When choosing a new pair of glasses, many of us are inevitably drawn to the vast selection of frames on display, and end up paying less attention than we should to the most important component of any pair of spectacles: the lenses. But to the average Joe, making an informed choice can be tricky. So, what should you look out for when picking your lenses?
1. Index Of Refraction
The refractive index of an eyeglass lens material is a value that quantifies how efficiently it refracts light, which in turn depends on how quickly light can pass through it. The higher this value, the longer it takes for light to travel through the material, and the greater the refraction of light rays. That is to say, for a given eyeglass lens power, lens made with a material with a high refractive index will be thinner than lens made with a material with a lower refractive index.
2. Abbe Value
The Abbe value of a lens material is a measure of how widely it disperses the different wavelengths of light that pass through it. Low Abbe values mean high dispersion, which could result in chromatic aberration, an optical error wherein coloured halos are perceptible around objects, particularly lights. When present, chromatic aberration tends to be most noticeable at the periphery of eyeglass lenses.
3. Aspheric Design
Aspheric designs, where lenses are designed to have a gradual curvature, allow for flatter curves without compromising optical performance. These designs also reduce unwanted magnification of the wearer's eyes, so that the wearer’s outward appearance is not negatively affected. In some cases, aspheric designs can also improve the clarity of the wearer's peripheral vision.
In addition to these factors, choosing the type of coating for your lenses – be it anti-scratch, UV-blocking or photochromic – can be just as important. When in doubt as to how to choose lenses most appropriate for your needs, don’t hesitate to consult your local eye doctor or optometrist!