What is the characteristic of simple astigmatism?

The characteristic of simple astigmatism is that it allows for one point of focus to fall directly on the retina. This condition occurs when the eye's cornea is not perfectly spherical, leading to different refractive powers along different meridians. As a result, images can be focused at varying distances. In simple astigmatism, one of these focal points is on the retina, which means that the eye has a degree of clarity for one axis of vision, while the other axis may result in blurred vision due to the other focal point being outside the optimal range for clear vision. This is why the characteristic correctly identifies that one point of focus falls on the retina, indicating that at least part of the visual range exhibits improved focus despite the astigmatic distortion.