What is a key characteristic of 'Against the Rule' (ATR) astigmatism?

What is a key characteristic of 'Against the Rule' (ATR) astigmatism?

• A. More power at the 90-degree axis
• B. More power at the 180-degree axis
• C. Equal power across meridians
• D. Less power vertically than horizontally

Answer: (B)

The key characteristic of 'Against the Rule' (ATR) astigmatism is that it has more power at the 180-degree axis compared to the 90-degree axis. In ATR astigmatism, the principal meridian that is oriented horizontally (0 or 180 degrees) has a greater refractive power than the vertical meridian (90 degrees). This results in the focus of light entering the eye being more spread out along the vertical axis, which can lead to blurriness when viewing objects especially in the horizontal plane. In contrast, the other options refer to different types of astigmatism or the characteristics of regular astigmatism. For instance, in 'With the Rule' (WTR) astigmatism, there is typically more power at the 90-degree axis. Equal power across meridians indicates a condition called regular astigmatism or spherical correction, effectively meaning there is no astigmatism. Less power vertically than horizontally would relate to a situation opposite to ATR, which is not a characteristic of ATR astigmatism. Understanding these distinctions helps in the diagnosis and correction of astigmatism in patients.

The key characteristic of 'Against the Rule' (ATR) astigmatism is that it has more power at the 180-degree axis compared to the 90-degree axis. In ATR astigmatism, the principal meridian that is oriented horizontally (0 or 180 degrees) has a greater refractive power than the vertical meridian (90 degrees). This results in the focus of light entering the eye being more spread out along the vertical axis, which can lead to blurriness when viewing objects especially in the horizontal plane.

In contrast, the other options refer to different types of astigmatism or the characteristics of regular astigmatism. For instance, in 'With the Rule' (WTR) astigmatism, there is typically more power at the 90-degree axis. Equal power across meridians indicates a condition called regular astigmatism or spherical correction, effectively meaning there is no astigmatism. Less power vertically than horizontally would relate to a situation opposite to ATR, which is not a characteristic of ATR astigmatism. Understanding these distinctions helps in the diagnosis and correction of astigmatism in patients.