SUMMARY: Guess who's nearsighted?
I do not have detailed data nor even much in the way of data at all. But I can give you a very quick overview of measurements that identify myopia (near-sightedness). Bear with me--I'll get to the point.
Myopia is measured in diopters--OK, you don't need to know the technical details, just get the idea that 0 is normal and -5.0, for example, is very very nearsighted. From Wikipedia's article citing numbers for humans:
Myopia, which is measured in diopters by the strength or optical power of a corrective lens that focuses distant images on the retina, has also been classified by degree or severity:
I can also point you to a study of myopia that shows it's more common in all breeds as they age (just like in humans) (and incidentally indicates that it's less common in guide dogs, which makes sense really--dogs who don't see optimally are unlikely to make excellent guide dogs): Myopia and Refractive Error in Dogs.
That study includes this graph--if you follow the line across, you'll see that younger dogs tend to be somewhat far-sighted (somewhere between 0 and 2) but tend to get more near-sighted with age (see that the line dips below 0):
Note also that, even with age, there are very few dogs with worse than -2 diopters.
I have had myopia since I was in about 5th grade. Wow, the world looked so much different when everything became sharp and clear as I donned my first pair of glasses! Now, after all these many years of aging and becoming more myopic, my left eye is -2.0 and my right is -4.5 (which, if my glasses were actually made of glass, would be very very very thick).
So. Some folks in the agility community and at UC Davis are doing studies on myopia in agility dogs. This apparently came out of one of many discussions about why some dogs have trouble jumping or who take off early when jumping. Or, for example, knocking bars when they jump or refusing jumps. (For anyone who has followed along here for 7 years or so, might recognize my frequent agonizing about Boost.)
They had an event at the end of August where we drove out to Davis and put our dogs over a straight line of jumps. We did this three times with and three times without some kind of contact lens in the eye (Yes! they make contacts for dogs!), sometimes to make the vision worse, sometimes to make it better) They took several people's evaluations of whether the dog did better in the first set of three or the 2nd set of three, before anyone other than the eye doc knew the state of the eyes.
I took Boost.
I have no recollection any more of whether she did better with or without the correction. However, her measurements are -3.5 in one eye and -3.25 in the other.
To understand how extreme that was, the largest adjustment in contacts that they brought with them were 3.0.
So. No wonder she knocks bars and bars and bars, and I get refusals so often, and she looks at me more and more for what to do next. Poor girlie, if it's been like this her whole life, she's done amazingly well. Seems like it can't have been--she always seemed superfast and confident on course to begin with.
Anyway. Now, what with my back issues and all, she's retired from jumping 22" in USDAA. I'm trying not to let it break my heart that we haven't gotten the 3rd Super-Q and completed her championship. But she has really done amazingly well, with or without consideration for her eyesight.
We'll probably just play at agility from now on, assuming that I can actually run and feel safe doing so.