Filter for enhanced contrast
The contrast is enhanced with filter lenses
Reduced contrast sensitivity
Our contrast sensitivity is in simple terms our ability to see different shades of brightness. When testing visual acuity or reading a book we normally have black letters on a white background (100 % contrast) but the reality is not configured that way. Some people can have good visual acuity under good lighting conditions but have trouble seeing at dusk, when foggy or other situations.
With a yellow filter, some of the disturbing blue light is absorbed and we experience an increased contrast sensitivity. This improves comfort a lot for some patients.
There are a lot of different filters to use. The simplest one is the UV block that absorbs the energetic UV light up to 400 nanometer. In sunglasses there is often a tag with UV 400 or similar. That means that the sunglasses absorbs all UV light.
Absorbing blue light
Using more powerful filters absorbs more of the blue light and increases contrast even more. This is possible due to the fact that blue light is scattered more than other wavelengths, causing a slight blurry image on the retina. Visually impaired people have most advantage from using filter lenses but in some situation, all people can experience enhanced contrast from blue blocking filters, such as skiing in a snowy environment.
Filter lenses is often combined with a polarized layer to reduce the total amount of light that is transmitted into the eye. Filter combined with polarized is also a cosmetically attractice combination, hard to tell from normal sunglasses but with better visual quality.
In case you have had cataract surgery and had the crystalline lens replaced with an artificial lens it's an extra reason to why you should protect the eye from the harmful UV and blue light. The crystalline lens have better protection against UV light than an artificial lens.
Yellow filter lenses that absorbs blue light up to 450, 511 or 527 nanometer is very useful for persons with low contrast sensitivity. It's particularly recommended for older people espescially after cataract surgery.