My personal research interest

Long-term research interest

Visual impairment, resulting from an ocular disorder, limits social participations and daily living activities of people with low vision: tasks such as reading, walking or driving, once accomplished with ease, can present significant challenges. For these people not only medical assistance to treat their eye diseases is required, but also rehabilitative assistance (which is much lacking) to address their vision loss and associated functional problems. More research in low vision rehabilitation and its application in clinical optometry are thus essential. Through this kind of research we can then set up cost-effective rehabilitation models. The ultimate goal of my career is to improve the visual function of people with visual impairment to a level that their normal activities are not affected.
Psychophysics of reading in normal and low vision

Reading is one of the activities most adversely affected for people with low vision due to central field loss. Yet reading is also one of the most valued activities in our society. Any ocular disorder, which deprives people of reading, creates severe vision disability.

People with low vision could successfully read small print using stand magnifiers of appropriate magnification, provided that sufficient office training was given. Supervised, short-term, in-office practice with the magnifier rather than the more extensive training that is often used in rehabilitation programs, was effective in improving magnifier reading performance.

Page navigation (moving the magnifier across each line of text) is an important aspect of learning to use a magnifier. My doctoral thesis included an investigation of the effects on navigation performance of attaching a line-guide to the base of a stand magnifier; however a study of changes in navigation performance across time was not carried out. It is hypothesized that navigation techniques when using a magnifier will be poor when the magnifier is first introduced; however, they will improve with practice. In future research, I would like to build on my initial studies of page navigation and manual tracking performance by conducting a clinical longitudinal study recording the navigation performance of naïve subjects in the learning period of magnifier use.

Despite the restoration of reading ability through the use of a magnifier, reading rate per se is apparently slower for visually impaired people than people with normal vision. This implies that there are other underlying factors, accounting for the slower reading rates, which have not been fully investigated. An important factor determining reading rate is the visual span, which is defined as the number and accuracy with which letters are recognized on each eye fixation in reading. Previous research studies have suggested that visual span imposes a significant limitation on the visual input to reading for people with low vision. There appears to be a fundamental correlation between the size of the visual span and reading rate.

For people with central field loss, the high-resolution central portion of the retina (macula) is no longer functioning. They must select an area in the peripheral retina to perform the visual tasks that the non-functioning macula used to perform. Reading rate for people with a central field deficit is substantially slower than that for people with other causes of low vision. Reduced visual span in peripheral vision is hypothesized to be the principal factor behind the severe reduction in reading rate in people with central field loss. Currently, I am working on the research study which investigates visual span profile for people with low vision (mainly due to macular degeneration) and the linkage between the visual span and other reading parameters. If reduction in visual span for people with central vision loss is the major factor limiting reading performance, is it possible to “enhance the capacity of peripheral vision” to read? A rehabilitative model on peripheral vision training on reading may possibly improve the reading performance on people with macular degeneration.

Fig A shows the information in a single glance by a person with normal vision--information in the visual span.

Fig B shows a simulation of reading with a central field loss, typical of macular degeneration. The normal visual span becomes doughnut-shaped because of the scotoma and the "visual span" for reading gets smaller.

Mobility and perception

For people with impairments in peripheral visual function, mobility (rather than reading) may be severely hampered. Although there have been numerous studies that addressed the relationship of general mobility performance with visual impairment, there is limited knowledge of the eye gaze behavior of people with low vision while they are participating in a mobility task. My postdoctoral research studies at Wilmer Eye Institute compared the gap detection ability and the associated eye gaze behavior of people with normal vision with that of people with severe peripheral field loss before they crossed the street. Results suggested that severe peripheral field impairment significantly interferred people's fixation behavior but it did not affect their gap detection ability. In addition to the analysis of the fixation behaviour, we also investigated the effect of visual sampling on the judgement of a whether a gap in oncoming traffic is sufficient for a safe crossing.

Crossing a street safely is a complex activity, which involves complex visuomotor transformation of different systems such as information gathering, decision-making, and good mobility skills. Vision impairment may only explain a minor proportion of the variance in street crossing performance, implying that other factors such as visuomotor transformation process and cognitive status are also contributing to the variability in this mobility task. My research projects also focus on the process of visuomotor transformation and cognitive processing in relation to visual impairment while people with low vision are crossing a street.

In general, the projects I am presently doing have been focused on the rehabilitative aspects of low vision research, which provides important insights into the performance of two common activities of daily living - reading and mobility - for people with low vision. More importantly, it expands our knowledge of the functional deficit due to the vision disorders. Since low vision creates many complicated functional problems, the need for and importance of such studies is significant. Furthermore I believe it is important to take an interdisciplinary approach to low vision research. I am confident that my clinical experience and research skills in low vision, combined with my innovation, dedication and hard work can help me to achieve my research goals and become a strong researcher in the field of low vision research.