Information about Lenses:
Recorded in a measurement know as diopters (D), the strength of a lens can be manipulated by changing the material it is made from and by altering the curvature and shape of the lens. A minus (-) sign in front of the diopter numerical indicates that the lens is concave, a lens shape typically used to enhance distance vision. A plus (+) sign in front of the diopter numerical typically indicates a convex lens, a lens shape typically used to enhance close up vision.
Single Vision Lenses are utilized for accommodating ones prescription typically just for either near vision needs or distance vision need. However, many find that a pair of glasses ‘just for computer use’ offers another utilization of a single vision lens. A single vision lens has the same focal power throughout the entire lens. Single Vision lenses corrects ones vision for nearsightedness, farsightedness or astigmatism.
This lens design was created to accommodate strictly near point needs and distant needs in one lens. The lens will have a visible horizontal line that is anywhere from 22 millimeters to 45 millimeters in size. This distinctive line is the dividing line between the distance and reading prescriptions of the lens.
Trifocal Lenses: A trifocal lens accommodates ones prescription with three distinct segments of vision. These segments are for near, mid-range and distance vision. Each segment of the lens accommodates only that specific aspect of the prescription. A trifocal lens has two visible lines in the lens.
An Occupational Lens is a truly custom lens that is designed to accommodate specific visual needs typically for ones profession. This lens may be fabricated to have an individuals multi-focal placed in both the lower portions of the lens – which is where a bifocal is traditional placed – and this lens will also have the bifocal in the upper portion of the lens. This type of lens is often used by tradesmen, such as an electrician or a plumber, who’s job requires being able to see objects up close by looking through either the upper or lower portion of the lens in their glasses.
Progressive lenses provide an individual with the ability to have precise vision for any focal length. The intent of this lens is to restore one’s ‘natural vision’ allowing an individual to have clarity no matter what they may need to focus on seeing. By design, a progressive lens give one a smooth transition from one focal length to another. There is no visible line in this product. Esthetically, a progressive lens will enhance the cosmetics of an individuals’ glasses, as it will appear to be a single vision lens since there are no visible lines that appear on the surface. Considering there are over 34 manufacturers of progressive lenses and more than 585 designs of a progressive lens, one should carefully consider the expertise, and availability to the lens products that are on the market, when choosing an eye care professional to fabricate the prescription that the Optometrist or Ophthalmologist has written.
The use of digital lenses, also know as ‘free-form lenses’ or ‘high-definition lenses’, in ophthalmic eyeglasses is increasing in eye care practices all over the world. Although this technology has been around for quite some time, it is becoming more common and preferred. Digital lens processing offers a higher level of precision when creating the lens for both single vision prescriptions and multifocal prescriptions and also opens up the possibility to create extremely unique and versatile lenses in terms of shape and prescription. By using processing equipment that requires the measure, analysis and computation of lens data in the form of numerical digits, both surfaces of a lens can be directly surfaced with a high level of accuracy. Digital eyeglass lenses offer an unprecedented degree of customization. Therefore, with this improved level of precision a patient will experience more comfort in their prescription and a greater level of visual satisfaction. In the end, we can compare a regular lens to a tube television and a digital lens to a plasma flat panel television. Due to the manufacturing process, a digital lens allows for more peripheral vision and a sharper picture.
Glass was the original material used to make spectacle lenses and still is used today. Glass lenses offer excellent optics and are the most scratch-resistant. The primary disadvantage to glass lenses is that it is the heaviest of the lens materials on the market today. Glass lenses may weigh more than twice the weight of other lens products. Glass lenses are heat or chemically treated to increase impact resistance and are made to certain safety standards that will protect the eyes under normal wearing conditions.
Hi-Index materials offer a thinner material to accommodate higher prescriptions. This lens material is extremely aesthetic and offers excellent visual quality. A high index lens has a higher index of refraction so that light will have an increased refraction without an increase in the thickness of the lens material. The index of a glass lens is 1.523 while the index for a plastic lens (CR-39) is 1.498. Hi-Index lens materials are available with the index of refraction ranging between 1.60 to 1.74. The thinner the lens material used, the lighter in weight ones prescription will be.
Lenses are available in CR-39, more commonly known as ‘plastic lenses’. This lens offers an alternative to glass lenses. Columbian Resin #39 is a plastic polymer that was introduced in the late 1940’s. Plastic lenses transmit visible light and absorb ultraviolet light better then glass lenses. CR-39 plastic has an index of refraction of 1.498. CR-39 is now a trademarked product of PPG Industries (Pittsburgh Plate Glass Company).
When maximum eye protection is appropriate or when treating a child, polycarbonate lenses are typically recommended. Polycarbonate lenses are impact resistant. They are used in safety and sports eyewear and often will be used to accommodate more significant powers in ones prescription when a hi-index lens is not used. It is the lens of choice for children’s eye-wear due to the safety properties of the lens material..
Trivex lenses have the impact resistance and inherent UV protection of polycarbonate. Trivex rises above polycarbonate with both its optical quality and suitability for drill mounting three-piece rimless frames. Due to the ease with which Trivex can be drilled, as well as its resistance to cracking around the drill holes, Trivex is a preferred lens for this application. One other advantage that Trivex has over polycarbonate is that it can be more easily tinted. In addition, a Trivex lens may not scratch as easily as a polycarbonate lens. Trivex material provides a ‘complete package’ of lightweight comfort, strength and protection, and superior optical quality. When considering Trivex lenses remember that you are purchasing a premium product.
ANTI-REFLECTION TREATMENT (A/R)
Anti-Reflective (AR) coatings serve many purposes, from promoting healthy vision to enhancing your physical appearance. Opticians dispense ‘anti-reflective lenses’ because of the decrease reflections off of the lens surface, which makes the lens look cosmetically better and the lens produces less glare, which is particularly noticeable when driving at night or when working in front of a computer monitor. With this decrease in glare one finds that their eyes are less tired, particularly at the end of the day. An anti-reflective lens allows more light to pass through the lens increasing contrast and therefore increasing ones visual acuity. This is very noticeable in low light settings. Typically used today is a multi-layer anti-reflective treatment to both surfaces of the lens. This highly sophisticated treatment eliminates virtually all surface reflections; hence night driving and many other tasks are safer and more comfortable.
SCRATCH RESISTANT TREATMENT
A scratch-resistant treatment or anti-scratch coating does not interfere with the function of a lens therefore it does not affect ones vision. This lens treatment, typically applied to plastic lenses, creates a bond directly with the lens that reduces the potential for hairline scratches. Keep in mind that a scratch-resistant lens is NOT 100% scratch proof; it is an aid to help prevent minor scratches! Minor scratches can damage the surface of a lens and impair ones vision. The scratch-resistant treatment adds a protective layer to the lens thus making it more durable. No material is scratch proof, all lenses can be scratched, even glass.
An application to a lens may include a color tint. Plastic lenses are generally tinted at the lab during the fabrication process of ones eyewear while glass lens tints are created during the manufacturing process of the lens.
Tints may be applied for various reasons that include cosmetic purposes, fashion style, and sun protection. The application of a tint may be in a solid color that is uniform through out the lens or a gradient tint that has a graduated color of a darker color at the top of the lens to a lighter color at the lower edge of the lens. While a tinted lens will look very fresh and crisp when first made, over time a plastic lens that has been tinted may fade.
ULTRA-VIOLET PROCECTION (UV)
Ultra-Violet radiation from sunlight is invisible to the human eye. Molecules known as chromophores, which are present in the eye cells and tissues, absorb UV light. Chromophores absorb light energy from various wavelengths at different rates – a pattern known as absorption spectrum. If the eye structures such as the cornea, the lens, and the retina absorb too much UV light these structures can be damaged. The damaging effects of UV light are most commonly known as ‘sunburn’. In protecting ones eyes from the damaging effects of UV light it is recommended that all individuals wear lenses that provide UV protection. Sunglasses with the appropriate UV protection serve as sunscreen for your eyes to help protect them from the harmful UV rays. Lenses with appropriate UV treatment will give better protection but keep in mind that that light that arrives to the eye from around the lens will not be protected. Polycarbonate lenses include ‘built-in UV’ protection that filters the radiation in the in the UVA and UVB areas.
Photochromic lenses darken when exposed to UV radiation (sunlight) and the lens will lighten to its clear state in its absence. Originally photochromic lenses were only available in glass material, however today they are also available in plastic (CR39) and polycarbonate materials. Grey and brown are the two most popular colors of photochromic lenses. Keep in mind that automobile windows also block UV so photochromic lenses would darken less in a car. Authentic sunglass lenses that are either polarized or UV treated and tinted, are the best choice for driving, as a photochromic lens is limited in its ability to change to a dark enough color for comfort in driving. A photochromic lens offers continuous protection of the sun’s harmful Ultraviolet radiation.
Polarized sun lenses have an important advantage over regular sunglasses. A polarized lens blocks reflective glare where regular sunglasses do not. As an example, light reflected off a surface such as water or the hood of a car is bright and annoying. Polarized lenses have a special filter designed to block that reflective glare. The benefits of polarized lenses can be demonstrated at The Eye Store.
ROLL and EDGE POLISH LENSES
The process of ‘rolling and edge polishing’ a lens will provide the lens with a smooth finish to help the lens cosmetically ‘blend’ into the frame.
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Polarized sunglasses have been popular for years with boaters and fishermen who need to reduce reflected glare from the water surrounding them. But now that many others who spend time outdoors have discovered the benefits of polarized lenses, the interest in these types of sunglass lenses has soared! One fact to keep in mind when considering polarized lenses is that these lenses may reduce the visibility of images produced by liquid crystal displays (LCD’s) found on the dashboards of some cars or in other places such as the digital screens on automatic teller (bank) machines. With polarized lenses, you also may be unable to see your cell phone or GPS device. Boaters and pilots also have reported similar problems when viewing LCD displays on instrument panels, which can be a crucial issue when it comes to making split-second decisions based strictly on information displayed on a panel. However, for the majority individuals driving, most other sports and activities, polarized sunglasses offer great advantages. And today, many polarized lenses are available in combination with other features that can enhance outdoor experiences.