multifocal

Multifocal describes an optical system that provides more than one focal point, allowing clear vision at multiple distances. The term is used for lenses and other devices designed to reduce the need for continual reading or distance spectacles. It spans eyeglasses, contact lenses, and intraocular lenses (IOLs) used in eye surgery, as well as certain optical products in photography and instrumentation.

In eyeglasses, multifocal forms include bifocals, trifocals, and progressive addition lenses (PALs). Bifocals have two distinct optical zones for distance and near vision, while trifocals add a middle intermediate zone. Progressive lenses provide a seamless gradient of focus from distance through intermediate to near, without visible lines. These designs trade off field of view, adaptation ease, and potential distortions for broader usable vision without switching glasses.

Multifocal contact lenses use multiple focal zones on a single lens to deliver simultaneous vision at several distances. Designs may be refractive or diffractive and can require a period of adaptation. Benefits include greater freedom from glasses; drawbacks include reduced contrast sensitivity and potential halos or glare in low light.

Intraocular multifocal lenses are implanted during cataract surgery to restore vision at multiple distances. They come in refractive, diffractive, or hybrid configurations, sometimes combined with extended depth of focus technologies. While many patients achieve reduced dependence on spectacles, possible downsides include glare, halos, and decreased night vision, and suitability depends on individual eye health and lifestyle.

Overall, multifocal devices aim to expand functional vision range, with success hinging on patient selection, expectation management, and proper fitting or implantation.