Which lens type is best suited for treatment of difficult visual problems, such as keratoconus or irregular corneal surface?

Rigid gas-permeable lenses are the best-suited option for treating difficult visual problems such as keratoconus or irregular corneal surfaces. These lenses are made from a firm material that maintains its shape while on the eye, which is crucial for providing a smooth optical surface over a distorted cornea. This ability to maintain a stable shape helps in correcting vision more effectively than soft contact lenses, which can mold to the irregular shape of the cornea and may not provide the necessary optical clarity.

In conditions like keratoconus, where the cornea is thin and has an irregular bulging shape, the irregularities can significantly interfere with vision. Rigid gas-permeable lenses create a new, regular surface for light to focus through, thereby improving visual acuity significantly. They also allow for oxygen transmission to the cornea, which is essential for eye health.

In contrast, bifocal and multifocal lenses are primarily designed for correcting presbyopia and do not specifically address the irregularities of the corneal surface. While soft contact lenses can be used in some cases of keratoconus, they often offer less optical correction and stability compared to rigid gas-permeable lenses.