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The cornea is a part of the eyeball that has refractive properties and is part of the anterior segment of the eye, Together with crystalline as well as the conjunctiva.

The cornea is a fundamental structure to enjoy correct vision, as it acts as a natural protector of the eye against external agents and allows the passage of light from the outside to the retina.

En Área Oftalmológica Avanzada We explain below the definition of the cornea and what are the most common diseases that affect this part of the eye.

What is the cornea?

The cornea is a transparent structure at the anterior pole of the eye that allows light to enter from the outside and protects the lens and the iris.

The cornea has refractive properties and its correct curvature is essential for the individual to see correctly. 

Many people who wonder what the cornea is are unaware that it is a transparent tissue that must maintain an adequate curvature in order to enjoy clear vision. 

Function of the cornea of ​​the eye

The cornea has a dual function. On the one hand, it protects the eye against external agents and, on the other hand, it performs a correct refraction of the images in our eye.

protect the eye

The main function of the cornea is to protect the eye from external agents such as dust, mites, infections, germs and bacteria and any other external factor that may pose a risk.

This protective function is shared with other agents related to the eye such as tears, sclera and Eyelids.

For this reason, it is common for many bacteria or diseases to affect the cornea before other parts of the eyeball.

Therefore, an examination of the cornea to see its condition can transmit a lot of information about the ocular health of the eye to the ophthalmologist.


The second is the focus property that it has. The cornea is the eye's first natural lens, and it helps the lens focus images.

To fulfill this function, the cornea must be transparent and with the correct curvature at all times so that the light that comes from objects is reflected exactly on the retina.

When this does not happen, we say that we have refractive defects and myopia, farsightedness or astigmatism.

The transparency of the cornea also plays a very important role, since it depends on it, among other parts of the eye and brain, the visual capacity of each person.

Any deformity in the transparency or shape of the cornea can result in the formation of a poor projection of the cornea. light on the retina, what we know as myopia, farsightedness o astigmatism.

Layers of the cornea

The cornea is made up of six cell layers that we will explain below. We will detail them in order, from outside the eye to inside the eye.

Corneal epithelium

The corneal epithelium is the layer responsible for maintaining the transparency of the cornea and protecting it from external factors as well as giving stability to the cornea. tear film.

The epithelium is made up of layers, known as epithelial layers and consists of 5 in the peripheral part and up to 10 in the central part. These epithelial layers have different types of cells in each of them, known as epithelial cells.

As data, the epithelium has an excellent healing capacity. 

Bowman Stratum 

Bowman's layer or membrane is an acellular layer about 17 microns thick and transparent. This layer decreases its thickness over time since it cannot regenerate itself and is responsible for protecting the nerve plexus and helping sensory recovery. 

Corneal stroma 

It is the thickest part of the cornea formed by collagen fibers, matrix and keratocytes.

Its approximate size is about 500 microns and its function is to help maintain the transparency of the cornea.  

Dua layer 

It is the last layer discovered in the anatomy of the cornea and is named after its discoverer, Harminder Dua.

This layer is made up of collagen plates and is 15 microns thick. The dua layer separates the last group of keratocytes.

Descemet Membrane 

It is the basement membrane of the endothelium and is also composed of collagen. This layer is approximately 2 to 20 microns thick.

Irregularities in this part of the cornea are called cornea gutata. This pathology can affect the endothelium and the health of the cornea, ending in a keratoplasty.

Today we can make a cornea transplant, this technique is known as DSAEK.

Corneal endothelium

The endothelium is made up of a single layer of squamous cells with a thickness of 5 microns. It is the last layer of the cornea and consequently is in contact with the interior of the cornea and the aqueous humor located at the anterior pole of the eye.

It consists of a semi-permeable barrier that allows the entry of nutrients from the aqueous humor into the interior of the cornea. As an opposite effect, it also has to evacuate fluids to the outside of the cornea to maintain its transparency and maintain fluid balance.

If there is not this balance, because the endothelium is not able to evacuate the fluids, the stroma will swell causing a loss of transparency of the cornea.

Most common corneal diseases

The most common diseases that can cause damage to the cornea are: 

corneal opacity 

It is the loss of transparency of the cornea due to trauma or hereditary factors. The corneal opacity It can be treated definitively through a corneal transplant. 

Corneal ulcers

It is the formation of a corneal ulcer It is usually due to an uncontrolled infection.


La keratitis is a inflammation of the cornea by ocular dryness, viral or bacterial infections and excess sun exposure without protection. The incorrect use of contact lenses is one of the main causes of keratitis


La Blepharitis It is a very common pathology that consists of the inflammation of the edge of the eyelids evidencing a swelling of the same. This is caused by dysfunction of the meibomian glands (DGM).

This incorrect operation means that the tear does not contain fat, it is of poor quality and we notice that our eyes hurt as a result of the eyelid "scratching" the cornea when blinking.


El keratoconus It is the alteration of the collagen fibers that make up the stroma and causes the deformity of the cornea, which adopts a cone shape.

Refractive defects

Refractive errors such as myopia, hyperopia or astigmatism also affect the cornea.

Today, modern laser platforms for refractive surgery They allow us to correct and shape the cornea to recover a clear vision of the world around us.

Dry Eye

El Dry Eye is the inability to keep the ocular surface properly lubricated. The main reasons for dry eyes are the lack of tears or the poor quality of them.

The main symptoms of Dry Eye They are the sensation of grit, foreign body, eye redness or excessive tearing.


El pterygium It is an abnormal growth of the conjunctiva towards the cornea.

The origin of this proliferative growth is in the basal epithelial stem cells of the limbal bed (ELMC), which are activated and transformed into connective tissue.

Corneal Treatments

In some occasions, as is the case of myopia, hyperopia or astigmatism, the keratoconus and corneal opacity may require refractive surgery, a cornea operation or even a corneal transplant.

En Área Oftalmológica Avanzada We have a team specialized in the review and diagnosis of diseases associated with the cornea. Do you need to arrange a visit? Contact us!

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The cornea is a structure of the eye that plays a vital role in achieving clear vision. We tell you what it is and its associated diseases.
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Área Oftalmológica Avanzada
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