Try this: Stand about 6 feet away from someone and look at his/her right hand. Then ask the person to wave that hand and see if you can see it. If you can, chances are you can see enough to do a kote (wrist) strike. I am choosing kote because it is the smallest target you would strike. Mathematically: Assuming you are roughly 6 feet away and need to be able to see the opponent's kote, which is say 1/3 foot in height. That constitutes an angle of 3.179 degrees. Now a person with 20/20 vision has an acuity of 1 minute of arc - ie 1/60 of a degree. A person with 20/200 has an acuity of 10 minutes of arc - ie 1/6 of a degree. Since 3.179 is 18x greater than 1/6 of a degree, theoretically that means you should be able to see the kote.