A few misconceptions need to be addressed from your comment :
now that I think about it, from my parents who cautioned me not to take photos of their cat too close with a flash when I was a kid.
It's unlikely the cat's eyesight would be permanently damaged by a camera flash. This was simply your parents discouraging you from doing silly things which might have resulted in a mighty angry cat swiping at you with it's claws !
But what about flash blindness which “can be temporary or permanent”?
Permanent flash blindness would require a significantly higher output over a longer period than a normal camera flash would output. Camera flashes are of very short duration ( of the order of 1/10,000 th second ) and designed to provide a brief intense burst of light. But it spreads out according to an inverse square law, so it rapidly diminishes in intensity.
I'd generally advice against setting of a flash right up close to your eye, because that's at best unpleasant and has no useful photographic purpose.
Most typically you'd need an extreme source like a laser pointer to do permanent damage. Some welding kits can produce permanent eye damage - arc welding is particularly dangerous, but this is because it's also high in UV light and extremely intense over a significant time scale (way longer than a camera flash). Camera flashes do not have high UV levels.
Also, pets (at least cats and mice) seem to dislike light from strobes even when shot at 1/32 or less and from a distance of 50 cm. or more.
Most people dislike them too. It's simply the context of taking a shot for a human that makes it less unpleasant. However "dislike" is not the same as "damaging". It's simply your brain's normal reaction to sudden bright light - turn away, get away. Animals lack the understanding and learned behavior to understand it's not going to be a problem, but can even be fun.
Same for people. I'm pretty sure that if I trigger my flash at 1/1 at a few centimeters from my face, it would probably result in permanent blindness.
I cannot see why you'd so that. I'm skeptical it would result in permanent blindness for someone with healthy eyes, but too close and it might be quite unpleasant and possibly result in significant temporary blindness and possibly even a bit of pain.
As usual, don't try this at home (or anywhere else).
However flash is sometimes used to photograph the human eye in macro photography as this article discusses. Here's a flickr discussion about various approaches to photographing the eye.
Best results (IMO) are diffuse light (e.g. bounced flash or even natural light) with a long focal length. This produces a soft lighting without unwanted reflections.
