Keratitis
Introduction
Keratitis is an inflammation of the cornea, the transparent front part of the eye that covers the iris, pupil, and anterior chamber. This condition can result from various causes, including infections, injuries, and underlying medical conditions. Keratitis can lead to significant discomfort, visual impairment, and, if left untreated, permanent damage to the cornea and vision loss.
Etiology
Keratitis can be classified based on its etiology into infectious and non-infectious types.
Infectious Keratitis
Infectious keratitis is caused by various microorganisms, including bacteria, viruses, fungi, and parasites.
Bacterial Keratitis
Bacterial keratitis is commonly associated with contact lens wear, trauma, or pre-existing ocular surface disease. The most frequent pathogens include Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pneumoniae. Symptoms typically include severe pain, redness, discharge, and decreased vision.
Viral Keratitis
Viral keratitis is often caused by the Herpes simplex virus (HSV) and the Varicella-zoster virus (VZV). HSV keratitis can present as dendritic ulcers, geographic ulcers, or stromal keratitis. VZV keratitis is associated with herpes zoster ophthalmicus, which can cause necrotizing stromal keratitis and endotheliitis.
Fungal Keratitis
Fungal keratitis is more common in tropical and subtropical regions and is often related to trauma involving plant material. Common fungi include Fusarium, Aspergillus, and Candida species. Symptoms include pain, redness, discharge, and a characteristic feathery infiltrate in the cornea.
Parasitic Keratitis
Parasitic keratitis, particularly Acanthamoeba keratitis, is associated with contact lens wear and exposure to contaminated water. It is characterized by severe pain, ring infiltrates, and a prolonged course.
Non-Infectious Keratitis
Non-infectious keratitis can result from various causes, including autoimmune diseases, exposure to toxins, and physical trauma.
Autoimmune Keratitis
Autoimmune keratitis is associated with systemic autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjogren's syndrome. It can present as peripheral ulcerative keratitis or interstitial keratitis.
Exposure Keratitis
Exposure keratitis occurs when the cornea is exposed to the environment due to incomplete eyelid closure, as seen in conditions like Bell's palsy or thyroid eye disease. It can lead to dryness, ulceration, and secondary infection.
Traumatic Keratitis
Traumatic keratitis results from physical injury to the cornea, such as abrasions, foreign bodies, or chemical burns. Prompt treatment is essential to prevent secondary infection and scarring.
Pathophysiology
The pathophysiology of keratitis involves a complex interplay between the causative agent and the host's immune response. In infectious keratitis, pathogens invade the corneal epithelium and stroma, leading to inflammation, necrosis, and ulceration. The host immune response, including the release of cytokines and recruitment of inflammatory cells, can exacerbate tissue damage.
In non-infectious keratitis, the underlying cause, such as autoimmune disease or trauma, triggers an inflammatory response in the cornea. This can result in epithelial defects, stromal thinning, and neovascularization.
Clinical Presentation
The clinical presentation of keratitis varies depending on the etiology but generally includes the following symptoms:
- Pain: Often severe and disproportionate to clinical findings.
- Redness: Conjunctival and ciliary injection.
- Discharge: Purulent in bacterial keratitis, watery in viral keratitis.
- Photophobia: Sensitivity to light.
- Blurred vision: Due to corneal edema and irregularity.
- Foreign body sensation: Due to epithelial disruption.
Diagnosis
The diagnosis of keratitis involves a thorough clinical examination and appropriate diagnostic tests.
Clinical Examination
A slit-lamp examination is essential for evaluating the cornea. Key findings may include:
- Epithelial defects: Staining with fluorescein dye.
- Infiltrates: Focal or diffuse opacities in the stroma.
- Hypopyon: Accumulation of inflammatory cells in the anterior chamber.
- Keratic precipitates: Inflammatory deposits on the endothelium.
Diagnostic Tests
- Microbiological cultures: Corneal scrapings for bacterial, fungal, and parasitic cultures.
- Polymerase chain reaction (PCR): For viral and atypical infections.
- Confocal microscopy: For detecting Acanthamoeba cysts.
- Serological tests: For autoimmune markers.
Treatment
The treatment of keratitis depends on the underlying cause and severity of the condition.
Infectious Keratitis
- Bacterial keratitis: Broad-spectrum topical antibiotics, such as fluoroquinolones or fortified antibiotics, are the mainstay of treatment. Severe cases may require systemic antibiotics and hospitalization.
- Viral keratitis: Topical and oral antiviral agents, such as acyclovir or ganciclovir, are used. Corticosteroids may be added in stromal keratitis to reduce inflammation.
- Fungal keratitis: Topical antifungal agents, such as natamycin or voriconazole, are used. Systemic antifungals may be required for severe cases.
- Parasitic keratitis: A combination of topical antiseptics, such as polyhexamethylene biguanide (PHMB), and systemic antiparasitic agents is used. Treatment is often prolonged and challenging.
Non-Infectious Keratitis
- Autoimmune keratitis: Topical corticosteroids and immunosuppressive agents are used to control inflammation. Systemic treatment may be necessary for associated autoimmune diseases.
- Exposure keratitis: Lubricating eye drops, ointments, and moisture chambers are used to protect the cornea. Surgical interventions, such as tarsorrhaphy, may be required in severe cases.
- Traumatic keratitis: Prompt removal of foreign bodies, irrigation of chemical burns, and use of topical antibiotics to prevent secondary infection.
Prognosis
The prognosis of keratitis varies depending on the etiology, promptness of treatment, and patient compliance. Infectious keratitis, if treated early and appropriately, has a good prognosis. However, delayed treatment or resistant organisms can lead to complications such as corneal scarring, perforation, and vision loss. Non-infectious keratitis generally has a better prognosis with appropriate management of the underlying cause.
Complications
Complications of keratitis can be severe and include:
- Corneal scarring: Leading to permanent visual impairment.
- Corneal perforation: Requiring surgical intervention, such as corneal transplantation.
- Secondary glaucoma: Due to increased intraocular pressure from inflammation.
- Endophthalmitis: A severe intraocular infection that can result in blindness.
Prevention
Preventive measures for keratitis include:
- Proper contact lens hygiene: Regular cleaning and disinfection of lenses.
- Protective eyewear: To prevent trauma and exposure to harmful substances.
- Prompt treatment of ocular surface diseases: To prevent secondary infection.
- Vaccination: Against herpes zoster for individuals over 50 years old.
See Also
References
- [1] Kanski, J.J., Bowling, B. (2011). Clinical Ophthalmology: A Systematic Approach. Elsevier.
- [2] Foster, C.S., Azar, D.T., Dohlman, C.H. (2005). Smolin and Thoft's The Cornea: Scientific Foundations and Clinical Practice. Lippincott Williams & Wilkins.
- [3] American Academy of Ophthalmology. (2020). Corneal and External Eye Disease: Clinical Diagnosis and Management.