Here are some of the basic terms you may come across when looking or buying new lenses. If you’re not sure of the kind of lens that you’re looking for or you don’t know the terms that well, please speak to one of our team members. Our experienced, knowledgeable opticians and optometric assistants will help you pick the lens that will work best for you.
Single Vision Lenses
These lenses provide focus at one particular distance. This may be used to see things that are far away, such as driving, or for seeing things at a closer distance, such as reading or browsing on a computer. 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.
Bifocals provide vision at two specific distances, with a dividing line evident on the surface of the lens. These are mostly used when driving and reading. However, bifocals are often made of two lenses – one on the top when using a computer and the other at the bottom for reading.
These lenses give variable powers throughout the lens. They usually have a distance lens on top, a reading lens at 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 lens is for the computer and the bottom lens 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 that you get blue-filtering coating for computer glasses to protect your eyes from short-wavelength light emitted from electronic screens.
This is a special lens material usually used for higher-powered lenses, to reduce thickness, weight, and peripheral distortion in the lens.
These lenses come with computer-generated lens designs. The best brands are even customized to suit the shape of your optical frame shape, the distance from your eyes, your 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.
Scratch-resistant coatings are 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 scratchproof. 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.
These types of coatings 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. 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.
Blue-filtering coatings 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 and decrease fatigue by eliminating some of the glare inherent with short-wavelength light.
Basic Sunglasses Terminology
Browse 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 or wet days when there is a lot of reflection off the road or for fishing or water sports to decrease reflections off the water.
These are lenses are clear indoors and darken when exposed to UV light, 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.
Grey tints decrease light transmission evenly across the colour spectrum. These are great for decreasing brightness without affecting colour perception.
Brown tints reduce 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, yellow tints help increase contrast without cutting down on the light transmission as much as a standard sunglass lens.