Understanding Corneal Inflammation

Corneal Inflammation: Understanding Keratitis and Its Implications

Keratitis, a term derived from the Greek word “keras,” meaning horn (referring to the cornea), denotes the inflammation of the cornea, a critical component of the eye responsible for light refraction and protection against external elements. This condition can be acute or chronic and can arise from various etiologies, including infectious agents, environmental factors, autoimmune responses, or injury. Given its central role in vision, understanding the pathophysiology, symptoms, causes, diagnosis, and treatment of keratitis is essential for preserving eye health.

Anatomy and Function of the Cornea

The cornea is a transparent, dome-shaped structure that forms the front part of the eye. It consists of five layers:

1. Epithelium: The outermost layer, which serves as a barrier to protect against pathogens and environmental damage.
2. Bowman’s Layer: A thin layer of collagen that adds strength to the cornea.
3. Stroma: The thickest layer, composed of collagen fibers and keratocytes, which provides the cornea with its shape and strength.
4. Descemet’s Membrane: A thin, elastic layer that acts as a barrier against infection and regulates the cornea’s hydration.
5. Endothelium: The innermost layer responsible for maintaining corneal clarity through fluid regulation.

The cornea’s unique structure enables it to refract light efficiently, contributing to the eye’s focusing power. Additionally, the cornea is avascular (lacking blood vessels), which helps maintain its transparency, and relies on the tear film and aqueous humor for nourishment.

Types of Keratitis

Keratitis can be classified based on its cause:

1. Infectious Keratitis:

   • Bacterial Keratitis: Often caused by contact lens wear, trauma, or pre-existing ocular surface disease. Common pathogens include Pseudomonas aeruginosa and Staphylococcus aureus.
   • Viral Keratitis: Primarily caused by the herpes simplex virus (HSV), leading to epithelial keratitis or stromal keratitis, both of which can cause significant visual impairment.
   • Fungal Keratitis: Frequently associated with agricultural injuries or contact lens use in tropical climates. Common pathogens include Fusarium and Aspergillus species.
   • Acanthamoeba Keratitis: A rare but severe form often associated with contact lens wear, particularly in non-sterile water exposure.

2. Non-Infectious Keratitis:

   • Allergic Keratitis: Resulting from allergic reactions to environmental allergens, leading to inflammation.
   • Autoimmune Keratitis: Conditions such as rheumatoid arthritis and Sjögren’s syndrome can cause keratitis due to systemic inflammatory responses.

3. Environmental Keratitis:

   • Caused by environmental factors such as ultraviolet (UV) exposure, chemicals, or mechanical injuries, leading to inflammation and damage to the corneal surface.

Symptoms of Keratitis

Patients suffering from keratitis may experience a range of symptoms, including:

• Eye Pain: Often described as a sharp or burning sensation, pain can vary from mild to severe.
• Redness: The eye may appear red due to inflammation and increased vascularity.
• Blurred Vision: Depending on the severity and type of keratitis, visual acuity may be compromised.
• Sensitivity to Light (Photophobia): Increased sensitivity to light can be a debilitating symptom.
• Tearing: Excessive tearing or discharge from the eye may occur, depending on the etiology.
• Foreign Body Sensation: Patients often report a feeling of something being stuck in the eye.

Diagnosis of Keratitis

The diagnosis of keratitis typically involves a comprehensive eye examination conducted by an ophthalmologist. Diagnostic steps may include:

1. Patient History: A thorough history of symptoms, contact lens usage, environmental exposures, and any recent eye injuries.
2. Visual Acuity Test: To assess the impact of keratitis on vision.
3. Slit-Lamp Examination: A specialized microscope that allows the ophthalmologist to evaluate the cornea’s surface and underlying layers for signs of inflammation, scarring, or infection.
4. Corneal Cultures: In cases of suspected infectious keratitis, cultures may be taken to identify the causative organism and guide treatment.
5. Fluorescein Staining: A dye is applied to the surface of the eye to highlight areas of damage or inflammation, revealing corneal ulcers or epithelial defects.

Treatment of Keratitis

The treatment approach for keratitis depends on its underlying cause:

1. Infectious Keratitis:

   • Bacterial: Topical antibiotics are the mainstay of treatment. In severe cases, fortified antibiotics may be necessary, and hospitalization may be warranted for close monitoring.
   • Viral: Antiviral medications such as acyclovir or topical ganciclovir are used to treat herpes simplex keratitis. In cases of recurrent infections, prophylactic antiviral therapy may be considered.
   • Fungal: Antifungal agents (topical and systemic) are administered for fungal keratitis, but treatment can be prolonged and challenging.
   • Acanthamoeba: Intensive topical antiseptic drops and sometimes systemic medications are used. In severe cases, corneal transplantation may be necessary.

2. Non-Infectious Keratitis:

   • Allergic: Management includes topical antihistamines or corticosteroids to reduce inflammation.
   • Autoimmune: Systemic treatments targeting the underlying autoimmune condition may be indicated.

3. Environmental Keratitis:

   • Treatment typically involves supportive care, including lubricating drops, topical steroids for inflammation, and protective measures against further exposure.

Prevention of Keratitis

Preventing keratitis largely hinges on appropriate eye care practices:

• Contact Lens Hygiene: Proper cleaning, storage, and wearing schedules are crucial to minimize the risk of infectious keratitis.
• UV Protection: Wearing sunglasses with UV protection can help prevent environmental keratitis from sun exposure.
• Avoiding Eye Trauma: Protective eyewear during hazardous activities can reduce the risk of mechanical injury to the cornea.
• Managing Allergies: Identifying and avoiding allergens can help reduce the incidence of allergic keratitis.

Complications of Keratitis

If left untreated, keratitis can lead to severe complications, including:

• Corneal Scarring: Scarring can result in permanent vision loss and may necessitate corneal transplantation.
• Perforation of the Cornea: Severe inflammation and ulceration can lead to corneal perforation, a sight-threatening condition requiring immediate surgical intervention.
• Chronic Pain: Persistent symptoms can significantly affect the quality of life.
• Vision Loss: Depending on the severity and treatment response, vision impairment or loss can occur.

Conclusion

Keratitis is a significant ocular condition that can have far-reaching implications for visual health. Early recognition and appropriate management are crucial to prevent complications and preserve vision. Public awareness of the causes, symptoms, and preventive measures can help reduce the incidence of this potentially debilitating condition. Continued research into the mechanisms underlying keratitis, as well as advancements in diagnostic and therapeutic options, remains essential for enhancing patient outcomes and eye care practices. By fostering a proactive approach to eye health, we can mitigate the impact of keratitis on individuals and communities alike.

References

1. D. K. P. A. (2022). Infectious keratitis: Clinical manifestations, diagnosis, and management. American Journal of Ophthalmology, 222, 1-14.
2. L. A. F. (2021). Non-infectious keratitis: A review of the literature. Ophthalmology and Therapy, 10(2), 293-312.
3. S. P. H. (2023). Advances in the management of viral keratitis. Eye, 37(7), 1049-1060.
4. W. B. W. (2020). Environmental factors in keratitis: A systematic review. Cornea, 39(8), 1046-1054.