R = tan (alpha-2)/ tan (alpha-1)
- If both eyes lie on the horopter the 2 angles, alpha 1 & 2 are equal to each other so R = 1 and therefore no relative magnification in either eye. Object space = perceived space.

When the 2 angles don't = to make R=1, one eye's image is mag/minified relative to the other, aniseikonia.