Question:
What is the against-the-rule correction in astigmatism?
What is the against-the-rule correction in astigmatism?
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Against-the-rule equals plus cyl at 180 or minus cyl at 90.
Updated On: Jun 23, 2026
- -1.25 cyl 90
- -2 spherical 180
- -3 cyl 180
- +2 cyl 180
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The Correct Option is A
Solution and Explanation
Step 1: In regular astigmatism the two principal meridia are at right angles. In against-the-rule astigmatism the HORIZONTAL meridian is more curved than the vertical meridian (the opposite of the normal with-the-rule pattern).
Step 2: The standard correction for against-the-rule astigmatism is a convex (plus) cylinder at 180 degrees axis OR a concave (minus) cylinder at 90 degrees axis (each plus or minus about 20 degrees).
Step 3: Option (a) -1.25 cyl 90 is a minus (concave) cylinder at 90 degrees, which fits the against-the-rule correction. Option (d) +2 cyl 180 is a plus (convex) cylinder at 180 degrees, which also fits, so both (a) and (d) describe against-the-rule correction; the marked key here is (a).
Step 4: Option (b) is a spherical lens (no cylinder, so not relevant to astigmatism axis) and option (c) -3 cyl 180 is a minus cylinder at 180 which corresponds to with-the-rule correction. Hence the answer is option (a).
Step 2: The standard correction for against-the-rule astigmatism is a convex (plus) cylinder at 180 degrees axis OR a concave (minus) cylinder at 90 degrees axis (each plus or minus about 20 degrees).
Step 3: Option (a) -1.25 cyl 90 is a minus (concave) cylinder at 90 degrees, which fits the against-the-rule correction. Option (d) +2 cyl 180 is a plus (convex) cylinder at 180 degrees, which also fits, so both (a) and (d) describe against-the-rule correction; the marked key here is (a).
Step 4: Option (b) is a spherical lens (no cylinder, so not relevant to astigmatism axis) and option (c) -3 cyl 180 is a minus cylinder at 180 which corresponds to with-the-rule correction. Hence the answer is option (a).
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