Single Vision
Single vision lenses are uncoated, plastic lenses with a single prescription that corrects myopia, hyperopia, or astigmatism.
Bifocal
Bifocal lenses are uncoated, plastic lenses that correct both for distance and near vision in individuals with presbyopia. The top of the lens corrects for distance vision. In the lower part of the lens, there is a visible semicircle ground into the lens that corrects for near vision.
Trifocal
Trifocal lenses are uncoated, plastic lenses that correct for vision at three distances. The top of the lens corrects for distance vision. In the lower part of the lens, there is a visible semicircle ground into the lens that corrects for near vision. Just above this semicircle is an additional lens segment that corrects for distances of about an arm's length away.
Lenticular
Lenticular lenses are designed to treat eye conditions that are more serious than simply myopia, hyperopia, presbyopia, or astigmatism. They are often prescribed after cataract surgery for patients without intraocular implants.
Progressive
Commonly called "no-line bifocals", progressive lenses are bifocal or trifocal lenses that have an invisible corridor of increasing power that leads from the distance portion of the lens down to the reading portion.
EYEGLASS MATERIALS/OPTIONS
Plastic
Common uncoated lens material.
Polycarbonate
Polycarbonate lenses are made of a material similar to standard plastic, but are lighter in weight and thinner than uncoated plastic lenses. They offer protection from surface abrasions like scratch resistant coated plastic lenses, and they do not shatter like glass or standard plastic lenses.
Photochromic
Photochromic lenses are light sensitive glass lenses. The glass contains silver halide crystals that darken when exposed to ultraviolet (UV) light and become clear when removed from the light. In their darkened state, photochromic lenses offer protection from potentially damaging UV rays.
Transition
Transition lenses are light sensitive plastic lenses, which makes them lighter in weight than photochromic glass lenses. They become darker when exposed to ultraviolet light and lighten when removed from the light. Transition lenses resist UV radiation both when light and dark, and the lenses are scratch-resistant.
Glass
Glass lenses are generally heavier than plastic lenses and resist scratching better than uncoated plastic lenses.
Scratch Resistant Coating
Scratch-resistant coated lenses offer protection from most surface abrasions. The coating is included as a part of polycarbonate lenses, but is also available as an option that is applied to the surface of standard plastic lenses after the lenses are ground.
Ultra-Violet Filter
Reduces transmission of harmful ultra-violet rays from the sun.
Anti-Reflective Coating
Increases light transmission through the lens by reducing reflections that cause unwanted glare. Anti-reflective coating can improve vision while driving at night.
Polarized
Polarized lenses reduce light transmission and reflection from horizontal surfaces, such as snow or water and may improve vision during outdoor activities.
Tint
Tinted lenses reduce light transmission.
CONTACT LENS TYPES
Daily Wear
Daily Wear contact lenses can be soft or rigid contact lenses made of different types of plastic, depending on the specific type of lens. Daily wear lenses are to be worn for periods of less than 24 hours at a time, and should be removed each night before the wearer goes to sleep. Lenses generally need to be replaced annually or biannually.
Extended Wear
Extended Wear contact lenses are usually soft contact lenses, but are designed to be worn for 24 hours or more at a time. Some lenses are FDA approved for up to 30 days of continuous wear, but most doctors recommend removing and cleaning the lenses at least weekly. Extended wear lenses have replacement schedules that vary significantly by the specific type of lens and length of continuous wear.
Disposable
Disposable contact lenses are soft contact lenses, either daily wear or extended wear, that are replaced on a 7 to 30 day cycle. Wearers generally purchase a supply of disposable lenses that will last six months to one year.
Hard
Hard contact lenses are made from a rigid plastic resin, polymethylemethacrylate (PMMA). The lenses are more durable and easier to handle than soft contact lenses, but many people may find them uncomfortable. PMMA does not absorb water, and does not allow for the transmission of oxygen through the lens to the eye. Hard contact lenses should be removed daily.
Rigid Gas Permeable
Rigid gas permeable (RGP) contact lenses are made of a non-absorbent material that is oxygen permeable. RGP lenses are durable and easy to handle like hard contact lenses, but more comfortable to wear, though usually not as comfortable as soft contact lenses. Most RGP lenses are used for daily wear, but some lenses can be worn for extended periods of time.
Toric
Toric lenses are either hard or soft contact lenses used to treat astigmatism, which cannot be corrected with traditional spherical contact lenses.
