Keratitis and Corneal Ulcers - Types, Symptoms, and Treatment

Introduction:

The transparent portion of the eye that covers the pupil, iris and the anterior chamber is known as the cornea. The primary function of this clear dome-shaped structure is to focus light. Other than this, it also helps to protect the internal structures of the eye and provides refractive power to the eye. Keratitis is one of the most common ophthalmologic problems, often associated with additional complications like corneal ulcers.

What Is Keratitis?

Inflammation of the cornea is known as keratitis. Based on etiology, keratitis can be classified into the following categories:

1. Infectious Keratitis - Infections caused by various pathogens are associated with this. These are further divided into several types:

• Bacterial Keratitis - It is the most common type of keratitis. Staphylococcal species, Pseudomonas aeruginosa, and Streptococcus pneumoniae are the most common pathogens in this case. Other than this, pathogens like Mycobacterium, Moraxella species Nocardia and actinomyces are also associated with these conditions. The most common cause of this type of disorder is lens wear. Also, trauma, contamination through foreign substances, and immunocompromised conditions.

• Viral Keratitis - Viral keratitis is caused by herpes simplex virus (HSV), herpes zoster virus (HZV), and adenovirus. Among all these, keratitides caused by herpes simplex and herpes zoster virus are the most common. Recurrent keratitis caused by the remission of these viruses is very common.

• Fungal Keratitis - Fusarium, aspergillus and candida species are causative organisms for fungal keratitis. Poor hygiene, overnight contact lens wear, and immunocompromised conditions are responsible for such situations.

• Parasitic Keratitis - This type of keratitis is caused by Acanthamoeba and this type of infectious keratitis is known as Acanthamoeba keratitis. This type of infection mainly occurs during swimming, walking in forest areas, or soil contamination

2. Non-Infectious Keratitis - The cause of inflation of these cases is noninfectious in origin. The responsible factors are:

• Collagen Vascular Diseases - Peripheral corneal ulcer is the distinctive feature of this keratitis. This is mainly caused by rheumatoid arthritis. Also, diseases like Wegener granulomatosis (a disorder of nose and lungs blood vessels), relapsing polychondritis (an immune disorder characterized by inflammation of cartilages), systemic lupus erythematosus (an immune disorder which affects the skin and joints), and classic polyarteritis nodosa (a disease of blood vessels inflammation) are involved in these conditions.

• Dryness of Cornea - Dryness of cornea or xerophthalmia can be caused by several factors like acute vitamin A deficiency and Sjogren syndrome.

What Are the Symptoms?

Patients suffering from keratitis often complain of:

• Dryness and redness of the eye.

• Pain in the eye.

• Excessive tearing and discharge from the eye.

• Blurred vision.

• Decreased vision.

• Photophobia or sensitivity to the light.

On examination following things are noted in keratitis:

• Conjunctival injection (enlargement of the conjunctival vessels), and focal areas of white infiltration.

• Corneal thinning.

• Stromal edema (presence of fluid within the fibrous layer of the cornea).

• Descemet’s folds or presence of fold in between stroma and endothelial cell layer.

• Hypopyon or presence of white blood cells in the anterior chamber.

• Posterior synechiae oradhesion of anatomical structures like the iris to the cornea due to edema.

• Hyphema or presence of blood in the anterior chamber.

What Is Corneal Ulcer?

Defects in the corneal surface epithelium involving the underlying stroma are known as corneal ulcers.

What Is the Pathophysiology?

The pathophysiology of a corneal ulcer is as follows:

1. Stage of Progressive Infiltration - In this stage, adherence and entry of the organism with the help of pili or fimbriae. In noninfectious conditions presence of autoantibodies can also be detected.

2. Stage of Active Ulceration - In this stage, Necrosis and sloughing of epithelium, basement. Grey infiltration and sloughing can be observed at the margins and floor.

3. Stage of Regression - In this stage, the natural immune response is seen. Infiltration of neutrophils and PMNs (polymorphonuclear leukocytes) is seen.

4. Stage of Cicatrization - The formation of scar tissue can be seen in the place of the necrotic stroma. The appearance of the newly formed blood vessels can also be seen.

The inflammatory process causes the activation of plasminogen to plasmin (types of plasma protein) via proteolytic methods. Protease, chymase, and tryptase (different cellular enzymes) cause epithelial microlesions. Also, endotoxins like 56 kilodaltons released by Serratia species and pneumolysin released by streptococcus pneumonia cause cellular destruction. Gradually the ulcerative process reaches up to the Descemet membrane (basement membrane of corneal endothelium). Due to the high resistance, the descemet membrane bulges out; it results in the formation of the Descemetocele.

Activation of inflammatory pathways causes pro-inflammatory cytokines to accumulate in the infection site. Also, toll‐like receptors (TLRs) (receptors for identification of foreign bodies) present on the surface of the epithelial lead to rapid production of proinflammatory and chemotactic cytokines. Collagenolyitc enzymes released by the PMNs and bacterial endotoxins cause epithelial destruction and thinning. This causes active ulceration and swelling of the walls of the epithelium and bowman’s membrane (the outermost portion of the cornea). Hypopyon formation occurs due to the migration of exudates from the iris and ciliary body to the anterior chamber.

What Are the different ulcers?

Several types of corneal ulcers can also be observed in different keratitis. They are:

• Peripheral Ulcerative Keratitis - This is seen in non-infectious conditions and characterized by crescent-shaped peripheral corneal thinning is seen in these cases. Superficial vascularization and infiltration of inflammatory cells can also be seen.

• Vernal Ulcer - This is very rare and caused by allergens. It is also called a shield ulcer. These ulcers are unilateral and involve only one-third of the cornea.

• Mooren Ulcer - This ulcer is also associated with autoimmune conditions. The fibrovascular membrane replaces the corneal stroma in this type of ulcer.

• Phlyctenular Keratitis - Ulcers in these conditions are also caused by allergic infections to foreign bodies.

• Fungal Ulcer - The distinctive feature of a fungal ulcer is ring-like infiltration. Also, cheesy hypopyon is a classical feature in this case.

How to Treat It?

Infectious conditions can be treated using topical antibiotics (Ciprofloxacin, Levofloxacin), and corticosteroids can be applied. Topical application of Natamycin (5 percent), Amphotericin B (0.15 to 0.30 percent), topical Voriconazole (1 percent), and Miconazole (1 percent) is indicated in fungal infections. Surgical intervention is indicated only in severe cases.

Conclusion:

Keratitis is a common complication of the eye. Various conditions like infections and autoimmune disorders are responsible for this. Corneal ulcers are distinctive features of this condition. Assessment of the types and nature of ulcers is necessary to determine the cause. Also, it helps to diagnose the damage caused by disorders.