What does the acronym ATR stand for in astigmatism terminology?

• A. Against The Rule
• B. Across The Rule
• C. Across The Radius
• D. Against The Radius

Answer: (A)

ATR stands for Against The Rule. In astigmatism, the cornea has two principal meridians with different curvatures, and the cylinder power is applied in the meridian perpendicular to its axis. When the steepest meridian is horizontal, this orientation is described as “Against The Rule” because it goes against the common pattern in younger eyes, where the vertical meridian tends to be steeper (with-the-rule). As people age, a shift toward horizontal steepness (ATR) is more common. The other phrases don’t correctly describe this horizontal steepness orientation.