Dr.saifalshamarti. Objective. Where is cornea? Functions of the cornea

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1 Cornea Dr.saifalshamarti Objective Functions Anatomy: detailed description of the 5 layers: epithelium, Bowman s layer, stroma, Descement s membrane, endothelium. Diseases of the cornea: - infection: bacterial keratitis, viral keratitis, fungal keratitis, Acanthameba keratitis. - Keratoconus: Definition, symptoms & Signs, corneal topography &pachymetry, management option. Where is cornea? The cornea is the eye's outermost layer. It is the clear, dome-shaped surface that covers the front of the eye. Covers: iris, pupil and the anterior chamber Greek name : kerato Functions of the cornea Protection: germs, dusts and UV light. Light transmission( nm) Refraction of light. 2/3 of the of the refractive power of the eye((43diopters)).

2 Structure.Transparent. The cornea has unmyelinated nerve endings.very sensitive; touch, temperature and chemicals.avascular :Dimensions.Diameter : 11.5 mm horizentally, 10.5 vertically ) Thickness:center(0.5 mm), periphery ( 1 mm It borders with the sclera by the corneal limbus The shape of the cornea is not spherical, it is aspherical. It is steeper at the center. It flattens out toward the edge. The steep central portion is called the corneal cap and it is about 4mm wide.

3 Why the cornea is clear? Relative dehydration of the cornea Lack of blood vessels. No pigments. Regular arrangement of collagen fiber. Consistent refractive index of all layers

4 Layers : "EBSDE"From out to in : 1-Corneal epithelium - 10% of the thickness. - Stratified squamous epithelium ; fast growing and easily regenerated. - Basement membrane ; on which the epithelium is anchored and organized 2- Bowman's layer Irregularly arranged collagen. - Protects the stroma. 3-Corneal stroma -80% of thickness -Consists primarily of water (78 percent) and collagen (16 percent); regularly arranged. -Collagen gives the cornea strength, elasticity, and form from Keratocytes. 4-Descemet's membrane - A thin acellular layer; collagen( by endothelial cells ) Modified basement membrane of the endothelium. - - Descemet's membrane is regenerated readily after injury 5-Corneal endothelium -The thinnest layer. monolayer. -Regulating fluid and solute transport. - NO WAY BACK - If too many endothelial cells are destroyed, corneal edema and blindness

5 Innervation Trigeminal nerve( Opthalmic division) long posterior ciliary nerves. Annular plexus at limbus. Subepithelial plexus just below bowmans. Intraepithelial plexus. COMMON CORNEAL CONDITIONS 1. INFECTION BACTERIAL VIRAL FUNGAL ACANTHAOMEBA 2. KERATOCONUS BACTERIAL KERATITIS Common causative agents : (affecting corneal epithelial integrity) Staph. epidermidis Staph. Aureus Strept. Pneumonia H.infleunza P.aeruginosa N.gonorrhea

6 Predisposing factors: contact lens users keratoconjunctivitissicca (dry eye) prolonged use of topical steroids Trauma (breach in a corneal epithelium) use of contaminated ocular medications Recent corneal disease (herpetic keratitis, neurotrophickeratopathy) Symptoms: Reduced vision Pain in the eye (often sudden) Purulent discharge Excessive tearing Increased light sensitivity Signs: Hypopyon ( a mass white cells collected in ant chamber) White corneal opacity Conjuctival injection (redness of eyes) Complications: Corneal ulcer Corneal perforation 2ndary endopthalmitis Vision loss Corneal leukoma (scar tissue formation with corneal vascularization)

7 Treatment: Perform a corneal scrape. Intensive topical antibiotic treatment FF gentamycin 15mg/ml hourly. FF Cephazolin 50 mg/ml hourly. OR fluoroquinolones is an alternative treatment.(monotherapy) Corneal graft ( in severe cases) VIRAL KERATITIS HERPES SIMPLEX KERATITIS HERPES ZOSTER OPTHALMICUS HERPES SIMPLEX KERATITIS HSV 1: common viral cause of ocular diseases HSV 2: genital dis. Rarely can cause ocular manifestations (rarely) such as keratitis & infantile chorioretinitis. HSV Primary infections is usually early in life. Enters a latent period in the trigeminal ganglion, When activated it moves along the sensory part of the N. toward the target epith. causing damage & ulceration. Factors leading to activation :psychiatric stress., systemic illnesses, immunocompromised pt.

8 Symptoms: -Typically unilateral red eye -Variable degree of pain -Occular irritation -Tearing Signs: -Vision may or may not be affected -Vesicular skin rash and follicular conjunctivitis A dendritic corneal ulcer(hallmark sign of HSV infection) Ulcer may heal without scar but may progressed to stromal keratitis Associated with inflammatory infiltration and edema Loss of corneal transparency in more severe presentations. Uveitis and glaucoma may accompany disease Disciform keratitis: herpes virus antigens resulting in stromal edema & clouding w/o ulceration Often associated with iritis. Diagnosed with a slit lamp examination Treatment : topical antivirals acyclovir ointment DON T USE TOPICAL STEROIDS as they worsen the ulcer to geographic ulcer If recur more than twice a year give oral acyclovir

9 HERPES ZOSTER OPTHALMICUS Varicela zoster virus -affect the ophthalmic division of the trigeminal N. (15% ) Increases with age (6 th -7 th decades). The ocular manifestations more likely if the nasocillary N. is involved >>lid swelling (maybe bilateral), keratitis,iritis, secondary glaucoma. Symptoms: Other ocular manifest. :ptosis, mucus secreting conjunctivitis, neuralgia&scleritis which may lead to scleral atrophy Have prodromal period, typically presents with nondescript facial pain, fever and general malaise. About four days after onset, a unilateral vesicular skin rash over forehead, upper eyelid, nose (1 st div of 5 th CN), characteristically respecting the vertical midline. The pain is extreme during the inflammatory stage.. Signs: Cornea: Punctate epithelial keratitis (swollen epithelium, 1-2 d); dendritic keratitis (tree branchlike epithelial defects, 4-6 d); stromal keratitis (fine infiltrates beneath the surface, 1-2 wk); deep stromal keratitis (lipid infiltrates and corneal neovascularization, 1 month to years); neurotrophickeratopathy(erosions, persistent defects, corneal ulcers, months to years) Ocular involvement may include follicular conjunctivitis, epithelial and/or interstitial keratitis, dendritic keratitis, ant chamber uveitis, scleritis or episcleritis, chorioretinitis, optic neuropathy, and even neurogenic motility disorders (especially fourth cranial nerve palsy).

10 Prognostic indicator: Hutchinson s Sign Hutchinson s Sign Lesions at tip, side, root of nose nose Innervated by ant ethmoidal branch of nasociliary N. Nasociliary N. also innervates corneal n.& ciliary body. Treatment: Oral and topical antiviral : acyclovir, valcyclovir or famcyclovir ( prevent post-infective neuralgia-severe chronic pain over the rash) +/- a cycloplegic agent. Fungal keratitis Infections are rare, but very severe & devastating as they cause stromal necrosis. They are capable of penetrating the descemet s membrane reaching the ant. chamber where we cannot do anything because of the poor penetration of antimycotic agents to the ant. Chamber. Most common causative pathogens: Filamentous (aspergillus&fusarium) fungi Candida albicans Progression is much slower &less painful than in bacterial. Keratomycosis in consideration when we find lack of response to antibacterial therapy of corneal ulceration.

11 Signs include : Filamentous infections: grayish infiltrate with indistinct margins( flufy ) Candidal infections: yellow to white ulcer withwith feathery borders ulcer suppuration similar to bacterial keratitis. Treatment: topical antifungals natamycin. Acanthamoeba keratitis Protozoa found in air, soil, fresh or brackish water. This infection has become more common with increased soft contact lens user. Severe &disproportional persistent painful infection & the corneal nerves are infiltrated Keratoneuritis. It may co-exist in pt. having herpetic keratitis. Dx is by scraping of the acanthmoeba from the cornea & culture on (nonnutrient agar with E.coli) Treatment : Acanthamoeba keratitis is potentially blinding condition which needs immediate, multible drugs, long duration of treatments &may involve surgary, 1.Aminoglycoside (neomycin) 2.Biguanides (PHMB) polyhexamethlenebiguanide. 3.Diamidines (hexamidine). 4.imidazoles(ecanazole).