Yorkie dog sporting sunglasses

Sunglasses can be more than a tint used to decrease the amount of sunlight that gets to your eye.  While visual comfort is important, sunglasses are also about protection and optimizing visual function. It is not just about how much light is transmitted through the lens, but how the lens performs. Ideally, they should enhance the vision of the visually impaired.

Here’s how sunglasses can help the visually impaired:

  • reducing glare and haze to provide clearer, sharper vision,
  • enhancing color definition,
  • reducing reflections off the lenses, and
  • most importantly, 100% UV protection.

What manufacturers of premium sunglasses are doing is using their knowledge about how the eye functions with different wavelengths of light and creating color-enhancing technologies. For example, there are lenses that absorb some, but not all, blue  and yellow light, while enhancing green and red wavelengths of light. These specialized filtering lenses are combined with UV absorbers, polarization, and anti-reflective coatings to make a premium sunglass lens. Hence, the reason why some sunglasses are more expensive. 

Generally, when we think of performance sunglasses it is non-prescription eyewear.  Many of these premium sunglass companies offer their lenses in prescription by special order:  Ray-Ban, Oakley, Maui Jim, Costa del Mar, Bolle, Serengeti, and Wiley X to name a few.

Here I will discuss four aspects of sunglass technology and the role they play in not only protecting the eyes, but optimizing vision:

  1. Tints,
  2. UV protection,
  3. polarization, and
  4. anti-reflection coatings.

How to Determine the Best Sunglass Tint

While you may think that sunglasses are just glasses with a tint, protecting the eyes requires more than just a tint.  The tint decreases the amount of light that reaches your eyes.  Tints not only vary in color but also vary in transmissibility. The amount of light that is transmitted is the amount of light  allowed to pass through the lens. Generally, the darker the tint, the less light that is transmitted through the lens. Someone who is outdoors and needs to decrease the brightness of sunlight will choose a lens with low transmittance.  Keep in mind, that the darkness of the tint does not indicate its capability to protect against harmful UV light.

While some individuals with low vision find that increased light levels help to optimize their vision, others, especially those with inherited eye disease, find the lower light levels to be beneficial and may help with visual function.  The flip side is that someone with impaired vision may find some tinted lenses too dark to allow them adequate vision.

Confused as to what you may need?  The truth is that what you may need, can vary by the environment, activity, and the light level that day or time of day.

The three most common lens colors are  grey, brown, and  yellow.

image of grey inited sunglasses
Grey

Grey is a neutral tint, meaning it doesn’t significantly  change the perception of colors.  What it does not do is increase contrast. It does have the overall effect of decreasing brightness. This tint is good for those who are light-sensitive and is especially good for driving.

image of sunglasses with a brown tint
Brown

Brown imparts its own color flavor, meaning it does change the color perception by absorbing more blue and enhancing reds.  For this reason, brown increases contrast. The color temperature is not “grayed out’ so the environment is still bright.  This tint is good for those that feel the grey makes it too dim and they need more contrast.

image of sunglasses with a yellow tint
Yellow

Yellow and Amber are the blue-blocking lenses.  While it neutralizes scattered blue light, which increases contrast, the environment is still ‘bright.’  For low vision persons, this tint would be best for cloudy, hazy days to help with contrast. Yellow or amber (yellow-brown color) are not good for driving because they can confuse the color of light signals and warning signs.

I might also suggest different sunglasses for different light levels. Dark grey for those very bright sunny days to cut harsh sunlight. Brown tints work well for days that may be overcast.  This has the effect of not making your vision dimmer and still keeping things bright for clarity, while still giving UV protection.  Yellow/amber for early morning or twilight to give  contrast (but not for driving!). 

For outdoor activities like camping, hiking, or golfing, consider the green, (G-15 from Ray-Ban for example) which is good for making objects stand out from the green foliage.

Do All Sunglasses Provide UV Protection?

Decreasing light levels with a tint may give a greater level of visual comfort, but may not offer enough protection against wavelengths of light known to be harmful to the sensitive tissues of the eye. Specifically, protection from the high energy, damaging, short- wavelength UV light.  Lens materials such as plastic and polycarbonate have some UV absorbing capability. (see Lens Materials).

For added protection from UV light, sunglasses should have UV light absorbing properties that eliminate the damaging light rays from reaching the eyes.   Look for ‘100% UV protection’ or ‘UV 400’ labeling on a tag or lens sticker.

For regular eyeglasses, a UV coating can be applied (see Lens Technology). Regular clear plastic prescription eyewear, a plastic called CR-39, does provide some UV protection.  A UV coating takes it a step further to 100% UV protection. Polycarbonate, which is known as safety ‘impact resistant’ plastic, does not need an additional UV coating for 100% UV protection.

Polarized Lenses: Are polarized lenses the same as UV protection?

NO. Keep in mind that sunglass lenses that are labeled as polarized do not mean UV protection. Polarization is a feature added to lenses to decrease glare and increase visual comfort.

Polarized  lenses have a molecular structure which gives them  the ability to reduce glare. Glare is light reflected and scattered off of a surface that is brighter than the surrounding light.  Glare can decrease our capability to see clearly and can cause visual discomfort.

Polarized sunglass lenses are designed to filter reflected light in order to reduce glare from horizontal surfaces. Veiling glare from the hood of a car, a dashboard, reflection off of snow, or the surface of the water can be reduced or eliminated. For this reason, they are helpful for driving and sports.

The benefit of polarized sunglasses versus non-polarized sunglasses are:

  • Reduces surface reflections and glare,
  • perception of seeing things clearer,
  • Improves visual comfort, and
  • reduces squinting and eye fatigue.

Keep in mind, that not all polarized lenses are the same. Lenses differ in their capability to reduce glare.  That could explain why an inexpensive set of polarized sunglasses do not seem to work as well as a higher quality pair.

Those with eye disease should wear protective sun wear to reduce exposure to harmful UV light.  Polarized lenses are an add-on feature beneficial to those with low vision to reduce light scatter in order to optimize vision.

Anti-reflective Coatings (Anti-Glare) are not just for sunglasses

Anti-reflective coating is applied to the surface of the eyeglass lens to optimize vision by reducing glare. Ideally, it should be applied to both the front and back surfaces of the lens for maximum benefit. It serves several purposes:

  • Reduces reflections off of surfaces like wet roads and glare from headlights. For this reason, it is recommended for night driving. The above photo shows an anti-reflective coating on the right lens  ‘dampens’ water reflections.  (from Crizal ®)
  • Reduces internal lens reflections, especially important for those with thick eyeglass lenses. High index lenses, which are the lighter, thinner premium prescription eyeglass lenses, may have annoying internal reflections, which are minimized by an anti-reflective coating
  • Reduces reflections of light that hit the eyeglass lenses from behind and reflect back into the eye.
  • Cosmetically a more attractive appearance, because the coating reduces glare from the front surface of the lens.  The eyeglass lens with an anti-reflective coating and no surface reflections seems to ‘disappear:’

Reflections off the surface of the lenses on the left make it difficult to see the person’s eyes. The lenses on the right have an AR coating which reduces reflections off the surface. (from Crizal®)

In the End…

Can basic off-the-shelf sunglasses provide the 100% UV protection, and cut light transmission? Sure they can, but expect more! Those with eye disease are encouraged to wear protective UV absorbing lenses. The additional features of tints, polarization, and AR coatings can help to optimize contrast, enhance colors, reduce glare, and increase overall visual comfort.