The world's ageing population is leading to rising healthcare costs. In response, many parties have developed wearable health monitoring systems for ubiquitous elderly care. Before each monitoring session, the user may need to spend considerable effort in setting up and attaching sensors at specific locations on the body, and intervention may be required during use. Some users, especially the elderly, may find these procedures difficult and intimidating. This impedes the widespread deployment of such monitoring services in the community. Noting the above drawback, there is continual search for alternative biosignals which can be easily accessed. Recent studies suggest that there is a rich amount of information embedded in ocular behaviours, which can be monitored in a non-invasive and unobtrusive fashion. Among these is pupil size variability (PSV), which refers to the continuous fluctuation of pupil size without visual accommodation or light stimulation. It was found that PSV contains signals that correlate with respiratory rhythm and cardiovascular variabilities, from which useful indicators of cardiovascular diseases can be extracted. As an effort in understanding PSV and its potential use in mobile health, the current work comprises three parts: experiments, modelling, and design of an eye-based mobile health system. Findings suggest that PSV is of prognostic value. With appropriate calibration techniques, PSV can be monitored with wearable technologies in order to provide an alternative approach for ubiquitous monitoring of cardiovascular conditions.