Visual perception in 'low vision'

'Low vision' has an international classification as an impairment of vision that is defined by loss of visual acuity and the size of the visual field, Functional classification that would depict capability to use vision in di fferent activities has not yet been agreed upon. Abnormal visual informatio n leads to changes in visual perception, and brain-damage-related visual im pairment may alter or prevent one or several cognitive visual functions. Ab normal visual perception opens a window into brain mechanisms that the psyc hophysicists otherwise do not have. Together with clinicians, psychophysici sts can help visually impaired persons to understand the nature of their di sability by thoroughly studying the nature of the altered image and the pro file of cognitive visual functions.