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 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.
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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.
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
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.
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.
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). Infiniti Eye Hospital was one of the first centres in India to start this treatment in 2007. (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.
Corneal infections are a leading cause of ocular morbidity. These infections are due to different microbes such as bacteria, virus, fungi and protozoa like acanthamoeba, microsporidia. 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. ..
Common predisposing risk factors are corneal trauma, poor hygiene in contact lens users, and abuse of steroid eye drops. Diagnosis depends on the typical clinical feature of each offending microbe and it can be confirmed on corneal scraping with subsequent microbiological evaluation. Treatment is instituted based on the clinical features and the microbiology report; it is specific for each infecting organism. Appropriate treatment if started early usually results in resolution of the infection with minimal loss of vision, however a delay in diagnosis and treatment can have devastating visual outcome. Sometimes drastic surgical intervention has to be undertaken. After elimination of the infection, if there is significant residual scarring of the cornea, which requires corneal transplantation for restoration of vision.
What is Cornea Transplant?
A transplant is the replacement of damaged or diseased tissues or organs with healthy tissues or organs. What people refer to as Eye transplant is actually a Cornea transplant; the entire eyeball cannot be replaced. In a Corneal transplant, the cloudy or warped Cornea is replaced with a healthy Cornea. If the new Cornea heals without problem there will be tremendous improvement in vision.
The healthy corneal tissue used for transplantation is supplied by an Eye Bank. Eye Banks work round the clock to collect, evaluate, and store donated corneas. The Corneas are collected from human donors within hours of death. Stringent tests are done to ensure safety of the person receiving the cornea. The Eye Bank verifies the donor’s medical history and cause of death, and performs blood tests to ensure the deceased person did not have any contagious disease such as AIDS or hepatitis.
Cornea was one of the first parts of the body to be transplanted, and is among the most common and most successful of all organ transplants.
Some facts you may like to know
- It is not necessary to find a cornea with a matching tissue or blood type
- The race, gender, eye color of the donor is not important
- A Cornea transplant won’t change your natural eye color
- The Cornea heals slowly and improvement in vision may take a year or more
- It is difficult to shape the new Cornea perfectly. So, astigmatism (a condition where the Cornea has an irregular shape, making images seem blurred or distorted) is common after a cornea transplant. However, this can be corrected.
Preparing for a transplant
If you are advised to undergo a cornea transplant your Ophthalmologist will tell you what is required. The transplant will be scheduled according to the condition of your eye and the availability of a donor Cornea. Occasionally a shortage of donor corneas may delay surgery. If both your eyes need new corneas, the second transplant will not be performed until the first eye has stabilized, which may take up to a year.
Usually local anesthesia is used for surgery, so you will be awake but feel no pain. The nerves in your eye will be numb so you cannot see or move your eye. Sometimes the doctor may use general anesthesia.
The transplant procedure
For the transplant procedure doctors use an operating microscope and very delicate instruments. Once the old Cornea is removed the new Cornea is stitched into place. The sutures are not visible and are not painful.
If necessary other procedures may be performed at the same time as your transplant. For example a cataract may be removed and replaced with an intraocular lens (IOL). An IOL may be replaced or removed, the iris may be repaired, and the additional procedure required will be explained to you by your ophthalmologist.
Nowadays only the diseased portion of the cornea can be replaced known as lamellar corneal transplant. There are conditions of the Cornea such as Scars, dystrophies, degenerations, keratoconus where the pathology is limited to the anterior portion of the cornea and only that portion is replaced known as anterior lamellar keratoplasty. There are conditions such as Endothelial dystrophy, aphakic and pseudophakic corneal edema where the corneal endothelium is affected and only that is replaced known as endothelial keratoplasty. However these are not an option for every patient who needs a cornea transplant and you need to discuss the appropriate option with your ophthalmologist.
Some potential risks
As with other surgical procedures, a corneal transplant involves some risk – most of them can be treated. Some possible complications are
- Eye Infections
- Failure of the donor cornea to function normally
- Rejection of the donor cornea by your body
- Cataract, Glaucoma
Rejection of the transplant- danger signals !
Rejection of the transplanted cornea can occur any time, but is more likely to happen in the first year after surgery, however timely diagnosis and prompt intervention can save the corneal graft.
The acronym RSVP can help remember these symptoms
- Sensitivity to light
- Vision loss
If you experience any of these symptoms contact the nearest Ophthalmologist preferably a Cornea surgeon immediately.
Medication and follow up
Please follow the instructions regarding medication given by your doctor, do not abruptly stop the drops it can be detrimental for the corneal graft and do adhere to a regular follow up schedule for long term success.
These are primary, inherited, bilateral changes of the Cornea that occur unaccompanied by systemic disease, which affect the normal transparency of the Cornea and result in reduced vision. Dystrophies can affect the Corneal Epithelium, Stroma, or Endothelium. The epithelial and stromal dystrophies in the early stage can be managed by phototherapeutic keratectomy (PTK) whereby the laser can removed the affected portion of the Cornea, when the deeper Cornea is involved a lamellar or full thickness corneal transplant will be required depending on the extent of involvement. The endothelial dystrophies require either an endothelial or full thickness corneal transplant.
Degenerative or Aging Changes of the Cornea
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.