Eye and Vision

It is said that science gets its inspiration from nature to understand and create.  This could not be truer with the eye, which is the “natural” version of a camera.

Indeed, both the eye and the camera capture images through lenses, a diaphragm, and a film.  The eye uses the cornea and the crystalline lens to focus on an image.  The iris is the camera diaphragm, opening and closing according to light.  Finally, the image is projected on a fine film covering the back of the eye called the retina.

Here is a short explanation of the eye and its behaviour.

Cornea: The cornea is a five-layer transparent membrane in direct contact with the exterior. It is the most tactilely sensitive structure of the human body.

Aqueous humour: Transparent liquid constantly filtered and renewed that, along with the vitreous humour, maintains the eye pressure and the shape of the ocular globe.

Iris: It is the diaphragm that controls the amount of light penetrating the eye.  The iris pigments give the eye its colour.

Lens: Optical lens located behind the iris and focusing to obtain clear images at all distances.  Light penetrates through the cornea, the aqueous humour, and the pupil.  Then the lens focuses the light on the retina.

Vitreous humour: Viscous liquid responsible for the eye’s shape and consistency.  It represents 90% of the eye’s volume.

Retina: A very sensitive film on which images are projected. It is a nervous membrane, 0.25 mm thick and equal in size to a postage stamp, that lies at the back of the eye.  The retina has over 130 million nerve cells.  It can see a very feeble light such as a candle flame from 10 km away in total obscurity!  It can see over 100 different shades and 750 luminosity levels.       

Pupil: The central orifice of the iris acting like a camera diaphragm. Its diameter varies according to luminosity.

Optic nerve: It is the second pair of cranial nerves: the optic nerve, which is about 35 to 55 mm long, goes from the retina to the optic chiasma (where the left and right optic nerves cross path in the brain).  It contains about one million fibres distributed in many separate bundles.  Its function is to transmit the images on the retina to the brain.

How the Eye Operates

When the eye looks at a far away object, the image projected on the retina is clear.

If the object is close, the image is projected behind the retina.  The lens, quite supple until about 40 years of age, will thicken, providing accommodation and thus bringing the image back on the retina.  The brain will then receive a clear image.