[citation][nom]willard[/nom]But this still leaves major problems. How do you account for the differing concentrations of rods and cones? You may be able to perceive 20k horizontal pixels, but the majority of those are going to be concentrated in a very small area of visibility.You can get a number, but that number isn't very meaningful. That's what I was driving at, that you're not going to be able to compare the human eye's abilities to pixel counts in a meaningful way.[/citation]
The retina display is simply the display resolution (taking into account typical viewing distance) where a typical viewer is unable to distinguish between the pixels on the device, when they look at, say, text on that screen.
This refers to the specific part of the screen the user is focused on, and thus differing concentrations of rods and cones in peripheral vision are irrelevant.
It's not about the user being able to see the whole screen in one go - it's about there not being an appearance of pixelation in the area on which the users eyes are focused.