Corneal Disorders

The cornea, which acts as a lens, is easily damaged by external foreign substances such as pollen, house dust, contact lens wear, and strong light.
It’s important to note that the cornea is even more vulnerable to damage when the eye is dry.
Minor injuries can heal with treatment, but severe cases can lead to blindness.

This article describes following topics.

・Structure of the cornea
・Major causes of corneal disorders
・How to prevent and treat corneal disorders

The cornea is the outermost tissue of the eyeball, and when distinguishing between the white and the black of the eye, it is often recognized as the black of the eye, but this is because the tissues at the back of the eyeball, such as the iris and pupil, appear black, while a healthy cornea is transparent.

The cornea is made up of five layers, as shown in the figure, and have the following order from the outside in.

・Epithelium
・Bowman’s membrane
・Stroma
・Descemet’s membrane
・Endothelium

The corneal epithelium, the outermost of the cornea’s five layers, acts as a barrier to prevent foreign substances from entering the eye.
The portion made of collagen fibers, which accounts for 90% of the total thickness, is the Stroma, which also functions as the lens. The endothelium, the innermost part of the cornea, regulates the amount of water in the cornea.

The causes and symptoms of corneal diseases vary depending on the location where they occur.

Corneal Epithelium Disorder

Corneal epitheliopathy is a condition in which the epithelium, the outermost layer of the cornea, is damaged, causing severe pain on the surface of the eye.
There are two types: superficial punctate keratitis, in which the epithelial defect is shallow and small, and corneal erosion, in which the wound reaches the entire thickness of the corneal epithelium. If the condition progresses further and the wound extends into the stroma or endothelium, a corneal ulcer or corneal perforation may result. Even mild symptoms of superficial punctate keratitis may cause glare, a sensation of a foreign body, and constant tearing.
As the condition progresses, you may experience eye pain, redness, eye discharge, and a white clouding of parts of the cornea.
The cornea is often damaged by fingernails, foreign objects, contact lenses, etc., but in cases of dry eye caused by dry indoor air or long hours of VDT work, the cornea is particularly susceptible to damage, so care must be taken.

Sleeping while wearing contact lenses can also cause corneal epithelial damage. In addition, eye drops, ultraviolet light, and welding light can also cause corneal epithelium disorder.

Corneal Endothelial Disorder

Once the cells of the corneal endothelium are damaged, they cannot regenerate. The corneal endothelium prevents water from entering the cornea, but as the number of cells decreases, water gradually enters the corneal layer, and the normally transparent cornea becomes cloudy. As corneal endothelial damage progresses, vision loss is seen due to edema of the cornea. As the disease progresses further, blistering and erosion in the epithelium occurs, which is often accompanied by severe pain.
This is called bullous keratopathy. In severe cases, an endothelial or corneal transplant (entire cornea) may be required.
In addition to trauma, other causes of endothelial damage include increased intraocular pressure due to a glaucoma attack or laser iridotomy. Other causes include contact lens use and aging.

Corneal epithelial disorders can occur for a variety of reasons, so it is important to treat the underlying disease, including allergic conjunctivitis caused by pollen or house dust, and viral infections such as epidemic keratoconjunctivitis and herpes keratitis.
Contact lenses are also often the cause of problems, so you should avoid wearing them for long periods of time or sleeping with them on. If you find that the use of hard contact lenses reduces corneal endothelial cells, we recommend that you stop using contact lenses and switch to glasses.
To prevent damage to the epithelium caused by ultraviolet rays from welding light or snow eyes, it’s important to use protective spectacles or goggles.
It’s also known that preservatives in eye drops can damage corneal epithelial cells. It’s dangerous not to follow the frequency of eye drops prescribed by a doctor or to increase the use of over-the-counter medications on one’s own judgment.
Corneal erosion is covered by the epithelium within 1-2 days and pain is disappeared. However, it may persist for a long time due to sensory impairment, inflammation, poor adhesion, etc. If you have impaired sensation due to diabetes, etc., you should be careful as you are more susceptible to infection.

While there are many different eye diseases, corneal disorders should be considered relatively urgent. It’s important to see an ophthalmologist as soon as possible if symptoms such as severe redness, eye pain, or eye discharge are present, and a corneal infection is suspected.
If the condition is mild, it will usually be cured within a month with treatment, but if it becomes severe, it may lead to blindness, so follow-up observation is also necessary.
Corneal infections are generally treated with eye drops to protect the cornea and antibiotic eye drops, but in severe cases, eye ointment may be applied directly to the eye. A variety of treatments are used depending on the severity of the symptoms.
In cases of advanced corneal endothelial disorders, corneal endothelial transplantation or total corneal transplantation may be necessary.

Corneal Transplantation Methods

Corneal transplants aim to correct clouding, swelling, and distortion of the cornea.

Conventionally, as shown in the figure, the method of total corneal transplantation, in which the central portion of the cornea is removed and replaced, has been used. However, surgical methods have advanced to the present, and many patients are now undergoing part transplantation, in which only the diseased part of the cornea is transplanted.
Corneal endothelial transplantation, which replaces only the inner part of the cornea, is said to be less likely to cause transplant rejection and to cause less irregular astigmatism after surgery.

How long does it take for corneal epithelial disorders to heal?

When the cornea is damaged, old cells are usually renewed in 5-7 days. It takes 1-4 weeks for the epithelium to repair itself and recover to its normal structure.

What should I do if my cornea is damaged by contact lenses?

When the cornea is damaged by a contact lens or foreign object, most of the damage occurs to the epithelial layer and heals within a few days. It is important not to interfere with the repair process by continuing to wear contact lenses.
If you are concerned, see an ophthalmologist.

I heard that a scratch on the cornea can lead to vision loss.

There is no concern if the surface of the cornea is scratched. However, if the damage is caused by an infection, corneal epithelial damage may progress, and the damage may extend to the inside of the cornea.
This can result in severe pain, redness, and loss of vision. Depending on the type of infection, the condition can rapidly worsen and cause a hole in the cornea, so we recommend seeing an ophthalmologist as soon as possible.