What type of astigmatism occurs when both points of focus are positioned in front of or behind the retina?

The correct identification of compound astigmatism is tied to its defining characteristic: it occurs when both focal points are either in front of or behind the retina. This situation arises due to the cornea or lens having unequal curvatures, leading to two principal meridians that each have different refractive powers.

In compound astigmatism, if both foci are located in front of the retina, it typically indicates that the individual is nearsighted in both meridians, while if they are behind the retina, it indicates that the person is farsighted. This dual situation is what separates compound astigmatism from simple astigmatism, where only one of the meridians is ametropic (either myopic or hyperopic) and the other is emmetropic (normal vision).

Understanding this condition allows for more accurate diagnosis and appropriate corrective strategies, such as specially designed lenses that account for the varying refractive errors in the different meridians.