The cornea is the clear tissue situated at the front of the eye. It allows light into the eye, helps focus and see clear images. If the cornea is damaged due to a disease or inherited condition, it may become blur or cloudy and sometimes distorted or scarred. Cornea diseases stop the light from reaching the rest of the eye and hinder its normal process.
Cornea unlike most tissues in the body contains no blood vessels to nourish or protect it against infection. This causes dryness and vision problems and in extreme cases leads to blindness. Certain eye drops, and medications are prescribed to the patient but if they fail to restore corneal clarity, a patient may need a corneal transplant.
Symptoms of Corneal disease
The cornea is prone to many conditions that affect a certain part of the eye. These includes infections, tissue breakdown, and other trauma. The cornea usually heals itself after most minor injuries or infections.
During the healing process symptoms like Pain, Blurred vision, Teary or watery eyes, Redness, and extreme sensitivity to light is noticed. These symptoms are followed by other eye problems, so they may signal a graver issue that requires special attention and treatment. Seek immediate medical help in case these symptoms persist.
Cornea in depth
Cornea though it appears clear and seems to lack substance it is a highly organized tissue. The cornea helps to shield the rest of the eye from germs, dust, bacteria and other harmful objects. The cornea also serves as a filter for screening out some of the most damaging ultraviolet (UV) waves in sunlight. Without UV protection, other parts of the eye might be harmed by the radiation. The cornea receives its nourishment from tears and the aqueous humor. The tissues of the cornea consist of 5 layers. Each of these five layers has an important function.
These layers are:
The epithelium is the cornea’s outermost layer. Its primary functions are to block the passage into the eye and restrict foreign material, such as dust, water, and bacteria. It also helps provide a smooth surface that allows the cornea to absorb oxygen and nutrients from tears which are then distributed to the other layers of the cornea. The epithelium is filled with thousands of tiny nerve endings, which is why the eye may hurt when it is rubbed or scratched. The part of the epithelium that epithelial cells anchor and organize themselves is called the basement membrane.
The next layer of the basement membrane of the epithelium is a transparent film of tissue called Bowman’s layer. It is composed of protein fibers called collagen. If injured, Bowman’s layer can form a scar as it heals. If these scars are large and located centrally, they may interfere with vision.
Behind Bowman’s layer is the stroma, which is the thickest layer of the cornea about 90% of the cornea. It is composed primarily of water and collagen. Collagen gives the cornea its strength, elasticity, and form. The collagen’s unique shape, arrangement, and spacing are important in allowing light to pass through the cornea and conducting transparency.
Behind the stroma is Descemet’s membrane, a thin but strong film of tissue that protects against infection and injuries. Descemet’s membrane is composed of collagen fibers that are made by cells in the endothelial layer of the cornea. Descemet’s membrane repairs itself easily after injury.
The endothelium is the thin, innermost layer of the cornea. Endothelial cells are important in keeping the cornea clean & clear. Normally, fluid leaks slowly from inside the eye into the stroma. The endothelium’s primary task is to pump this excess fluid out of the stroma. Without this pumping action, the stroma would swell with water and become thick and opaque.
In a healthy eye, a perfect balance is maintained between the fluid moving into the cornea and the fluid pumping out of the cornea. Unlike the cells in Descemet’s membrane, endothelial cells that have been destroyed by disease or trauma are not repaired or replaced by the body and require a corneal transplant in extreme cases.
Diseases that affect the cornea
Corneal infections– They can be bacterial, viral or fungal.Infection can come after injury or with contact lenses too.
Dry eye – Dry eyes produces fewer or low-quality tears and is unable to keep itself moist and comfortable. It also causes scratchy eyes.
Corneal dystrophies – A corneal dystrophy is a condition in which most part of the cornea loses their normal clarity due to a buildup of cloudy material.
- Granular dystrophy
- Lattice dystrophy
- Map-dot-fingerprint dystrophy
Treatment of Cornea
A corneal graft (transplant) may be carried out to improve the sight. This operation is also known as a keratoplasty and involves the replacement of part or whole cornea with human donor tissue.
Using healthy tissue from donors
The tissue used in the operation is obtained from donated corneas. The tissue is carefully screened before it is used to make sure it is not infected.
Why is a corneal graft needed?
The cornea can be damaged by:
- Corneal dystrophy which is known as a genetically determined abnormality of the corneal tissue
- Corneal disease or degeneration affecting the clarity of the cornea.
- Trauma or accidental damage
The aim of the surgery is to replace the damaged cornea with a healthy tissue.
There are three types of corneal graft
- Fully thick (Penetrating) grafts – It is when the whole of the cornea needs replacing.
- Partially thick grafts which replace the front of the cornea (Deep Lamellar) to repair the damage caused to the surface only.
- Partial thickness grafts replacing the back of the cornea (Endothelial Lamellar) used to treat conditions affecting only the innermost cornea or endothelium.
There are few types of Corneal Keratoplasty methods
A circular piece is removed from the center of the cornea and replaced with the one taken from a donor’s eye. It is then stitched into place with very fine stitches. These stitches are gradually removed over the following month’s post-surgery
Deep Lamellar Keratoplasty
In DLK, the cornea is split, leaving the deepest 5% or 0.025mm (including the endothelium in place, whilst removing the top 95%. A donor cornea with the endothelium removed is then stitched into position in the same way as penetrating keratoplasty. In approximately 10% of cases, the tissues tear, and conversion to penetrating keratoplasty is required.
Where the cornea is healthy except for a damaged innermost layer, or endothelium, a fine sheet of replacement tissue approximately 0.025mm thick is removed from a donor’s cornea. The unhealthy endothelium is then stripped from the patient’s eye. The donor endothelium is gently folded and posted into the eye, unrolled and floated into position. It sits in place without stitches due to its fluid pumping action which sucks it into position.
If this has not already been done, it can be performed before or as part of the DSEK procedure.
Anterior Lamellar Keratoplasty
Anterior lamellar keratoplasty is a method of corneal transplant indicated for corneal damage limited to the anterior portion of the cornea. The procedure only involves the diseased portion while the healthy portion of the cornea is left intact.
The procedure utilizes a cutting instrument or a trephine in removing the diseased portion of the anterior layer of the cornea. After the diseased layer has been removed, the donor tissue is then sutured in place.
As opposed to traditional corneal transplant surgery, anterior lamellar keratoplasty has fewer post-operative complications and with a diminished risk of damage or infection of the other part of the eye including less risk of graft rejection.
The procedure also entails similar visual result with a brief period of recovery as opposed to traditional corneal transplant surgery. It is, however, a technically precise procedure that Descemet’s membrane perforation is potential which may call for a full thickness or Penetrating keratoplasty.
Why choose currae Hospital?
Receive treatment from best in class eye experts at Currae Eye Speciality Hospital that is guaranteed to speed healing. Experience a vast and ever-expanding array of amenities at NABH accredited infrastructure with post-operative care.