The cornea is the eye's outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fills the chamber behind it. 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.
The cornea must remain transparent to refract light properly, and the presence of even the tiniest blood vessels can interfere with this process. To see well, all layers of the cornea must be free of any cloudy or opaque areas. The corneal tissue is arranged in five basic layers, each having an important function
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. The retina changes the light into electrical signals, which are then transmitted to the brain by the optic nerve to be perceived as images. The cornea provides about two thirds of the eye's focusing power. It gives us a clear window to look through and is the key to good vision. It also helps shield the rest of the eye from germs, dust, and other harmful pollutants.
The Corneal Service at DIVA delivers medical and surgical care to a wide variety of corneal, external eye related diseases and anterior segment eye disorders.
Disorders of the Cornea:Ocular Surface Disorders:
Diseases affecting the ocular surface result in non-specific symptoms and can range from a tired or itching eye to diminished vision in severe cases. The common conditions are:
- Dry Eye
- Corneal diseases with stem-cell deficiency
- Pterygium and other conjunctival disorders
- Ocular sensitivity and Neurotrophic Keratopathy
- Ocular allergic diseases
- Eyelid margin diseases such as Blepharitis and Meibomitis
Corneal infections:Infections must be quickly and effectively tackled in order to minimize visual loss, relieve pain, eliminate the infectious agent, and minimize structural damage to the cornea and the other ocular structures. The common conditions are:
- Conjunctivitis (red eye)
- Corneal ulcers
- Scleral ulcers
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, it requires corneal transplantation for restoration of vision.
Corneal Dystrophies:Corneal dystrophy is a condition in which one or more parts of the cornea lose their normal clarity. There are over twenty corneal dystrophies that affect all parts of the cornea. Some cause severe visual impairment while a few cause no vision problem and are discovered during a routine eye examination. Other dystrophies may cause repeated episodes of pain without leading to permanent loss of vision. Some of the most common corneal dystrophies include:
- Fuchs' dystrophy
- Lattice dystrophy
- Map-dot-fingerprint dystrophy
Corneal Ectatic Disorders:These disorders are characterized by a progressive change in the shape of the cornea that results in a decrease in vision. Contact lenses are of benefit and obviate the need for surgery in most cases. However, a small portion of patients reachthe point where they need a cornea transplant. Some of the common diseases include:
- Pellucid marginal degeneration
- Terriens marginal degeneration
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 improve vision to nearly that of a normal person's, and significantly improve 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) 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 Injury:Corneal injuries may result from severe blunt trauma or any kind of penetrating injury. The aim is to restore and maintain the integrity of the globe, avoid further intraocular damage and prevent permanent corneal scarring and astigmatism.
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 injury 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.
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, thepterygium 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 CorneaDegenerative 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
Surgical facilities offered by the Cornea Service:Corneal transplantation (see below) involves replacing a diseased or scarred cornea with a new one. In corneal transplant surgery the surgeon removes the central portion of the cloudy cornea and replaces it with a clear cornea. The chances of success of this operation have risen dramatically because of technological advances. Corneal transplantation has restored sight to many, who a generation ago would have been blinded permanently by corneal injury, infection, or inherited corneal diseases or degeneration. Recent modified forms of corneal transplant called Lamellar Keratoplasty are also performed. This involves removing only the partial thickness of the cornea that is diseased leaving the rest of the healthy cornea undisturbed. Lamellar Keratoplasty is of two types: Deep anterior lamellar Keratoplasty (DALK) and Deep lamellar endothelial keratoplasty (DLEK)
Other Corneal surgical procedures:
- Amniotic Membrane Transplantation
- Pterygium surgeries
- Limbal Stem Cell Transplantation
- Patch Grafts- Corneal and scleral patch grafts
- Corneal perforation repair with anterior segment reconstruction
- Corneal biopsy
1. Blephritis: It is the inflammation of eyelids. Devided into Anterior Blephritis (Includes eyelashes) and posterior blephritis (Includes eyelid margin & meibomian gland). Usually it tends to give redness and crusting.Treated conservatively.
2. Corneal Dystrophies & scars: These are inherited conditions. It mainly affects the clarity of the cornea. Dystrophies & scars can be present in any front, middle or back of the corneal layers.
3. Pterygium: A pterygium is an elevated, wing shaped superficial mass that usually forms over the conjunctiva and extends onto the corneal surface. It is seen more on the nasal side. Pterygium can cause discomfort & if large then also vision is impaired. It is surgically removed.
4. Corneal Topography: It is a rapid non-invasive test that evaluates the curvature of cornea.It helps to detect whether the corneal surface is regular or irregular. Early Keratoconus can often be diagnosed with the use of corneal topography.
5. Corneal Collagen Cross-linking with Riboflavin(C3R): Eyes with keratoconus & ectasia after LASIK surgery are thought to be weaker, so that the cornea bulges. In this procedure the surface epithelium of cornea is removed & riboflavin (vitamin B2) drops are placed. It can stabilise the keratoconus and ectasia.
6. Specular Microscopy (Endothelial cell count): It is the test which evaluates the cont of cells at the deepest layer (Endothelial layer) of the cornea. These cells pump fluid out of the cornea to keep it clear. This test can examine the size, shape &density of the cells. Certain conditions like endothelial dystrophies & Fuch's dystrophy which affects endothelial cells, can be evaluated.
7. Contact lens: Soft contact lenses are useful for many patients with myopia & hypermetropia. Toric soft lenses are used in patients with astigmatism.
Rigid gas permeable lens: Most commonly used in eyes with irregular corneas like keratoconus, after corneal transplant surgery.
Rose K lens: This has become the world's most frequently prescribed gas permeable contact lens for keratoconus.Unlike traditional contact lenses, the complex geometry built into every Rose K contact lens closely mimics the cone-like shape of the cornea for every stage of the condition.The result is a more comfortable fitting lens for patients and better sight (visual acuity).
8. LASIK (Laser in-situ Keratomileusis): The procedure is a type of refractive surgery which is used to treat myopia, hypermetropia & astigmatism of mild to moderate dregree. In this the microkeratome is used to create a corneal flap and excimer laser is used to reshape the cornea.
9. Phototherapeutic keratectomy (PTK): Certain conditions involving front layers of the cornea can be treated with excimer laser PTK. Many inherited dystrophies, opacities and scars can do well with this.
10. Descemet's stripping endothelial keratoplasty (DSEK): is a corneal transplant technique where the unhealthy, diseased, posterior portion of a patient's cornea is removed and replaced with healthy donor tissue obtained from an eye bank. Unlike traditional corneal transplant surgery, the DSEK procedure utilizes a much smaller surgical incision and requires no corneal sutures. DSEK usually results in more rapid visual recovery and also reduces the risk of sight threatening complications that may occur with a corneal transplant.
11. Deep anterior lamellar keratoplasty (DALK): Is a newer method of corneal surgical procedure that selectively removes the diseased anterior layers of the cornea and retains the healthy innermost layer (endothelium). This is the functional layer of the cornea that contains cells that pump fluid out of the cornea and maintain its clarity.) However in fullthickness corneal transplantation procedures (conventional corneal grafting surgery) this layer is also sacrificed and replaced with donor tissue.
12. Penetrating keratoplasty (PK): In corneal transplant, also known as keratoplasty, a patient's damaged cornea is replaced by thecornea from the eye of a human cadaver. Some of the disease conditions that might require cornealtransplant include the bulging outward of the cornea (keratoconus), a malfunction of the innerlayer of the cornea (Fuchs' dystrophy), and painful swelling of the cornea (pseudophakic bullouskeratopathy). Some of these conditions cause cloudiness of the cornea; others alter its natural curvature, which can also reduce the quality of vision.
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.
What is Corneal 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 transplantIf 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 procedureFor 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 risksAs 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.