Bifokaali

Bifokaali refers to a type of optical lens that contains two distinct optical powers within a single lens, designed to correct presbyopia while allowing simultaneous distance and near vision. The term originates from the Latin word “bifoculus,” meaning ‘two lenses.’ The concept was first popularized by the American ophthalmologist Benjamin Franklin in the 18th century, who patented a bifocal eyeglass that featured a rectangular division at the bottom of the lens. Franklin’s version was a practical solution for people who needed help reading while still being able to see at a distance, and it laid the groundwork for modern refractive correction strategies.

Contemporary bifocals are manufactured using a range of techniques such as ground optics, laser machining, and fresnel patterns. Common embodiments include: (1) the conventional segmented bifocal, which presents a clear horizontal border that separates the lower reading zone from the upper distance zone; (2) the “progressive” bifocal, which smoothly transitions optical power across the lens surface without a visible breakpoint; and (3) the “simulated” bifocal, where discrete zones are formed to reduce distortion when viewed from certain angles. Besides eyewear, bifocal technology is also applied in contact lenses, intraocular lenses, and seeing glasses for animals.

The main advantages of bifocal lenses are convenience, cost efficiency compared with monovision, and improved visual comfort. Common drawbacks include a learning curve for adaptation, potential distortion at the breakpoint in segmented designs, and reduced field of peripheral vision for progressive styles. Wide adoption of modern progressive lenses, lens coatings, and high-index materials has largely mitigated these issues. In clinical practice, bifocals remain a staple for patients with senile or accommodative esotropia and are frequently prescribed alongside prisms or augmentation therapies.