How could my friend not able to read the school board, while I can?

Question

My friend is -1.25

I'm -1.50 with cylindrical power of -0.50

He said he can't read the board while not wearing the glasses and I can (though barely).

How can that be?

Both our corrected vision is 20/20...

Answer 1

What you are asking does not make sense, his resultant power is -1.25(I presume he doesn't have a cyl component in his prescription?) yours is -1.75(you take your spherical component and add half of your cyl component). So you can see that your eye's are worse of than his. I think the difference is in subjective perception. You are more tolerable to the distance blur than what he is. He would only be able to see perfectly clear from about 90cm(40") and you from about 75cm(30"). So he should actually see clear further than what you can.