Light is refracted through a transparent prism by passing through its three rectangular lateral surfaces. The triangular glass prism has two triangular bases and three rectangular lateral surfaces that are inclined to each other.

In a glass slab with parallel refracting surfaces, the emergent ray is parallel to the incident ray, but it is slightly displaced laterally.

Modern alternatives for correcting refractive defects include contact lenses and surgical interventions. These options provide additional choices beyond traditional corrective eye-glasses.

Bi-focal lenses are designed with the upper portion as a concave lens for distant vision and the lower part as a convex lens for near vision. This design allows individuals to see clearly at both distances.

Individuals experiencing both myopia and hypermetropia often require bi-focal lenses, which consist of both concave and convex lenses. The upper part facilitates distant vision, while the lower part assists near vision.