Bacterial Keratitis

Updated: Apr 07, 2023
  • Author: Jean Deschênes, MD, FRCSC; Chief Editor: Hampton Roy, Sr, MD  more...
  • Print


Bacterial keratitis is a serious ocular problem that can, if not appropriately treated, lead to sight-threatening complications such as corneal scarring, perforation, endophthalmitis, and, ultimately, blindness. A particular feature of bacterial keratitis is its rapid progression; corneal destruction may be complete in 24-48 hours with some of the more virulent bacteria. Corneal ulceration, stromal abscess formation, surrounding corneal edema, and anterior segment inflammation are characteristics of this disease. (See image below.)

Human eye anatomy. Human eye anatomy.

Bacterial keratitis remains one of the most important potential complications of contact lens use. Keeping this in mind, early diagnosis and treatment are key to minimizing any visual-threatening sequelae. In addition, close follow-up, attention to laboratory data, and changing antimicrobials if no clinical improvement is evident are important elements for a successful outcome.



Normally infection in a healthy cornea is rare. Interruption of an intact corneal epithelium and/or abnormal tear film permits the entrance of microorganisms into the corneal stroma, where they may proliferate and cause ulceration. In addition, some bacteria can penetrate an intact corneal epithelium to cause infection. Virulence factors may initiate microbial invasion, or secondary effector molecules may assist the infective process. Many bacteria display several adhesins on fimbriated and non-fimbriated structures that may aid in their adherence to host corneal cells. During the initial stages, the epithelium and stroma in the area of injury and infection swell and undergo necrosis. Acute inflammatory cells (mainly neutrophils) surround the beginning ulcer and cause necrosis of the stromal lamellae.

Diffusion of inflammatory products (including cytokines) posteriorly elicits an outpouring of inflammatory cells into the anterior chamber and may create a hypopyon. Different bacterial toxins and enzymes (including elastase and alkaline protease) may be produced during corneal infection, contributing to the destruction of corneal substances.

The most common groups of bacteria responsible for bacterial keratitis are as follows: Streptococcus, Pseudomonas, Enterobacteriaceae (including Klebsiella, Enterobacter, Serratia, and Proteus), and Staphylococcus species.

Up to 20% of cases of fungal keratitis (particularly candidiasis) are complicated by bacterial coinfection.




An estimated 2.0–3.5 million cases of bacterial keratitis are reported annually. But these data are considered significantly lower than the actual incidence rate due to underreporting from the developing world.  [1]

United States

Approximately 71,000  cases of Bacterial Keratitis are diagnosed in the United States annually [2] .


In cases of severe inflammation, a deep ulcer and a stromal abscess may coalesce, resulting in thinning of the cornea and sloughing of the infected stroma. These processes may create some of the following complications:

Corneal leukoma

Scar tissue formation with the presence of corneal vascularization may be the end result of a bacterial keratitis. Depending on the location and depth of stromal involvement, the resulting corneal leukoma may be visually significant and necessitate corneal surgery for visual rehabilitation (including phototherapeutic keratectomy [PTK] or penetrating keratoplasty [PK]).

Irregular astigmatism

Another possible complication of these infections is uneven healing of the stroma, resulting in irregular astigmatism (that may require a gas-permeable contact lens or PTK to improve vision).


Bacteria can penetrate the cornea and infect the internal contents of the eye, potentially requiring intravitreal injection of antibiotics or surgery for treatment.

Corneal perforation

This is one of the most feared complications of bacterial keratitis that may result in secondary endophthalmitis and possible loss of the eye.



The visual prognosis depends on several factors, as outlined below, and may result in a mild-to-severe decrease in best-corrected visual acuity or loss of vision.

  • Virulence of the organism responsible for the keratitis

  • Extent, depth, and location of the corneal ulcer

  • Resulting vascularization and/or collagen deposition

  • Other pre-existing ocular conditions that may affect treatment outcomes


Patient Education

Patients who are contact lens wearers (in particular extended-wear contact lenses) should be instructed not to force the use of contact lenses when they have hyperemia, irritation, or foreign body sensation, and to use sterile contact lens solutions to avoid contamination.

For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education article Corneal Ulcer.