Astigmatism axis question

[pasadena_commut]

If I look at a starburst or spoke pattern the near focus has the bars at 45 degrees sharp, and the far focus has the bars at 135 degrees sharp.  Angles were measured clockwise from 0 degrees at 9:00 O'Clock as seen through the observing eye, so I think these are the same angles as on a prescription which are measured counterclockwise from 3:00 O'Clock as seen looking at the patient's face.  Yet my latest prescription, presumably read right off the phoropter, lists a  cylinder axis for that eye of 180.  I don't get it.  How can the axis be 180 if the two principal meridians are at 45 and 135 degrees?  The rest of the prescription seems to be correct, with the near and far diopter numbers pretty close to what I measure with a tape from the eye to the star pattern, including the 0.5D of astigmatism.

[pasadena_commut]

Went back in yesterday and had it rechecked.  The axis was indeed 135, not 180.  They also changed the cylinder from .5 to .75, leaving the sphere was the same.  I think the actual cylinder is in between those values, but I guess lens cylinders only come in steps of .25, so depending on who knows what variables the cylinder measurement could turn out either way.

Thanks

[Ray T Oyakawa, MD]

You are correct.  Get rechecked.

Dr. O.