What type of astigmatism is characterized by focal lines positioned between 31° and 59° Meridian and between 121° and 149° Meridian?

The correct choice is oblique astigmatism, which is defined by the orientation of its principal meridians. In oblique astigmatism, the focal lines are positioned in meridians that are neither horizontal nor vertical, which typically falls within the 31° to 59° and 121° to 149° meridian ranges. This means that the astigmatism has its axes oriented at oblique angles rather than at the conventional 90° or 180° orientations seen in regular astigmatism. As a result, the vision distortion associated with oblique astigmatism manifests differently compared to other types and usually requires specialized correction.

In contrast, regular astigmatism features principal meridians that are perpendicular to one another, typically aligned along the horizontal (0° and 90°) or vertical (90° and 180°) meridians, which does not fit the parameters given in this question. Mixed astigmatism involves one principal meridian being myopic and the other being hyperopic, which is a distinct characteristic from merely having oblique axes. Myopic astigmatism specifically refers to a type of regular astigmatism where both principal meridians are