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What are the physiological effects of retinal exposure to 380–400nm light?

Biology Asked on January 2, 2022

There are two categories of sunglasses: UV380 sunglasses block all light with wavelength 380nm or lower, while UV400 sunglasses block all light with wavelength 400nm or lower.

This made me wonder, what are the physiological effects of retinal exposure to the 380–400nm band of light, which is not covered by UV380 sunglasses?

Also, assuming that the 380–400nm UV light does cause eye damage, does any potential pupil dilation caused by the dark tint of such glasses have an effect on the amount of damage caused?

2 Answers

Answering my own question after thorough research:

Definitions

First, I noticed that there is no consensus on where the UV spectrum ends and the blue portion of the visible light spectrum begins.

According to the WHO, as well as to most other sources, the UV spectrum covers the wavelength range 100–400nm (1). However, a few other sources, notably the SCENIHR, define visible light as starting at 380nm (2), hence UV light would be 100–380nm.

Another source, the ICNIRP, directly mentions that the boundary is not clear-cut, “the band 315 to 380–400 nm is designated as UVA” (3) . At least one source refers to the 385–405nm band as the “UV/Visible Radiation Boundary Region” (4).

Tinted Lenses

To address the part about the dark tint of lenses causing pupil dilation, it is first worth noting that not all lenses that filter out UV light have a dark tint. In fact, clear lenses can actually offer up to UV400 protection (5). There is even some research specifically on UV protection by clear lenses (6).

Back reflection of UV light

UV380 and UV400 are not the only eyeglass specifications relevant to UV protection. There is also eye-sun protection factor (E-SPF®), which was introduced in order to also account for back reflection of UV light from eyeglass lenses to the eyes (7). Therefore, this back reflection should also be taken into account when examining the effects of 380–400nm light exposure on the eye.

The 380–400nm Band

Now let’s get to answering the question.

According to the Texas Technical University Health Sciences Center, 40% of the radiation harmful to our eyes falls within 380–400nm, which they call the “UV protection gap” (8). Another source states that, while 100–380nm light is “very harmful”, 400–460nm blue light can still cause retinal damage and macular degeneration (9). The American Optometric Association also states that blue light, which they define as the range 380–500nm, may cause eye damage (10).

An article by ZEISS Vision Care explains that the UV380 standard was a “pragmatic choice” by the ophthalmic industry, and does not reflect “biomedical realities” (11). The article refers to the 380–400nm spectrum as the “most intense portion of solar UVR on Earth”. I assume the author is referring to the physical definition of intensity of radiant energy, which is the power transferred per unit area, however I am not 100% sure that this is the intended meaning of “most intense”.

I also found an article claiming that the WHO recommends UV protection up to 400nm (12), which again implies that 380–400nm does cause significant retinal damage. However, I couldn’t find the actual WHO publication stating the recommendation.

Answered by hb20007 on January 2, 2022

Hello and welcome hb20007,

I would like to introduce the types of Ultraviolet light to you first.

  • Ultraviolet A - UVA - 400–315 nanometers
  • Ultraviolet B - UVB - 315–280 nanometers
  • Ultraviolet C - UVC - 280–100 nanometers

UV380 sunglasses block all light with a wavelength < 380nm. Blocking most UVA, UVB & UVC.

UV400 sunglasses block all light with a wavelength < 400nm. Blocking all UVA, UVB & UVC.

The first article you attached is poorly written. It states that quality control is at fault by some sunglasses manufacturers. Meaning some sunglasses aren't made right because they do not meet appropriate manufacturing standards. Therefore they are damaging to eyes. Which is true.

The second article is also true.

UV380 sunglasses are fine for UV eye protection, if you would like greater protection from ultraviolet light (all of UVA), then buy UV400 sunglasses.

I talk more about ultraviolet (UV) light and it's cancerous consequences here.

Wikipedia has well-written free scientific information that I would highly recommend.

Answered by Andrew on January 2, 2022

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