Why Lens Quality Matters
Choosing frames is the fun part, but your lenses are the most important factor in good vision. Lenses vary in what they are designed to do. There are numerous design considerations and a range of quality available depending on your needs and budget.
- Lens Type – single vision, anti-fatigue, office, progressives, bifocals, polarized and many more. All of these lenses have pros and cons depending on the tasks they are used for
- Material, index and surfacing – these determine the optical quality (level of distortion) and lens thickness
- Coatings – these determine the level of glare, UV protection, blue-light filtering, scratch resistance, ease of cleaning and much more
Making sense of it all is our job. We will help you choose lenses best suited to your lifestyle, budget and and vision needs. Read on for more information on lens designs and options.
This is the most simple type of lens, providing clear vision at a single focal distance. For most people, these lenses are made for either far, computer, or reading viewing distance. We can categorize these lenses into 2 types:
These lenses are the least expensive since they are mass produced in a variety of common powers. Depending on optical quality and coatings (more on this below), they are a good option for low prescriptions. The drawback is that when your eyes are not looking through the optical centre, the vision can get distorted or blurry. The amount of blur is dependent on the distance from the eye to the lens, the curvature (wrap) of the frame, as well as the lens power.
For ideal vision with these lenses, they must be centered precisely to your pupils, in a well fitting frame that does not sit far from the eyes. Proper centration requires 2 measurements, monocular PD and OC height (see below for what these are). Without these measurements, centration is impossible. Because online eyewear purchases cannot take into account where your pupil sits in the frame, the only measurement they can use is the horizontal distance between your eyes (PD), not enough to properly center the lens, often leading to eye strain and blur when looking off center.
These lenses provide superior vision because they are custom made to account for the optics of how the eyes move relative to the lenses. The complex calculations take into account the following measurements:
- Monocular PD – the distance from the centre of your nose to the centre of the pupil on each side
OC height – the vertical distance from the bottom of the frame to your pupil
- Frame wrap – the curvature of the frame
- Pantoscopic tilt – the tilt angle of the bottom of your frame relative to the front plane of the face
- Vertex distance – the distance from the back of the lens to the front of your eye
These measurements can only be taken once you have selected a frame and it is properly adjusted on your face. Because they provide correct optics across the ENTIRE lens, they give you superior clarity from edge to edge. See the bottom of this page for more on the importance of accurate measurements.
This type of lens came to market a few years ago to address the problem of digital eye strain. Our eyes were designed by nature to suit our “hunter-gatherer” ancestors who were not glued to their iphones. These days, we are using our eyes up close more than for distance, resulting in a huge amount of stress on our focusing muscles. This leads to eye strain, fatigue and dry eyes from reduced blinking.
An anti-fatigue lens has a “near activated zone” in the bottom with an adjusted focal power suited for viewing digital devices at near. This helps reduce the strain on the focusing system leading to less fatigue and more comfortable vision. Again, accurate measurements are critical to ensure proper placement of this near zone.
Progressive lenses are designed to have increased reading power the further down you look in the lens. As with all lenses, accurate measurements are essential for correct placement of your distance, intermediate and reading zones. If this is not done properly, you will have a very narrow field of clear vision find yourself “hunting” for a clear image.
These lenses are all unique in how the power transitions from distance to near. Some lenses are designed with wider distance and reading zones but have a very narrow computer zone, others have wide computer viewing zones but narrow fields of view at distance. The design choice is based on what you need the most. For those that need very wide reading areas and don’t mind a line, there are always traditional bifocals.
Higher end progressives will have less side blur because the prescription is controlled for points further from the centre. These digital progressives require precise measurements of the way your frame sits on your face and provide a optimal vision. There are also newer designs that equalize the magnification difference between lenses, this is especially important if your prescription is quite different between eyes.
Because single vision lenses give clear vision only for near distances, they often require you to lean in to your screen to see clearly (as shown here). Progressives on the other hand, have a relatively narrow near focal zone located lower down in the lens, requiring you to tilt your chin up and do a lot of head turning to find the “sweet spot” for computer viewing. This leads to eye strain, frustration and literally a pain in the neck!
Office lenses are the ideal solution and designed to allow clear computer viewing without tilting your head. This is because the focal point in the centre of the lens is at your computer distance. Above this point there is slightly less power to allow you to see a few metres across a room, and below this point is added reading power to allow you to read items up close and see your keyboard clearly. These variable near focus lenses have minimal side blur and allow wider fields of view than progressives. They can be customized for a slightly farther distance for those that need to see clients or get up from their desks more often, but are not suitable for driving or far distance viewing.
Almost all lenses nowadays have anti-glare coatings but they are NOT created equal.
Conventional single vision lenses come pre-coated from the factory. These coatings can vary in quality, which is often price dependent. Lower end lenses have few layers of anti-glare. The more layers, the better the glare reduction since each layer is specific for eliminating glare of a certain wavelength. Good quality anti-glare coatings will transmit over 99.5% of visible light!
Better lenses also have oil-resistant, water-resistant and anti-static coatings to make them easier to clean. To test if your lenses have these higher end coatings, put a sticky note on them and see if it sticks (it shouldn’t)! They should also bead up when you try to write on them with marker, but we don’t want you to try this at home.
Blue light coatings
These lenses have a blue tinge to them since they are designed to reflect (filter) short wavelength blue light from LED devices. There is conflicting evidence if long term exposure to this light at close distance can cause damage to the eyes, but there are other reasons to consider these coatings:
- Blue light affects your circadian rhythm. When you look at digital devices, especially towards bedtime, the body wants to stay awake as if it were daytime. By blocking this light, you may have an easier time going to sleep after some late night phone surfing!
- Blue light is the most out of focus wavelength. Because it focuses in front of the retina, the eyes will often strain to get it into focus. By blocking this light, the images are sharper and the eyes stay more relaxed and blink normally. This can also help with dry eyes
This is a type of lens designed specifically for night and low-light driving to reduce glare. They have an anti-glare coating specifically tuned to substantially reduce glare from modern LED and HID headlights as well as street light glare and light scatter from rain and fog. They also have a very faint yellow tint to enhance low light contrast and brighten up the vision at dawn and dusk. These lenses have a blue tinge similar to blue light coatings.
Transitions and Polarized Lenses
These are not coatings but they are materials embedded in your lens. Transitions or photochromic films are designed to turn dark in response to UV or short wavelength light. Good quality photochromics darken quickly and provide 100% UV protection, as well as turn clear more quickly than older type films.
Polarized sunglass lenses are designed to reduce reflected light from horizontal surfaces. Some manufacturers use dual layer polarization for even better glare reduction. These provide the best clarity and glare reduction for driving, golfing, fishing, water and winter sports.
Accurate Measurements Matter
Better Vision through Technology
While online retailers make you take your own “PD” with a ruler, we use the latest high tech digital measurement devices. Simply put, more precise measurements mean better optics, and therefore better vision. This modern tech is similar to motion capture technology used in the movie industry to create realistic animations. By adapting this technology to measuring the way your eyes sit and move in your frame, we can give you quality optics and the clearest and most comfortable vision possible.
This tech, combined with the expert knowledge of your optical consultant at Mission Eye Care will ensure you are looking and seeing to your fullest potential.