Diseases of the cornea

First lectureFirst lecture

Anatomy of the corneaGross Anatomy:The cornea is the clear transparent anterior one sixth of

the fibrous tunic of the eyeball. The cornea is set into the opaque sclera like a watch glass, the corneo-scleral junction is called the limbus.

The cornea has the following features:1.a smooth brilliant surface.2. very richly supplied with nerve fibres.3.has no blood vessels.4. It is the most powerful refractive medium of the eye..

Minute Anatomy:Minute Anatomy:Epithelium:Epithelium: is a regular layer of uniform thickness of non- is a regular layer of uniform thickness of non- keratinized stratified squamous epithelium. keratinized stratified squamous epithelium. Bowman’s MembraneBowman’s Membrane:is a clear uniform structureless :is a clear uniform structureless membrane that runs under the epithelium throughout the membrane that runs under the epithelium throughout the cornea and ends abruptly at the limbus.cornea and ends abruptly at the limbus.StromaStroma: It forms about 90% of the entire thickness of the : It forms about 90% of the entire thickness of the cornea.cornea. It is made up of regularly arranged lamellae of It is made up of regularly arranged lamellae of collagenous collagenous fibresfibres associated with some associated with some elastic fibreselastic fibres lying in a lying in a mucopolysaccharide matrixmucopolysaccharide matrix..Descemet’s MembraneDescemet’s Membrane:is a thin fine transparent and :is a thin fine transparent and highly highly elasticelastic layer situated posterior to the stroma of the cornea. layer situated posterior to the stroma of the cornea.EndotheliumEndothelium: A single layer of flat hexagonal cells arranged : A single layer of flat hexagonal cells arranged along the inner surface of Descemet's membrane.along the inner surface of Descemet's membrane.Nerve Supply:Nerve Supply: from the naso-ciliary branch of the ophthalmic from the naso-ciliary branch of the ophthalmic division of the trigeminal nerve through its long ciliary nervesdivision of the trigeminal nerve through its long ciliary nerves

Functions of the cornea:1.Optical: The cornea is the most

powerful refractive medium of the eye (+42Dioptres).

2.Protective: The extreme sensitivity of the cornea is an efficient protective mechanism producing a very quick lid reflex.

Inflammations of the corneaInflammations of the cornea::

may be divided into two types:may be divided into two types:

Ulcerative KeratitisUlcerative Keratitis: A corneal ulcer is a condition in : A corneal ulcer is a condition in which there is destruction of some portion of both the which there is destruction of some portion of both the epithelium and the underlying stroma of the cornea. epithelium and the underlying stroma of the cornea. UlcerativeUlcerative keratitiskeratitis clinically appears as a saucer-shaped clinically appears as a saucer-shaped yellowish grey pit, which stains green with fluoresceinyellowish grey pit, which stains green with fluorescein

Non-ulcerative keratitisNon-ulcerative keratitis: in which the stroma of the : in which the stroma of the cornea is only affected by the inflammatory process cornea is only affected by the inflammatory process while the overlying epithelium remains intact.while the overlying epithelium remains intact.

Causes of Corneal Ulceration:Exogenous Infections: The cornea is exposed

throughout life to miner trauma, virulent micro-organisms present in the conjunctival sac may gain access to the corneal tissue.

Endogenous Agents: The inflammation is typically a cell-mediated immune response to a foreign antigen and often occurs in the periphery of the cornea, e.g. phlyctenular ulcer.

Chemical Agents: Acids, alkali, tincture of iodine or lime produce corneal ulceration by destroying the epithelium and the superficial layers of the stroma.

ExposureExposure:: Incomplete covering of the cornea Incomplete covering of the cornea (by the eyelids) leads to dryness of the (by the eyelids) leads to dryness of the cornea and a constant ulceration.cornea and a constant ulceration.Loss of corneal sensationLoss of corneal sensation: Corneal : Corneal anesthesia, caused by anesthesia, caused by trigeminal nerve trigeminal nerve paralysisparalysis, leads to trophic changes in the , leads to trophic changes in the corneal epithelium resulting in degeneration corneal epithelium resulting in degeneration and ulceration. This condition is called and ulceration. This condition is called neuroparalytic keratitisneuroparalytic keratitis..Vitamin A DeficiencyVitamin A Deficiency:: This leads to This leads to degenerative changes in the corneal degenerative changes in the corneal epithelium leading to ulceration, it also epithelium leading to ulceration, it also induces lack of resistance of the cornea to induces lack of resistance of the cornea to micro-organisms of low virulencemicro-organisms of low virulence..

Bacterial ulcerative keratitis:Hypopyon ulcer: Also called pneumococcal ulcer, is a

disc-shaped ulcer of destructive nature near the centre of the cornea associated with a diffuse keratitis, a violent iridocyclitis and a hypopyon.

Aetiology:Any defect in the basic defense mechanism of the

cornea, e.g. from trauma can predispose to corneal ulceration. Hence, hypopyon ulcer often starts as a minor abrasion to the cornea, e.g. by a scratch with a finger nail or by a foreign body. Virulent conjunctival pathogens can then lodge in the exposed corneal stroma and cause necrosis of the corneal parenchyma.

Symptoms:Symptoms: PainPain: It is of a neuralgic nature and is often referred to the : It is of a neuralgic nature and is often referred to the eyebrow region.eyebrow region.PhotophobiaPhotophobia..Blepharospasm.Blepharospasm.Excessive Reflex Lacrimation.Excessive Reflex Lacrimation.Defective vision.Defective vision.Signs:Signs:Circumcorneal Vascular Injection.Circumcorneal Vascular Injection.Haziness and Dullness of the Corneal Surface.Haziness and Dullness of the Corneal Surface.Central disc-Shaped Ulcer.Central disc-Shaped Ulcer.Vascularization of the cornea.Vascularization of the cornea.Mild to Severe Iridocyclitis.Mild to Severe Iridocyclitis.Secondary Rise of Ocular tensionSecondary Rise of Ocular tension..

Complications of the Hypopyon Ulcer:Complication before Perforation:1.Anterior uveitis.2.Secondary glaucoma.3.Corneal opacity.Complication after perforation:1.Prolapse of the iris.2.Anterior Synechia.3.Leucoma Adherent.4.Anterior Staphyloma.5.Anterior Polar Cataract.6.Corneal fistula.7. Intra-ocular Haemorrhage.8.Endophthalmitis and Panophthalmitis.

Treatment of Uncomplicated Corneal Ulcer:

1. Antibiotic to control infection.2. Atropine to Relieve Uveal

Irritation.3. Application of heat to increase

blood flow.4. Wash out of conjunctival

discharge.5. Protection of the eye.6. Promotion of re-epithelialization.

Systemic medical treatmentSystemic medical treatment.. Treatment of the cause. Treatment of the cause.Surgical treatment:Surgical treatment:Cauterization of the ulcer.Cauterization of the ulcer.Paracentesis.Paracentesis.Central Tarsorraphy.Central Tarsorraphy.Therapeutic Keratoplasty.Therapeutic Keratoplasty.Treatment of Perforated Corneal Ulcer:Treatment of Perforated Corneal Ulcer:A pressure bandage is applied to the eye. A pressure bandage is applied to the eye. Rest in bed and avoid all causes of forced Rest in bed and avoid all causes of forced expirationexpiration..

Viral Ulcerative Keratitis:Herpes Simplex Keratitis:Is primarily a superficial epithelial infection of the cornea,

usually develops after common colds or upper respiratory tract infections, in association with herpetic vesicles in the lips and face. The disease has a definite tendency to recurrences. Primary ocular involvement may present as an acute follicular conjunctivitis or kerato-conjunctivitis with nonsupurative preauricular lymphadenopathy and often with notable vesiculating periocular skin involvement.

Clinical picture:Clinical picture:Symptoms:Symptoms: Photophobia, reflex lacrimation, pain blurring of Photophobia, reflex lacrimation, pain blurring of vision, foreign body sensation and corneal hyposthesia.vision, foreign body sensation and corneal hyposthesia.Signs of Primary Ocular InfectionSigns of Primary Ocular Infection::Vesicles involving the lids and periorbital area.Vesicles involving the lids and periorbital area.Acute follicular conjunctivitis.Acute follicular conjunctivitis.Fine or coarse epithelial punctate keratitis which may progress Fine or coarse epithelial punctate keratitis which may progress to dendritic figure.to dendritic figure.Signs of Recurrent herpetic Keratitis:Signs of Recurrent herpetic Keratitis:Dendritic Epithelial Ulceration.Dendritic Epithelial Ulceration.Geographical Herpetic Ulceration.Geographical Herpetic Ulceration.Stromal Herpetic Keratitis without or with Epithelium Ulceration.Stromal Herpetic Keratitis without or with Epithelium Ulceration.Herpetic iridocyclitisHerpetic iridocyclitis..

Treatment of Herpes Simplex Keratitis:Medical lines of Treatment:Antiviral agents are usually the first line of

treatment in addition to the usual routine treatment of corneal ulcers, namely, atropine drops, antibiotic against secondary bacterial infection, pad and bandage.

Surgical lines of treatment:1.Debridement: removal of virus-containing cells is

indicated in recurrent dendritic ulcers.2.Lamellar Keratoplasty3.Central tarsorraphy.4.Penetrating Keratoplasty.

Herpes Zoster ophthalmicus:Herpes Zoster ophthalmicus:Is caused by a virus identical with that causing Is caused by a virus identical with that causing

chicken-pox, the chief focus of infection is in the chicken-pox, the chief focus of infection is in the Gasserian ganglion whence the virus travels down Gasserian ganglion whence the virus travels down

one or more of the branches of the ophthalmic one or more of the branches of the ophthalmic division of the fifth nerve. Ocular complications division of the fifth nerve. Ocular complications

usually arise when the naso-ciliary branch of the usually arise when the naso-ciliary branch of the trigeminal nerve is involved. The appearance of trigeminal nerve is involved. The appearance of vesicles on the tip of the nose often precedes vesicles on the tip of the nose often precedes

corneal affection (Hutchinson’s SIGN).corneal affection (Hutchinson’s SIGN). Herpes Zoster affects elderly and often it is rare Herpes Zoster affects elderly and often it is rare

under 40Years of ageunder 40Years of age..

KERATITIS IN RHEUMATOID ARTHRITISClinical featuresRheumatoid arthritis is the most common collagen vascular disorder to affect the peripheral cornea. Peripheral corneal thinning (contact lens cornea) is characterized by gradual resorption of peripheral corneal tissue leaving the epithelium intact. Because the central part of the cornea remains normal, the appearance resembles a contact lens placed on the eye .

Peripheral corneal melting is an acute and severe melting of the cornea. This may occur in an area of already thinned peripheral cornea of the contact lens type not associated with inflammation or more commonly, there is intense inflammation at the limbus . In some cases, the entire corneal stroma melts within a few days resulting in descemetocele formation.

Other ocular complications of rheumatoid arthritis are keratoconjunctivitis sicca and scleritis.Treatment1. Topical steroids may be useful in acute stromal keratitis, but they should be avoided in peripheral corneal guttering and keratolysis for fear of inducing further corneal thinning and possibly perforation.2. Systemic therapy with steroids and/or cytotoxic drugs is required for active scleritis .3. Conjunctival excision may halt the progression of corneal furrowing in refractory cases.4. Keratoplasty may be required either as an emergency measure to prevent perforation or, electively, to restore visual acuity.