Dorothy, age 65, is beginning to have trouble driving at night. this is probably because

As people get older (past the original "limits" of our pre-modern ancestors), their bodies begin to degenerate and decline in a number of ways; due to both age, environmental, and societal factors. In this case, the systems of the eye break down and connections weaken. The eye is not able to process light in the same way and this leads to night-sight errors. It is a common problem that people have as age approaches.