London - They really are man’s best friend – and it’s not just their owners who say it.
Research suggests that pet dogs guard against glaucoma, one of the most common causes of blindness – but exposure to cats increases the risk.
It is thought that the germs dogs bring in from playing outdoors protect the eyes, while proteins carried by cats have the opposite effect.
David Allamby, a leading laser eye surgeon, said: “Not only is Fido man’s best friend, he may also save your sight.”
Glaucoma, which affects more than 500 000 Britons and is the second biggest cause of blindness worldwide, is caused by damage to the optic nerve, the vital link between the brain and the eye.
With the damage thought to be partly fuelled by a faulty immune response, US scientists tested more than 1 600 people for immune reactions to a variety of animals and insects. All were aged 40-plus and 5 per cent had glaucoma. House dust mites were most likely to trigger a response, followed by cockroaches, then cats and finally dogs.
Further analysis showed that those who were sensitive to cats were more than three times as likely to have glaucoma as others.
However, those whose immune systems reacted to dogs were much less likely to have been diagnosed with the condition. They had just a quarter of the usual risk, the American Journal of Ophthalmology reported.
The University of California researchers said that while they can’t prove cats are to blame, their results suggest that “prolonged exposure” to the creatures may increase the odds of glaucoma. It is thought that compounds found in cat skin, urine or saliva may have the right size or chemistry to make the immune system turn on the optic nerve.
By contrast, the compounds carried by dogs may protect against damage. Another possibility is that the germs that dogs bring in from outdoors boost the immune system.
Cats’ love of cleanliness means that any such “good bacteria” are quickly licked away.
The study is far from the first to find dogs confer more health benefits than cats. Dog owners may have better heart health from taking their pets for walks. Dogs are also better than cats at keeping loneliness at bay.
Dr Allamby said: “If you plan to get a pet, a dog may be the healthier choice. They encourage us to exercise more. This has a positive effect on our general health, and with children in particular, the more time they spend outdoors, the less chance they have of developing myopia or short sightedness.’
Daily Mail