What type of astigmatism occurs when the horizontal meridian is steeper than the vertical meridian?

The type of astigmatism that occurs when the horizontal meridian is steeper than the vertical meridian is known as against-the-rule astigmatism. In this condition, the curvature of the horizontal meridian is greater, which generally means that the vertical meridian is relatively flatter. This results in a situation where the eye is more sensitive to light coming from horizontal orientations, leading to blurriness or distortion in this direction.

Understanding the terminology helps clarify why this is referred to as against-the-rule. Typically, astigmatism is categorized by how the steepest meridian is oriented in relation to the rule, which usually refers to the vertical meridian being the steepest (with-the-rule astigmatism). In contrast, when the steepest meridian lies horizontally, it is termed against-the-rule.

Recognizing the differences among types of astigmatism, such as compound and simple astigmatism, is important as these involve different relationships between the two principal meridians in the eye. Compound astigmatism involves two different powers for the meridians, and simple astigmatism contains one meridian that is either myopic or hyperopic, but not both. Understanding these distinctions reinforces the importance