History and exam

Key diagnostic factors

common

corneal infiltrate

Presence of pathogens and inflammatory cells in the corneal stroma causes edema and opacification of the normally transparent cornea.

corneal ulcer

A corneal infiltrate with an overlying epithelial defect is termed a corneal ulcer.

dendritic or geographic epithelial lesion

Branching staining pattern characteristic of herpetic infection.

uncommon

periocular skin lesions

Characteristic vesicular herpes simplex virus lesions or dermatomal varicella zoster virus rash in V1 distribution.

multifocal corneal ulcer with feathery edges

Typical of fungal corneal ulcer.

corneal perineuritis

Enlarged corneal nerves visible with slit lamp microscopy are typical of Acanthamoeba.

interstitial keratitis

Typical of syphilis and herpetic keratitis. May also be rarely seen in infections with Lyme disease, mycobacteria, and Acanthamoeba. In the developing world, also seen in onchocerciasis (river blindness) and leishmaniasis.

Other diagnostic factors

common

redness

Dilated conjunctival and episcleral vessels, especially in the perilimbal distribution, are almost invariably present in infectious keratitis.

pain

Corneal lesion can be exquisitely painful due to high concentration of pain fibers in the cornea. Herpetic lesions may be conspicuously asymptomatic.

increased lacrimation

Accompanies eye inflammation and irritation.

lid edema

General sign of eye inflammation and irritation.

discharge

General sign of eye inflammation and irritation.

decreased visual acuity

Caused by corneal opacities.

photophobia

Caused by intraocular inflammation.

high intraocular pressure

Typical of herpetic infection.

uncommon

history of herpes simplex virus or varicella zoster virus infection

Recurrences are common and occur in the same eye.

multiple old stromal scars

Typical of recurrent herpetic keratitis.

iris transillumination

Typical of recurrent herpetic infection.

corneal hypoesthesia

Typical of herpetic infection.

Risk factors

strong

contact lens wear

Increasingly important as a cause of corneal infections in countries where rates of contact lens use are high; associated with poor lens hygiene or overnight lens wear.[3][4]​​​[12]​​​​​​​​​[21]

Increases in the rates of Acanthamoeba and Fusarium species keratitis are attributed to contact lens wear.​​​[22][23]​​

In cases of bacterial infection, more virulent strains such as Pseudomonas species should be suspected in contact lens wearers.​​[24][25]

corneal trauma

This remains the major cause of corneal infections in most developing nations and agricultural settings.​[3]​​

Corneal foreign bodies, especially those containing vegetable matter, should raise suspicion of fungal pathogens.[3]​​[12]​​​​​

corneal abrasion/erosion

A break in the corneal epithelium is a major breach in the defense mechanisms of the cornea and leaves it vulnerable to invasion by a range of pathogens.​[4]​​

recurrent corneal erosions

Recurrent epithelial breakdown may occur due to hereditary corneal dystrophies or poor epithelial healing from previous trauma. Predisposes to bacterial keratitis.​[26]

immunocompromise

Poor immune function increases the risk for all infections. It predisposes to opportunistic infections (e.g., microsporidiosis).[4][5]​​

history of autoimmune disease

Autoimmune keratitis, most commonly peripheral ulcerative keratitis, is associated with systemic autoimmune disease (e.g. rheumatoid arthritis, systemic lupus erythematosus, polyarteritis nodosa, granulomatosis with polyangiitis [formerly known as Wegener granulomatosis], relapsing polychondritis, Behcet disease, sarcoidosis, inflammatory bowel disease, or rosacea).

Corneal findings can be the initial manifestation of systemic disease process in up to 25% of patients who present with peripheral ulcerative keratitis.[27]

weak

trichiasis

Misdirected lashes that scrape the corneal surface cause breaks in the epithelium and can allow commensal and abnormal ocular surface flora into the resulting defect.​[4]​​

blepharitis

Chronic lid inflammation is often accompanied by overgrowth of the commensal ocular surface flora and may also cause irritation of the corneal epithelium.​​​​[4][28]

dry eye

Severe dry eye results in corneal surface irritation and epithelial defects; lack of IgA and other immune mediators (normally present in the tear film) compromises corneal defenses.​​[4][29]

poor eyelid function

Lagophthalmos due to paralytic (cranial nerve VII palsy, inadequate eye closure during sedation), mechanical (proptosis in thyroid orbitopathy), or other lid dysfunction can result in exposure keratitis and epithelial breakdown. Predisposes to bacterial keratitis.

previous herpetic disease

Herpes simplex virus and varicella zoster virus keratitis tend to recur.​[13]

These pathogens are not fully eliminated by medical treatment and remain dormant in neurons and ganglia. Corneal complications occur in 40% of herpes zoster ophthalmicus.[18]​​​​

exposure keratitis

Exposure keratitis due to poor lid function causes severe drying of the corneal surface and compromise of the epithelium.

contaminated water exposure

May lead to Acanthamoeba species keratitis from sites such as hot tubs, rivers, and seawater.[30]​​

topical corticosteroid use

May trigger reactivation of latent herpes simplex virus keratitis.[13]​​​

topical anesthetic use

Frequent use of topical anesthetic drops (e.g., proparacaine) cause epithelial breakdown. May be sterile but result in clinical picture similar to microbial keratitis.

previous eye surgery

Any corneal incision (laser refractive surgery, cataract surgery) may become infected.[4]​​ An abscess may develop around corneal sutures. Predisposes to bacterial keratitis. Atypical mycobacteria may be seen.

Laser in situ keratomileusis (LASIK) surgery specifically predisposes patient to diffuse lamellar keratitis if recent history of surgery is obtained.​[31]​​​

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