Eyeglasses and prescription question

My son's prescription is plano, +2.25 x90
His eyeglasses instructions say +2.25, -2.25 axis 180.

I thought when they rotate the prescription to make eyeglasses that
it's a 180 degree rotation, not a 90 degree rotation. Wouldn't the
axis still be at 90 instead of 180? Did they make a mistake or am I
missing something?

My son's only 5 so it's hard to tell if his vision is better or worse.
He says the glasses make his vision better, but I want to be sure. .
..

 

(lasik advocate with flap melt) wrote in

No. The axis is rotated 90 degrees. 180 makes no sense, since it winds up
being the same. The notation is based on a 180 degree convention, not 360
degrees.

DrG

 

So 90 degrees one way and 180 degrees the other way are the same
location? I thought it would be 180 degrees different, not 90
degrees? Would you mind explaining?

 

If you rotated 180 deg you'd be back to the original rx! The transposition
of the rx'es you stated are correct- just in different forms (plus cylinder
converted to minus cylinder).

frank

 

Thank you all for the explanation.

I don't want to take any chances knowing what I know now. I Appreciate it.