What is the name of astigmatism where one point of focus falls on the retina?

Simple astigmatism refers to a specific type of astigmatism in which one point of focus falls directly on the retina while the other point of focus is either in front of or behind the retina. This condition occurs when one meridian of the eye has a normal refractive power—resulting in a clear image at the retina—while the other meridian is either myopic or hyperopic. The presence of one clear image on the retina distinguishes simple astigmatism from other forms of astigmatism, such as compound astigmatism, where both principal meridians are affected but to varying degrees.

In contrast to simple astigmatism, compound astigmatism involves both principal meridians being either myopic or hyperopic, leading to neither focus being on the retina. Refractive ametropia is a broader term that describes an overall abnormality in the eye's refractive power rather than specifying the nature of astigmatism. Axial ametropia refers to conditions primarily related to the axial length of the eye, which does not apply directly to the geometric configuration of astigmatism.

Understanding these definitions and classifications helps in recognizing how light focuses in the eye, which is crucial for