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Occupational / Recreational Lenses

 

There are many lens forms that have been specifically designed for various occupational and recreational uses. Recommending the best lens for the application is not an easy task. A great deal of information must be gathered from the patient about environment, activity, home, work, hobby, and recreation. The dispenser should become acquainted with the wide range of lens possibilities including custom options. The following are some typical considerations for selecting occupational or recreational lenses.


Lens Materials and treatments:


Trivex® - Advantage: Superior Optics, Durability and Impact Resistance

 

Does the wearer have an active life style demanding impact resistance and high performance optics while wearing the latest fashions in frames? Trivex lenses are the best choice for these wearers. Impact resistance like that of poly, ABBE values matching that of the human eye providing superior optics, material integrity for drill and rimless style frames. Light weight with a specific gravity of 1.11, and an index of 1.523. Trivex is the lightest lens material available to date.

 

Mid and High Index – Advantage: Thinner and lighter weight lenses

 

Mid-Index lenses, typically with indices ranging from 1.53 to 1.59 offer the wearer a thinner option from regular plastic at a slightly higher cost but less than the high index materials lenses. They are typically very tintable and compatible with most premium AR coatings and available in most styles for even the most difficult of Rx’s.


High-Index lenses, typically with indices of 1.60 to 1.74 offer the thinnest lens options for the latest in lens and frame designs. MR-10 for example is a 1.67 material which offers a water white clear lens, thinness and material integrity for drill and rimless frames.

 

Polycarbonate - Advantage: Durability and Impact resistance, Light Weight

 

Is there a potential danger of accidents from flying or falling debris, objects, tools or equipment? Are there objects in the environment that might injure the eye? Does the wearer go through regular or random motions that might put them in contact with an object that is potentially dangerous? Is there potential for aggressive physical contact with humans or objects? If so, polycarbonate may be the lens material of choice.

 

Glass - Advantage: Performance, Durability, Variety and Scratch resistance.

 

Is the wearer's environment full of flying abrasive materials? Is it dusty, sandy, dirty or oily? Will the wearer frequently have to clean the lenses? Is the wearer likely to clean the lenses without lubrication or clean cloth? In these circumstances, glass lenses may be the answer.


Let’s face it – glass lenses last! They perform like they were new long after the features of other lenses have fatigued, bleached, sagged, scratched or worn out. Glass lenses retain the exact, original prescription power and edge diameter under any naturally occurring temperature extremes. They even remain stable on a sizzling-hot dashboard where plastic and poly lenses have been known to deform. As a rigid material, glass lenses maintain prescribed power even if wide variations in frame eye-wire tension occur. Glass generally has a high ABBE value, low dispersion; and is suitable for the vast majority of prescription powers, particularly those between +2.50 and –2.50. Glass is more scratch resistant than any other lens material. The scratch resistance of plastic lenses coated or not, doesn't even come close to that of glass.

 

Glass lenses are the preferred lenses for A.R. coating, a popular add-on. Since A.R. coatings are applied to glass at higher temperatures, the coatings bond more firmly and will hold up much longer than on softer lens materials like plastic and poly. A.R. of course, will enhance the beauty and visible transmission of any lens material and reduce reflections for the wearer.

 

Do glass lenses break easily? If the records of eye injuries over the last several years are any indication, the answer is, no. Besides the fact that new glass materials are more impact resistant when properly finished and tempered, glass lenses meet a unique challenge before being dispensed. No ophthalmic lens is tested quite as rigorously as glass, for impact resistance. All glass lenses must pass the standard F.D.A. “drop ball” test. This additional processing and quality certification, while it may take a bit longer, is an important point of differentiation for the high-end dispenser. An increasing number of large retail chains are discouraging consumers from glass lenses because they can’t be completed in one hour.


Scratch resistant coated plastic - Advantage: Improved scratch resistance over uncoated plastic

 

Will the wearer occasionally have to clean the lenses? Is the wearer’s prescription, lens size, or sensitivity such that weight may be a consideration, precluding glass lenses? Is moderate protection from scratching while cleaning important? Scratch resistant coatings may increase the life of a prescription for this type of eyeglass wearer.


Anti-reflective coatings - Advantage: Reduction of visually or cosmetically interfering reflections

 

Is the wearer particularly sensitive to reflections (moving light)? Does the environment have high intensity stationary or moving light sources? Is the person working near a surface that will reflect light? Are there differences in the intensity of light from background to immediate environment? Is it important that vision and concentration not be interrupted by random reflections? Is it important that other people see the wearer’s eyes clearly? Anti-reflective coatings are becoming very popular for all these reasons.

 

Hydrophobic coatings - Advantage: Reduced fog, mist, or droplet accumulation on the lenses

 

Is the wearer's environment continuously or predictably subject to wide temperature or humidity changes? Does equipment, tools, or activity create an environment of mist, spray or splash? Is the person’s activity level likely to create perspiration? Does the person frequently move from indoors to outdoors and back during changing seasons? Is it important that the wearer’s vision be continuously unobstructed from fog, mist, or rain? Hydrophobic coatings can help in all these situations.

 

Fixed tint lenses - Advantage: They are specially formulated to block specific (visible and invisible) wavelengths of light

 

Fixed tints are consistent in their ability to absorb light over the full surface of the lens and do not change their physical properties when exposed to light. They are often used for sun protection, or to reduce visual fatigue from exposure to high intensity, fluctuating or continuous light sources. Certain fixed tints can be used as a defense against irritating and potentially dangerous light sources. They may allow wearers to work comfortably near light sources that would be harmful without protection. There are a wide variety of fixed tint colors and they are often used for cosmetic reasons. Fixed tint lenses are traditionally made of glass; however specific dyes may be used on plastic lenses in a controlled process to create fixed tint lenses.


It is important to distinguish between protective and cosmetic fixed tint lenses. The dispenser should identify the source and type of light rays that will reach the eye, ask questions about any irritation the wearer may experience, and there choice from a wide variety of tints. It is helpful to have a reliable resource, display, or listing as a guide. In some cases it may be necessary to further consult authorities on the light source if it is potentially dangerous. Get professional recommendations on the type of lenses or shields required for blocking specific wavelengths.

 

Photochromic lenses - Advantage: Decreases light transmission when exposed to sunlight (UV present), and returns to clear indoors (absence of UV)

 

Photochromic lenses are now available in glass, plastic, Trivex®, polycarbonate, and high index materials. The primary features are: plastic offers reduced weight, polycarbonate is impact resistant, glass is scratch resistant, and high index materials permit thinner lenses. Consult manufacturer information for availability, performance and durability.

 

Putting the power where it’s needed

 

One of the most important questions in any occupational or recreational lens application is "What is the working distance?" That is, what is the "eye – to – object" distance? Often the eye doctor will refract the patient at the working distance in order to determine the precise power correction for a specific visual task. Unaided, the wearer will have to accommodate (bring the image into focus), frequently for prolonged periods of time, to maintain good vision. This can be quite tiring for some people and consequently having the optimum prescription power is of great importance. Single vision lenses are frequently prescribed to give a person precise vision at a specific distance. Special lenses for close-up work or for computer use are prime examples. A second, separate prescription is commonly provided for general use.

 

If a person wears a multifocal and their head and eye movements are restricted, or if they must view critical objects at different focal lengths or at the extremes of the field of vision, then the multifocal size and location can sometimes be varied to the most suitable position.

 

Perhaps the most well known occupational lens is the "Double D." This lens has two bifocal "add-power" segments. Typically one segment is located at the normal reading position with the "flat-top" up. The other one is located directly above the reading segment with the "flat-top" down. The traditional distance between segments is 14mm. The purpose of the lens is to provide good "near" visual acuity both above and below eye level as well as normal distance vision. Happy users include auto mechanics, librarians, pilots, dentists, painters, and others – a perfect example of an occupational lens.

 

The Double D type of lens is available in practically unlimited powers, segment sizes and segment locations in glass lens material. With a trifocal, instead of a bifocal, at the reading position it is called a "Quadrifocal." Double D’s are also available in limited variety in plastic. There are even similar progressive style lenses that offer most of the same visual advantages. When custom versions are needed they are usually only economically possible in glass because glass lens are manufactured using component pieces, whereas a complete new mold would have to be made in order to cast such a complicated lens in plastic.

 

There are several styles of lenses that provide invaluable assistance to their wearers while they perform daily visual tasks. Some are listed below with a short explanation. Reference to a good complete guide is essential.

 

Office - Type Multifocal - A variation of a progressive lens or an "Exec." Style that provide a wide field of view. Wide Multifocals, 35-40mm are other examples.

 

Read-rite - A lens with distance vision correction in a minor area of the lens (a segment or bottom area), and near vision in the major portion of the lens.

 

Acclaim 61 - Lenses that offer larger intermediate-power areas for viewing computer screens. These lenses usually have increased intermediate power (60% to 63%) to provide easy accommodation at typical computer viewing distances.

 

Bar or Ribbon Segments - These lenses have narrow rectangular multifocal segments that allow distance viewing both above and below the segment. Common users are mail carriers, carpet layers and tractor drivers.

 

Round bifocal segments - The classic "golfer's glasses" often have a small round segment located at the periphery of the lens. Golfers use the bifocal to see score cards, while distance vision remains unobstructed. Round segments are also perhaps the most useful of occupational multifocals. They are available in many different sizes; and they can be rotated to just about any position in a lens, offering additional power just where it is needed in or out of the normal viewing area.

 

 

 

 

Finally, it is important to be aware of the following guidelines:

 

  • Single Vision lenses can be made to have most any power.
  • Multifocal segments can be custom located in a lens, within limits.
  • Multifocal powers, bifocal or trifocal, can be varied within limits.
  • Several different shapes of multifocals are possible, within limits: (Round, D style, straight-line style, rectangular (B or R segments), and combinations of these are sometimes possible.

 

 

 

 

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