Functional crosstalk between the lung and eye: a new frontier in chronic lung diseases

Respiratory diseases are among the main causes of morbidity and mortality worldwide, encompassing a wide array of illnesses. Among these diseases, including acute lung injury, chronic obstructive pulmonary disease (COPD), asthma, pulmonary fibrosis, obstructive sleep apnoea (OSA), and pathogenic infections, the immune system plays a significant role in whole-body pathophysiology. These occurrences have been recognised to affect the ocular system, bringing about the novel idea of the lung-eye axis with emerging literature highlighting the fundamental connection of exacerbation between systems. Prior literature has recognised axial activity across systems, the gut and eye, where gut microbiota has an indicated correlation with the ocular environment. In addition, crosstalk has been hypothesized in a brain-lung axis via neurological anatomy, immune mechanisms and microbial pathways. Such cascades offer foundation for the lung-eye axis, supporting the potential for a correlative relationship between the ocular and respiratory system through anatomical, mucosal and inflammatory crosstalk. Although in its infancy, the interconnection between ocular and respiratory systems has been considered in the development of chronic diseases. Amid chronic diseases, COPD, OSA and glaucoma exhibit underlying mechanisms, incorporating hypoxia, oxidative stress and vascular dysfunction, postulating dual system pathophysiology. Finally, potential biomarkers are proposed following pathophysiological mechanism exploration, with an advocation for longitudinal studies in future. The current review proposes a novel axis in the field of lung diseases and aims to provide significant insights for respiratory and ocular clinicians, in addition to translational researchers, paving a new path for understanding systemic disease and treatment modality.