People could permanently damage their eyesight and even risk blindness if they look directly at an astral event which is due to take place next week.

The Chief Medical Officer, Sir Liam Donaldson, warned that if people looked at Venus as it passes across the face of the Sun on June 8 they could risk their sight.

The event is similar to a solar eclipse, but instead of the Moon being in-line between the Earth and the Sun, it will be the planet Venus. The second planet looks much smaller from Earth so viewers would have to be specifically observing the Sun to see the small disc of Venus passing by.

The planet will cross the Sun between approximately 6am and midday - the last time the event occurred was 1882.

Sir Liam warned that under no circumstances should viewers look at this event directly – the risks to sight from looking at the Sun are "very real" and could lead to "irreversible damage" to eyesight and even blindness.

"The safest way to view the event is on the television or live webcasts on the internet," he said.

"Using a small telescope to project the event onto a screen is safe but I must stress that observation directly through a telescope, binoculars or camera is not safe, even just to line up the projection. In addition sunglasses, and photographic film are totally inadequate and should not be used to view the transit under any circumstances."

Anita Lightstone from the Royal National Institute of the Blind, said that it was "vital" that people take the issue seriously to avoid "tragedy".

"People who look directly at the sun during the transit, even for as little as five seconds, risk permanent eye damage, even blindness," she said.

Andrew Elliott from The Royal College of Ophthalmologists, said that damage to the back of the eye can happen in an instant and once it occurs, there is no treatment.

(gmcg)