Given this image:


I just assume that the eye is made out of glass, so I wonder how is it that IR and UV radiation is absorbed by it? I would understand one of them but why is it transmissible for light between these two regions (visible light)?

Whyever I can't find an absorption spectrum of glass. But I found one of water:


and it shows the behaviour I'd expect for glass. I have to admit I don't know of what our eye is made of but then I would just replace glass by water and ask the same question.

  • 1
    $\begingroup$ encyclopedia2.thefreedictionary.com/Eye+(vertebrate) $\endgroup$ Commented Aug 14, 2020 at 13:49
  • $\begingroup$ Well you almost got it already I would say! The biggest part, the vitreous body, is made of 98% water, so this absorption spectrum should explain the major part. And for the reason why this spectrum looks that way, you will find some literature. $\endgroup$
    – Martin
    Commented Aug 14, 2020 at 13:52
  • $\begingroup$ so it isn't glass but water..? $\endgroup$
    – Ben
    Commented Aug 14, 2020 at 13:59
  • $\begingroup$ No, glass is not water. As you know, water comprises oxygen and hydrogen. Typical transparent glass can be made from a number of different compound. Silicon, boron, sodium, calcium and others. Glass has little in common with water, the most prominent being transparency to visible frequencies. $\endgroup$
    – garyp
    Commented Aug 14, 2020 at 19:29
  • $\begingroup$ @Ben Is there anything missing for you in the presented answer below that you still would like to be addressed or elaborated on? $\endgroup$ Commented Aug 28, 2020 at 11:52

1 Answer 1


Technically, all important aspects why the human eye has such a narrow window of transmission for the electromagnetic spectrum are already mentioned in the comments. As Martin correctly points out, that the bulk of the chemical composition is attributed to water.

The pocket of hydrous fluid that separates the Cornea with the crystalline lens, in pertinent literature called 'aqueous humor', as well as the vitreous humor (which refers to the fluid in the eyeball itself) are made out of > 95 % of water.

The only constitutents of the human eye, that the incident light has to pass as well and which have a lesser share of water in their total mass are the Cornea and the crystalline lens. However, it is also very reasonable to assume that both are still >>50 % made out of water. That can be easily deduced from the absorption spectrum of water you shared above, as it already truncates the effective transmission at the near-infrared as well as the near-ultraviolet border of what we call the 'optical range of the electromagnetical spectrum'. So the main reason for our limited sensitivity has be water itself.

What is more, as you might have heard before the exact range of sensitivity is also unique for each person, i.e. for some people their visual sensitivity can extend to as far into the 'blue-end' or near-UV as approx. 310 nm and also as far into the near-IR regime as 1,000 nm. Depending which source one is refering to of course, the general regime a healthy human eye is sensitive to, is often given as the range, 390 to 780 nm.

A wonderful resource online which covers your question en passant and much more can be found at ASTR 5110 (Majewski) Lecture Notes. The lecture is primarily covering astronomical instrumentation, but it covers the human eye in a very exhaustive way in its first entry (as a welcoming alternative to the respective wikipedia articles).

To conclude my answer, a quote from the website above, which hopefully adds another intriguing clue to your question,

The UV sensitivity is set by transmission of the crystalline lens (so people with replaced lenses actually have improved UV sensitivity).

I hope this is helpful for tackling your question.


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