Keratitis is an inflammation of the cornea. The cornea is the transparent tissue at the front and center of your eye. It is an essential barrier against dirt, microbes, and other particles that can harm the eye. The cornea’s curvature also focuses light through the pupil and lens and onto the retina at the back of the eye.
Corneal disorders
The term “corneal disorder” refers to a variety of conditions that mainly affect the cornea. These include infections and many other diseases that may arise as a result of heredity.
Corneal diseases due to infectious causes need immediate attention because visual disability can be preventable if treatment started on time. These corneal diseases caused by infections include corneal ulcer, microbial keratitis, herpes zoster ophthalmicus, peripheral ulcerative keratitis, and phlyctenular keratoconjunctivitis.
Corneal Ulcer
A corneal ulcer is a defect in the epithelial (corneal outer layer,) which may have traumatic, mechanical, infective, or neurotrophic (growth of nervous tissue) causes. Direct trauma to the cornea leads to corneal abrasions, leaving an apparent defect of the cornea’s outer layer. Such defects can also be caused by burns, which may be thermal, chemical, or radiation, known as corneal burns.
Mechanical causes of corneal ulcers are:
- Drying out and shedding of the outer layer of the cornea due to eyes not closing completely during sleep
- Eyelid defects
- Lower eyelid sagging away from the eye
- Chronic allergic eye disease such as vernal keratoconjunctivitis
Neurotrophic corneal ulcers develop in the case of the cornea losing sensitivity due to nerve damage. It is a painless ulcer with a depressed corneal sensation. Management involves promoting epithelial healing, prevention of infection, and pain relief.
Patching of the affected eye helps in epithelial healing and pain relief. Topical antibiotics are prescribed for preventing possible superimposed infections. Adequate tear supplementation is warranted in the case of mechanical causes of corneal ulcers. Infective corneal ulcers are known as microbial keratitis.
Microbial Keratitis
Microbial keratitis is an ophthalmic emergency that involves a loss of integrity of the cornea’s outermost layer. It is a severe bacterial infection of the cornea, which can, in severe cases, cause loss of vision. Microbial keratitis may be caused by bacteria, fungi, viruses, or parasites.
Predisposing risk factors for microbial keratitis are ocular trauma, contact lens use, topical steroid use, chronic ocular surface disease, eyelid abnormalities, previous ocular surgery, and diabetes. It is a potentially vision-threatening condition that requires early diagnosis and management to prevent serious outcomes.
The typical sign and symptoms are pain, redness, photophobia, blurring of vision, watering, or discharge from the eye. Presumed microbial keratitis is mainly investigated with microscopy and culture of corneal scrapings from the infiltrated area. Smears, culture, and antimicrobial drug susceptibility are the most common and fundamental tools for the laboratory diagnosis of microbial keratitis.
Herpes Zoster Ophthalmicus
Herpes Zoster Ophthalmicus (HZO) is caused by the reactivation of the varicella-zoster virus (shingles,) which is present as a painful dermatomal rash on the skin and mucosa. It also affects the ophthalmic part of the trigeminal nerve (a cranial nerve responsible for sensation in the face) and subsequent eye. HZO often includes severe chronic pain and vision loss; that’s why it is considered an ophthalmologic emergency. Primarily, diagnosis is based on history and findings of the skin.
Varicella is caused by human herpesvirus type 3 in childhood. After primary infection, the virus remains dormant in cell bodies of sensory neurons. After years it may be reactivated, resulting in shingles.
According to the Center for Disease Control and Prevention (CDC), annually, there are an estimated 1 million cases of herpes zoster in the US, and approximately 1 in 3 people have developed shingles during their lifetime. Up to 4% of patients presenting with HZO require hospitalization to manage complications and decrease long-term morbidity.
Peripheral Ulcerative Keratitis (PUK)
PUK includes infectious and inflammatory conditions that usually result in peripheral corneal thinning. It is associated with an epithelial defect and progressive loss of the corneal stroma (the thickest layer of the cornea.) Inflammatory causes are associated with autoimmune connective tissue diseases.
Local autoimmune syndromes, e.g., Mooren’s ulcers, are also a possibility. Blepharitis (inflammation of the eyelids) can cause such conditions (marginal keratitis). Intensive immunosuppression and adequate management of the blepharitis is important in these cases.
In addition to autoimmune disorders, microbial organisms such as bacteria, fungi, viruses, and chlamydia can cause PUK. The exact pathophysiologic mechanism of PUK is yet unclear.
The main symptoms are pain, redness, tearing, photophobia, and decreased vision secondary to corneal opacity in advanced cases. Treatment of underlying systemic autoimmune disease has beneficial effects on ocular manifestations, mainly a systemic corticosteroid plus a cytotoxic agent (according to the underlying systemic disease) during the acute phase of the disease.
Phlyctenular Keratoconjunctivitis
It is a nodular inflammation of conjunctiva or cornea that results from an allergic reaction to a foreign antigen, which represents a cell-mediated hypersensitivity response. Due to the high prevalence of tuberculosis in the last century, as a consequence of a hypersensitivity reaction to tuberculin protein, this disease occurred predominantly in children with positive tuberculin skin tests.
It occurs primarily in pediatrics from 6 months to 16 years of age group. Microbial proteins of Staphylococcus aureus are the most common causative antigens of phlyctenular keratoconjunctivitis in developed countries like the United States. In a study, 80.4% of patients had a mean age of 10.2 years with female preponderance.
Antigens of Mycobacterium tuberculosis and Staphylococcus aureus are most commonly associated; however, Streptococcus viridians, chlamydia, and intestinal parasites, including Hymenolepis nana, have also been reported as causative agents. Conjunctival lesions may cause mild to moderate irritation in the eye, while corneal lesions are presented with severe pain and photophobia.
The diagnosis is based on history and clinical examination findings. Further investigation is required when the possibility of chlamydia or tuberculosis is suspected. Chest radiographs, tuberculin skin tests should be done for patients with a history or symptoms of tuberculosis infection.
For patients suspected of chlamydia infection, immunofluorescent antibody test, and PCR of conjunctival swabs provide accurate and quick screening. The first line of treatment is to decrease the inflammatory response, which generally responds to topical steroids.
Conclusions
Corneal disorders have been described for a long time. However, even today, despite the availability of advanced diagnostic techniques and a wide range of antimicrobials, they still pose a diagnostic and therapeutic challenge.
These disorders are a public health problem not only in developing countries but also in developed nations. Corneal diseases are the major contributing factor in vision loss in all age groups of patients.
So, there is a need for knowledge and awareness about these diseases for early detection and prompt administration of correct treatment to prevent fatal ocular consequences.
