Corneal ulcer Corneal anatomy Transparent lack blood vessels
Corneal ulcer
Corneal anatomy • Transparent -lack blood vessels, pigmentation, and keratin, and through the organization of the collagen fibers. • It refracts light and protects the contents of the eye. • It is about one-half to one millimeter thick in the dog and cat.
Innervation • The trigeminal nerve supplies the cornea via the long ciliary nerves. • There are pain receptors in the outer layers and pressure receptors deeper.
Microscopic anatomy • 5 layers • 1) Anterior epithelium – outermost and continuous with the conjunctiva. • 2) Bowman's layer-non elastic • 3) Stroma (substantia propria)-constitute 90% of cornea-collagen fibres and connective tissue cells • 4) Descemet's membrane (posterior limiting membrane)-elastic membrane • 5) Posterior epithelium/endothelium
Physiology • The cornea derives its nourishment via the tear film, the aqueous humor, and the perilimbal capillary loops
Corneal healing • Cornea heals by two methods: Ø Migration - mitosis (dividing) -introduction of blood vessels from the conjunctiva. Ø Superficial ulcers heal rapidly by the first method. Ø Larger or deeper ulcers often require the presence of blood vessels to supply inflammatory cells. Ø White blood cells and fibroblasts - granulation tissue - scar tissue-healing the cornea.
Ulcerative keratitis • A corneal ulcer, or ulcerative keratitis, is an inflammatory condition of the cornea involving loss of its outer layer. • May be superficial, deep with descemetocele, or perforating
Severe perilimbal neovascularity, mild corneal edema, mid-stromal central corneal ulcer.
Causes • Trauma, detergent burns, and infections. • Entropion, distichiae, corneal dystrophy, and keratoconjunctivitis sicca (dry eye). • Infections: • Bacterial – Pseudomonas • Viral - canine distemper, herpesvirus • Mycotic - numerous species • Metabolic disturbances: Conditions such as hypoestrogenism (e. g. , in ovariohysterectomized dogs)
Location • Depends on the cause. • Central ulcers are typically caused by trauma, dry eye, or exposure from facial nerve paralysis or exophthalmos. • Inferior nasal corneal ulcer may be caused by foreign material trapped under the third eyelid. • Entropion or distichiae may cause ulceration of the peripheral cornea. • Immune-mediated eye disease can cause ulcers at the border of the cornea and sclera.
Symptoms • Blepharospasm, photophobia. • Anterior uveitis-miosis , aqueous flare (protein in the aqueous humour), and redness of the eye. • Discharge - usually serous then may become purulent.
• The corneal ulcer is characterized by a loss of corneal epithelium and activation of stromal fibroblasts, leading to swelling of the stroma, and migration of inflammatory cells, with a subsequently loss of corneal integrity and transparency. • Once the ulcer is infected, the healing process is retarded and can lead to an endophthalmitis, or glaucoma
Diagnosis • Fluorescein stain • With descemetoceles-appear as a dark circle with a green boundary, because it does not absorb the stain. • Schirmer's test for KCS and an analysis of facial nerve function for facial nerve paralysis.
• Fluorescein is a water-soluble dye that is retained by all hydrophilic but not hydrophobic structures. • The classic example of its use is in the identification of a corneal ulcer, in which the fluorescein is retained by the hydrophilic stroma wherever it is exposed by loss of the hydrophobic epithelium
Fluorescein stain positive
Seidel test • Assess the presence of anterior chamber leakage in the cornea. • It is used as a screening test for many corneal disorders including corneal post-trauma, corneal perforation and corneal degeneration
Procedure • A fluorescein strip containing 10% fluorescein is applied topically to the affected area and is examined with a cobalt blue filter. • At this point, the fluorescein appears dark orange in color. • Any changes in color of the fluorescein strip indicate the presence of corneal deformities. • Pale color-dilution with aqueous humor
Treatment • Drops may be better than ointment because of less interference with healing. • Broad spectrum antibiotic usually is sufficient to prevent infection by opportunistic bacteria. Treat 4 times a day. • Iridocycloplegic - 1% atropine 3 or 4 times a day for 2 - 3 days, then once or twice a day.
• Anticollagenase agents-Acetylcysteine is available commercially , Autologous serum • Treat 3 -4 times a day with either. • NSAID’s like flurbiprofen, ketorolac can be instilled • conjunctival grafts or conjunctival flaps, soft contact lenses, or corneal transplant.
• Sodium EDTA blocks the melting effects of collagenases and proteinases. • Sodium EDTA 0. 05% should be administered every 1 -2 hours. It may be used with other antiproteolytics such as, autologous serum and acetylcysteine. • Sodium EDTA blocks the melting effects of collagenases and proteinases.
Ø Superficial ulcers usually heal in less than a week. Ø Deep ulcers and descemetoceles may require corneal suturing, conjunctival grafts or conjunctival flaps, soft contact lenses, or corneal transplant. Ø Topical corticosteroids and anesthetics should not be used on any type of corneal ulcer because they delay the healing process
Melting ulcers • Progressive loss of stroma - Pseudomonas infection - other types of bacteria or fungi produce proteases and collagenases- break down the corneal stroma - Complete loss within 24 hours. • Treatment includes antibiotics and collagenase inhibitors such as acetylcysteine and blood serum. • Surgery may be necessary.
• A variety of factors contribute to destruction of the cornea, including the up-regulation of cytokines in the tear film in response to infection, and the production of proteolytic enzymes by corneal epithelial cells, WBC, and the pathogenic organism. • There are two groups of proteinases that affect the corneal matrix: metalloproteinases and serine proteinases. • Sodium EDTA specifically inhibits matrix metalloproteinases.
Mycotic keratits • Prolonged use of topical corticosteroids in cases of corneal ulceration • reduction of local immune mediated responses • Eg-candida, aspergillus, mucor, fusarium
• signs and behavior similar to that caused by any other keratitis or ulcer. • creamy appearance to the site, or there may be lines of inflammation radiating from the main focus of inflammation. • There often are satellite lesions in the cornea.
• Fungal keratitis is usually characterised by a dry raised slough, stromal infiltrate with feathery edges, satellite lesions, and a thick endothelial exudates
Treatment • topical miconazole, nystatin or amphotericin B until you get more information on the organism, or the condition disappears. Absolutely no corticosteroids should be used. • 5%natamycin eyedrops
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