Slow Eyes, as was reported in an EJ Manuel scouting report is a real thing-I know because I have them.
Basically, slow eyes means you cannot shift your focus at the speed that most other people doing the same task can. I'll give you 2 examples.
Example #1-when I play card games on the computer I make mistakes because I'm trying to keep my speed up but cannot focus on the current card fast enough. For example when I play hearts, I cannot immediately focus on the card dealt immediately to my right when it's the 3rd card dealt. Instead, I tend to remain focused on the 1st 2 cards drawn.
Example #2- I used to go out walking with a group of 3 or 4 other guys. As we walked someone would point out something of interest to look at and I would always be focused on something the other guys were not focused on-usually because I had zeroed in on something that caught my attention & my slow eyes couldn't adjust to new things in my vision range as fast as the other guys. I tended to keep focus on things closer to me while the others focused on things further away. I had to ask exact locations in order to shift to what the other guy pointed out. I always said to one friend-"We're never looking in the same place."
Now lets shift this to a football field and the speed of an NFL game and the requirement to read defenses quickly. If as scouted, EJ has slow eyes there's nothing he can do to ever overcome what is his lack of ability to adjust to the speed of what is happening on the field. For most of us with a similar condition we are able to overcome it in most daily tasks because we have the time to adjust and not get clobbered by someone looking to tackle us as we adjust or trying to throw an object to someone running in the opposite direction of where we are standing.