Infectious Keratitis

Dr Ben Wild

Overview

The cornea is the outermost layer of the eye in front of the iris (the colored part of the eye). It is a clear tissue, void of any blood vessels, and is one of the main optical components responsible focusing light on the retina. Infectious keratitis occurs when a microbe (bacteria, fungus, or protozoa), or virus infects at least one of the layers of the cornea.

A frontal view of a healthy eye.

Bacterial keratitis is due to either Gram (+) or Gram (-) bacteria. Swabbing and culturing the bacteria can help in identification and treatment.

Fungal keratitis is broken down into yeasts or filamentary fungal infections. They take longer to infect the cornea but tend to be much more symptomatic.

Protozoa keratitis is caused by the Acanthamoeba organism. It is the most difficult to treat of all keratitis’ and often most symptomatic but is also the most rare.

Viral keratitis’ vary greatly depending on which virus infects the eye. From the cold sore virus to the common cold virus and many more in between. They can infect all layers of the cornea and most typically don’t respond to treatment but do resolve on their own.

Bacterial corneal ulcer (top left), filamentary and yeast ulcers (top right), ring ulcer from protozoa (bottom left), dendrite and punctate keratitis from 2 different viruses (bottom right).

Signs and Symptoms

Signs

Bacterial	​White dot on cornea, red eye(s), cloudy cornea, swollen eye or eyelids, uveitis (inflammation insdie the eye), scleritis (inflammation of the white's of the eye).
Fungal	White dot (yeast) or fluffy dot (filamentary) on cornea, red eye, uveitis, scleritis.
Protozoan	White dots merging into a white ring on the cornea, red eye, scleritis.
Viral	Large follicles (clear bumps) on the inner eyelids, skin lesions on eyelids, white dots on cornea, red eyes, cloudy + swollen cornea.

Symptoms

Bacterial	Pain, light sensitivity, blurred vision, off white discharge.
Fungal	Gradual onset of pain, grittiness, light sensitivity, blurred vision, mucous-like off white discharge.
Protozoan	Blurred vision, discomfort, pain.
Viral	Mild to moderate discomfort, light sensitivity, watery eyes, blurred vision, numb eye.

Causes and Risk Factors

Causes

Infection by bacteria, fungus, protozoa or virus.

Risk Factors

Contact lens wear (much higher risk if sleeping in lenses), contaminated water or soil in the eyes, skin conditions such as atopic dermatitis, rosacea, etc., malnutrition, immunodeficiency, blepharitis, trauma, diabetes, vitamin A deficiency.

Prevention and Treatment

Prevention

Proper contact lens wear and disposal. Proper eye and eyelid hygiene.

Treatments

Common: discontinue contact lens wear, throw out contact lenses, case, solution and makeup that touches the lids. Change to daily contact lenses. Steroid eye drops if infection is associated with ulceration, uveitis or scleritis. Avoid steroids in cold sore viral infections. Dilating drops for pain. Surgery through keratoplasty or keratectomy if unresponsive.

Bacterial	Antibacterial drops. Hospital admission and IV antibiotics if centrally located on the cornea.
Fungal	Antifungal drops. Antibiotic drops. Systemic antivirals. Tetracycline pills.
Protozoan	Amebicides drops. Non steroidal anti-inflammatory pills.
Viral	​Antiviral drops if cold sore/shingles virus. Antibiotic drops to avoid superinfection.

Prognosis

Each type of infectious keratitis can be vision threatening and lead to corneal transplant and permanently reduced vision. Bacterial keratitis’ are usually the easiest to treat but also tend to progress the fastest and necessitate the earliest treatment. Fungal and protozoan keratitis tend to progress much slower and are more difficult to treat leading to higher odds of needing surgical intervention. Viral keratitis is often recurrent and can be triggered by UV, trauma, and stress but rarely leads to permanent vision loss.