General Question

Mariah's avatar

Do we see only that light which hits our pupils?

Asked by Mariah (18398 points ) July 17th, 2011

This is probably a dumb question, but just for the sake of curiosity: Light hits our eyes, and then of course a process occurs inside the eye and in the brain to create “seeing,” but that part of the process is not what I’m after. Do we only see those photons that hit our pupils, or do we see any of the light that hits our irises or the whites of our eyes?

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9 Answers

woodcutter's avatar

I will say yes, not that I know for certain but I got to thinking about when cataracts grow the vision is bad around the periphery and goes all bad when it covers the pupil.

Grisson's avatar

The iris and the whites of the eyes are certainly not completely opaque. So there would be some transient light that would be diffused through the internal fluid and strikes the retina. It would not form an image because it did not pass through the lens.

Plucky's avatar

We do not see light that does not enter the pupil. The iris is responsible for changing the size of the pupil – controlling how much light is let in through the pupil.

As @Grisson stated ..light may hit the rest of the eye, but it does not form an image. It must go through the pupil, lens and so on ..to produce what we see.

Mariah's avatar

Thanks all. This question popped into my head and made me wonder if eye color could affect vision at all. If we did see photons that hit the irises, then I would think people of different eye colors would perceive light differently, since of course blue irises reflect (and therefore do not absorb) blue light, and brown irises reflect brown light, etc. But if we don’t see the photons that hit the irises, then there is no conundrum.

RealEyesRealizeRealLies's avatar

We don’t see infra red or ultra violet spectrums of light… but they are just as real as the radio waves we don’t see either.

thorninmud's avatar

The pigmentation of the eye isn’t restricted to the iris. The interior wall of the eye is also pigmented. In fair eyes, there is much less pigmentation than in both the iris and the eye wall; in dark eyes both the iris and the eye wall are more pigmented. That pigment is always brown, no matter what color the iris appears. Any blue tone (including the blue component of green eyes) is not caused by pigmentation, but by a light-scattering effect. That light scattering happens just as much in a brown iris, but it’s masked by the heavy pigmentation.

As @Grisson said, both the iris and the eye wall transmit some light (the wall more than the iris). But the heavier the pigmentation, the less light gets through. The light that does get through is also largely skewed towards the red end of the spectrum because of the blood supply in the eye wall.

Optomologists call the unfocused light that enters the eye through the iris and wall the “homogenous veil”, because it creates a kind of light fog in the eye (this also includes light that’s reflected from the surface of the retina back toward the eye wall and bounces around a bit). In light blue eyes with a 4mm pupil diameter exposed to red light, about 17% of the light in the eye will be homogenous veil. If exposed to green light, only about 5% will be homogenous veil. In heavily pigmented eyes, the transmission can be 100 times less. (study)

sophiesword's avatar

obviously… if a certain ray of light is not entering your pupil and therefore not being refracted which basically means its not forming an image on your retina then yes…you wont be able to see it.

Mariah's avatar

@sophiesword I didn’t know that only light that enters the pupil forms an image on the retina, so it wasn’t all that obvious to me. Thanks for your answer, welcome to Fluther.

sophiesword's avatar

@Mariah my pleasure. Sorry for coming off arrogant I’m a pre-med student.

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