Anatomy of the eye: understanding the structures that enable us to see

At first glance, the eye consists of two main parts:

• The sclera, the white part of the eye,

• The colored part, comprising the iris and pupil, covered by the cornea andaqueous humor.

Behind this visible area, protected by the eyelids, are the lens, the vitreous, the retina, and the optic nerve, each playing a specific role in vision.

The cornea is a very thin, transparent membrane made up of cells organized like a honeycomb.

• Diameter: 11 mm

• Thickness: 0.4 mm

• Water content: 78%

To remain perfectly transparent and fulfill its optical function, the cornea is constantly hydrated by tears and kept clean by blinking.

The pupil, located in the center of the iris, functions like the diaphragm of a camera, regulating the amount of light that enters the eye.

• Diameter: 1–2 mm in bright light, up to 8 mm in darkness

• Variation influenced by light and emotions

For example, a particular interest or surprise can cause a reflex dilation of the pupil.

The iris gives the eye its color, which is determined by:

• the thickness of its pigment lamellae

• melanin concentration

The more pigmented the iris, the darker the eye.
It also controls the size of the pupil and receives its nutrition fromthe aqueous humor and small arterioles.

The lens is a lens located behind the iris.

• Its function: to focus light on the retina

• Adjustment: it bulges for nearby objects andflattens for distant objects

• This adjustment mechanism is called accommodation and works from 10 cm to infinity.

The vitreous is a gelatinous substance that is 95% water and accounts for 90% of the volume of the eye.

• It absorbs shocks and maintains the shape of the eyeball.

• It also helps keep the retina firmly in place at the back of the eye.

The retina is a thin membrane (0.1 to 0.4 mm) lining the back of the eye, composed of hundreds of millions of nerve cells:

• Cones (6 to 7 million): perception of colors and details

• Rods (≈130 million): night vision and motion detection

The retina is extremely sensitive, capable of perceiving faint light 10 km away in total darkness. It converts light into nerve impulses, which are transmitted to the brain via the optic nerve.

The optic nerve is approximately 4 mm in diameter and 5 cm long. It acts as a transmission belt, sending electrical signals from the retina to the brain.
The brain interprets these signals and translates them into clear, coherent images, thus completing the complex process of vision.

At Optique Moitzheim, our opticians explain the anatomy of the eye, help you choose the right glasses, and advise you on protection and visual comfort.

Make an appointment in store to receive personalized advice.