What is the base curve of the Back Toric lens?

The base curve of a Back Toric lens is defined as a toric surface, which relates to its ability to correct astigmatism. In such lenses, the curvature on the back is not uniform; it varies in different meridians to match the shape of the cornea and to provide the necessary correction for astigmatism. This variable curvature is essential for ensuring a proper fit on the eye and delivering optimal visual acuity, particularly for patients with astigmatism.

A Back Toric lens is specifically designed with a toric back surface, allowing it to provide the appropriate power in different orientations. This is crucial because astigmatism occurs when the corneal curve is not spherical, leading to different refractive errors in different meridians. The toric base curve of the lens aligns with the irregular shape of the cornea, facilitating better vision.

In contrast, a spherical front with a spherical back would not adequately correct for astigmatism since it assumes uniform curvature, which is not suitable for irregular corneas. An aspheric front with cylindrical back might not be the primary feature of Back Toric lenses. Ground flat on both sides would not facilitate the needed curvature changes required to manage astigmatism properly.