WHAT YOU SHOULD KNOW ABOUT THE CORNEA AND CORNEAL DISEASE
Christiane Tourtet B.A.
December 01, 2008
The cornea is the clear surface, dome- shaped, that covers the front of the eye. It is the eye´s outermost layer. The cornea, unlike most tissues in the body, does not contain blood vessels to nourish and protect it against infection. The cornea is nourished by the tears and aqueous humor that fills the chamber behind it, and must remain transparent to refract light properly. All the layers of the cornea must be free of any opaque or cloudy areas. The corneal tissue has five basic layers, and each of them have an important function.
The epithelium is the cornea´s outermost region, which comprises about 10 percent of the thickness of the tissue. Its function primarily, is to block the passage of foreign material, such as bacteria, water, dust, into the eye and other layers of the cornea.
It also provides a smooth surface that absorbs cell nutrients from tears and oxygen, then distributes to the rest of the cornea these nutrients. The epithelium is filled with tiny nerves endings, by the thousands, that make the cornea extremely sensitive to pain if it is scratched or rubbed. The foundation on which the epithelial cells organize and anchor themselves, is called, the basement membrane.
The Bowman´s layer lies directly below the basement membrane of the epithelium, and is a transparent sheet of tissue composed of strong layered protein fibers called collagen.
If injured, Bowman´s layer, as it heals, can form a scar, and if these scars are centrally located and large, then, some vision loss can occur.
The Stroma, is beneath the Bowman´s layer and comprises about 90 percent of the thickness of the cornea. It is made mostly of about 78 percent water and about 16 percent collagen. It does not contain any vessels or blood, and the collagen gives form, strength, and elasticity to the cornea. The collagen´s quite unique shape, spacing, and arrangement are essential in producing the light-conducting transparency of the cornea.
The Descemet´s membrane, located under the stroma, is a strong, but thin sheet of tissue that serves as a protective barrier against injuries and infection. It is composed of collagen fibers that are different from those of the stroma, and is made by endothelial cells that are below it. After injury, Descemet´s membrane is readily regenerated.
The endothelium is the innermost layer of the cornea and is extremely thin .To keep the cornea clear endothelial cells are essential, as their primary task is to pump excess fluid out of the stroma. If a trauma or a disease, destroy the endothelium cells, they are lost forever, and if too many endothelial cells are destroyed, edema in the cornea and blindness ensue and corneal transplantation is the only available therapy.
There are about 120 million people in the United States who wear contact lenses or eyeglasses, in order to correct astigmatism, nearsightedness, or farsightedness. These disorders of the vision, are called refractive errors and affect the cornea. They occur when the curve of the cornea is irregularly shaped, such as being too flat or too steep. If the eye is too long, or when the cornea is too much curved, faraway objects will appear blurry, because they are focused in front of the retina, and this is what is called nearsightedness or myopia. About 15 percent of all adult people in America have myopia.
Farsightedness or hyperopia, is the opposite of myopia, as distant objects are clear, but close-up objects appear blurry. Hyperopia results from an eye that is too short and images focus on a point beyond the retina.
Astigmatism is a condition in which the uneven curvature of the cornea distorts and blurs both near and distant objects. A normal cornea is round, and has even curves from top to bottom and from side to side. With astigmatism, the cornea is shaped like the back of a spoon and curved more in one direction than in another, which causes light rays to have more than one focal point and focus on two separate areas of the retina, thus, distorting the visual image. Two third pf people in America who have myopia also have astigmatism. These refractive errors usually are corrected by contact lenses or by eyeglasses, and they are effective and safe. However, refractive surgeries are becoming more and more a popular option.
There are many disorders and diseases of the cornea, among them are:
Allergies: It is fairly common to have allergies affecting the eye. The most common allergies are those related to pollen especially when the weather is dry and warm. Symptoms can include itching, burning, redness, stinging, watery discharge. Usually decongestant eye drops, antihistamine, can effectively reduce these symptoms. There are also an increasing number of eye allergy related to contact lens wear, medications, animal hair and certain cosmetics, such as face creams, eyebrow pencil, mascara, lip gloss, eye make up, soaps, and rubbing or touching eyes after handling nail polish or chemicals. However these allergy symptoms, are temporary and can be eliminated by avoiding contact with the offending detergent or cosmetics.
Conjunctivitis (Pink eye): Conjunctivitis, is a group of diseases that cause redness, burning, swelling, itching of the conjunctiva, the protective membrane that covers exposed areas of the sclera or white of the eye and lines the eyelids. It can spread from one person to another and at any given time affects millions of people in America. It can be caused by viral infection, allergy, eye ointments, contact lens products, eye drops, environmental irritants. At its beginning conjunctivitis is usually painless, and does not adversely affect vision. In most cases infection will clear without requiring medical care. However, some forms of conjunctivitis will require treatment, and if treatment is delayed, the infection may worsen and cause an inflammation of the cornea and a loss of vision.
Corneal Infections: Sometimes after a foreign object has penetrated the tissue, such as a poke in the eye, the cornea is damaged. At other times fungi or bacteria from a contaminated contact lens can pass into the cornea, and can cause painful inflammation and corneal infections called keratitis. These infections can produce corneal discharges, reduce visual clarity, can lead to corneal scarring, which can impair vision and may require a corneal transplant. The deeper the corneal infection, the more severe are the symptoms and complications. Minor corneal infections are usually treated with anti-bacterial eye drops. Severe corneal infections may require more intensive anti-fungal or antibiotic treatment, as well as steroids eye drops. It might be necessary to visit frequently an eye care professional for several months to eliminate the problem.
Dry Eye: Dry eye is more common in women, especially after the menopause, and the main symptom is usually a sandy or scratchy feeling as if something is in the eye. It can also include burning, stinging, stringy discharge, pain , redness of the eye, episodes of excess tearing following periods of very dry sensation, heaviness of the eyelids, or decreased , blurred, changing, vision. In climates with dry air, as well as with the use of nasal decongestants, anti-depressants, drugs, including antihistamines, tranquilizers, dry eyes can occur. People who experience dry eyes should let their health care providers know all the medications they are taking, since some of them may intensify the symptoms of dry eyes.
People with rheumatoid arthritis can also develop dry eye. Sometimes dry eye can be a symptom of Sjogren´s syndrome, which is a disease that attacks the lubricating glands of the body, such as salivary and tear glands.
The principal treatment for dry eye is artificial tears, as eye drops available over-the –counter, which lubricate the eye. At night sterile ointments are sometimes used to help in preventing the eye from drying, humidifiers can help too. When outside, wearing wrap-around glasses, avoiding dry and windy conditions, may bring some relief.
Fuchs´Dystrophy: Fuch´s dystrophy, usually affects both eyes, is slightly more common in women than men. It is a slowly progressing disease, which can be seen often by doctors in people in their 30s and 40s. It rarely affects vision until people reach their 50´s and 60´s. Fuchs´ dystrophy happens, when, without apparent reason the endothelial cells gradually deteriorate, and as more of these cells are lost over the years, the endothelium becomes much less efficient at pumping water out of the stroma which causes the cornea to swell, distort vision, and as eventually the epithelium also takes on water, it can result in severe pain and visual impairment.
The swelling of the epithelial damages vision, can produce tiny blisters on the surface of the cornea, which can be extremely painful when they burst. Usually, a doctor, will try first to reduce the swelling with drops, soft contact lenses, or ointments, but if the disease interferes with daily activities, then if may be necessary to consider having a corneal transplant to restore sight. The short -term success rate of corneal transplant, is quite good for people with this disease, but some studies have suggested that the long-term survival of the new cornea can be a problem.
Ocular Herpes: Ocular herpes, herpes of the eye is caused by the herpes simplex virus, and is a recurrent viral infection, which is the most common cause of corneal blindness in America. Studies show that once people develop herpes of the eye, they have up to a 50 percent chance of having a recurrence, which could come weeks or even years after the initial occurrence. Ocular herpes can cause inflammation of the cornea and painful sore on the eyelid or surface of the eye. Anti-viral drugs used promptly can help stop the herpes virus from multiplying and destroying epithelial cells. However the infection might spread deeper into the cornea and develop into a much more severe infection called stromal keratitis, which causes the body´s immune system to attack and destroy stromal cells. It is more difficult to treat stromal keratitis than less severe ocular herpes infections.
Scaring of the cornea can occur due to recurrent episodes of stromal keratitis, which can lead to loss of vision and even blindness. An estimated 400.000 people in America have had some form of ocular herpes, and each year, nearly 50.000 recurrent and new cases are diagnosed in the United States, with the more serious form, stromal keratitis, accounting for about 25 percent.
Besides corneal transplant , there are alternatives, to treat corneal dystrophies, corneal scars and some corneal infections. Phototherapeutic Keratectomy (PTK) is one of them.
Studies have shown nearly 85 percent success rate in corneal repair using PTK for well-selected patients. This procedure is especially useful for people who have inherited disorders of corneal opacities or scars which limit vision.
The excimer laser which is a device emitting pulses of ultraviolet light, a laser beam to basically etch away irregularities on the surface or corneal tissue. Due to the precision of the laser, damage to healthy, adjoining tissue is reduced or even eliminated.
The National Eye Institute (NEI) has funded vision research which is leading to progress in understanding and treating disease of the cornea.
Reference:
The National Eye Institute (NEI)
© 2008 Christiane Tourtet, all rights reserved.
The epithelium is the cornea´s outermost region, which comprises about 10 percent of the thickness of the tissue. Its function primarily, is to block the passage of foreign material, such as bacteria, water, dust, into the eye and other layers of the cornea.
It also provides a smooth surface that absorbs cell nutrients from tears and oxygen, then distributes to the rest of the cornea these nutrients. The epithelium is filled with tiny nerves endings, by the thousands, that make the cornea extremely sensitive to pain if it is scratched or rubbed. The foundation on which the epithelial cells organize and anchor themselves, is called, the basement membrane.
The Bowman´s layer lies directly below the basement membrane of the epithelium, and is a transparent sheet of tissue composed of strong layered protein fibers called collagen.
If injured, Bowman´s layer, as it heals, can form a scar, and if these scars are centrally located and large, then, some vision loss can occur.
The Stroma, is beneath the Bowman´s layer and comprises about 90 percent of the thickness of the cornea. It is made mostly of about 78 percent water and about 16 percent collagen. It does not contain any vessels or blood, and the collagen gives form, strength, and elasticity to the cornea. The collagen´s quite unique shape, spacing, and arrangement are essential in producing the light-conducting transparency of the cornea.
The Descemet´s membrane, located under the stroma, is a strong, but thin sheet of tissue that serves as a protective barrier against injuries and infection. It is composed of collagen fibers that are different from those of the stroma, and is made by endothelial cells that are below it. After injury, Descemet´s membrane is readily regenerated.
The endothelium is the innermost layer of the cornea and is extremely thin .To keep the cornea clear endothelial cells are essential, as their primary task is to pump excess fluid out of the stroma. If a trauma or a disease, destroy the endothelium cells, they are lost forever, and if too many endothelial cells are destroyed, edema in the cornea and blindness ensue and corneal transplantation is the only available therapy.
There are about 120 million people in the United States who wear contact lenses or eyeglasses, in order to correct astigmatism, nearsightedness, or farsightedness. These disorders of the vision, are called refractive errors and affect the cornea. They occur when the curve of the cornea is irregularly shaped, such as being too flat or too steep. If the eye is too long, or when the cornea is too much curved, faraway objects will appear blurry, because they are focused in front of the retina, and this is what is called nearsightedness or myopia. About 15 percent of all adult people in America have myopia.
Farsightedness or hyperopia, is the opposite of myopia, as distant objects are clear, but close-up objects appear blurry. Hyperopia results from an eye that is too short and images focus on a point beyond the retina.
Astigmatism is a condition in which the uneven curvature of the cornea distorts and blurs both near and distant objects. A normal cornea is round, and has even curves from top to bottom and from side to side. With astigmatism, the cornea is shaped like the back of a spoon and curved more in one direction than in another, which causes light rays to have more than one focal point and focus on two separate areas of the retina, thus, distorting the visual image. Two third pf people in America who have myopia also have astigmatism. These refractive errors usually are corrected by contact lenses or by eyeglasses, and they are effective and safe. However, refractive surgeries are becoming more and more a popular option.
There are many disorders and diseases of the cornea, among them are:
Allergies: It is fairly common to have allergies affecting the eye. The most common allergies are those related to pollen especially when the weather is dry and warm. Symptoms can include itching, burning, redness, stinging, watery discharge. Usually decongestant eye drops, antihistamine, can effectively reduce these symptoms. There are also an increasing number of eye allergy related to contact lens wear, medications, animal hair and certain cosmetics, such as face creams, eyebrow pencil, mascara, lip gloss, eye make up, soaps, and rubbing or touching eyes after handling nail polish or chemicals. However these allergy symptoms, are temporary and can be eliminated by avoiding contact with the offending detergent or cosmetics.
Conjunctivitis (Pink eye): Conjunctivitis, is a group of diseases that cause redness, burning, swelling, itching of the conjunctiva, the protective membrane that covers exposed areas of the sclera or white of the eye and lines the eyelids. It can spread from one person to another and at any given time affects millions of people in America. It can be caused by viral infection, allergy, eye ointments, contact lens products, eye drops, environmental irritants. At its beginning conjunctivitis is usually painless, and does not adversely affect vision. In most cases infection will clear without requiring medical care. However, some forms of conjunctivitis will require treatment, and if treatment is delayed, the infection may worsen and cause an inflammation of the cornea and a loss of vision.
Corneal Infections: Sometimes after a foreign object has penetrated the tissue, such as a poke in the eye, the cornea is damaged. At other times fungi or bacteria from a contaminated contact lens can pass into the cornea, and can cause painful inflammation and corneal infections called keratitis. These infections can produce corneal discharges, reduce visual clarity, can lead to corneal scarring, which can impair vision and may require a corneal transplant. The deeper the corneal infection, the more severe are the symptoms and complications. Minor corneal infections are usually treated with anti-bacterial eye drops. Severe corneal infections may require more intensive anti-fungal or antibiotic treatment, as well as steroids eye drops. It might be necessary to visit frequently an eye care professional for several months to eliminate the problem.
Dry Eye: Dry eye is more common in women, especially after the menopause, and the main symptom is usually a sandy or scratchy feeling as if something is in the eye. It can also include burning, stinging, stringy discharge, pain , redness of the eye, episodes of excess tearing following periods of very dry sensation, heaviness of the eyelids, or decreased , blurred, changing, vision. In climates with dry air, as well as with the use of nasal decongestants, anti-depressants, drugs, including antihistamines, tranquilizers, dry eyes can occur. People who experience dry eyes should let their health care providers know all the medications they are taking, since some of them may intensify the symptoms of dry eyes.
People with rheumatoid arthritis can also develop dry eye. Sometimes dry eye can be a symptom of Sjogren´s syndrome, which is a disease that attacks the lubricating glands of the body, such as salivary and tear glands.
The principal treatment for dry eye is artificial tears, as eye drops available over-the –counter, which lubricate the eye. At night sterile ointments are sometimes used to help in preventing the eye from drying, humidifiers can help too. When outside, wearing wrap-around glasses, avoiding dry and windy conditions, may bring some relief.
Fuchs´Dystrophy: Fuch´s dystrophy, usually affects both eyes, is slightly more common in women than men. It is a slowly progressing disease, which can be seen often by doctors in people in their 30s and 40s. It rarely affects vision until people reach their 50´s and 60´s. Fuchs´ dystrophy happens, when, without apparent reason the endothelial cells gradually deteriorate, and as more of these cells are lost over the years, the endothelium becomes much less efficient at pumping water out of the stroma which causes the cornea to swell, distort vision, and as eventually the epithelium also takes on water, it can result in severe pain and visual impairment.
The swelling of the epithelial damages vision, can produce tiny blisters on the surface of the cornea, which can be extremely painful when they burst. Usually, a doctor, will try first to reduce the swelling with drops, soft contact lenses, or ointments, but if the disease interferes with daily activities, then if may be necessary to consider having a corneal transplant to restore sight. The short -term success rate of corneal transplant, is quite good for people with this disease, but some studies have suggested that the long-term survival of the new cornea can be a problem.
Ocular Herpes: Ocular herpes, herpes of the eye is caused by the herpes simplex virus, and is a recurrent viral infection, which is the most common cause of corneal blindness in America. Studies show that once people develop herpes of the eye, they have up to a 50 percent chance of having a recurrence, which could come weeks or even years after the initial occurrence. Ocular herpes can cause inflammation of the cornea and painful sore on the eyelid or surface of the eye. Anti-viral drugs used promptly can help stop the herpes virus from multiplying and destroying epithelial cells. However the infection might spread deeper into the cornea and develop into a much more severe infection called stromal keratitis, which causes the body´s immune system to attack and destroy stromal cells. It is more difficult to treat stromal keratitis than less severe ocular herpes infections.
Scaring of the cornea can occur due to recurrent episodes of stromal keratitis, which can lead to loss of vision and even blindness. An estimated 400.000 people in America have had some form of ocular herpes, and each year, nearly 50.000 recurrent and new cases are diagnosed in the United States, with the more serious form, stromal keratitis, accounting for about 25 percent.
Besides corneal transplant , there are alternatives, to treat corneal dystrophies, corneal scars and some corneal infections. Phototherapeutic Keratectomy (PTK) is one of them.
Studies have shown nearly 85 percent success rate in corneal repair using PTK for well-selected patients. This procedure is especially useful for people who have inherited disorders of corneal opacities or scars which limit vision.
The excimer laser which is a device emitting pulses of ultraviolet light, a laser beam to basically etch away irregularities on the surface or corneal tissue. Due to the precision of the laser, damage to healthy, adjoining tissue is reduced or even eliminated.
The National Eye Institute (NEI) has funded vision research which is leading to progress in understanding and treating disease of the cornea.
Reference:
The National Eye Institute (NEI)
© 2008 Christiane Tourtet, all rights reserved.
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