PRESCRIPTION Eyeglass Types: Which One IS Right for You?
Whether you are shopping for new lenses for a frame you had before, or are just trying to understand what those cryptic acronyms and numbers on your prescription really mean, the first step is to understand the different types of prescription lenses that exist, and to which group yours belong.
Since the details can get too technical, in this first post we will keep this section short and sweet, just enough for you to have a good idea to which group you belong, which will in turn help you decide what eyeglasses types are right for you.
And for those optics aficionados who seek a deeper understanding of the topic, make sure you bookmark this page and check back with us again soon, as our ophthalmologists and optometrists are writing those segments as we speak, and good stuff will be added regularly to the site that would make you an optics connoisseur!
Prescription Eyeglass Types
One way of categorizing prescription eyeglasses is based on the type of correction they provide, that is, the field of vision –aka field of view – they are accommodating for. In optometry, there are three fields of vision:
- The near field: includes a range of distances from about 10, up to 18 inches away from your face. This is the distance ideal for activities such as reading or texting.
- The intermediate field: this is the range of 18 to 25 inches from your face, ideal for computer use.
- The distance field: this include distance beyond 25 inches from your face. When you drive a car, reading signs on the highway, watch TV at home, take notes off of the board in the classroom at school, watch a movie in the theater, play sports, talk to a colleague from across the table, look at the scenery on a trip, etc. you are using your distance field of vision.
Single Vision
This is the most common type of prescription lens, which accommodates for only a single field of vision (see above for what a field of vision is). These lenses have a single prescription power throughout the entire lens, which means they provide the same amount of vision correction everywhere on the lens, and that is why they can only correct for one field of view. They are ideal for correcting nearsightedness (myopia) for people who have trouble seeing far away objects, farsightedness (hyperopia) for those who have difficulty seeing close distances, and presbyopia which is a form of farsightedness caused by aging.
If you have a good distance vision, but have trouble seeing close distances – whether you are farsighted due to hyperopia or presbyopia– you can take advantage of single-vision glasses for reading, or for computer work, but not both.
Note that you should specify which activity you want to perform with these glasses otherwise it is assumed usually that you want reading glasses. If ordering single-vision lenses on our website, and you want your single visions for computer work, please either leave us a note right during the checkout process, or contact customer service to emphasize what type of Single Vision lenses you want, otherwise reading glasses would be assumed.
Unlike purely farsighted or nearsighted people who have trouble with only one field of view –near or far, but not both – there are plenty of people who need correction at both close and far distances. In such a case the individual might find it very inconvenient to carry two single-vision eyeglasses at all times, one for the near, and one for the distance view. While a single vision can only accommodate for one distance, bifocal and progressive lenses are able to accommodate more than one power and one field of view.
Bifocals
Bifocal lenses are a type of multi-focal lens – one that has more than one point of focus. Therefore, for those who need glasses for both reading and distance, bifocals seems to offer an attractive alternative.
Unlike single-vision lenses, bifocals have two viewing regions, each with a different correcting power, marked by a visible separating line. The larger upper portion of these lenses are meant for distance vision, while a smaller segment below is meant for reading.
Therefore in order to clearly see distant objects, the wearer of the bifocals would need to look straight through the lenses (through the upper distant vision region), while reading a book would require them to adjust the tilt of their head, and the book placement such that the book would be visible through the bottom near-vision segment of the lens.
As the patient’s eyes glide from one region to the other, crossing the separation line, there is a noticeable and abrupt change in the lens power. Thus, it takes first-time wearers of these glasses some time to get accustomed to bifocals, as they learn how to best move their eyes between the reading and the distance sections of the lens.
If you need corrective power at both near and distance, but don’t want bifocals due to their visible separation line, consider progressive lenses explained further below.
If you need corrective power at both near and intermediate distances –for example for both reading and computer use –you might want to consider workspace progressive lenses. See the appropriate section below.
Progressives
Even though bifocals can serve as a convenient option for those who need corrective power for distance, as well as near or intermediate vision, they are sometimes disliked and avoided due to their visible line that separates the two viewing regions.
Progressive lenses, also referred to as standard progressive, are a type of multi-focal lens that can provide corrective power for all three fields of vision: near, intermediate and distance. Yet, unlike bifocals, they have no visible separation lines. This is the result of advancements in lens production and optometry that has made it possible to manufacture lenses where that the power changes across the lens so gradually that no separation lines are left behind.
Similar to the bifocals, most of the upper region of the progressive lens is for distance vision, and that is the primary viewing region of these lenses. As you go from the top area of the lens towards the bottom, the prescription power progressively and smoothly changes, until you reach the bottom, where a smaller region of the lens provides correction for the near vision. During the transition from the larger distance-vision region to the smaller near-vision segment, there exists an even smaller area that provides corrective power for intermediate vision.
Although unlike bifocals, there are no abrupt changes in the lens power as the patient’s eyes move from one region to the next in a progressive, the wearers of the lenses, just as it was the case with bifocals, would need to get accustomed to using these lenses. So if you are planning to use this type of lenses, and you are a first-time progressive wearer, expects no less than 2-4 weeks before you get comfortable finding the sweet spot needed for your activity, by learning how to move your eyes and adjust the tilt of your head appropriately.
Workspace/Office Progressives
While standard progressive lenses try to handle the full spectrum of distant all the way to near vision, the shift in the corrective power across the lens can sometimes be so dramatic (depending on the prescription and correction levels needed) that could potentially introduce slight distortions on either of the left or right edges of the lens.
Now if you are planning to use your progressives in an indoor environment such as an office, where you would spend majority of your time at the computer, interacting with the colleagues around, you may not really need distant-vision correction. In such cases you might only need near and intermediate distance correction; and that is where you can use workspace progressives.
As opposed to standard progressives, the workspace progressive lenses only offer correction for intermediate and near vision. Thus since the overall range of prescription powers covered by the workspace progressive is smaller than that of the standard type, the introduced distortions are also far less in this type compared to those of the standard ones.
Lens Material
While there are numerous different types of material used in production of prescription lenses, the following are three of the most common one.
CR-39
CR-39 which is also referred to as regular plastic, have better visual clarity than the thinner polycarbonate or High Index lenses, and they are less expensive. For low prescriptions, regular plastic lenses are usually the best choice for prescription lens material. However, regular plastic prescription lenses also have some drawbacks and limitations in certain situations. For example, if your prescription is higher than ±3.00, the regular plastic lens will become thicker and heavier, and you could benefit from using a Polycarbonate or High Index lens instead. Also, if you have a three-piece rimless eyeglass frame, you should not use a regular plastic lens because it is likely to crack under the strain.
Finally, children and sporting adults are recommended to use Polycarbonate or High Index lenses because they offer better eye protection than regular plastic ones. CR-39 is the standard type of plastic used for everyday use, around the office, or for shopping. These lenses have the least distortion of any non-glass lens. For children or active adults engaged in sporting activities, we strongly recommend polycarbonate (impact resistant) lenses.
Poly Lens
Poly lens, also known as polycarbonate lenses, are among the most popular lens materials in the market. Polycarbonate lenses have the following features:
- Ability to block UV rays.
- Shatter resistant.
- Scratch resistant.
- Polycarbonate is lighter weight than normal plastic.
- Due to its refractive index, Poly lens provides highest quality vision compared to many other lens materials including High-index plastics.
These properties of Poly lenses makes them a great candidate for use in sports glasses and glasses for children and teenagers. Athletes and anyone who wears rimless glasses are great candidates for polycarbonate lenses. Because polycarbonate is soft and will scratch easily, scratch resistant coating is typically applied after shaping and polishing the lens. Polycarbonate lenses are thinner and lighter than standard plastic varieties, and also have much more durability.
Polycarbonate is ideal for strong prescriptions because it corrects vision without adding thickness, which can distort the wearer’s appearance. Best of all, polycarbonate lenses are virtually unbreakable, making them a great choice for children and active adults, as already mentioned.
Another impressive addition to the polycarbonate lenses is that they provide 100% UV protection.
High-index Plastics
Benefits: No-distortion, shatterproof lens for kids, active adults Polycarbonate lenses are thinner and lighter than standard plastic varieties, and also much more durable. Polycarbonate is ideal for strong prescriptions because it corrects vision without adding thickness, which can distort the wearer’s appearance. Best of all, polycarbonate lenses are virtually unbreakable, making them a great choice for children and active adults.
Lens Options and Customizations
Clear Lenses
This is the most basic type of lens, made of clear material, as opposed to polarized lenses which are basically sunglasses, or the transition lenses that darken when exposed to sunlight.
Transition Lenses
Another popular type of eyeglass lenses are transition, also known as photochromic, lenses. This type of lenses adapt to the lighting you are exposed to; if you are in a dark or soft-light setting –such as indoors – the lenses will be clear just like any normal clear lens. However, if you get exposed to bright sunlight, the transition lenses start darkening rapidly, reaching their full capacity within about a minute from exposure. And once you’re back indoors, they slowly start clearing up.
In a way these lenses try to offer best of both worlds, that is, a clear lens for indoors, and sunglasses for sunny outdoors, and even though they might be pricey, they can eliminate the need to carry prescription sunglasses with you at all times.
However, there are some caveats that you must know about before deciding whether to buy transition lenses or not.
One drawback of normal transition lenses is that although they work beautifully in almost all sunny settings, they do not work when you are driving! This is because transition lenses are only activated when exposed to large amounts of ultraviolet radiation around. However, since the windshield screen of most modern cars today block majority of the UV light passing through, these normal transition lenses may never get activated while driving!
One solution is using Extra Active transition lenses that are more sensitive to UV light, and therefore they do darken during driving. However, while these lenses fix one problem, they introduce another drawback. Due to their extra sensitivity to UV radiation, they may darken just a little bit even when you are indoors, if there is plenty of natural lighting in the room.
In conclusion, how you are planning to use a pair of sunglasses can determine if transition lenses are a good choice for you or not. If your indoor setting is mostly an office space without much natural lighting, you can take advantage of Extra Active transition lenses so that you get the darkening effect while driving as well. On the other hand, if you plan to use your glasses in any indoor condition where there may or may not be natural lighting, you should avoid Extra Active transition lenses, and go with either normal transition lenses –in which case they won’t be effective during driving– or forgo transition lenses altogether and opt to use a separate pair of sunglasses when in sunlight –in which case you should carry both your normal prescription glasses and your prescription sunglasses at all times.
Please note that in our ordering system, we have eliminated the Extra Active option in favor of simplicity. However, if you are interested in this type of transition lenses, please contact our customer service so we can help you with ordering of this type of lenses.
Polarized Lenses
Polarized lenses are basically high quality prescription sunglasses. If you need to use prescription glasses while driving, and would like to protect your eyes from the intense sunlight or from the annoying glare on the road, polarized lenses are your best bet. Unlike majority of the transition lens types, polarized lenses work flawlessly while sitting in the car.
The polarization of these lenses means that they can reduce the intensity of the light that is reflected off of shiny surfaces such as cars, windshields, wet roads or even your own dashboard.
Polarized lenses are a great choice if you enjoy water sports, such as sailing or fishing, and would like to eliminate the glare that comes from the water surface. Skiers and snowboarders, however, should preferably avoid polarized lenses since the movements of the head can change the brightness of the light you see which can in turn interfere with your judgement regarding snow conditions.
It should also be noted that since the light coming from LCD displays (such as your cellphone screen, or some gauges on your car dashboard) is polarized, using polarized lens to view these surfaces would
Anti Reflective (AR) Lenses
Anti-Reflective (AR) Coatings are designed such that they increase the optical quality of the lenses by allowing more light through. A lens without AR usually reflects off about 20% of the light hitting it. This can look unattractive since there will be reflection off of your lenses and people would not be able to see your eyes. AR coated lenses, however, look almost clear with no reflections, and moreover, you receive more light into your eyes, which will improve your optical experience. Another advantage of AR coating is that it will reduce halos and glares around bright objects at night, thus improving the night vision significantly. This effect is especially noticeable when driving at night looking at oncoming headlights. What about the back surface of the lens (the one facing your eyes). Back surface reflections cause you to see things that you really do not want to see, such as your eye, your eyelashes, and the skin around your eyes. Reflections and glare combined with light reduction cause eye fatigue, eye strain, and reduced visual acuity. At LensOnUs, we apply this coating not only to the front surface of your lenses (the side visible to others), but to the back side of the lenses as well. This will ensure even greater optical quality and clarity and less glare and eye fatigue. At LensOnUs, our high quality AR has even more coatings than usual that would provide extra benefits. These additional layers will make the lens more scratch-resistant, will block more UV radiations, and will make the lens harder to smudge and easier to clean (thanks to an extra hydrophobic coating) If you want more benefits, check out our Blue-blocking AR!
Blue Defense Anti Reflective Lenses
Our Blue Defense AR provides all the benefits offered by standard AR, plus an additional benefit that can protect your eyes. The advantages of standard AR are: Less reflections off of the front surface of your lens, greater optical quality due to more light reaching your eyes, higher scratch-resistance, reducing UV radiations to your eyes, harder to smudge and easier to clean, less halo and glares around bright objects at night. Now, in addition to all these great benefits, our Blue-Defense AR is designed to block a portion of the visible blue light, which will not only reduce glare at greater extent, but will protect your eyes against unwanted high energy blue light which will in turn reduces the change of macular degeneration and other retinal damage. While most blue-blocking AR on the market reflect this portion of the blue light off of the front surface of your lens, our Blue-Defense AR coating does not reflect the unwanted blue light, as that would defeat the whole purpose of the AR coatings in the first place! Our Blue-Defense AR achieves this feat by absorbing and essentially cancelling these blue lights without reflecting them back.
