Types of Eye Glass Lenses
Eyeglass lenses can be designed to help people see at various distances. At Real Eyes Optometry, we believe that it is important to know your options so you can make the right choices.
Types of Eye Glass Lenses: Single Vision Lenses
Amongst the different types of eye glass lenses, single-vision lenses are designed to help people see at one viewing distance. This is the most common type of lens used. A single-vision lens can be used to help with either nearsightedness or farsightedness, but it cannot do both simultaneously.
Types of Eye Glass Lenses: Bifocal Lenses
Bifocal eye glass lenses are designed to help people see at two viewing distances. They are designed with a smaller reading area (good for reading books, magazines, prescription bottles, and newspapers), usually in the shape of a sideways ‘D’ near the bottom of the lens.
Above this segment is the distance viewing portion. Bifocal lenses do not correct for an intermediate/computer viewing distance (50-60cm). If you are having trouble with this intermediate area, a Trifocal or Progressive Lens may be a better option for you (discussed below).
Types of Eye Glass Lenses: Trifocal Lenses
In addition to offering a viewing area for both near and far objects, the trifocal eye glass lenses offer clarity for intermediate distances as well (50-60cm). This intermediate area can include computer screens, the dashboard of your car or viewing items on a grocery shelf. Each of these different viewing zones is demarcated with a visible line on the lens.
Types of Eye Glass Lenses: Progressive Lenses
This is another type of eyeglass lenses that offers clarity for your full visual range, all distances including intermediate, near, and far. However, unlike Trifocal lenses, there is no line demarcating the different viewing areas. Instead, they offer a smooth transition for focusing on objects in the distance to nearby objects. A gradual change in lens power occurs allowing clear distance vision through the top portion of the lens, clear intermediate vision through the middle portion of the lens, and clear near vision through the lower part of the lens. For more information, watch this video.
Types of Eye Glass Lenses: Computer Vision
These types of eyeglass lenses are specialized to relieve eye strain, vision blur, redness, and other symptoms of discomfort associated with computer use. With the increased amount of time spent working and relaxing in front of a screen, they are designed to correct your vision for an intermediate distance (50-70cm away) and can be combined with a ‘blue blocking’ lens coating (ideal for regular computer use).
Another option are computer progressives (AKA an office lens), where the top of the lens is for computer use and the bottom of the lens is for near use (reading or looking at the keyboard).
Types of Eye Glass Lenses: Aspheric
These lenses are designed to have a flatter curvature compared to conventional lenses. This makes the lenses have a slimmer profile while reducing distortion created by not looking through the center of the lens.
This results in better peripheral vision by widening your field of view. These lenses are a great option for patients with stronger prescriptions for farsightedness and nearsightedness because they reduce the magnification and minification effects created by such prescriptions. The magnification effects created by a strong farsighted prescription lens can create a “bug-eyed” look on the wearer.
Eye Glass Lenses: Material
High Index Lenses: These lenses are designed to be noticeably thinner and lighter compared to glass, CR-39 (hard resin), and other plastic lenses. They allow the wearer to avoid having “coke-bottle” lenses. There are different types of high index lenses, most of them are classified by a number. In general, the higher the number, the thinner and lighter the lens is. Aspheric + High Index Lenses: Combining these two lens options creates a lens that is noticeably lighter, slimmer, and thinner.
High-Index includes 1.60, 1.67, and 1.74. These lenses are thinner than mid-index, glass, or plastic lenses.
Mid-Index includes 1.54, 1.56, and 1.57. These lenses that are thinner than glass but not as strong as CR-39.
Polycarbonate Lenses: These lenses are thin and light with enhanced impact resistance compared to plastic lenses (10x more). They are commonly used in safety eyewear, sports eyewear, and children’s lenses. However, they can scratch easily therefore a scratch-coating is advised.
Eye Glass Lenses: Coatings and Tints
Photochromic Lenses/Transitions: These are lenses that are capable of darkening when exposed to UV light. There are photochromic molecules that are either arranged throughout the entire lens or on a coating on the front of the lens. When these molecules are exposed to UV light, it causes the lens to tint and become darker. When not exposed to UV light, the lens returns to being clear.
There are various types of photochromic options available. Some lenses will only darken when exposed to direct sunlight, while others can darken in low light or no light conditions. There are also a variety of lens tint colors available. Transition lenses are great lenses for those wanting to avoid the hassle of needing both prescription glasses and prescription sunglasses or for patients who are sensitive to light.
Polarized Lenses: These lenses significantly reduce glare from flat, reflective surfaces like water or the road. They are a great option for driving, water activities like fishing, and many other outdoor sports like golfing, jogging, biking, skiing and snowboarding.
Here is how polarized lenses work: most glare occurs from horizontal surfaces which makes the light “horizontally polarized”. Polarized lenses are vertically-oriented “polarizers”, which blocks horizontally polarized light. This creates a view of the world almost free of glare with increased visibility and reduced eye strain all at the same time.
Anti-Reflective Coating (AR Coating): These eye glass lenses help to eliminate glare, reflections, and ghost images. The AR coating blocks light reflections from the front and back surface of the lens, allowing 99.5% of light to be transmitted through the lens. Not only does this mean that your vision will have greater clarity, it will also enhance the cosmetic appeal of your lenses by making them nearly invisible. This coating is especially useful for driving at night and comes standard in most lens packages.
Scratch Resistant Coating: No lens can be completely scratch proof, however, adding a scratch resistant coating to your lens creates a harder lens surface that will be more resistant to scratching. Scratches can interfere with the clarity and quality of your vision, and most lenses do come with a scratch resistant coating.
‘Blue-blocker’ Lenses: Blue light radiation can be emitted from overhead lights and digital screens (computer, tablet, phone, etc), and an increasing amount of research has come out on the harmful effects of blue light. These effects include damage to the crystalline lens (which can result in cataracts), retina (which can result in macular degeneration), and inflammation of the cornea and conjunctiva. It can also lead to visual discomfort by causing glare and eye strain. ‘Blue-blocking’ lenses block this wavelength of light to reduce visual discomfort and the harmful effects of blue light.
Cosmetic Tinted Lenses: Eye glass lenses can come in a variety of different tints. Feel free to ask one of our opticians or optometrists about which color options may be best for you to increase the quality of your vision or achieve an aesthetic look.