Easy eye anatomy

The eyes are one of the most important and complex organs we have. They are composed of multiple structures with very specific and precise functions. But many times we confuse these structures and give them functions or ailments that do not correspond to them. In this post we will describe the most important parts, their function and the main conditions that they can suffer.
At Clínica Castanera we like to compare the functioning of the eye with that of a camera. A camera has a pair of lenses to focus, which in the case of the eye would be the cornea and lens, a diaphragm that regulates the entry of light, which is the proper function of the iris, and a photographic film where the images are reflected , which in the case of the eye would be the retina. These would be, roughly, the 4 main structures of the eye. But let’s look at each of them in more detail:


It is the transparent part in front of the eye. It is the first of the two lenses that we have and the one with the highest power. The transparency is due to the fact that it is an avascular structure, it does not have blood vessels. When the cornea loses its transparency, either from disease or trauma, or if it becomes too thin, as with a condition called keratoconus, the only option may be to perform a corneal transplant.

It is approximately 0.5mm thick in its central part divided into three layers: epithelium, stroma and endothelium.


It is a muscle that expands or contracts depending on the amount of ambient light. It acts like the diaphragm of a camera, the darker the environment, the more it will open to allow more light to enter our retina.

The color of our eyes is defined by the amount of pigment in our iris. The more pigment, the darker they will be, that is, light eyes are nothing more than eyes with less pigment.


The pupil is not a structure. It is simply the opening that the iris leaves when it is opened. We speak of dilated pupils when in reality it is the iris that dilates or contracts.


It is one of the most complex structures that the eye contains. It is the second of the lenses, after the cornea, that we have. It has a shape similar to a lentil and its main characteristic is that it is capable of varying its shape and size. This way you can change its power to focus both far and near objects.

The main conditions that the lens can suffer are two: presbyopia or tired eyesight and cataracts. Although presbyopia certainly does not affect the lens exactly as we will see below. As for cataracts, these occur when the lens, over the years, loses its transparency. This causes us to see increasingly blurred, with less sharpness and we suffer a notable loss in color perception.


It is the muscle that allows you to vary the shape of the lens. Both are joined by filaments called zonula. As the ciliary muscle contracts or expands, the lens lengthens or shrinks, varying its dioptric power. From the age of 45-50, this muscle begins to lose range of motion. This causes us to no longer be able to focus correctly at all distances. This is when we talk about presbyopia or eyestrain. That is why we said before that presbyopia is not so much a disorder of the lens but of the ciliary muscle.


It is the white part of the eye that lines the eye from the cornea to the back of the eye. It is formed mainly of collagen and its function is mainly to protect the eye against external damage and maintain intraocular pressure.


In the eye there is a constant flow of a liquid called aqueous humor. This liquid has the function of nourishing different structures and is constantly filtered through a mesh called trabecular meshwork or simply trabeculum that is located right on the edge of the iris.

When, for whatever reason, this mesh is obstructed, the passage of liquid is carried out more and more expensively. This causes an increase in intraocular pressure that is transmitted directly to the back of the eye, where the retina and optic nerve meet. When this happens is when we talk about the appearance of one of the most serious eye diseases that we can suffer: glaucoma


The entire back of our eye is covered with a photosensitive layer called the retina. Thanks to a multitude of receptors that capture the information of what we see, we can interpret our environment. There is a very specific and important point on the retina: the macula. It is a very special area since it is where everything we fix our gaze on is focused, that is, our central point of view.

If there is a tear in the retina, it can become detached and obstruct the passage of light and therefore our vision. The only alternative in this case is to perform a surgical procedure called a vitrectomy.

If it is the macula that presents some damage, such as when AMD (Age-Related Macular Degeneration) appears, it is when we can suffer a significant loss of vision. In this case, there are drug alternatives that can solve the problem, otherwise it would be necessary to also opt for the surgical option.


It is a kind of gel that fills the eye behind the lens to the queen and gives it consistency.

Sometimes some parts of this gel are densified. It is then that myodesopsia or floaters appear, those small spots that we can see especially when observing a light background such as a white wall or a blue sky. If they become very annoying, the only option is again vitrectomy.


This nerve connects directly to our brain. It is in charge of collecting all the information received by both the retina and the macula and transmitting it to the brain so that it can interpret it.

Any damage caused to this structure is difficult to recover. It must be borne in mind that they are nerve fibers and that they cannot regenerate. That is why it is so important to anticipate diseases such as glaucoma that cause irreparable damage to our optic nerve that can end in blindness. To do this, the only way is to have regular ophthalmological reviews.