Question

What is against the rule correction in astigmatism:

• A. -1.25 cyl 90
• B. -2 spherical 180
• C. -3 cyl 180
• D. +2 cyl 180

Answer 1

The Correct Option is D

To determine which option represents "against the rule" astigmatism, we need to understand the different types of astigmatism. Astigmatism is an eye condition where the cornea or lens is irregularly shaped, causing blurred vision. It is classified based on the orientation of the steepest (greatest curvature) meridian:

• With the Rule Astigmatism: The steepest curvature is along the vertical axis (around 90 degrees).
• Against the Rule Astigmatism: The steepest curvature is along the horizontal axis (around 180 degrees).
• Oblique Astigmatism: The steepest curvature is at an angle other than 90 or 180 degrees.

In our options, we are specifically looking for "against the rule" astigmatism. This means we seek an astigmatism correction where the cylinder (cyl) power is prescribed at or around 180 degrees. Let's analyze the options:

• -1.25 cyl 90: With the rule astigmatism, as the cylinder is at 90 degrees.
• -2 spherical 180: This is a spherical correction, not a cylindrical one, so not applicable for astigmatism.
• -3 cyl 180: This can be against the rule astigmatism since the cylindrical correction is at 180 degrees and is negative, traditionally could be classified as myopic against, but we are specifically looking for against with positive cylinders.
• +2 cyl 180: This is against the rule astigmatism as it has positive cylinder power at 180 degrees.

Thus, the correct answer is +2 cyl 180, which represents against the rule astigmatism, as the correction is oriented at the horizontal axis with a positive cylinder power.