Corneal disorders FAQ

Home >> Corneal disorders FAQ

 Learn about common corneal disorders and their treatment.

 

The Normal Cornea

The eye is like a camera in which lenses focus the picture on a light sensitive film. In the human eye, the transparent cornea and lens focus light on the retina, which changes it into electrical signals, which are then transmitted to the brain by the optic nerve to be perceived as images.

 

The cornea is the front transparent window of the eye and forms the outermost one-sixth of the eyeball. It is lamellar in nature (like plywood) and is made up of 5 layers, each of which has a definite function. In order to be effective it must remain transparent. Freezing, heating, molding, lathing, tattooing, excising, incising and transplanting are all means by which the delicate and sensitive cornea has been altered for optical, therapeutic and cosmetic purposes. Due to absence of blood vessels in the cornea, much of its oxygen requirement comes from atmospheric oxygen dissolved in the tear film. When the eyelids are closed, oxygen enters the cornea from the superficial conjunctival vessels. Nutrients needed for the cornea pass into it by diffusion. Hence, carbon dioxide and waste products are also removed across the tear film. Hence, any deficiency of the tear film will directly or indirectly affect the cornea.

 

Foreign Bodies, Corneal Abrasions & Injuries

Since the abundant nerve supply of the cornea makes it one of the most sensitive parts of the body, it serves as an excellent "watchdog" for foreign material entering the eye. Dirt or specks lodging in the eye may produce scratching, knife-cutting sensations that the sensitive corneal nerves transmit to the brain. If the cornea loses this sensitivity due to in- jury or impairment by disease, it loses its protective function. Foreign bodies may embed in the cornea. A foreign body on the cornea needs urgent attention by an ophthalmologist. One should not attempt to remove it by rubbing the eye

 

A twig of a tree, a piece of paper, or a fingernail can produce corneal abrasions. If not attended to immediately, secondary infection can occur which could lead to vision-threatening complications. Contact lenses also can produce an irritable eye from a corneal abrasion. Until an eye specialist can be consulted, the contact lens should be removed and the eye patched.
Injuries to the eye with sharp or blunt objects require urgent attention of your ophthalmologist, especially to rule out corneal injuries, which can be sight-threatening.

 

Chemical Burns

Acid or alkaline solutions splashed into the eye may be potentially sight threatening. Symptoms (such as pain, redness, watering and light-sensitivity) occur immediately after exposure to the chemical and may be severe in nature. Chemicals in the eye need to be thoroughly washed out immediately with water. THEREAFTER, URGENT CONSULTATION WITH AN EYE SPECIALIST IS NECESSARY.

 

Infections of the Cornea

Inflammation of the cornea, or keratitis, may be secondary to conjunctivitis, blepharitis (inflammation of eyelid margins), or injury. Keratitis is characterized by a painful red eye, sensitivity to light, and an occasional scratching sensation upon blinking. An ulcer may develop in the cornea after a bacterial, viral, fungal, or other infectious organism invades its outer layer. Herpes simplex, a virus can invade the cornea after injury, producing keratitis. Herpes zoster, another viral agent, produces inflammation of the cornea, especially if the skin of the nose is involved. A marginal ulcer is a corneal infection that occurs near the outer edge of the cornea. Central corneal ulcers due to bacteria, viruses, or fungi can be severe and serious; they may even cause loss of the eye. With these severe ulcers, the eye sets up a defense reaction to help fight the infection. This disease requires the immediate attention of an ophthalmologist. With intensive medical treatment, the infection is brought under control. Sometimes drastic surgical intervention has to be undertaken. Often after elimination of the infection, there is residual scarring of the cornea, which requires corneal transplantation for restoration of vision..

 

Pterygium

This grayish elevated growth of elastic and connective tissue containing blood vessels invades and grows over the cornea. It may result from irritation to the eye from wind, heat of the sun, dust, or smoke. If the pterygium progresses to grow over the center of the cornea, sight may be impaired or even lost. Before this occurs, the pterygium should be removed surgically. At our centre, pterygium is removed by a specialized technique called Conjunctival Autografting, where, the pterygium is excised, and a conjunctival graft, taken from a healthy part of the same eye is used to cover the defect. This technique prevents recurrence of the pterygium, which would normally occur after conventional pterygium removal without grafting. Some people confuse a cataract with a pterygium by calling a cataract a "skin growing over the eye." A cataract, however, is a clouding of the lens, which is located inside the eyeball.

 

Degenerative or Aging Changes of the Cornea

Dystrophies or degenerative aging processes may develop in the cornea and interfere with vision. They are slowly progressive, non-inflammatory, and usually affect or involve both eyes. They may produce a haziness or cloudiness of the cornea. If the vision is markedly impaired, contact lenses may be prescribed to improve vision. If they do not help, a corneal transplantation may be performed to restore useful sight.

 

What is Dry Eye Syndrome?

Dry eye syndrome is a leading cause of ocular discomfort affecting millions of people. Dry eye conditions are a spectrum of disorders with varied etiology ranging from mild eyestrain to very severe dry eyes with sight threatening complications.

 

Although the typical patient of dry eyes is elderly, or suffers from autoimmune disease, increasing numbers of patients do not fit this profile. Younger patients who work with computers can suffer from dry eyes more often than elderly patients. Dry eye condition is also aggravated in polluted conditions, dry weather, decreased ambient humidity as seen with air conditioning and indoor heaters. It may also result from the abnormalities in one or more of the tear film components, ocular or systemic diseases, and various drugs.

Dry eye syndrome is usually treated with tear supplements and lubricants. However, if these do not help, the insertion of microscopic plugs (temporary or permanent) can be inserted to help conserve tears and prevent them from draining away. In severe cases, surgical intervention may be essential

 

Keratoconus

Normally the cornea is nearly spherically shaped thus allowing light to be focused clearly on the back of the eye (retina). However in a condition called Keratoconus, the cornea begins to thin, and this allows the normal pressure of the eye to make the cornea bulge forward taking on a cone-shape. As the cornea gradually becomes more cone-shaped, the vision blurs and becomes distorted due to a high degree of astigmatism. Initially vision may be correctable with spectacles, but as the condition progresses, and the cornea becomes more irregular causing distorted vision, spectacles become less effective. In such a situation, contact lenses not only provide better vision, but also help to retard the progress of the disorder. A rigid contact lens (RGP / "semi-soft" contact lenses) must be used, so that it can hold its shape, as a soft lens would simply mould to the existing shape and thus not allow complete correction of the problem. Sometimes the patient is fitted with soft lenses (for comfort), over which semi-soft lenses are fitted ("piggy-back" lenses).

 

Fitting contact lenses for keratoconus requires expertise. Well-fitting contact lenses dramatically improves such a patient's vision to nearly that of a normal person's, and significantly improves his or her quality of life. Any excessive pressure of a poorly fitting lens on the cone apex can cause permanent scarring within months or years (This scarring can also occur naturally). For this reason it is important for regular follow-up visits to be made so that any corneal changes that have occurred can be compensated for in the design of a new lens. It is quite common for patients to be refitted at irregular intervals as the condition progresses. Rarely, scarring is so severe that a corneal graft (transplant) is necessary.

 

A recent promising treatment modality for keratoconus is C3R (Corneal Collagen Cross-linking with Riboflavin). Shreya Eye Centre now offers you Cross Linking of the Cornea with Riboflavin (C3R), which is a new curative approach to increase the mechanical stability of corneal tissue. The aim of this treatment is to create additional chemical bonds inside the corneal stroma by means of a highly localized photo polymerization.
The indications for cross linking today are corneal ectasia the disorders such as keratoconus and pellucid marginal degeneration, iatrogenic keratectasia after refractive lamellar surgery and corneal melting that is not responding to conventional therapy.

 

What is Corneal Transplantation?

Corneal transplantation, or keratoplasty, is an operation designed to correct blindness resulting from corneal disease. When the cornea is involved by degenerative change, infection, or injury, scar tissue may form as healing occurs. If the scar involves the center of the cornea or the entire cornea, vision is impaired. Depending upon the degree of involvement, the person may not be able to see to perform his daily tasks. Contact lenses rather than spectacles may partially improve vision, but often they are ineffective and a corneal transplant is required. Eye tissue from one person is transplanted into the eye of another person who has been blinded by a corneal scar or disease.

 

Many people are under the false impression that one good eyeball is transplanted for another eyeball which is diseased. Some mistakenly believe that a blue-eyed person's eyes cannot be used for transplantation in a brown-eyed person. Neither of these statements is true. The only tissue used in the transplant is the cornea, which has nothing to do with the colored part of the eye. Since the eye is connected to the brain by the optic nerve, which is a part of the central nervous system, the eye is not and cannot be transplanted.

 

If the eye were compared to a watch, the crystal of the watch would be synonymous with the cornea of the eye. The face of the watch would be equivalent to the iris and lens. If the watch crystal is clean and transparent, the face of the watch will be seen clearly. However, if paint is smeared over the crystal of the watch, the face of the watch will not be seen and the paint cannot be wiped off. To see the watch face clearly again, the crystal must be removed and replaced with a new clean crystal.

 

How is a cornea transplanted?

A corneal transplantation, like a cataract operation, is usually performed under local anesthesia. General anesthesia is used for children and apprehensive or nervous patients. The operation is completely painless and takes about one hour to perform.

 

The diseased, cloudy, opaque cornea is removed from the recipient's (living patient's) eye using a special blade, and replaced by a new clear cornea (graft) from the donor's (deceased person's) eye. Earlier we transplanted the entire thickness of the cornea (Penetrating Keratoplasty). Today depending on the extent, location and type of the corneal disorder, we can selectively transplant either the front part (Anterior Lamellar Keratoplasty), or the back portion (Endothelial Lamellar Keratoplasty). The new cornea is then sutured or stitched into place. As few as eight and as many as 20 or more sutures may be used, according to the size of the graft, to hold the border of the graft to the border of the recipient. If the operation is successful and the graft "takes" and remains clear, the patient should see well again, provided the lens and the retina behind the cloudy cornea are normal. The patient is usually hospitalized for one day but requires rest for the next one month although returning to light work is not a problem. However frequent follow-ups are required over the following six months to one year.

 

How successful is corneal transplantation?

In favorable subjects the rate of success of corneal transplantation may be as high as 60%, with good final visual acuity with glasses. In unfavorable subjects, the rate of success may be around 10 to 20%. Each patient is evaluated individually before definite results can be predicted. The most important factors in determining the final results are:

  • Basic corneal disease (some types of corneal disease respond better to corneal transplantation than others).
  • State of the donor's cornea.
  • Surgical technique and skill.
  • Healing ability of the recipient cornea.
  • Sensitivity reactions between donor and recipient cornea may lead to transplant rejection.

 

The advantages of lamellar keratoplasty (newer techniques) are better visual outcome, quicker rehabilitation and lower rates of transplant rejection.

 

A corneal transplantation will not help every blind person to see again. If a person is blinded by glaucoma, a detached retina, or degenerative change and the retina has been damaged or destroyed, nothing can restore lost sight. Corneal transplantation restores vision only in eyes that have been partially blinded by corneal disease. Some vision must be present before transplantation is even contemplated.

THE OCCURRENCE OF PAIN, REDNESS, WATERING, LIGHT-SENSITIVITY AND DIMINISHED VISION, ANY TIME (EVEN MONTHS OR YEARS) AFTER CORNEAL TRANSPLANTATION SURGERY, REQUIRES IMMEDIATE ATTENTION OF YOUR OPHTHALMOLOGIST.