Single lens or single vision lens is a lens that allows viewing at only one distance. It is a lens with a single prescription power, used to correct either nearsightedness or farsightedness, and can also include a prescription for astigmatism.

Single lens or single vision lenses commonly come in four main structures, which are:

1. Spherical lens is a lens with equal curvature on both the front and back. It provides clear vision at the center of the lens, while the edges may cause distortion or blurred images. The higher the prescription, the greater the distortion at the sides, making it difficult to adjust and uncomfortable for the eyes.
2. Aspherical lens has less curvature and a flatter surface than spherical lenses, reducing image distortion, which is mainly concentrated at the edges of the lens. **Not suitable for glasses frames with a high curvature.
3. Double aspheric lens features a much flatter front and back surface, crafted with high precision. This makes it lighter, thinner, and clearer than other types, providing a wider field of view and minimal distortion. It is ideal for those with high prescriptions. **Not suitable for highly curved frames.
4. Freeform lens is crafted with high precision and diamond-tipped tools, and parameters of the frame are considered to personalize the lens. The lens is thinner, lighter, and custom-made, ideal for those with high prescriptions. It offers easy adaptation, comfort, and minimal edge distortion.