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The Lens System of the Eyes


Explanations > Perception > Visual Perception > The Lens System of the Eyes

Cornea| Lens | Iris | Vitreous humor | So what?


The front system of the eye is like the lens of a camera that lets in light from the outside world. It focuses light from the objects we look at on the retina at the back of the eye.


The cornea is the outer 'skin' of the eye. Behind the cornea is the anterior chamber which is filled with fluid. The cornea is curved, so this acts as a lens, bending light to feed to the 'real' lens in the eye.


The eye's lens is a liquid-filled bag that takes in light from the outside world, bending the light rays so they focus on the retina at the back of the eye. The image appears upside down, but our brains take care of turning it the right way up. Camera lenses have multiple glass elements that are moved to create focus. The human eye focuses by changing shape, using the ciliary muscles.


The iris is a variable diameter circle in front of the lens that reduces the amount of light by making the 'hole' smaller (constricting) or larger (dilating). The iris can be of different hues, commonly brown, gray or blue, though it can also be amber, green and even purple. Blue eyes are classically considered attractive, along with blonde hair, though unusual shades and deep saturation can be very attractive too.

The iris dilates when we want to let in more light. This happens when it is dark and when we are particularly interested in something. Classically, it signifies either aggression or romantic interest.

Vitreous humor

The middle of the eye is filled with liquid. The edge curvature and refractive index in this acts as a third lens. Mostly, however, it just conducts the light from the front to the rear of the lens.

So what?

What we see is constrained by the lens system. If this is defective, we may find things out of focus (as in short- or long-sightedness) or suffer other problems.

When we look at a person, we stare carefully at the eyes to see where and how people are looking. Their appearance can hence have a disproportionate effect on how we perceive others.

See also



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