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Anatomy of the eye

Explore the complex structure of the human eye and discover how each part contributes to your vision.

It is a thin membrane that covers the anterior surface of the white part of the eye (sclera) and the inner surface of the eyelids. It has a protective and immunocompetent function. It is very vascularised so that in case of inflammation it appears very red (red eye).

The ciliary body is an inner muscle of the eye that is connected to the lens by filaments (Zonula of the Zinn). In this way, the function of the ciliary body is to modify the conformation of the crystalline lens, making it suitable for viewing near or far objects. In practice, the ciliary body/crystal complex is responsible for the eye's ability to focus on objects. It is responsible for the production of aqueous humour.

The iris is a diaphragm that regulates through the pupil the amount of light that penetrates into the eye. In fact, the iris narrows or widens, changing the diameter of the pupil, depending on the ambient light. In intense light, it shrinks while it gradually expands as its intensity is reduced.

It is that part of the eye between the posterior face of the cornea and the anterior face of the iris. It contains the aqueous humour. At the point where the cornea and iris meet (camerular angle), there is a structure resembling a filter, called a trabecula. This structure serves the elimination of the aqueous humour that is continuously produced by the ciliary body and maintains a constant pressure inside the eye.

The cornea is a transparent structure, devoid of blood vessels, richly innervated. It is protected by the tear film on its front surface while it is nourished and protected by the aqueous humour on its inner surface. Its transparency is crucial for the quality of vision.

Located in the centre of the iris, light rays penetrate the eye through it. It varies in size depending on the intensity of the light.

The crystalline lens is a lens located in the posterior chamber, between the iris and the ciliary body with which it is connected by filaments (Zonula of the Zinn). This structure is one of the main components of the eye's dioptric apparatus: thanks to the action of the ciliary muscle, the crystalline lens is able to change its shape to 'automatically' adjust the focusing of light rays on the retina, depending on whether or not the object to be viewed is close by (refractive power variation). The crystalline lens undergoes a loss of transparency with age (cataract).

It is located below the conjunctiva. It is a robust tunic that determines the shape of the eye. Together with the internal fluids (aqueous humour and vitreous humour) it determines the shape of the eye.

The iris and the zonular apparatus of Zinn separate it from the anterior chamber and the vitreous body, respectively. In the posterior chamber, the aqueous humour produced by the ciliary process is released and then also fills the anterior chamber, the posterior chamber and anterior chamber are connected.

The choroid is a tunic rich in blood vessels that is closely connected to the retina. It provides nourishment to the sclera in its anterior part and to the retina in its posterior part.

The macula is the portion of the retina responsible for distinct and colour vision due to the maximum density of photoreceptors (cones and rods).

The images formed on the retina have to be processed by the brain. The optic nerve has precisely the function of transporting nerve impulses from the retina to the brain. It contains nerve fibres that originate from the retina and end up mainly, but not exclusively, at the occipital lobe of the brain where the transformation from nerve stimulus to image takes place.

The retina is the innermost tunic that forms the wall of the eyeball. It is the fundamental component for vision as it is made up of nerve cells including receptor cells. These are photoreceptors of two types: rods for black and white vision, active mainly at low luminance, and cones for colour vision active mainly in good lighting conditions. Photoreceptors are capable of capturing light energy and transforming it into electrical signals that are then transported to the brain via the optic nerve, thus enabling us to see the world around us.

It has a gelatinous consistency and is more than 99% water. The vitreous body fills the posterior cavity of the eyeball, and is in contact anteriorly with the posterior aspect of the crystalline lens and the ciliary body, while posteriorly it is in direct contact with the retina. The remaining composition is due to plots of collagen that give it structure and hyaluronic acid that give it its gelatinous consistency. Being in front of the retina, its transparency is crucial for the passage of light. The so-called flying flies (myodesopias) are precisely protein aggregates that form in the vitreous and obstruct the free passage of light, causing the perception of small, annoying dark spots in the visual field.