الفهرس 
Corneal Layers Response to DamageOnly 14 pages are availabe for public view
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Abstract
An understanding of the pathophysiology of corneal ulceration requires a review of the processes involved in epithelial and stromal wound healing, as well as an examination of the role of pre-corneal tear film, corneal nerves, proteolytic enzymes, and cytokines
Rapid and proper corneal healing are essential elements for restoration of the cornea and to prevent blindness, which may occur due to corneal affection. There is physiological importance for the corneal epithelial, endothelial barriers and metabolic pump functions. If either limiting layer is compromised, the cornea will become edematous and show decrease in corneal transparency.
There are many aspects of corneal healing, the corneal epithelium is re-epithelizied by epithelial migration and proliferation. But corneal stromal healing is divided into many phases in which the keratocytes become activated and migrated with collagen synthesis. Bowman’s layer does not regenerate and it is replaced by fibrosis. The endothelium, no mitosis occur, the defect covered by spreading and enlargement of cells with deposition of new Descemet’s membrane. Many factors have been found that have ability to enhance and promote corneal healing.
Corneal wound healing is mediated by many proteins that are inducers of corneal cell migration, proliferation, and differentiation,these proteins include growth factors: epithelial growth factors, fibroblast growth factors, and platelet growth factors. Corneal nerves provide important protective and trophic functions, and interruption of corneal innervation may result in altered epithelial morphology and function, MMPs are strongly induced during wound healing. Metalloproteinases are secreted as proenzymes by neutrophils infiltrating the wound, injured epithelial cells, and keratocytes
Bacterial corneal ulcers generally follow a traumatic break in the corneal epithelium, thereby providing an entry for bacteria. The traumatic episode may be minor, such as a minute abrasion from a small foreign body, or may result from other causes as tear insufficiency and malnutrition.
Viral infections are also possible causes of corneal ulcers. Such viruses include herpes simplex and varicella virus, which is a serious viral infection. It may cause repeated attacks that are triggered by stress, exposure to sunlight, or any condition that impairs the immune system.
Fungal keratitis can occur after a corneal injury involving plant material, in immunosuppressed people or overuse eye DROPs that contain steroids.
Acanthamoeba keratitis and Pseudomonas aeruginosa occur in contact lens users’ .People who wear contact lenses are at an increased risk of ten folds when using extended-wear soft contact lenses.
Hence, an understanding of the etiologic agents, epidemiologic features and risk factors that occur in specific region are important in rapid recognition, timely institution of therapy, optimal management and prevention of disease entity. Treatment for infectious corneal ulcers depends on the cause. Treatment should be started as soon as possible to prevent corneal sequelae .If the exact cause is not known, patients may start treatment with antibiotic DROPs that work against many kinds of bacteria.Once the exact cause is known; specific medication are prescribed.Corticosteroid eye DROPs may be used to reduce inflammation in certain conditions
Non-infectious corneal ulcers can occur as an isolated ocular problem may be associated with various collagen vascular or other autoimmune diseases, sometimes being the presenting sign of the disease. Conditions that affect the integrity of the ocular surface epithelium (exposure keratitis, neurotrophic keratitis, keratomalacia, recurrent corneal erosions) may also lead to development of sterile corneal ulcers. Rarely, these ulcers occur as a complication following cataract surgery. With recent advances in the understanding of the causes and pathophysiology of corneal melting, rapid and effective medical and surgical treatment is often able to halt relentless destruction of the cornea. Treatment varies vastly depending on the underlying cause of the ulceration
A number of Growth factors including (epidermal growth factor, transforming growth factor-β keratinocyte growth factor, hepatocyte growth factor, fibroblast growth factor and platelet-derived growth factor) also play a vital role in corneal wound healing, mediating the proliferation of epithelial and stromal tissue and affecting the remodeling of the extracellular matrix (ECM). Growth factors may be targeted in therapeutic ophthalmic applications, through exogenous application or selective inhibition, and may be used to elicit specific cellular responses to ophthalmic materials. Production of growth factors by corneal cells and their presence in the tear fluid and aqueous humour is essential for maintenance and renewal of normal tissue.
Vitamin A could enhance migration rates through the production of extracellular matrix components that might be used for adhesion or through a more general mechanism in which growth hormone could induce increased metabolic or mitotic rates while Vitamin C is essential for normal tissue metabolism and wound healing. Topical use of the ascorbic DROPs helps to reduce the incidence of corneal ulceration and perforation.
Honey is an effective treatment of wounds because it is non-irritating, non-toxic, self-sterile, bactericidal, nutritive, easily applied and more comfortable than other dressings. Propolis extract is a potential candidate as an anti-angiogenic agent and can inhibit cell proliferation, migration and capillary tube formation
When persistent corneal ulceration does not respond to medical treatment, including antibiotics, therapeutic soft contact lenses, or tarsorrhaphy, surgical intervention is indicated as, conjunctival flaps and amniotic membrane transplantation and Limbal stem cells transplantation lamellar and penetrating keratoplasty
Corneal Debridement is Surgical removal of corneal epithelium without causing injury to the basement membrane. While Superficial Keratectomy is surgical removal of corneal epithelium including Bowman’s membrane and anterior stroma of the diseased cornea. Biopsy in non-healing corneal ulcer. Debulking of infective material used to obtain cornea tissue for Microbiological or histological examination
Amniotic membrane transplantation (AMT) is used as a treatment for corneal perforation to restore corneal stromal thickness so that urgent penetrating keratoplasty can be avoided. AMT is a good alternative to penetrating keratoplasty, especially in acute cases in which graft rejection risk is high
Conjunctival flaps are used in cases with indolent progression and corneal thinning.A conjunctival flap brings in superficial blood vessels to promote healing of corneal ulcers therefore preventing the occurrence of corneal perforation