(Kelly of the Clue Crew shows an anatomical diagram on the monitor.)  This irregularity in the eye's surface bends the ray of light so that it can't be brought to a single focus, resulting in blurring
This irregularity in the eye's surface bends the ray of 
light so that it can't be brought to a single focus, resulting in blurring ... -7.5 
dioptres in both eyes and also astigmatism no idea what that's measured in; I 
have astigmatism.