If you haven't already, you will have an eye exam upon certification as an inspector. No matter how great the technology is at detecting even the smallest of discontinuities, your eyes still must be able to distinguish the results.
NAS 410, ASME Section V Article 9, and SNT-TC-1A require all technicians to be capable of reading a minimum of Jaeger Number 1 or 2 at a distance of 12" for near vision acuity upon initial certification.
So, what is visual acuity?
In simple terms, it’s the ability of the eye to resolve fine details at a given distance. Look at the picture below. Can you read the bottom line at 40cm? If so, you have the ability to distinguish the letters as separate entities from the word. Take the test for yourself: http://ow.ly/Hw5z30dWv8z