CORNEAL INFECTIONS

Pathogenesis.

Common bacteria cannot invade intact epithelium. The bacteria that invade intact epithelium are neisseria, H.influenza and corynebacterium diphtheriae. 

Clinical features

lid edema

conjunctival congestion

corneal epithelial defect

corneal infiltrate

Anterior chamber reaction

hypopyon

Corneal staining with flouriscen which stain margins of ulcer. It is yellow dye which appears green when seen with cobalt blue filter. Other stain is rose bengal which stain pink dead and devitalized cells

Investigation

corneal scrape for staining and culture. 

common stains is Gram stain. Common culture is blood culture

Treatment

Hospitaliztion if ulcer is very large. central, only eyed patient or patient noncompliant at home

Broad spectrum antibiotis are started. For example moxifloxacin eye drops 1 hourly and reduced then depending upon response

Fortified dual antibiotic may be started if no response or very severe condition at presentation. Method of preparation is as follows. 

combination of 

Fortified tobramycin eye drops: Add 2 ml of tobramycin injection (40mg/ml) injection into commercially available 5 ml of tobramycin eye drops (0.3%) . Refrigerate for 2 weeks. Final concentration is 15mg/ml (1.5%). For gram negative coverage.

Fortified cefazolin eye drops: Add 2.5 ml distill water to 500mg of injection cefazolin and then add to 7.5ml of artificial tears. Refrigerate for 4 days. Final concentration is  50 mg/ml (5%). For gram positive coverage

or  combination of following my be used.

 Fortified vancomycin eye drops: Same as cefazolin. For gram positive organisms

Fortified ceftazidime eye drops: Same as cefazolin. For gram negative organisms

Complications

1.       Corneal opacity

a.       Nebula is corneal opacity when bowman’s membrane and anterior 1/3rd of stroma is involved and iris can be seen clearly

b.       Macula is corneal opacity when half of cornea is involved and iris is difficult to see

c.       Leucoma is complete opacity of cornea when all layers are involved and no iris details can be seen

2.       Keratectasia:  As cornea is thinned, it bulges forward called keratectasia

3.       Descemetocele: after thinning of cornea, the Descemet’s membrane bulges forward forming descemetocele

4.       Perforation

a.       Prolapse of iris

b.       Anterior synechiae: adhesion of iris to posterior surface of cornea

c.       Adherent leucoma: corneal opacity with attachment of iris to cornea

d.       Anterior staphyloma: corneal bulges out and is lined with iris tissure

e.       Cataract

f.        Dislocation of lens

g.       Iridocyclitis

h.       Panophthalmitis

FUNGAL INFECTION

PATHOGENESIS

Common fungal organisms are filamentous and non-filamentous fungi. Example of filamentous fungi is Aspergillus and fusarium. while non-filamentous fungi are candida

CLINICAL FEATURES

Similar to bacterial keratitis but there is usually history of vegetative trauma. Signs are more severe as compared to symptoms. There is subacute onset with history of usually 1 to 2 weeks.

1. yellow-white coloured ulcer with indistinct margin. 

2. minimum vascularization.

3.  dry in appearance with

4. small satellite lesions around the ulcer 

5. delicate feathery, finger-like hyphate edges protruding into adjacent stroma.

6. Ulcer margin is often elevated above the surface.

7. Massive hypopyon is dense and organized.

8. 5. Slit-lamp examination—Endothelial plaque and immune ring may be seen around the ulcer. 

9. Some degree of iridocyclitis

INVESTIGATIONS

Staining on KOH readily detects filamentous fungi. Other stains are gram stain and PAS. Although blood culture yield most fungi, specifically Culture on Sabouraud’s agar is done.

TREATMENT

As in bacterial keratitis, treatment is medical and surgical. Specific commercially prepared eye drops antifungal is Natamycin eye drops. Flucozole is available as parenteral injection and can be used as such by putting it in empty eye drop bottle. parenteral injection of Amphotericin B is also option, but problem is its availability.

1. Scraping and debridement of the ulcer is useful in drug penetration.

2. 1% Atropine eyedrop or ointment controls associated iritis and prevents synechiae formation.

3. systemic antifungals are indicated if the infection spreads to the sclera and there is impending perforation, e.g   fluconazole 200 mg daily may be given for 2-3 weeks

4. conjunctival flap in non-healing ulcer

5. therapeutic keratoplasty

VIRAL KERATITIS 

HERPES SIMPLEX

symptoms: 

1. Skin lesion—vesicles with crusts are formed

2. Severe follicular keratoconjunctivitis 

3. preauricular lymph node enlargement

signs

1. superficial punctate keratits

2. dendritic ulcer

3. geographical ulcer

4. disciform keratitis

INVESTIGATIONS

Corneal scrape sent in viral transport media for 

1. culture

2. PCR

3. immunohistochemistry

4. Giemsa staining

Treatment

1. Topical acyclovir eye ointment 5 times a day

2. Debridement of resistant cases 

3. Oral acyclovir 400 mg 5 times day for immunodeficient people

4. Interferon monotherapy

5. skin lesions with acyclovir cream

6. cycloplegics with cyclopentolate twice a day

7. IOP control, avoid prostaglandin analogues that increase inflammation

8. topical steroids are indicated in disciform keratitis , but not in epithelial disease

9. full thickness keratoplasty in case of corneal opacity

Differential diagnosis of dendritic ulceration 

1. herpes zoster keratitis

2. healing corneal abrasion

3. acanthamoeba keratitis

4. epithelial rejection in a corneal graft

5. tyrosinaemia type 2

6. the epithelial effects of soft contact lenses

7. toxic keratopathy

8. secondary to topical medication

herpes zoster

clinical features

1. Rows of vesicular eruption take place along the branches of the ophthalmic division of the 5th cranial nerve.

2. Severe neuralgic pain along the course of the nerves is present 

3. Fever and malaise 

4. Skin of lid and face becomes red and  oedematous.

5. Hutchinson’s rule—Ocular involvement is usually associated with eruption of vesicles on the skin of tip of the nose (nasociliary branch)

6.  Corneal and skin anaesthesia

7.  Superficial punctate keratitis is a most common feature

8. Micro dendritic epithelial ulcers—Unlike herpes simplex, these ulcers are small, peripheral, stellate and with tapered ends, i.e. without rounded bulbs.

9.  Nummular keratitis—Larger discoid lesions surrounded by stromal haze are seen.

10. Disciform keratitis may be seen in few cases.

11. Deep stromal involvement is often associated with iridocyclitis.

complications

1. Iridocyclitis and scleritis

2. Secondary glaucoma may occur due to trabeculitis or peripheral anterior synechia

3. 3rd, 6th, 7th cranial nerve palsy and optic neuritis 

4. Exposure keratitis results due to facial nerve paralysis.

5. Postherpetic neuralgia

6. Acute retinal necrosis 

treatment

systemic: oral acyclovir 800mg five times a day for 10 days started within 3 days of appearing rash

topical acyclovir 3% applied 5 time  a day for 3 weeks

analgesic and ani-inflammatory

topical atropine in case of keratitis iridocyclitis and scleritis

PATHOGENESIS

Two mechanism are postulated. 

1. One is active infection of herpes of keratocytes. 

2. Two is hypersensitivity reaction to viral antigen.

SYMPTOMS

1. Reduced vision of gradual onset. 

2. Halos around lights. Redness and discomfort

SIGNS

1. Stromal and epithelial edema. 

2. Large granulomatous Keratic precipitates.

3. A surrounding ring of deep stromal haze (wessely ring), a hypersensitivity response of antigen and antibody deposition.

4. Increased intraocular pressure

5. Reduced corneal sensation

6. consecutive episodes result  in stromal scarring and deep vascularization

TREATMENT

1. Topical steroid eye drops as prednisolone 1% 4 times a day

2. Topical antiviral eye ointment as acyclovir eye ointment 5 times a day

3. Oral steriods to reverse stromal vasculariztion

4. Topical cyclosporin 0.05% twice a day in case of elevated IOP

5. Fine needle diathermy and argon laser ablation of neovascularization

6. In case of epithelial defect. steriods are used in less frequency under acyclovir ointment

PATHOGENESIS

Acanthamoeba is a free water living protozoa. contact lens user especially who washes contact lens with tap water or go to swimming pool is a risk factor

CLINICAL FEATURES

1. These are similar to bacterial keratitis. 

2. Its common in contact lens user. 

3. specific features are pain out of proportion to the clinical signs. 

4. Radial perineuritis when present is pathognomic.

5. ring shaped lesion with stromal infilterate

6. there may be overlying epithelial defect

INVESTIGATION

1. Corneal scrape is used over PAS stain gram and Giemsa stain. 

2. Specific culture is non-nutrient agar with E.coli overlay. 

3. immunohistochemistry, 

4. PCR, 

5. confocal microscopy and 

6. corneal biopsy

TREATMENT

1. Chlorohexidine 0.02 %is prepared from mouth wash 0.2%. It comes with the name of clinca .  It is only drug available in Pakistan.

2. atropine eye drops as cycloplegia

3. Broline, PHMB and other anti-acanthamoeba drugs are not available in Pakistan.

4. therapeutic keratoplasty in cases of non-responsive ulcer