Excessive exposure to light can cause deterioration in eye-sight in middle and old age, Australian scientists say. Hence they advise sunglasses.

A team of researchers led by Professor Jonathan Stone of The Vision Centre, University of Sydney and Australian National University, say there is now persuasive evidence that cumulative exposure to light all through life causes deterioration and loss of sight in age.

"We're born with about 150 million light-sensitive cells – known as photoreceptors – in each eye. All through our life we lose these at a steady rate of hundreds every day, but some people lose them much faster than others, with the result that they go blind – sometimes quite early in life."

These light-sensitive photoreceptors are remarkably tough, and most people still have 100 million or so left by the time they reach their 70s or 80s, Professor Stone says. However, in later decades of life, the individual is starting to outlast their eye cells and eyesight begins to dim.

"The eye contains a great many highly-specialised genes, which affect no other part of the body, and these in turn produce many random mutations. It is these mutations which make the normally gradual degeneration of the retina more acute in some people than in others.

"However our research clearly indicates that there are also environmental factors at work which cause the eye to lose photoreceptors more rapidly, especially in people with a certain genetic makeup."