The dogs with poor vision could still do their job

Seven out of 61 Labrador Retriever guide dogs were nearsighted, researchers at the University of Auckland in New Zealand found.

Despite their impaired vision, the dogs were still able to act as good guides for their owners.

The dogs may rely on other senses to do their job, said the authors at the International Myopia Conference.

Past studies have shown different species of dog suffer from the same type of nearsightedness that humans get, which is called myopia.

Nearsighted

A nearsighted person sees near objects clearly, while objects in the distance are blurred.

This blurred vision occurs because the image falls short of its target, which is the back wall of the eye known as the retina which sends messages about the image to the brain.

The image can miss its target if the surface of the eye called the cornea is more curved than normal or if the eye is too long.

Myopia often develops in children, and progresses during the growth years, requiring frequent changes in glasses or contact lenses.

We can only assume that the dogs rely on other senses to carry out their duties Researcher Dr Andrew Collins

It usually stops progressing as growth is completed in the early twenties.

Myopia tends to run in families. People whose parents have myopia are more likely to develop it.

The severity of myopia is measured in dioptres, which are a measurement of the focusing power of the lens.

Myopia up to minus 3D is termed mild degree, minus 3 to minus 6D is moderate degree and high degree is minus 6D and over.

Dr Andrew Collins and colleagues at the University of Auckland developed a computerised method for measuring how well dogs can see - a test of visual acuity.

They tested the sight of 61 Labrador Retriever guide dogs and found myopia of at least minus 0.5D in seven of the animals.

Some had myopia of minus 3.63D.

The researchers then checked how well the dogs performed their duties by looking at training scores from a guide dog centre.

Duties unaffected

The dogs with myopia performed equally as well as those that were not shortsighted.

Dr Collins said: "Although some of the dogs had myopia, their ability to act as good guide dogs appeared to be unaffected.

"We can only assume that the dogs rely on other senses to carry out their duties," he said.

Professor Karla Zany at Ohio State University in the US, who has conducted similar research into myopia in dogs, said the findings were very interesting.

"It's what you really want to know, whether there are things these dogs have that would affect their ability to do their work.

"What's important about this work is it looks like they are indeed developing a method where the dog's vision correlates pretty well with whether the dog is nearsighted or not.

"That tells you this measurement you are making of the dog's vision has some validity to it," she said.

She said dogs with more severe myopia - minus 2-3 and over - might have problems seeing well enough to carry out their duties.

She said such tests might be used to check a dog's suitability to be trained as a guide dog or be used to breed other guide dogs.

A spokesman for The Guide Dogs for the Blind Association said: "Our dogs are screened in accordance with the British Veterinary Association's eye-screening programme.

"In addition, our breeding dogs are issued with eye-test certificates, which are renewed on an annual basis.

"This screening shows that there is no familial myopia in the UK's stock of guide dogs.

"If any ailment caused problems with a dog's workability, we would have to consider retiring the animal, as it essential that they are completely alert to act as mobility aids for their visually impaired owners."