The working of the eye

We can compare the working of the eye with a camera. Both the eye and the camera can be considered as the diaphragm. The retina functions as a sensitive “film” on which the image from outside is pictured.

Just like a photo- or film camera the eye needs light in the first place. When a ray of light reaches the eye it will bend by the system of the lenses. Therefore the ray of light falls on the retina. The image which is formed through that is upside-down and is reduced. The image only gets its meaning when via the optic nerve it reaches the visual centre of the brains. Here the images of both eyes are combined and the interpretation takes place.

Retina

An important part of seeing so happens on the retina which contains sensitive cells. When such a cell is moved by a ray of light an electricstimulus exists which is passed on through the optic nerve to the brains. There are two types of sensitive cells: cones and rods.The cones receive strong light and can distinguish colours. The rods react on weak light, through which one is able to see in the twilight or at night. On the retina, right behind the pupil, there is a place with a high concentration of cones which is called the yellow spot. From the yellow spot to the edges of the eye the cones reduce and the rods increase.

Intensive and detailed watching happens through the yellow spot. But if you would like to spot a weak star at night, you better focus right next to it.Then the image of that star won't be much longer at the yellow spot but next to it on the retina, where there are more rods. Because those rods are more sensitive than cones, such a star can be looked at much better.

Iris and pupil

The iris is coloured and that colouring depends on the pigmentation. When there is less pigmentation the iris is blue, when there is much pigmentation the iris is brown. The opening in the centre is the pupil and through the pupil the eye regulates the ray of light. The pupil will narrow at much light and wider at less light. Both pupils change at the same time, in a reflex. Not only the light influences the pupils. Reduction also takes place when one takes a close look at objects, while the pupils are widening if the see something touching or exciting.