Bacterial Keratitis - Causes, Symptoms, and Treatment

Introduction

The eye comprises many layers like the conjunctiva, sclera, iris, cornea, lens, retina, etc. Here the light will enter the eye through the cornea, pass through the iris and lens, and from the lens, it is directed towards the retina to create an image for vision. If any one of the layers is infected or damaged, the vision will be partially or wholly impaired. Loss of vision will impact a life so much as the eyes are considered the gateway to the soul. Without a good vision, the quality of life will be majorly affected.

The cornea is an avascular structure (devoid of blood vessels). The corneal layer is considered the protective covering for the eye's structures and is also responsible for directing the light towards the retina. The cornea is the dome-shaped structure of the eye. The most common condition of the corneal layer is bacterial keratitis. The dense connective tissue of the cornea is the corneal stroma, and this is the most common site affected by bacterial keratitis.

Keratitis is the inflammation of the corneal layer and is caused by many factors like bacteria, viruses, fungi, trauma, and contact lenses. The keratitis condition caused by the bacteria is called bacterial keratitis. If this condition is not treated earlier and properly, life-threatening complications will occur. This condition presents with whitish or yellowish infiltrates and inflammation.

What Are the Symptoms of Bacterial Keratitis?

• Painful eyes.

• Redness of the eyes due to inflammation.

• Sensitive to light.

• Tearing of the eyes.

• Discharge from the eyes is seen.

• Blurred vision.

If any of these symptoms occur, remove the contact lenses and seek a doctor as soon as possible. If bacterial keratitis is left untreated, it can result in complications like vision loss.

What Are the Causes of Bacterial Keratitis?

Two types of bacteria cause bacterial keratitis. They are,

• Pseudomonas aeruginosa is a gram-negative bacteria and the most common cause of bacterial keratitis. It affects the contact lens wearers majorly. Wearing contact lenses for a longer time will encourage the adhesion of Pseudomonas aeruginosa.

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Pseudomonas aeruginosa contains factors like glycocalyx and exotins, which enable adherence. It can also be seen in aged people who do not wear contact lenses.

• Staphylococcus aureus - It is a gram-positive bacteria that is responsible for several skin infections. Staphylococcus aureus will form a biofilm over the cornea causing bacterial keratitis.

What Are the Risk Factors of Bacterial Keratitis?

• Wearing contact lenses overnight.

• Improper disinfection of the contact lenses.

• Cleaning and storing the lenses in water rather than a disinfectant solution.

• Cleaning the contact lenses with contaminated solutions.

• Eye injury or eye disease.

• Weak immune system.

• Recent corneal infections like herpetic keratitis and neurotrophic keratopathy.

What Are the Possible Complications of Bacterial Keratitis?

• Corneal Scarring - scarring of the cornea with corneal vascularization is a common complication of bacterial keratitis. Vision impairment occurs, and it can be treated with corneal surgeries.

• Blindness.

• Endophthalmitis - Here, the bacteria will penetrate the cornea and attack the other contents of the eye. Aqueous humor (responsible for providing nutrients to the eye) and vitreous humor (which keeps the eye lubricated) are most commonly affected.

• Corneal Perforation - The corneal surface will be penetrated and cause damage. This is the most severe complication of bacterial keratitis as it might even result in the loss of the eye.

• Irregular Astigmatism - Due to the corneal scarring, the cornea will not have a proper round shape, and thus irregularities can be seen. This is called irregular astigmatism.

How to Diagnose Bacterial Keratitis?

Physical Examination:

Physical examination of the affected eye will reveal the following.

• Swelling of the upper eyelid.

• Ulceration of the cornea.

• Redness of the conjunctival layer with associated dilation.

• The iris and the anterior part of the lens will be adherent.

• Descemet folds are seen.

Laboratory Tests:

The doctor will take scrapings from the surface of the eye (anesthetized by a topical medication) using a sterile blade and will send it for laboratory testing. Samples of the contact lens solution used can also be tested.

In case of deep stromal involvement, a corneal biopsy will be performed.

Slit-lamp Technique:

This is the procedure in which a microscope attached to a slit-lamp is used to examine the layers of the eye for any infection, injury, or irregularities in general. In this case,

• Visual acuity will be examined.

• The infiltration of the cornea will be examined.

• Edema of the cornea will be examined.

• The outermost layer of the cornea, which is the epithelial layer, will be examined for defects. A fluorescein dye will be applied to do this examination.

Another imaging technique preferred is the B-scan ultrasound of the eye.

How to Treat Bacterial Keratitis?

Eye Drops: This is the most traditional method of treating bacterial keratitis. Antibiotic eye drops like Tobramycin (one drop every hour) and Cefazolin or Vancomycin (one drop every hour) will be prescribed. In less severe cases, Fluoroquinolones like Moxifloxacin and Gatifloxacin are used widely. The frequency of the eyedrops usage has to be tapered as improvement in the condition is seen.

Surgical Care:

In the case of corneal perforation, surgery is needed. Sclerocorneal patch and cyanoacrylate adhesives are the most preferred ones. These procedures will mainly not require general anesthesia. Topical anesthesia is enough most of the time.

In case of severe damage, corneal transplantation is the only choice. Penetrating keratoplasty is done to remove the infected corneal tissue and is replaced with a healthy one and is secured with a suture which can be removed depending on the healing process. This surgery has shown 90 % success rates as per a study.

How Is the Prognosis of Bacterial Keratitis?

Prognosis ultimately depends on how well the vision has improved. It relies on,

• The site and size of the corneal ulcer.

• The pathogenicity of the bacterial organism causing keratitis.

• The level of vascularization and deposition of the collagen.

Educating the Patients About Prevention of Bacterial Keratitis:

Those wearing contact lenses have to be educated about their usage and handling.

• Should not wear contact lenses for a longer time than what is prescribed.

• Sterile contact lens solutions should be used to store the lenses.

• Do not handle the lenses with contaminated hands. Wash hands thoroughly before handling.

• Should not wear lenses when there is some irritation, a foreign body sensation, or an evident infection.

Conclusion

Bacterial keratitis is a demanding condition that requires a properly tailored treatment plan for a good prognosis. Most of the cases will need surgical intervention, and most of them have shown a good prognosis. In addition, following proper guidance on using and cleaning the contact lenses will prevent bacterial keratitis to a greater extent.

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