1. How to read a prescription?
Prescriptions have a certain format that is always followed. The first line of your prescription is always for the right eye, sometimes designated the “OD”. The second line is for the left eye, sometimes designated “OS”. The prescription for each eye is divided into Sphere, Cylinder, and Axis values. It is common to have no values for any one of these, in which case you might see the letters “PL” or “plano”, or to have values for all of these. Sometimes the prescription may say “OU” which means “both eyes”. If your prescription is for bifocals or trifocals, there may be additional information on the prescription that says for example “Add +2.50”. This is important information if you are ordering reading or multifocal lenses. The numbers are expressed in diopters that tells the power of the lens. A diopter is a value that is metric and universal worldwide.
2. How to choose a lens material?
Hard resin lenses are good for most people. Polycarbonate lenses are virtually shatterproof, and are highly recommended for children and adults in active situations. In general, if the sphere on your prescription is at +/-2.25 or lower, you will not benefit from the more expensive “thin” lens types. Hard resin or polycarbonate lenses will be just fine for you. If the sphere on your prescription is higher than +/-2.25, you will benefit from the selection of a “thin” lens type.
Thinner lenses have three advantages: they do not look “thick”, they do not magnify or minify your eyes when seen by others, and they are lighter. In general, the thinner and lighter the lens, the more expensive it will be. “High index” is the most common “thin” lens material, and “aspheric” is the most common “thin” lens design. You will not notice any difference in your vision between these two types of lenses, and your eye doctor can explain if one type may benefit you more than the other. Polycarbonate lenses can be purchased as “aspheric”, giving you the advantage of polycarbonate’s strength together with aspheric’s thinness. The thinness of high index lenses is characterized by the “index of refraction” (IR). Mid-high index lenses are commonly around a 1.56, high index lenses are around 1.60, and ultra-high index lenses are 1.67 and 1.74. After you have selected the best lens material for your personal situation, you can choose among other lens features and options, like photochromic, scratch coating, anti reflective coating, and UV protection (UV protection is always inherent in high index and polycarbonate lenses). If you want sunglasses, additional options could include tint, photopolarize or polarization, and mirror coatings.
3. How to choose a color?
Brown and gray are the most popular colors for sunglass lenses. Brown is the best color overall because it allows the wearer the widest light spectrum through to the eye, while blocking blue light and offering optimum contrast. Brown is great for applications where distances need to be constantly judged, like tennis or golf or skiing or other sports requiring acute visual perception and contrast differentiation. Brown is also best for lower light situations, like fishing in the late afternoon or early morning.
Grey tint is best for bright light situations like water sports because it blocks out the brightest of the suns rays. Other colors like green and blue are used more for fashion purposes than for utility. Blue is the overall worst color of all for the wearer because it enhances blue light which creates more glare. If you like blue as a fashion choice, consider a custom-made lens tinted brown but with a blue flash mirror coating. Yellow is used to heighten contrast without blocking too much light, and it is commonly used for shooting and skiing on cloudy days. Boll makes a special green tint that is designed specifically for tennis (the Competivision lens)the green tint helps to accentuate the yellow color of the tennis balls and make the white lines stand out.
4. How to compare the prices?
Your choice of lens brand is a personal decision, which is generally a tradeoff between price and quality. As in other areas, better quality brand merchandise is more expensive. In lenses, a more expensive lens usually means a better quality lens, or a lens with a wider viewing area (in the case of progressive lenses). In some cases however, it may be difficult or impossible for a consumer to notice the difference between a high quality lens and a low quality lens. Anti-reflective and scratch-resistance coatings typically adhere better to the lens if they are applied by the lens manufacturer than if it is applied by a lens laboratory.
It is most important to compare prices “apples to apples”. Two stores could have different prices for polycarbonate lenses because different manufacturers make them, or one includes scratch coating and the other does not (for example). Before you begin shopping for eyeglasses lenses, assemble a checklist of questions to ask each store. The following list includes all of the items that may cause a price difference:Type (single vision, multifocal), Material (plastic, polycarbonate, etc), Options (scratch coating, etc), and Manufacturer’s lens brand.
