How to Choose the Right Lenses
One of the most common questions asked of an optician upon first introductions is regarding price: "How much are glasses?" Though the question may seem reasonable enough, there is one major issue in answering said query. All glasses are not created equal. There are myriad coatings, add-ons, edge treatments, and other bells and whistles that can have an impact on the price of your glasses. This guide was designed to help you decide which lens upgrades are right for you and in which, if any, situations.
The first option to choose from has a direct relationship with your prescription: the lens material. Glass lenses have been the standard since the invention of spectacles, and to this day are preferred by some patients. The benefits of glass include a higher Abbe value (the measurement of dispersion through transparent material) which allows for greater acuity, and greater scratch resistance. Glass downsides include low impact resistance, weight, thickness, and discoloration over time.
Cr39 or Plastic lenses are now considered optical standard; when compared to glass lenses, Cr39 lenses are thinner, lighter, and not prone to discoloration. They also take less time to manufacture, and thus are a more convenient lens. Cr 39 lenses are likely to scratch and can even shatter with improper care; though they are less likely to do so than glass.
Polycarbonate lenses are still thinner and lighter than Cr39, and are the best selling lenses in the industry. Poly lenses are virtually shatterproof and have a great deal of scratch resistance. The downside to Poly lenses is a slight degradation in Abbe value, though most users of the material don't notice any imperfections in their vision.
High Index Lenses
High Index lenses come in several varieties, indicated by the index of refraction value (1.60, 1.66, 1.67, etc) where the higher the number, the thinner the lens will appear. These lenses offer similar properties to the Cr39 lens, with slightly lower Abbe Values with each increase of index. These lenses are generally recommended for patients with high prescriptions only (> +/- 5.00).
How Will Your Lenses Be Used?
Once the material is decided, the next move is to decide how the lenses will be used (e.g. computer work, night driving, reading, all day use, etc.). This allows the optician to narrow the scope of options to only those that will actually help you.
The anti-reflective (AR) coating, for example, is a lens add-on that increases light transmission to your eyes. This allows for greater clarity and reduced glare. A side benefit of this coating is an aesthetic one, where an AR coated lens will appear invisible, eliminating the glare that many glasses wearers find in photographs. This coating is primarily used for patients that wear their glasses all day, when at their computer, or when driving. There is no real downside to this coating, but if you're not careful with the glasses, the coating can and will scratch.
Transition lenses are specially designed with Ultra-Violet reactive materials that indicate to the lens when to darken and lighten. This feature is ideally suited to patients who spend dedicated time outdoors for gardening or hiking, and don't like the idea of carrying two pairs of glasses. They go from completely clear to sunglass dark in roughly a minute, and they do the reverse in roughly two. Downsides to transition lenses: after about six months of use there is a slight residual tint, and the lenses will not darken when driving, because UV light is filtered by most windshields.
Polarization is a filter within a sunglass lens that changes the way light enters the eye. Normally, light enters the eye from all directions and as such can sometimes cause blinding glare upon reflection. Polarizing filters eliminate this by filtering the light so that it comes in from only one direction or as a pole. This option is suited for any patient who wants sunglasses that make seeing in the sun more comfortable. You'll notice the greatest benefits of polarization when driving, taking part in water based activities, or skiing.