment control were lower, and although the score for illness coherence was similar to those described in Turkish and Singaporean (of Chinese descent) patients[43, 44], it was still lower than those in American and Australian patients. On the one hand, this difference might partly be attributed to diverse cultural backgrounds and inclusion criteria. On the other hand, the low timeline and illness coherence scores also indicate that most Chinese patients are not conscious of the chronic and permanent characteristics of glaucoma and that they do not know much about the illness, making it difficult for them to understand the nature of the medical condition. In contrast to other chronic diseases, such as diabetes and hypertension, there is a low public awareness of glaucoma. In addition, our sample mainly comprised elderly individuals with a primary educational level, whose capability and channels to receive reliable information about glaucoma are limited. The insufficient knowledge of this disease resulting from the above reasons can go hand in hand with the lack of awareness of its symptoms and consequences, further causing psychological changes, including an increase in uncertainty and concerns about the disease, as well as negative emotions such as fear, anxiety and depression, thus leading to high scores of illness consequence, identity, concern and emotional representation in BIPQ. Therefore, it is necessary to provide disease information according to patients' needs and improve the effectiveness of health education in clinical practice. Perhaps helping patients correctly identify the characteristics of glaucoma could be an important starting point for interventions.
One of the important results of our study was that clinical parameters such as VA and VF could explain the most variance in VRQoL in the model. LogMAR BCVA and MD of the better eye were independent predictors of VRQoL. This finding suggests that the condition of the better eye was more important for glaucoma patients' VRQoL than that of the worse eye, which is in line with previous studies[6, 8, 45]. Epidemiological studies show that diagnosis and treatment are often delayed due to the relatively asymptomatic damage caused by glaucoma in the early stages, and the majority of patients do not realize they have glaucoma until their condition deteriorates to the point where their bilateral vision is severely impaired. Therefore, early identification and treatment are the key to maintaining VRQoL. Nevertheless, ophthalmic examinations, surgeries, medications, and other treatments aimed at reducing IOP are usually concentrated on the worse eye. The results of our study emphasize the importance of monitoring the visual function of the better eye as early as possible. Noticeably, chronic comorbidities and the type of glaucoma were identified as predictors affecting VRQoL in this sample. This finding indicates that patients with other chronic comorbidities and patients with secondary glaucoma have a poorer VRQoL. However, a study of Chinese glaucoma patients conducted by Zhou et al. concluded that VRQoL was associated with economic burden, VA, VF, number of glaucoma surgeries and depression and did not mention the two factors we identified. This difference could be explained by the varied types of grouping and the different proportions of patients in each group; in addition, chronic comorbidities were not taken into account in their study. Unlike primary glaucoma, which has a covert onset, most of the secondary glaucoma patients included in our study had a specific cause of elevated IOP, such as trauma, certain medications (e.g., corticosteroids) or other diseases (e.g., tumour). We speculate that in addition to the primary disease, patients' illness perceptions over time that are potentially amenable to dynamic change related to the complex treatment experience, along with the increase in BIPQ scores, have a direct or indirect impact on VRQoL[46, 47]. For that reason, more attention and support should be given to patients with chronic comorbidities and secondary glaucoma, as their VRQoL is anticipated to be worse.
As a cross-sectional study, this study inevitably has some limitations. We cannot confirm the specific causal relationships between predictors and outcomes. In addition, the study population was recruited from a single medical centre, and the sample size was relatively small, which limits our power and generalizability. Further longitudinal studies or RCTs are necessary. We also expect that future studies will include more potential psychological variables that might influence patients' behaviour and QoL to deeply explore the functional routes of each factor and provide more empirical evidence for clinical psychological cognitive interventions.