What characteristic do most single vision CR-39 lens series share?

Most single vision CR-39 lens series share the characteristic of having a minus cylinder form. This form is particularly common for correcting myopia, where a concave lens is required to diverge light rays for proper focus on the retina. In the context of single vision lenses, which are designed for one specific focal distance, the curvature of the lens is critical for achieving the desired optical power.

A minus cylinder form allows for a uniform approach to lens manufacturing, addressing the majority of prescriptions for nearsightedness. This standardization contributes to efficient production and proficiency in lenses designed for this common visual impairment.

While various designs and forms exist, single vision lenses primarily cater to a wide range of myopic prescriptions with this minus cylinder configuration, making it a predominant feature in the CR-39 lens series. Other options, such as plus cylinder or square molded shapes, are less common in this category, as they pertain mostly to different types of lens configurations or corrective needs.