Which of the following statements describes the prescription: -5.00 +2.00 x 090 ?
Keratometry
No
U
A
C
If you see the cylinder portion of the prescription (i.e. the second number) as a positive number, then "plus cylinder notation" is being used. In with-the-rule astigmatism (WTR), the vertical meridian is steepest and thus a correcting plus cylinder should be placed at or near 90 degrees. The above prescription is therefore an example of WTR astigmatism and is being expressed in plus-notation.
In against-the-rule astigmatism(ATR), the horizontal meridian is steepest and a correcting plus cylinder should be placed at or near 180 degrees.
In oblique astigmatism, the principal meridians do not lie at or close to either 90 or 180 degrees. For example, a prescription of -5.00 +2.00 x 045 would be one of oblique astigmatism.
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