Which lens type includes bifocals and trifocals?

The correct response focuses on multifocal lenses, which are specifically designed to offer multiple prescriptions in one lens. Bifocals contain two optical powers separated by a visible line, catering to both distance and near vision needs. Trifocals add a third zone for intermediate vision, enabling the wearer to see at various distances without the need for multiple pairs of glasses.

This lens type is essential for individuals who have presbyopia, a condition that affects near vision as people age. Multifocal lenses enable seamless transitions between different visual fields, enhancing convenience and comfort for the wearer.

The other lenses mentioned have distinct purposes. Single-vision lenses are meant for a single prescription throughout the lens, typically addressing either distance or near vision, but not both. Flat-top lenses are a specific type of bifocal lens featuring a flat top section for reading, but they do not encompass trifocals or the broader category of multifocals. Photochromic lenses are designed to change tint in response to light exposure, primarily serving as sunglasses when outdoors but do not inherently include any multifocal properties.