Mortality are often accustomed define biological aging, which refers to an organisms increased rate of death because it progresses throughout its lifecycle and increases its age. Another possible way to define aging is through functional definitions, of which there are two main types. The first describes how varying types of deteriorative changes that accumulate in the life of a post-maturation organism can leave it vulnerable, resulting in a decreased ability of the organism to survive. The second is a senescence-based definition; this describes age-related changes in an organism that increase its mortality rate over time by negatively affecting its vitality and functional performance. An important distinction to form is that biological aging isnt an equivalent thing because the accumulation of diseases associated with old age; disease may be a blanket term wont to describe a process within an organism that causes a decrease in its functional ability. Age can result in visual impairment, whereby non-verbal communication is reduced, which can lead to isolation and possible depression. Older adults, however, might not suffer depression the maximum amount as younger adults, and were paradoxically found to possess improved mood despite declining physical health. Macular degeneration causes vision loss and increases with age, affecting nearly 12% of those above the age of 80.This degeneration is caused by systemic changes in the circulation of waste products and by growth of abnormal vessels round the retina.