What is Cornea?
Cornea is the eye’s outermost layer. It is the clear, dome-shaped surface that covers the front of the eye.
The corneal tissue is arranged in five basic layers, each having an important function. These five layers are:
Cornea and Anterior Structures Diagnoses
The Cornea and Refractive Surgery Service provides comprehensive care to the patients with corneal and anterior segment disease, and provides refractive surgery for vision correction. Common disorders of the cornea and anterior chamber (front of the eye) that can be evaluated in the cornea service:
- Allergic conditions, which can cause redness, itching, blurred vision and swollen eyelids
- Blepharitis, an inflammation of the eye lid
- Conjunctivitis, or inflammation of the covering of the eye and inner eye lid
- Dry eye, in which the quality or amount of tears is compromised, and the eye is unable to keep its surface well lubricated and comfortable
Less common disorders of the cornea and anterior chamber may require the attention of a cornea specialist for diagnosis and care. Some of these include:
- Cornea dystrophies, including Fuchs’ endothelial, Lattice and MDF dystrophies
- Infections (bacterial, viral and fungal), including herpes zoster (shingles), ocular herpes simplex, and others. Severe corneal infections can lead to corneal scarring, which can impair vision and may require a corneal transplant.
- Inflammatory disorders with significant eye implications (episcleritis, uveitis)
- Stevens-Johnson Syndrome, a skin disorder that can affect the eyes
- Pseudophakic Bullous Keratopathy (PBK), a rare complication of the cataract surgery
- Pterygium, a type of growth on the cornea
Allergic conjunctivitis is inflammation or irritation of the clear mucous membrane lining the inner eyelids and sclera called the conjunctiva.
This condition, which can be seasonal or year long, is caused by external allergens and is not contagious.
Symptoms can include redness, itching, tearing, burning, stinging, foreign body sensation, watery discharge, blurry vision, and swollen eyelids.
Treatment might include cold compresses, artificial tears and a variety of topical medications. Antihistamine decongestant eye drops can effectively reduce symptoms.
Blepharitis is a common inflammatory condition of the eyelids. It may be associated with an altered activity of the oil glands and skin surface bacteria.
The condition may cause debris and dandruff-like scales that form at the base of the eyelashes along the lid margin. In severe cases, it can involve the cornea and conjunctiva.
Dandruff-like scales along the base of the lashes and lid margins; foreign body sensation, burning, redness, dryness, excessive tearing, swelling and itching of the eyelids
Blepharitis is a chronic problem that can often be managed with eyelid care and hygiene. It may require medication in some instances. Topical medications such as eye drops or ointments or antibiotics can be used in the treatment of this condition.
Conjunctivitis is a group of diseases that results in an inflammation of the mucus membrane that covers the white of the eye and the inner lining of the eyelids.
At its onset, conjunctivitis is usually painless and does not adversely affect vision. It is usually caused by a viral infection, but can also result from bacterial infection, allergies, environmental irritants, eye drops and other eye products. Some forms are highly contagious and can spread from one person to another.
Signs and Symptoms
Discharge; redness, tearing, swelling, burning and itching of the eye
Prescribed eye drops or ointments
Tears keep the eye moist, help wounds heal, and protect against eye infection. In people with dry eye, the eye produces fewer tears, or tears of lesser quality, and is unable to keep its surface lubricated and comfortable.
The tear film consists of three layers–an outer, oily (lipid) layer that keeps tears from evaporating too quickly and helps tears remain on the eye; a middle (aqueous) layer that nourishes the cornea and conjunctiva; and a bottom (mucin) layer that helps to spread the aqueous layer across the eye to ensure that the eyes remain wet. Dry eyes result from problems with any of the three layers of the tears. Dry eye, more common in females, can occur in climates with dry air, as well as with the use of some drugs, including antihistamines, nasal decongestants, tranquilizers, and anti-depressant drugs.
The main symptom of dry eye is usually a scratchy or sandy feeling as if something is in the eye. Other symptoms may include stinging or burning of the eye; episodes of excess tearing that follow periods of very dry sensation; a stringy discharge from the eye; and pain and redness of the eye.
Artificial tears, which lubricate the eye, are the principal treatment for dry eye. They are available over-the-counter as eye drops or gel drops. Sterile ointments are sometimes used at night to help prevent the eye from drying. Using humidifiers, wearing wrap-around glasses when outside, and avoiding outside windy and dry conditions may bring relief. For patients with severe cases of dry eye, temporary or permanent closure of the tear drain with punctual plugs may be helpful.
Keratoconus arises when the middle of the cornea thins and gradually bulges outward, forming a rounded cone shape. It is a progressive disorder and is more prevalent in teenagers and adults in their 20s.
Keratoconus usually affects both eyes. At first, people can correct their vision with eyeglasses. But as the astigmatism worsens, they must rely on specially fitted contact lenses to reduce the distortion and provide better vision. It can also cause increased light sensitivity and glare. Although, finding a comfortable contact lens can be an extremely frustrating and difficult process, it is crucial because a poorly fitting lens could further damage the cornea and make it difficult and intolerable to wear a contact lens. In most cases, the cornea will stabilize after a few years without ever causing severe vision problems.
In about 10 to 20 percent of people with keratoconus, the cornea will eventually become too scarred or will not tolerate a contact lens. If either of these problems occurs, a corneal transplant may be needed. This operation is successful in more than 90 percent of those with advanced keratoconus. Several studies have also reported that 80 percent or more of these patients have 20/40 vision or better after the operation.
A pterygium is a pinkish, triangular-shaped tissue growth on the cornea.
Pterygia are more common in sunny climates and in the 20 to 40 year old age group. Scientists do not know what causes pterygia to develop. However, because people who have pterygia usually have spent a significant time outdoors, many doctors believe that ultraviolet (UV) light from the sun may be a factor. In areas where sunlight is strong, wearing protective eyeglasses, sunglasses, and/or hats with brims are suggested.
Because a pterygium is visible, many people want to have it removed for cosmetic reasons. It is usually not too noticeable unless it becomes red and swollen from dust or air pollutants.
Herpes of the eye, or ocular herpes, is a recurrent viral infection that is caused by the herpes simplex virus and is the one of the most common infectious cause of corneal blindness in North India. Previous studies show that once people develop ocular herpes, they have up to a 50 percent chance of having a recurrence. This second flare-up could come weeks or even years after the initial occurrence.
Ocular herpes can produce a painful sore on the eyelid or surface of the eye and cause inflammation of the cornea. Prompt treatment with anti-viral drugs help to stop the herpes virus from multiplying and destroying the epithelial cells. However, the infection may spread deeper into the cornea and develop into a more severe infection called stromal keratitis, which causes the body’s immune system to attack and destroy stromal cells. Stromal keratitis is more difficult to treat than less severe ocular herpes infections. Recurrent episodes of stromal keratitis can cause scarring of the cornea, which can lead to loss of vision and possibly blindness.
Some factors believed to be associated with recurrence include fever, stress, sunlight, and eye injury.
Signs and Symptoms
- Inflammation of the cornea
- Painful sores on the eyelid and surface of the eye
- Blurred vision
- Excess tearing
- Light sensitivity
- Corneal pain
- Cornea scarring
- Decrease in corneal sensation
- Oral anti-viral treatment
- Anti-inflammatory drops
Pseudophakic Bullous Keratopathy
Cataract surgery causes some damage to the back endothelial layer of the cornea. This cell loss is generally less than 10%, leaving enough of endothelial cells to keep the cornea clear.
Occasionally, during complicated cataract surgery, the endothelial layer of the cornea is damaged more than usual, leaving only a few cells to keep the cornea clear, and hence, the cornea becomes swollen. This can happen even with the best of cataract surgeons and is one of the known risks of cataract surgery. This condition, called pseudophakic bullous keratopathy, is a frequent cause for corneal transplantation.
Stevens-Johnson Syndrome (SJS), also called erythema multiforme major, is a disorder of the skin that can also affect the eyes.
SJS is characterized by painful, blistery lesions on the skin and the mucous membranes (the thin, moist tissues that line body cavities) of the mouth, throat, genital region, and eyelids. SJS can cause serious eye problems, such as severe conjunctivitis, iritis (an inflammation inside the eye), corneal blisters, erosions and corneal holes. In some cases, the ocular complications from SJS can be disabling and lead to severe vision loss.
The most commonly cited cause of SJS is an adverse allergic drug reaction. Almost any drug–but most particularly sulfa drugs can cause SJS. The allergic reaction to the drug may not occur until 7-14 days after first using it. SJS can also be preceded by a viral infection, such as herpes or the mumps, and its accompanying fever, sore throat, and sluggishness. Treatment for the eye may include artificial tears, antibiotics, or corticosteroids. About one-third of all the patients diagnosed with SJS have recurrences of the disease.
SJS occurs twice as often in men as women, and most cases appear in children and young adults under 30, although, it can develop in people at any age.
Corneal Surgical Procedures
A) Corneal Transplantation
In corneal transplantation, the aim is to replace a diseased, scarred, or cloudy cornea with a healthy one in order to allow light to reach the retina (similar to the film of a camera) in the back of your eye. Fine sutures secure the donor cornea in place, and antibiotic drops are given to prevent infection. The eye is dressed with sterile gauze pads and a protective shield. Following surgery, the eye needs to be protected and eye drops should be applied for several months to years to promote healing and prevent rejection (failure of the transplant). Some patients get good vision in two to three months, while others must wait about a year for complete healing.
If necessary, additional surgical procedures can be performed at the same time as the transplant. The most common combination is the removal of a cataract and the insertion of an artificial lens. Surgeons can also perform other procedures, such as a glaucoma surgery. Even a successful corneal transplant does not guarantee perfect vision. Glasses or contact lenses may be needed after the surgery to maximize vision.
Corneal transplants have restored sight of many people who would have been blinded permanently by corneal injury, infection, or inherited corneal disease or degeneration. In some cases, the body may start to reject the new cornea. If this happens, medication can be administered at the first sign of symptoms, which increases the chances of success. There are four signs of rejection that can be remembered by the mnemonic RSVP: Redness, Sensitivity to light, decreased Vision, or Pain which should be reported immediately.
B) Descemet’s Stripping Endothelial Keratoplasty (DSEK)
The aim of Descemet’s Stripping Endothelial Keratoplasty (DSEK), is to replace only the endothelium (innermost layer of the cornea), rather than the entire cornea. In people with Fuchs’ endothelial dystrophy or swelling of the cornea after cataract surgery(PBK), corneal clouding is caused by a decrease in the number of the endothelial cells, whose function is to pump fluid out of the cornea.
DSEK involves peeling only the diseased endothelial layer from the back of the patient’s cornea, which is replaced by back layer (endothelium) of the donor cornea through a small tunnel.
Advantages of DSEK as compared to the standard corneal transplantation are:
- The eye becomes much stronger and more resistant to injury
- There is minimal change in refractive error because the cornea is essentially intact
- Suture-related problems can be eliminated
- Visual recovery is significantly faster and better
- DSEK offers patients better visual recovery and a less protracted clinical course than standard corneal transplantation
C) Intacs Intracorneal Ring Segments
The Food and Drug Administration has approved Intacs™ for the treatment of keratoconus unable to achieve adequate vision with contact lenses or glasses. Nowadays, Intacs™ are inserted by using the IntraLase laser to create small curved incisional pockets in the cornea. This approach prevents scarring defects and helps to flatten the cornea, thus, minimizing astigmatism and distortions in the visual outcome.
D) Ocular Surface Reconstruction
Our specialists are using preserved amniotic membrane (the membrane from the inner surface of the placenta) to reconstruct the surface of the damaged eyes and eyelids.
E) Corneal Cross-Linking
Keratoconus is a corneal condition that affects 1 in 2000 individuals, and is characterized by progressive thinning and outward protrusion of the cornea. Progressive keratoconus results in an irregular, cone-shaped cornea which produces astigmatism that interferes with the ability of light to focus properly, resulting in deterioration of quality of vision. In early stages of keratoconus, vision can often be improved using cylindrical correction in glasses or soft contact lenses. However, in later stages most patients require rigid gas permeable lenses to achieve adequate vision. Advanced keratoconus often results in poor contact lens tolerance.
The placement of IntacsTM, (curved plastic ring segments) into the cornea can improve both vision and contact lens fit to a certain extent, but does not affect the underlying cause of the disease. It is estimated that as many as 20% of keratoconus patients ultimately progress to a very advanced stage, requiring corneal transplantation surgery to restore a more normal corneal shape and improve vision. Corneal transplants often improve vision with glasses and contact lenses, but the surgery is invasive, the risks are not low, recovery is lengthy and there is a lifelong risk of transplant rejection.
Corneal Collagen Cross-linking (C3R) with riboflavin can now be performed in mild to moderate cases of keratoconus to halt further progression of the disease.