Keratitis

IntroductionKeratitis is a condition which the eye’s

cornea become inflamed and clouded.

AnatomyThe cornea is the anterior, projecting, transparent part of the external tunic.

HistologyThe cornea consists of five layers arranged anteroposteriorly as follows: corneal epithelium, which is continuous with the conjunctival epithelium; anterior limiting lamina; substantia propria; posterior limiting lamina; endothelium.

PhysiologyThe cornea functions as a protective

membrane and a "window" through which light rays pass to the retina.

Its transparency is due to its uniform structure, avascularity, and deturgescence.

KeratitisKeratitis is corneal inflamation.Usually classified by affected layer into superficial and deep keratitis.Keratitis can be caused by infection, dry eyes, drug intoxication, allergy or chronic conjunctivitis.Signs : red eyes / bloodshot eyes & clouded image in cornea.Symptoms : pain & photophobia.Treatment based on etiology and atropine or mydriatric eye drops.

Bacterial KeratitisCorneal disease caused by bacterial

organisms.Bacterial keratitis is considered a leading

cause of monocular blindness in the developing world.

Clinical FeaturesThe clinical signs and symptoms of bacterial

keratitis depend greatly on the virulence of the organism and the duration of infection.

Key features : Cellular infiltration of the corneal epithelium or stroma, corneal inflammation, and necrosis.

Associated features : lid edema, conjunctival inflammation, discharge, anterior chamber reaction, hypopyon.

EtiologyMany bacteria can cause bacterial keratitis.Gram-Positive bacteria that infect cornea :

staphylococci, streptococci, Bacillus cereus, corynebacteria, Listeria monocytogenes, clostridium, and Propionibacterium acnes.

Gram-Negative bacteria that infect cornea : pseudomonas, serratia, escherichia, klebsiella, proteus, moraxella, haemophilus, neisseria, and Branhamella catarrhalis.

Mycobacterium.

Streptococcal Bacterial KeratitisStreptococcal bacterial keratitis with infiltration of the central cornea.

Pseudomonas Bacterial KeratitisIntraepithelial infiltration of the cornea by Pseudomonas organisms in a hydrophilic contact lens wearer.

DiagnosisThe presumptive diagnosis of infectious

keratitis is based primarily on the clinical history and physical examination, but confirmation of infectious infiltration and definitive identification of the offending organism can be achieved only by examining stained smears of corneal scrapings and laboratory cultures of these scrapings.

Corneal ScarpingThis procedure is performed at the slit lamp.The eye is anesthetized with topical anesthetic, and a heat-sterilized platinum spatula or blade is used to firmly scrape.Scrapings should be placed on a slide for staining and directly applied to culture media to maximize the chance of recovery.

StainingThe most commonly applied stains are

Gram's and Giemsa stains.Ziehl-Neelsen stain : suspect mycobacterium

infection.

TreatmentGram-Negative Gram-PositiveGentamicin.Tobramycin.Polimiksin.

Cefazolin.Vancomycin.Basitracin.

Fungal KeratitisCorneal disease caused by fungal organisms.Fungal infections of the cornea are relatively

infrequent in the developed world but constitute a larger proportion of keratitis cases in many parts of the developing world.

Clinical FeaturesFungal infection tends to arise in

traumatized, diseased, and immunocompromised corneas.

Key features : Cellular infiltration of the corneal epithelium or stroma, corneal inflammation, and necrosis.

Associated features : long-term steroid use, trauma involving vegetative matter, corneal infiltrate with feathery borders or satellite lesions.

DiagnosisA high level of suspicion for nonbacterial

keratitis must be maintained at all times.Definite diagnosis : laboratory confirmation,

by scraping for stains and cultures.

Treatment1. Polyenes : amphotericin B, natamycin.2. Imidazoles : ketoconazole, miconazole.3. Triazoles : fluconazole.4. Pyrimidines : flucytosine.

Herpes Simplex KeratitisHerpes simplex viral infection of the cornea.Human herpesviruses have in common a

state called “latency”.Keratitis caused by HSV is the most common

cause of cornea-derived blindness in developed nations.

Classification1. Epithelial keratitis,2. Stromal/endothelial keratitis,

Epithelial KeratitisCaused by actively replicating virus on the corneal surface.Initial episodes present with foreign body sensation but subsequent episodes are usually painless.Dendritic ulcer – classic feature of epithelial disease.

Stromal/Endothelial KeratitisThis is usually an immune-mediated response to nonreplicating viral particles, but more severe forms may be caused by live virus.Focal endotheliitis (disciform keratitis) – classic feature of stromal disease.

DiagnosisDiagnostic testing is seldom needed in

epithelial Herpes Simplex Virus Keratitis (HSVK) because of its classic clinical features and is not useful in stromal keratitis as there is usually no live virus present.

Diagnostic testing that can be used : culture, DNA testing, fluorescent antibody testing, Tzanck smear,and serum antibody testing.

TreatmentTreatment of HSV is diametrically different

from epithelial and stromal keratitis.Antiviral : acyclovir, valacyclovir, famciclovir.

Noninfectious KeratitisNoninfectious keratitis is typically

characterized by persistent corneal epithelial defects, stromal inflammation, and enzymatic degradation of the corneal collagen.

Mooren’s UlcerMooren’s ulcer is a rare, chronic, painful,

peripheral ulcerative keratitis.The pathogenesis of Mooren’s ulcer is

unknown but appears to involve an autoimmune reaction against a specific target molecule in the corneal stroma, which may occur in genetically susceptible individuals.

TypesLimited Types Second TypesUnilateral, Occurs in older

patients (fourth decade and older),

More responsive to local surgical and medical therapy.

More resistant to systemic immunosuppression

Involves a bilateral, painful, relentless, progressive destruction of the cornea,

Usually in younger individuals (third decade),

Many of whom are of African descent.

Ocular ManifestationMooren’s ulcer is characterized by a progressive, crescentic, peripheral corneal ulceration that is slightly central to the corneoscleral limbus.

Keratoconjunctivitis SiccaHappened due to dryness on the corneal

surface.Patient may complain itch, foreign body

sensation, and blurred vision.

TreatmentArtificial tears,Contact lens,Lacrimal puncta block.

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