Infections of the Eye PDF

## Infections of the Eyes ### Learning Objectives At the end of this chapter, the student should be able to: 1. Recognize manifestations of common eye infections. 2. Characterize the common pathogens causing infections of the eyes. 3. Discuss the appropriate laboratory diagnosis and treatment...

## Infections of the Eyes ### Learning Objectives At the end of this chapter, the student should be able to: 1. Recognize manifestations of common eye infections. 2. Characterize the common pathogens causing infections of the eyes. 3. Discuss the appropriate laboratory diagnosis and treatment of each infection. 4. Propose measures to prevent the development of eye infections. Infections involving the eyes may be in the form of: 1. Conjunctivitis, inflammation or infection involving the conjunctiva. 2. Keratitis, inflammation or infection involving the cornea. 3. Keratoconjunctivitis, inflammation or infection involving both the conjunctiva and the cornea. Eye infections may be caused by bacteria or viruses. ### Bacterial Infections #### Bacterial Conjunctivitis Bacterial conjunctivitis is also known as pink eye conjunctivitis and is highly contagious. The infection can be transmitted through: 1. Human-to-human transmission via contact with eye and respiratory discharges. 2. Contaminated fingers. 3. Fomites such as clothing, facial tissues, eye makeup, eye medications, and ophthalmic instruments. Manifestations of the infection include: 1. Eye irritation. 2. Reddening of the conjunctiva. 3. Swelling of the eyelids. 4. Mucopurulent discharge. 5. Sensitivity to light (photophobia). #### Etiologic Agents ##### Haemophilus influenzae biogroup aegypticus *H. influenzae biogroup aegypticus* (Koch-Weeks bacillus) is a gram-negative rod or *H. nullus*. It is associated with epidemics of acute, purulent conjunctivitis. The commonly recognized mechanism of transmission is via direct contact, such as touch or coccococcal attachment. Mechanical transmission through gnats has also been suspected as a mode of transmission. ##### Streptococcus pneumoniae *S. pneumoniae* are gram-positive diplococci, arranged in pairs of short chains and encapsulated. One side of the bacteria is slightly pointed, giving a *"Lancet- shape"* appearance. The virulence can be attributed to adhesins on its surface, capsule, pneumolysin toxin, and IgA protease. ##### Staphylococcus aureus and Pseudomonas aeruginosa For the discussions about *S. aureus* and *P. aeruginosa*, refer to chapter 16. ##### Chlamydia trachomatis *C. trachomatis* resembles gram-negative bacteria; however, it does not have peptidoglycan in its outer wall. The cell membrane has very high lipid content. *C. trachomatis* do not have the components to produce its own energy or ATP and are dependent on the host hence they are classified as obligate intracellular parasites or energy parasites. *C. trachomatis* have round vacuolar inclusions filled with glycogen and are susceptible to sulfonamides. It is associated with three types of eye infections - conjunctivitis, inclusion conjunctivitis, and trachoma. Conjunctivitis caused by *C. trachomatis* is usually acquired through swimming in non-chlorinated or poorly chlorinated swimming pool waters, hence, it is sometimes referred to as "swimming pool conjunctivitis." In adults, it may be a result of the transfer of the organisms from the genitals to the eyes and often occur concurrently with non-gonococcal urethritis or cervicitis. It manifests as mucopurulent eye discharge and occurs concurrently with chlamydial nasopharyngitis or pneumonia. ### Viral Infections Eye infections due to viruses may also take the form of conjunctivitis, keratitis, or keratoconjunctivitis. The infection is highly contagious and can spread through airborne means such as sneezing and coughing. The infection is self-limited. Clinically, viral conjunctivitis differs from bacterial conjunctivitis in that there is no purulent eye discharge. #### Etiology ##### Adenoviruses Adenoviruses are double-stranded DNA viruses. A unique characteristic of adenoviruses is that a penton base that projects from each penton base acts as hemagglutinin and have affinity to mucous epithelium that the virus binds to initiate infection. Adenoviruses are latent in the adenoids and tonsilar tissues and caused by *hemagglutinin*. Adenoviruses are resistant to mild chlorination. Eye infections caused by adenoviruses can range from mild to severe infections. The mild eye infection is called "swimming pool" conjunctivitis because the source of infection can be traced to poorly chlorinated swimming pool waters or ponds. It is most commonly caused by serotypes 3 and 7. Sometimes the conjunctivitis is accompanied by pharyngitis, hence called pharyngoconjunctival fever. A more severe eye infection caused by adenoviruses is epidemic keratoconjunctivitis. Adenovirus types 8, 19, and 23 are the most common causes of epidemic keratoconjunctivitis. This infection is more common in adults and considered an occupational hazard following exposure to dusts and other eye irritants. It may present as acute conjunctivitis, keratitis, and later leave residual sub-epithelial opacities in the cornea. ##### Enterovirus 70 and Coxsackie A24 virus Enterovirus 70 and Coxsackie A24 virus cause acute hemorrhagic conjunctivitis, a highly contagious eye infection. The infection is characterized by conjunctival congestion, vascular dilatation, and onset of edema. There is no available treatment. Management is purely symptomatic unless a secondary bacterial infection occurs, which will necessitate antimicrobial and steroid treatment. Most of the time, the infection resolves spontaneously. ##### Herpes simplex virus Herpes simplex virus type 1 causes severe keratoconjunctivitis and recurrences are common, which may present as dendritic keratitis and corneal ulcers which may lead to blindness. HSV type 1 is the second leading cause of blindness in the United States. ##### Measles virus Conjunctivitis is only one of the classical manifestations of rubeola observed in children. It is also associated with photophobia or sensitivity to light.