Question

Which of the following combinations of cylindrical lenses can be used to treat with the rule astigmatism?

• A. +5.00 DC x 180, -3.00 DC x 90
• B. +7.00 DC x 180, +5.00 DC x 90
• C. -4.00 DC x 180, -5.00 DC x 90
• D. -3.00 DC x 180, +1.00 DC x 90

Hint:

With-the-rule astigmatism is a common form of astigmatism where the vertical meridian (90 degrees) is steeper than the horizontal meridian (180 degrees).

Answer 1

The Correct Option is D

+5.00 DC x 180, -3.00 DC x 90: This combination would not treat with the rule astigmatism. In with-the-rule astigmatism, the steeper meridian (i.e., the most curvature) is typically along the vertical axis (90 degrees), and the flatter meridian is along the horizontal axis (0 or 180 degrees). This combination suggests a reversal of the expected meridians.
+7.00 DC x 180, +5.00 DC x 90: This combination does not represent astigmatism correction but rather would indicate a difference in power along the two axes. However, both powers are positive, which does not indicate astigmatism, particularly with-the-rule astigmatism.
-4.00 DC x 180, -5.00 DC x 90: This combination also does not correctly correct for with-the-rule astigmatism. In this case, both powers are negative, and it does not conform to the pattern of with-the-rule astigmatism where the vertical meridian is more curved.
-3.00 DC x 180, +1.00 DC x 90: This is the correct answer. In with-the-rule astigmatism, the steeper meridian (greater power) is along the vertical meridian (90 degrees), and the flatter meridian (lower power) is along the horizontal meridian (180 degrees). This combination correctly treats with-the-rule astigmatism. Thus, the correct answer is -3.00 DC x 180, +1.00 DC x 90 (4), as it is the correct treatment for with-the-rule astigmatism.