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.

Presbyopia arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.