Following are some of the basic terms you may encounter when ordering new lenses. If you're really not a details person, just come in and tell us about you, your lifestyle, and what you want the lenses to do for you. Our experienced, knowledgeable opticians and optometric assistants will direct you toward the lens that will work best for you.
Provide focus at one particular distance. This may be for far distances, such as driving, or for near distances, such as reading or computers. If you are under 40 years of age, you typically only need single vision lenses, and your eyes can adjust through those lenses for whatever distance you want to work at.
Provide vision at two specific distances, with a dividing line evident on the surface of the lens. Usually made for far distance/driving and reading. However, these are often made for computer on top and reading on the bottom, as well.
Gives variable powers throughout the lens, usually distance on top, reading on the bottom, and a gradual “progression” of power from the top to the bottom. This allows the greatest range of vision for different distances, and you just look through the part of the lens designed for the distance you are working at. If you are over 40 and your eyes don't have the range of focus they used to, progressive lenses can give you back your full range of vision without having to take the glasses on and off. There are no lines on these lenses.
These can be single vision – designed solely for the computer, bifocal – where the top is for the computer and the bottom is for reading with a dividing line, or progressive – the top is for the computer and the bottom is for reading with no line. We recommend for computer glasses to also get a blue-filtering coating to protect your eyes from short-wavelength light emitted from electronic screens.
A special lens material, usually used for higher powered lenses, to reduce thickness, weight, and peripheral distortion in the lens.
Computer-generated lens designs, the best brands are even customized for your frame shape, distance from your eyes, lens power, the tilt of your lenses, and your individual visual needs. These lenses differ from conventional lenses, which grind the surface of the lens for large areas resulting in distortion in the periphery, particularly in progressive lenses, and high-prescription lenses. Digitally surfaced or freeform lenses have the curves mathematically computed at multiple points over the lens and are manipulated to contrast the front and back of the lens to minimize distortions caused by the physics of a conventional lens. They also push any remaining distortion away from where the patient would typically look through the lens.
A hard coating on the lens surface to decrease scratching of the lens plastic. There is a wide variance in the hardness/toughness of scratch coatings from different lens suppliers – remember these are scratch-RESISTANT coatings, not scratch-PROOF. We typically recommend the best scratch-resistant coating you can afford, as it does prolong lens longevity. Most of the coatings we use have a two-year warranty.
Decrease reflections off the surface of the lens. For example, when on a computer, the lights around you can reflect off the inside of your lenses, causing glare. And in photographs, your lenses can have large reflections from camera flashes or surrounding lights/sunlight. A good anti-reflection coating decreases these reflections substantially, improving both the comfort and cosmetics of your glasses.
Decrease damage caused by short-wavelength light emitted from electronic screens and decrease glare from computer screens. For people spending multiple hours per day of screen time, the cumulative exposure to blue light can cause damage to their retinas, increasing the risk of macular degeneration. Special blue-filtering coatings minimize this risk. They also improve comfort/decrease fatigue by eliminating some of the glare inherent with short-wavelength light.
Scroll through these basic terms you may hear when you start looking for sunglasses. For more details on these or any other sunglass-related questions, our knowledgeable opticians and optometric assistants at Eye To Eye Optometry Clinic would be happy to help you:
Polarized lenses cut down glare. They are great for those snowy/wet days when there is a lot of reflection off the road or for fishing/water sports to decrease reflections off the water.
These are lenses that are clear indoors and go dark when exposed to UV light, such as during outdoor activities. Note that they do NOT darken significantly in a vehicle because the windows of the vehicle block out most of the UV light.
Decreases light transmission evenly across the colour spectrum. Great for decreasing brightness without impacting on colour perception.
Decreases light transmission more in the cooler colour spectrum than in the warm spectrum, therefore allowing a softer/warmer look to the day.
Often used for shooting or for overcast days to increase contrast without cutting down on the light transmission as much as a standard sunglass lens.
The top of the lens is tinted darker than the bottom of the lens. Some people prefer this because it allows for decreased brightness from the overhead rays of the sun, but still allows for reading clearly through the bottom of the lens.