Another clear-eyed reason to quit smoking: your vision

Among the better-known dangers of smoking, it can be easy to lose sight of the way smoking can make you lose your sight.

As we prepare to mark World No Tobacco Day tomorrow, here's one more very good reason not to smoke or to stop smoking: your eyes.

Of course, we are all aware of the damage that smoking can do to the body but less well known is the detrimental effect of smoking on vision. In fact, smoking is the single most important lifestyle factor when it comes to eye health, protecting the eyes and the quality of your sight.

Smoking has been directly linked to two of the leading causes of vision loss - cataracts and macular degeneration - and researchers believe smoking also causes or contributes to a range of other eye health problems for smokers and passive smokers, both adults and children.

We have now reached the point where there is a significant body of research-based evidence showing an increased risk of a number of eye disorders, not only in those who smoke, but also in those who are frequently exposed to tobacco smoke. Here's why:

Tobacco smoke contains over 4,000 different substances, including many known carcinogens, irritants and inflammatory agents. According to studies published in the British Medical Journal, cigarettes increase the chances of developing age-related macular degeneration and smokers are up to four times more likely to go blind in old age. Age-related macular degeneration (AMD) is the leading cause of adult blindness in the UK and results in severe and irreversible loss of central vision, especially in people over the age of 60.

According to the Royal National Institute for the Blind (RNIB) people fear losing their sight more than any other sense and so there is a need to create greater awareness of the link between smoking and the significantly increased risk of losing sight from AMD. The RNIB is going so far as to advocate putting an eye health warning on all cigarette packets (if they can find the space for yet another health warning).

There is much speculation about a whole range of eye-related diseases and possible connections with smoking - such as thyroid eye disease, eye inflammations and strabismus (cross eyes) in children.

Smoking is a clearly established risk factor for AMD. This means that smoking actually causes age-related macular degeneration, rather than just being indirectly associated with the condition. And the more people smoke, the more likely they are to develop AMD. (The association between environmental tobacco smoke exposure and AMD is less clear).

Macular degeneration affects the macula at the back of the eye, impairing central vision. The macula is a small area in the centre of the retina. The retina is the layer at the back of the eye which is sensitive to light. When light enters the eye it passes through the clear cornea and lens at the front of the eye, and the vitreous humour (jelly-like substance in the eye). The retina receives the images and passes them to the brain and this is how we see.

The macular area of the retina has the finest blood supply in the body, serving the retinal receptors that enable us to see minute detail clearly. Smoking promotes macular degeneration by interfering with blood flow to the retina.

Abnormalities in this area can cause macular degeneration either by blocking nutrition or causing blood vessels to grow under the retina; these blood vessels destroy structures around them as they grow. If the cells in the macula deteriorate then the central part of your field of vision becomes blurred.

There is some hope; stopping smoking improves the chances of avoiding eye disease. For example, studies show that people who quit smoking will have a 6.7 per cent reduced risk of developing macular degeneration after one year. After five years, the risk drops by another 5 per cent. The same goes for cataracts. The eyes can heal from the damage done by cigarette smoking, although very slowly.

The other good news is that researchers also suggest that giving up smoking helps reduce the risk of AMD in later life. So, avoiding smoking, or quitting, is one of the best investments you can make in your long-term eye health, along with diet and rest.

And of course, if you are experiencing unusual symptoms such as cloudy vision, blurred images, floating spots and loss of vision, head to an ophthalmologist to get them checked. And that's something to remember every day of the year.

Dr Chris Canning is Medical Director at Moorfields Eye Hospital Dubai