Dr Ben Wild
Overview |
The cornea is a clear tissue located infront of the iris. Its main functions are as a barrier to protect the inner eye and to focus light on the retina. It is composed of 5 layers. The 3 main layers include the epithelium (outermost barrier layer), the stroma (the middle layer providing the refractive power), and the endothelium (responsible for pumping fluid out of the stroma so that the cornea does not swell and cloud over).
Frontal view of a healthy eye.
Bacterial keratitis occurs when bacteria is able to adhere and colonize the cornea. This usually only occurs when the cornea is damaged because the corneal epithelium acts as a strong barrier, the tears contain active antimicrobial elements, and blinking flushes away any pathogens. There are, however, a few bacteria that can infect a healthy cornea. These bacteria include Neisseria gonorrhea, meningitidis, and Haemophilus influenza.
Bacteria are typically classified as gram-positive or gram-negative depending on whether they have a secondary outer layer or not. Pseudomonas aeruginosa is the most common gram-negative bacteria and accounts for over 60% of contact lens related keratitis. It usually comes from touching the eye with your finger or another part of the body. Staphylococcus aureus is the most common gram-positive bacteria and usually stems from an overgrowth of bacteria on the eyelids.
An eye showing a large bacterial colony and corneal infiltrate caused by bacterial keratitis.
Signs and Symptoms |
Signs
White spot on the cornea representing white blood cells and bacteria, epithelial damage above the affected area, corneal swelling, uveitis, swollen eye, thinning or ulceration of the cornea, can lead to scarring endophthalmitis and scleritis.
Symptoms
Moderate to intense pain, light sensitivity, blurred vision, mucopurulent or purulent discharge (green to off white gooey discharge). Note: symptoms depend on type of bacteria and severity of infection.
Causes and Risk Factors |
Causes
Bacteria colonizing the cornea.
Risk Factors
Contact lens wear, sleeping in contact lenses (increases chances of infection by 20x!), trauma to the eye, eye surgery, ocular surface disease like dry eye, blepharitis, trichiasis, exposure, etc., immunosuppression, diabetes, vitamin A deficiency.
Prevention and Treatment |
Prevention
Treat dry eyes, avoid contact lens over-use, avoid risk factors.
Treatments
Mild-moderate | · Discontinue contact lens wear. · Throw out contact lens solution and case. · Change to daily contact lenses (from monthly/bi-weekly). · Topical antibiotic drops. · Fortified (extra strength) antibiotic drops. · Cyclogyl drops for discomfort. |
Severe | · Hospital admittance for corneal scrapping and swabs to determine the type of bacteria. · Fortified antibiotic drops. · Oral antibiotics if the infection is spreading. · IV antibiotics or antibiotic injections into the eye. · Keratoplasty (corneal transplant) if the infection results in sufficient vision loss. |
Prognosis |
Most bacterial keratitis’ resolve with a permanent scar. If this scar is not in the middle of the cornea, which it usually is not, vision should not be affected. Early detection and treatment greatly increases the likelihood that there will be a full recovery. A corneal transplant can restore vision in extreme cases.
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