Researchers at the University of Cambridge and University College London have found that passive smoking can increase the risk of a disease that causes blindness in older people.

They linked passive smoking with age-related macular degeneration (AMD), an eye disease that can lead to blindness and affects 500,000 people in Britain, according to the university release.

The research, lead by Professor John Yates at the Cambridge Institute for Medical Research (CIMR), found that living with a smoker for five years can double the risk of developing the disease, and regular smokers triple their risk.

Regular smokers were those who smoked a pack or more a day for 40 years. Those who had given up smoking over 20 years brought their risk level down to that of a non-smoker.

AMD usually develops after a person reaches the age of 50. It is a disease that degenerates the central part of the retina, key necessary for reading and driving, leaving only peripheral vision unaffected. It can, but does not always, lead to blindness.