Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: neilep on 08/10/2007 02:08:16

Title: Why is so much of my eye exposed ?
Post by: neilep on 08/10/2007 02:08:16

Hello Ocular Ambassadors,

see these eyes ?

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Which part of them do I actually see through ?...just the small central pupil black bit yes?

Then WHY do I risk having so much of my eyes exposed ?

EYE don't know !!...but EYE want to know !!...and so do ewe !!

Title: Why is so much of my eye exposed ?
Post by: another_someone on 08/10/2007 02:45:46

One important thing to remember is that eye's are not only something you see with, they are also something you signal with (other people see the whites of your eyes, and will be able to say something about your general state of health, and you mood).

Beyond that, it is also useful to have a fair degree of open gap infront of the eyse to allow for rapid eye movement so that you can scan an image without having to constantly move your eyelids out of the way.

Title: Why is so much of my eye exposed ?
Post by: chris on 08/10/2007 22:04:03

Yes, the black central portion if the pupil that acts like the "aperture" of a camera lens.

But remember Neil that, just as a camera opens its aperture in the dark, your pupils are not always small pinpoints (unless you are a chronic abuser of morphine-like drugs). Under low-light conditions the pupil opens up to admit more light, and in near-pitch black conditions can become most of the iris. If your eyelids were in the way, together with attached eyelashes, this would impair vision.

There is one situation in which even more of the eye is chronically exposed, a condition known as proptosis (or exopthalamos), and this is associated with a thyroid problem called Grave's Disease. Normally the lower or upper eyelids always slightly overlaps the iris (the coloured part of the eye), but in patients with Graves a rim of white conjunctiva is visible right around the iris.

This causes the eyes to appear to be bulging and more prominent than normal, giving a startled or staring appearence to the patient. The cause is the growth of retro-orbital tissue (tissue behind the eye) triggered by the same auto-immune process that causes the thyroid to become overactive.

Chris