Certified Ophthalmic Assistant Practice Exam

What type of astigmatism is indicated when the power of the horizontal meridian is greater than the vertical meridian?

1. With-the-rule astigmatism

2. Against-the-rule astigmatism

3. Mixed astigmatism

4. Simple astigmatism

The correct answer is: Against-the-rule astigmatism

The correct answer is related to the orientation of the meridians in the eye. When the power of the horizontal meridian exceeds that of the vertical meridian, this condition is known as with-the-rule astigmatism. This type of astigmatism is characterized by its configuration where the steepest curvature of the cornea lies in the horizontal plane, which is often at or near the 180-degree meridian, resulting in greater refractive power in that direction. With-the-rule astigmatism typically affects vision by causing blurring of horizontal lines more than vertical ones, as the eye has more difficulty focusing light that is more “steep” or powerful along that horizontal axis. Understanding this condition is crucial for optimal correction and management in a clinical setting. The other types of astigmatism – such as against-the-rule astigmatism, mixed astigmatism, and simple astigmatism – reveal different characteristics regarding the relationship between the horizontal and vertical meridians and their associated refractive errors, but they do not accurately describe the scenario where the horizontal meridian has greater power.