According to wikipedia, These aren't ordinary fonts (with only 9 characters), they appear to be custom designed so the black balances with the white (notan? :^P) and the body height and width is five times the width (or thickness) of a stroke.

The sans-serif chart example appears to be this font.

The slab does bear a resemblance to Rockwell but I'm sure it is not.

Don't know the official typefaces. Judging by the vertical symmetry, lack of overshoots on the rounds (O,C), and tiny bowls (D,P) it seems clear that the slab version at least was made by scientists, doctors, or engineers -- not type designers. These are my closest matches:

Serif: Stymie Medium beats Rockwell mainly because of the width and it's shorter E,F crossbars.

Sans: Sackers Heavy Gothic

Ope! Geoff beat me to it with a better explanation.

I've actually always thought those eye charts used characters that had unfairly small bowls and counters. Kind of like when you see a sign for the fire department "F.D." but the period after the F is too tightly kerned and it causes it to look like it says "ED." ("Who's this Ed guy and why does he get to park here?")

I notice that Stymie Medium's "E" looks different here:

http://www.myfonts.com/fonts/bitstream/stymie/medium/

Are there multiple versions of this font?

Surely. The one to which I linked is from Linotype. There are often various interpretations of the old stuff.