Conjunctivitis pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [5] Associate Editor(s)-in-Chief: Sara Mehrsefat, M.D. [6]

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Overview

Conjunctivitis is defined as inflammation of bulbar and/or palpebral conjunctiva. Conjunctivitis has many etiologies, but majority of cases can be caused by allergies, viruses, or bacteria. Viral conjunctivitis, typically caused by Adenovirus, is a common, self-limiting condition. Bacterial conjunctivitis has many etiologies, the most common include: Staphylococcus, Streptococcus, Corynebacterium, Haemophilus, Pseudomonas, and Moraxella species. Allergic conjunctivitis may occur seasonally when pollen counts are high, and this type of conjunctivitis is a common occurrence in people who have other signs of allergic disease.

Pathophysiology

Infective conjunctivitis is an infection of the conjunctiva either cause by viruses, or bacteria . Both the palpebral and the bulbar ocular conjunctival surfaces are usually affected and typically become red, and inflamed. Bacterial, and viral conjunctivitis is spread from:

• Direct contact with the infected person’s eye drainage or drainage from the person’s cough, sneeze, or runny nose
• Contact with the infected person’s fingers, hands or objects (eye makeup applicators, towels, shared eye medications) that may have the infected person’s drainage on them
• Adjacent infectious sites (rubbing of the eyes)

Any change in the host defense, or in the species of normal flora of the eye (such as Streptococci, Staphylococci, and Corynebacteria) can lead to clinical infection and conjunctivitis. Change in the normal flora can occurred by:

• External contamination
• Contact lens wear
• Swimming

Viral conjunctivitis that is typically caused by adenovirus is a common, self-limiting condition. Viral conjunctivitis is highly contagious, and patients should avoid direct or indirect contact with other healthy individuals. Acute hemorrhagic conjunctivitis can caused by Picornaviruses that is clinically similar to adenovirus conjunctivitis but is more severe and hemorrhagic. It is also occurs in epidemics and characterized by sudden onset of painful, and swollen red eyes, with conjunctival hemorrhaging, and excessive tearing.

Neonatal conjunctivitis is often known as ophthalmia neonatorum. Newborns can be infected by bacteria in the birth canal. It is a disease characterized by conjunctivitis occurring in a newborn during the first month of life with clinical signs such as: erythema, and edema of the eyelids, the palpebral conjunctivae, purulent eye discharge with one or more polymorph nuclear per oil immersion field on a Gram stained conjunctival smear. Additionally, neonatal conjunctivitis is a pink eye in a newborn caused by irritation (Chemical Conjunctivitis) , a blocked tear duct, or infection.

Airborne antigens may be involved in the pathogenesis of allergic conjunctivitis. Common airborne antigens, include:

• Pollen
• Grass
• Weeds

Development of allergic conjunctivitis is result of type I hypersensitivity reactions involving the conjunctiva.

• IgE and Mast cell play an important role in these allergic inflammations.
• There is a strong association with atopic dermatitis and allergic conjunctivitis.

Combination of type I and type IV hypersensitivity reactions may be responsible in giant papillary conjunctivitis. Also prolonged mechanical irritation to the superior tarsal conjunctiva, of the upper lid, from any of a variety of foreign bodies may also be a contributing factor in giant papillary conjunctivitis.

Keratoconjunctivitis sicca or dry eye syndrome is multifactorial disease and associated with different medical conditions such as:

• Sjögren's syndrome
• Ocular surface disease
• Ocular allergy
• Dysfunction of the lacrimal gland with reduced tear production and Mucin deficiency

Keratoconjunctivitis sicca-associated Sjögren's syndrome may be is the result of an auto immunological sequelae which can lead to chronic inflammatory state with production of autoantibodies, such as: antinuclear antibody (ANA), rheumatoid factor (RF), fodrin (a cytoskeletal protein), the muscarinic M3 receptor, or Sjögren's syndrome-specific antibodies (anti-RO and anti-LA. Focal CD4+ T cells and B cells infiltration of the lacrimal gland can induce apoptosis in the conjunctiva and lacrimal glands and this results in dysfunction of the lacrimal gland with reduced tear production.

Superior limbic keratoconjunctivitis (SLK) is a disease characterised by inflammation of the upper palpebral and superior bulbar conjunctiva, keratinization of the superior limbus and corneal and conjunctival filaments. The exact pathogenesis of Superior limbic keratoconjunctivitis is not fully understood, however association between thyroid abnormalities (Graves ophthalmopathy) and Superior limbic keratoconjunctivitis has been reported.

Microscopic histopathological analysis

On microscopic histopathological analysis, the following are characteristic findings of conjunctivitis:

• Mild spongiotic reaction pattern (low power view of the histology)
• Eosinophils (Allergic conjunctivitis)
• Numerous neutrophils (Bacterial conjunctivitis)
• Hyperplastic with increase numbers of plasma cell (Chronic conjunctivitis)

Gross Pathology

On gross pathology, the following are characteristic findings of conjunctivitis:

• Conjunctival injection
• Mucopurulent or non-purulent discharge
• Pseudomembrane formation
• Chemosis
• Eyelid swelling
• Conjunctival hemorrhage (specific for Acute conjunctival hemorrhaging)

Images

The following are gross and microscopic images associated with conjunctivitis.

Viral conjunctivitis

Acute hemorrhagic conjunctivitis

Neonatal conjunctivitis

Chlamydial conjunctivitis (Day 5-14)

References

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