Bifocal, Trifocal and Progressive Glasses
Bifocal, Trifocal and Progressive Glasses are designed to improve vision for people with presbyopia. These eyeglass styles all solve the problem of needing a different lens curvature for correcting distance viewing than they would for close-up reading.
Nearly everyone will develop Presbyopia at some point in their life, as it is a natural result of aging. Most people will experience Presbyiopia starting around middle age, and presbyopia generally progresses at relatively a constant rate after onset. Presbyopia is caused by the stiffening of the eye’s lens, resulting in a weakened ability to focus and adjust the lens to close-range objects. Bifocal, Trifocal, and Progressive lenses actively counteract the effects of presbyopia by increasing short range focus in specific portions of the lens without changing the focus for distance vision.
How do Bifocal, Trifocal, and Progressive Eyeglasses Work?
Traditionally, bifocal glasses feature two distinctly separate lens powers separated by a distinct boundary. These lens styles work by allowing one to use the top part of the lens for distance viewing, and the bottom part of the lens for reading & short range vision. Most credit the invention of bifocal lens styles to Ben Franklin in the early 1800′s, although some speculate that bifocal lenses had been used prior to Franklin’s famous invention. While Bifocal lenses are still popular, many prefer to use trifocal lenses, which follow the same principle as a bifocal lens, but instead utilize three separate lens powers instead of just two.
More recently, progressive lens types have been made, which eschew “separations” in lens power in favor of utilizing a gradient lens power. Gradient curvature in progressive lenses changes the corrective power of the lens without having any distinct boundaries between lens powers as is seen in bifocal and trifocal lenses . Progressive lenses have become very popular these days as they offer a more natural field of vision than bifocal and trifocal lens types do. By definition, progressive lenses can also be categorized as a variety of aspheric lens due to the gradient nature of the lens.
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