Posted on August 26 2015
Glasses have existed for centuries, but they are now many more choices available to those with vision conditions than there used to be. Today people can choose what type of frames and lenses match their lives best. There are also a number of factors that eye-care professionals must consider when helping customers select lenses. Four of the most important factors for lenses are thickness, weight, the movement of light through the lenses and overall optical efficacy.
For many years, there was no alternative to having thick glasses. The thickness of the lenses relates to how much they refract light (in other words, how powerful they are). So if someone needed powerful glasses that bent light significantly, they would have to be quite thick. However, today there are many types of lens materials with strong refractive power even before a prescription is applied. The measurement “index of refraction” gauges how much a material will bend light. The higher the number in the index of refraction, the more it bends light. So someone who needs a very powerful lens can select a high index material, and the lenses will not need to be as thick as they were in the past.
Obviously, the thickness of your lenses will affect the weight of the lenses. A thicker lens will be heavier than a thinner lens of the same material. However, just as different materials have varying amounts of refractive power, they will also have different weights. Lens weight is measured through “density.” Some lens materials are much lighter, or less dense, than other materials. For example, a polycarbonate lens will be significantly less dense than a glass lens of the same size and thickness. However, some of the densest materials are also the most powerful. So the power, thickness and weight of a lens must all be considered together.
Another important factor for lenses is how much they transmit light. Ultraviolet light (often called UV rays) are not visible but these light waves, which come from the sun, can be damaging to eyes. So many glasses will come with a UV-protective coating on the lenses. Similarly, if you buy prescription sunglasses, the darker color of the lens will affect how much visible light reaches the eye, and that must be considered so the lens power isn’t diminished.
Probably the most important factor in lens composition is how well the lens does its main job: assisting the eye in seeing clearly. This must always be the top priority when selecting frames. So an eye-care professional may have to advise a customer against a type of lenses that will not provide proper vision aid. While comfort, stylishness, size and durability are all important concerns for customers when selecting lens types, vision clarity supersedes all else. So eye-care professionals have an important role in understanding all of these factors and guiding customers towards the type of lenses that have the right combination of optical efficacy, light transference, weight and thickness.