The cornea is the outermost layer of the eye, it is avascular and totally transparent and among its functions are those of protecting the iris and the lens and focusing together with the lens of the images on our retina. It is the most exposed layer of the eye, so it is very important for our vision.
A lack of transparency or a deformity in this tissue can cause a distortion of the image on the retina, causing refractive problems ( myopia, astigmatism, farsightedness ). But, in addition, being the most external part, it is more exposed to other pathogens that can cause various pathologies. The most frequent are the following:
There are numerous types of conditions of the ocular surface and cornea. The most frequent diseases of the cornea are the following:
A corneal ulcer is a lesion that occurs in the outermost layers of the cornea, usually affecting the epithelium and, occasionally, also Bowman’s layer and the anterior stroma.
It must be treated in time to prevent it from getting worse and having visual consequences, especially if it occurs close to the visual axis. Sometimes a corneal ulcer can give different symptoms that could be confused with conjunctivitis.
The development of this pathology can be due to several factors. It can be of sterile origin, such as trauma, abrasions of the surface of the eye, dry eye syndrome, or problems that prevent the correct functioning of the eyelids. Or it can be of infectious origin, bacterial, viral, caused by fungi or parasites.
Sometimes, misuse of contact lenses can be the reason for these corneal injuries. In the case of sterile ulcers, it is important to treat them early to prevent superinfection.
Corneal ulcers can cause pain, red eyes, inflammation of the eyelids, and photophobia (discomfort from light or brightness).
They can also produce a foreign body sensation inside the eye. These lesions can also cause tearing and sometimes appear as a white or greyish spot on the cornea, mainly when they are of infectious origin. In any case, it is essential to see an ophthalmologist as soon as possible to detect the origin of the injury and start the appropriate treatment.
Corneal edoema is an eye disease that consists of inflammation of the cornea as a result of fluid retention. In this way, the corneal endothelium (innermost layer of the cornea) stops working, and the cornea accumulates liquid, losing its transparency.
The symptoms of corneal oedema are varied, depending on the damage to the corneal endothelium, which can cause significant visual disturbances. In addition, these patients may also present intraocular foreign body sensations, hypersensitivity to light, and/or redness.
The origin of corneal edoema can be varied, from infections and/or trauma to specific corneal dystrophies, among others. However, the most frequent cause is a decrease in the number of endothelial cells due to genetics.
The diagnosis of this disease is determined using different diagnostic tests, which mainly include the use of the slit lamp and endothelial microscopy. Once the cause has been determined, the ophthalmologist will decide which is the best treatment for each specific case.
Keratitis means inflammation of the cornea. Due to its proximity to the conjunctiva, we speak of keratoconjunctivitis when the inflammation affects both structures. It is usually caused by palpebral problems, dry eye syndrome or decreased quality and quantity of tears, immunological disorders, irritation by physical and chemical agents (including ultraviolet radiation and the use of contact lenses), and infections (viral, bacterial, fungal and protozoan).
Keratitis usually affects the outermost layers of the cornea, but if it worsens, it could develop into corneal ulcers. The most frequent symptoms are usually: ocular redness, photophobia, pain or blurred vision. Before the appearance of any of them, it is important to go to the ophthalmologist to determine the origin and treatment of keratitis.
When the cause is dry eyes, the initial treatment is with artificial tears, which may require more intensive treatments if there is no improvement. Also, allergy sufferers should avoid contact with triggers; and those who wear contact lenses should wash and dry their hands well before and after use, as well as clean them properly, according to the guidelines established by the manufacturer.
Also, in the latter case, it is advisable to disinfect the cases where contact lenses are kept, which must always be kept clean and changed frequently.
Other types of pathologies related to the cornea would be the following:
Corneal neovascularization is the growth of blood vessels in the cornea, a tissue that, by nature, lacks them to favour its transparency and its role in refraction and visual acuity. It is a physiological mechanism, a reaction to the lack of oxygen (hypoxia) in the tissue, which tries to be solved with the appearance of new blood vessels. However, they can compromise visual acuity and, in patients with previous corneal transplants, they can be a determining factor for graft viability.
The most common causes of this hypoxia or lack of oxygen in the cornea that trigger neovascularization are infectious processes, misuse of contact lenses, certain immune responses, corneal innervation disorders, trauma, and/or dry eye syndrome.
The development of this corneal neovascularization could produce a significant decrease in visual acuity and constitutes the main risk factor for immune rejection in keratoplasty.Keratoconus
Keratoconus is one of the most frequent diseases of the cornea. It is a degeneration consisting of corneal thinning (ectasia) that causes a progressive increase in its curvature, which gradually adopts a conical shape and produces a gradual loss of vision.
According to the experts of God Service Eye Clinic one of the main symptoms of keratoconus is image distortion and visual impairment that cannot always be corrected with glasses.
At present, there are no definitive studies that specify in a specific way the causes for which this disease develops, but it is known that genetic factors and eye rubbing play an important role. Its treatment depends, to a large extent, on its early detection.
For this, we have high-resolution diagnostic tests such as corneal topographies. In most initial cases, different surgical treatments can be used to stop its evolution. In the most advanced cases of the disease, it is sometimes necessary to perform a corneal transplant. Fuchs‘ dystrophy Fuchs‘ endothelial dystrophy is one of the most common diseases of the endothelium, the deepest layer of the cornea. Its function is to keep the cornea transparent and dehydrated, thus allowing light to pass through properly.
When there is Fuchs’ dystrophy, its pump function works with difficulty, and the liquid ends up passing into the compact collagen layer (stroma), giving it a spongier texture, and producing corneal edoema.
In the early stage of Fuchs Dystrophy, mild symptoms such as glare or visualization of halos may appear. Something characteristic of this phase is blurred vision when waking up in the morning, a symptom that progressively improves during the day.
As the disease progresses, blurred vision may take longer to improve or not improve at all. In the most advanced stages of the disease, blisters of fluid may appear in the epithelium, the outermost layer of the cornea, causing pain and possibly becoming infected.
Fuchs’ dystrophy is usually hereditary. The genetic basis of the disease is complex: family members may or may not be affected to varying degrees. The best treatment available right now is endothelial transplantation (DMEK).Other corneal pathologies Although Fuchs’ endothelial dystrophy is a common disease of the cornea, there are numerous types of corneal pathologies that can affect all its layers. Many of them are due to hereditary causes and require specific treatments for their visual rehabilitation.
In addition, of all the diseases described above, the cornea can also be affected by others, such as blepharitis, a condition that causes inflammation of the eyelids. This disease can cause redness, burning, or the appearance of small scales around the base of the eyelashes.
The exact reason for blepharitis is unknown, but experts suggest that it may be caused by an overgrowth of bacteria, or by a decrease or alteration in the normal oils produced by the eyelid.
In the same way, the cornea can also be affected by the so-called pterygium. It is a growth of connective tissue that appears in the eyeball, usually in the part closest to the tear duct, and that can invade the cornea and alter its transparency, thus affecting vision and inducing astigmatism.
The main risk factor for developing a pterygium is sun exposure and other types of adverse environmental elements such as wind, environmental dryness, dust or heat. Therefore, to avoid its appearance, it is advisable to wear sunglasses with an ultraviolet filter, take eye protection measures against the action of external factors, and use artificial tears to keep the eyes hydrated.