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Microbial KeratitisByHaseeb Ahmed BhattiZiauddin Medical College

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CORNEAThe cornea is a round, convex, transparent, avascular structure that forms the anterior one-sixth of the outer coat of eyeball

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Vertical diameter is 10.6mmHorizontal diameter is11.7mmCornea is thinnest at its center and thicker at peripheryIs avascular and devoid of lymphatic drainageNerve supply is from long ciliary nerves, a branch of the ophthalmic division of trigeminal nerve.Refractory power = +43diopter

Histologically consists of five layersThe epitheliumThe bowmans membraneThe stromaThe descements membraneThe endothelium

The epithelium is stratified, squamous and non keratinized, about 50-60 um thickIt is devoid of melanocytes except at limbusSuperficial layer has microvillae and microplicae, facilitate the attachment of mucin layerMiddle zone cells are polyhedral called wing cellsBasal columnar cells are attached to basement membrane by hemidesmosomes and are responsible for complete turn over of surface epithelial cells.The stroma constitutes 90% of corneal thicknessComposed of regularly oriented collagen fibrilsContains chondroitin and keratan sulphate with interspersed fibroblasts (keratocytes).Descemets membrane is the basement membrane of the endotheliumThicker than endotheliumCan be easily separated from the substantia propria and the endotheliumThe endothelium consists of single layer of flattened, polygonal cells.Play a major role in controlling normal hydration of cornea.

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Microbial/Infective KeratitisInflammation of the cornea, resulting from the menace of micro-organisms.The keratitis may be :1. Bacterial2. Fungal3. Viral 4. Protozoal

Bacterial KeratitisMost common-Suppurative corneal ulcerationEtiologyStaphylococcus aureusStreptococcus pneumoniaeNiesseria gonorrheaHemophilus influenzaPseudomonas aerogenosaMoraxellaOther gram ve bacilli

Predisposing FactorsCorneal epithelial traumaContact lens WearersAqueous tear deficiencyChronic use of SteroidsHypovitaminosis A

Pathogenesis of Corneal ulcerOccurs through four stages:Infiltrative stage: Injury to epithelium causes inflammation, with PMN cell infiltrates and edema, giving rise to a yellow/white corneal opacity Active stage: Necrosis and sloughing off of epithelium causing ulcer formation. Regressive stage: A line of demarcation develops around the ulcer consisting of leucocytes while the surrounding cornea becomes clear. This is induced by treatment or natural host mechanisms.Cicatrization stage: Healing by epithelialization of ulcer with scarring. Degree of scarring depends on depth and size of ulcer

SymptomsSudden/Rapid onsetPainForeign body sensationPhotophobiaBlurred visionRedness of eyeMuco-purulent Discharge

Bacterial corneal Ulceration with Accumulation of Pus inside the Eye Anterior chamber (hypopyon).

SignsUpper eyelid Edema and dischargeCunjuctival hyperemiaSurrounding corneal inflammation (focal or difffuse) - HazinessUlceration of epitheliumCorneal Stain positiveHypopyon/Sterile pusRaised IOP

2% Flourescein stain taken by ulcerated cornea is da positive corneal stain sign.11

Acute painful red eye with White spot on Corneal surface.

Keratitis caused by Pseudomonas Aeroginosa. Chistory of Contact lens wear.12

Strep-pneumonia Corneal ulcer

ManagementAdmission if NecessaryProper History & Examination

InvestigationsBaseline Microbiological - C/S

Treatment

TreatmentInfection Control AntibioticsDual therapy (Aminoglycoside+cephalosporin)Mono therapy (Flouroquinolones)Systemic (Ciprofloxacin 750mg bd)Atropine 1%Pain reliefPrevent posterior synechie formationDecrease exudation by decreasing capillary permeability

Antigluacoma drugsDecrease IOP

Prevention of perforationPressure bandageConjuctival flapTherapeutic corneal graft

Treatment

ComplicationsToxic IridocyclitisSecondary GlaucomaDescemetocelePerforation of corneal ulcerCorneal scarring

Fungal keratitisAspergillusFusariumFilamentousMost common in Tropical climates

CandidaNon-filamentous/YeastMost common in temperate climate

Predisposing FactorsTrauma-organic matter (wood+plants)Chronic use of topical steroidsOcular surface diseaseCompromised immune system

SymptomsGradual onset - slow progressForeign body sensationPhotophobiaBlurred visionDischarge - Purulent

SignsGreyish white ulcer that has delicate fine feathery edgesElevated surface & irregular contourEndothelial plaque may be presentProgressive infiltration, may be surrounded by stellate lesionsImmune ringCiliary congestionYeast: Yellow white ulcer with dense suupuration

ManagementHistory & Examination

InvestigationBaselineGiemsa , KOH and methamine silver stainCulture

Treatment

TreatmentTopical Antifungal therapyNatamycin 5% suspensionFluconazole 2% suspensionAmphotericin B 0.15% solutionSystemic Antifungal therapyKetoconazole 200-600mg odFluconazloe 200-400mg odMechanical debridementTherapeutic keratoplasty

Protozoal keratitisAcanthamoeba spp.Microsporidea

Acanthamoeba is free living ubiquitous protozoa found in fresh water and soilActive trophozoite or dormant cyst

Risk factorsContact lensOcular trauma Corneal abrasionHerpetic keratitis

Clinical featuresSymptoms: Blurred vision, Severe pain & PhotophobiaSigns:Diffuse punctate EpitheliopathyEpithelial pseudodentritesLimbitis-diffuse or focal anterior stromal infiltratesRing AbcessPerineural infiltrates (radial keratoneuritis) enlargement of corneal nerves

DiagnosisSoft contact leans wearSevere persistant painRadial keratoneuritisIdentification of Amoebis cyst in smear & cultureCalcoflour white (flourescent dye)Laminar corneal biopsy

TreatmentDebridement infected epithelium

Topical Amoebicides as dual therapyPropamidine isethionate 0.1% (broline) + Polyhexamethyl biguanide 0.02%Neomycin + Broline + Chlorhexadine 0.02%

Therapeutic keratoplastyAvoid in Inflammed eyes

Viral KeratitisHerpes simplexHerpes zosterAdenovirusMeaslesParamyxovirus parotitisCMVEBV

Herpes Simplex keratitisDNA virus of he Herpesviridae FamilyInfection is extremely commonMajor cause ofunilateral corneal scarring worldwide

TYPE 1Predominantly causes infection above the waist.Droplet infection or close contact with infected individual

TYPE 2 Below the Waist (genital herpes)STDGenital secretions - Birth

Primary infection Infection in early life Uncommon during first six months Subclinical causing mild fever and malaise Virus eventually travels up the axon of sensory nerves into its ganglions. Type 1 remains dormant in trigeminal ganglion Type 2 in spinal ganglia.

Ocular involvement Blepharitis Acute Follicular Conjunctivitis Epithelial Punctuate Keratitis

Pathogenesis

Virus can remain dormant for years without any symptoms Reacivated virus replicates in ganglion and in target tissue33

Recurrent keratitis Poor health Exposure to ultraviolet rays Fever Psychatric disturbance Use of steroids.

Lesions

Acute/Active Epithelieal KeratitisStromal KeratitisKerato uveitis.

Clinical Features of HSV keratitisSymptoms Foreign Body Sensation Lacrimation Watery discharge Photophobia Pain (mild to moderate) Reduced VisionSignsCiliary congestionDiminished corneal Sensitivity

Active epithelial keratitis: Dendritic ulcerMost characteristic lesion, occurs in corneal epitheliumTypical branching, linear pattern with feathery edges and terminal bulbs at ends.Visualized by fluorescein staining

HSV dendritic ulcer stained with fluorescein

Definition: It is an acute or chronic corneal ilceration where an ulcer has theshape of linear branching tree => Dendritic or geographical (ameboid )configuration.

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Geographic/Amoeboid ulceration

Delicate dendritic lesions take a broader form.

Diagnosis

Morphological appearance of corneal ulcer Diminished corneal Sensitivity

Differential diagnosis

Herpes zoster Keratitis Acanthomebia Keratitis Healing Corneal ulcer Toxic drug Keratopathy

TreatmentTopical Anti-viral drugsAcycloguanosine - AcyclovirTrifluorothymidineAdenine ArabinosideIdoxuridine

DebridementTopical antibioticsCycloplegics

Debridement: under topical anesthesia affected cells removed with sterile cotton stripped bud 2mm beyond edge of ulcer40

Active viral invasion and destruction of Endothelium of cornea

Signs Stroma appears cheesy and necrotic. Keratic precipitates or KP bodies (Anterior Uveitis) Features of AEK may be present.

Stomal Necrotic KeratitisTreatmentTopical AntiviralsTopical AntibioticsTopical CycloplegicsLubricants/Pressure patching Bandage contact lens

Disiform Keratits

Definition: It is viral endothelitis in which there is disc shaped grey area of stromal edema with localised keratic precipitates

Reactivated viral infection of keratocytesand Endothelium Hypersensitivity reaction to viral antigen

Clinical Features Central zone of epithelial edema Stromal thickening - edema Folds in descemet;s membrane Mild to moderate anterior uveitis Keratic precipitates Reduced corneal sensitivity

Treatment

Topical Antiviral Topical antibiotics Topical weak steroids Cycloplegics

Caused by HHV3 (VZV) Primary infection as Chicken pox Virus may travel into sensory ganglia of dorsal root ganglion and trigeminal nerve ganglion Reactivation of virus causes Herpes Zoster or Herpes Zoster opthalmicus

Mechanism of damage.Cellular infiltrationIschemic vasculitisInflamatory granulomatous reactionHerpes Zoster Ophthalmicus (HZO)

PainRashesEdemaPost Herpetic Neuralgia

Corneal lesions Acute epithelial keratitis Microdendritic ulcer Nummular keratitis Diciform keratitis Reduced corneal sensation

Other Ocular Features Conjunctivitis Episcleritis Secondary glaucoma Anterior UveitisClinical Features

Neurologic complications

Cranial nerve palsyMostly 3rd nerve

Optic neuritis1:400

TreatmentSystemicAcyclovir 800mg 5/dayAnalgesicsAntibioticsSystemic steroids - prednisolone 40-60mg

ReferencesJack J. Kanski's Clinical Ophthalmoscopy a Systemic Approach fifth editionInfective keratitis lecture by Dr. Shabbir Hussain, Department of OphthalmologyEdward S. Harkness institute, columbia university college of physicians and surgeonsClinical Opthalmology; Shafi M. Jatoi

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