Infections of the Eyes, Ears, and Sinuses

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Infections of the Eyes, Ears, and Sinuses

Objectives

1. Describe the anatomy of the eye, including naming the external and internal structures.

2. Name the three tissues, outer to inner, of the eyeball.

3. Differentiate normal flora of the eye and potential pathogens.

4. Describe the defense mechanisms of the eye for the protection from infective agents.

5. Define the following diseases of the eye: blepharitis, conjunctivitis, keratitis, and endophthalmitis.

6. List the common types of eye infections, the associated etiologic agents, and the at-risk patient population for each.

7. Define keratitis, and identify the organisms associated with the infection, the virulence factors, and the antimicrobial-resistant properties for each.

8. Define endophthalmitis, explain how it is contracted, and identify the etiologic agents.

9. Explain mycotic endophthalmitis, and list the risk factors that may predispose an individual to this type of infection.

10. Define a periocular infection, and list some of the associated infectious agents and the different types of clinical presentations of the infection.

11. Identify the anatomic parts of the ear, and list the structures associated with each region within the ear.

12. Define the following external ear infections: acute externa otitis and chronic externa otitis; list the potential pathogens.

13. Define otitis media; differentiate acute and chronic otitis media, and name the most frequently encountered pathogens and the age group most often affected by this disease.

14. Explain the laboratory method used to culture the eye and the ear, including appropriate media; describe collection and transportation requirements.

15. Differentiate acute and chronic sinusitis.

16. Explain why the organisms causing otitis media are often the same ones responsible for sinusitis.

17. List the collection methods and culture media used for cases of sinusitis.

18. Correlate signs and symptoms of infection with the results of laboratory diagnostic procedures for the identification of the etiologic agent associated with infections of the eye, ear, and sinuses.

Eyes

Anatomy

Eye (ocular) infections can be divided based on the area of the eye infected and the exposed or external structures or the internal sites of the eye.

The external structures of the eye—eyelids, conjunctiva, sclera, and cornea—are depicted in Figure 72-1. The eyeball comprises three layers. From the outside in, these tissues are the sclera, choroid, and retina. The sclera is a tough, white, fibrous tissue (i.e., “white” of the eye). The anterior (toward the front) portion of the sclera is the cornea, which is transparent and has no blood vessels. A mucous membrane, called the conjunctiva, lines each eyelid and extends onto the surface of the eye itself.

Only a small portion of the eye is exposed to the environment; about five sixths of the eyeball is enclosed within bony orbits shaped like four-sided pyramids. The large interior space of the eyeball is divided into two sections: the anterior and posterior cavities (see Figure 72-1). The anterior cavity is filled with a clear and watery substance called aqueous humor; the posterior cavity is filled with a soft, gelatin-like substance called vitreous humor.

Infections can occur in the eye’s lacrimal (pertaining to tears) system. The major components of the lacrimal apparatus include the lacrimal gland, lacrimal canaliculi (short channel), and lacrimal sac.

Diseases

The eye and its associated structures are uniquely predisposed to infection by various microorganisms. The major infections of the eye are listed in Table 72-1 along with a brief description of the disease.

TABLE 72-1

Infections of the Eye

Infection Description Bacteria Viruses Fungi Parasites
Blepharitis Inflammation of the margins (edges) of the eyelids; (eyelids, eye lashes or associated pilosebaceous glands or meibomiam glawds) symptoms include irritation, redness, burning sensation, and occasional itching. Condition is typically bilateral Staphylococcus aureus Herpes simplex virus Staphylococcues epidermidrs
Malassezia furfar
Phthirus pulis
Conjunctivitis Inflammation of the conjunctiva; symptoms vary according to the etiologic agent, but most patients have swelling of the conjunctiva, inflammatory exudates, and burning and itching Streptococcus pneumoniae, Haemophilus influenzae, S. aureus, Haemophilus spp., Chlamydia trachomatis, Neisseria gonorrhoeae, Streptococcus pyogenes, Moraxella spp., Corynebacterium spp. Adenoviruses, herpes simplex (HSV), varicella zoster. Epstein-Barr virus (EBV) influeza vius, pararryxovirus, rubella, HIV enterovirus, coxscukie A    
Keratitis Inflammation of the cornea; although there are no specific clinical signs to confirm infection, most patients complain of pain and usually some decrease in vision, with or without discharge from the eye S. aureus S. pneumoniae, Pseudomonas, aeruginosa Moraxella lacunata, Bacillus spp. HSV, adenoviruses, varicella zoster Fusarium solani, Aspergillus spp., Candida spp., Acremonium, Curvularia Acanthamoeba spp.
Keratoconjunctivitis Infection involving both the conjunctiva and cornea; ophthalmia neonatorum is an acute conjunctivitis or keratoconjunctivitis of the newborn caused by either N. gonorrhoeae or C. trachomatis Refer to agents for keratitis/conjunctivitis Refer to agents for keratitis/conjunctivitis Refer to agents for keratitis Toxoplasma gondii, Toxocara
Chorioretinitis and uveitis Inflammation of the retina and underlying choroid or the uvea; infection can result in loss of vision Mycobacterium tuberculosis
Treponema pallidum, Borrelia burgdorferi
Cytomegalovirus, HSV Candida spp. Toxoplasma gondii, Toxocara
Treponema pallidum
Brucella spp.
Endophthalmitis Infection of the aqueous or vitreous humor. This infection is usually caused by bacteria or fungi, is rare, develops suddenly and progresses rapidly, often leading to blindness. Pain, especially while moving the eye, and decreased vision, are prominent features. S. aureus, S. epidermidis, S. pneumoniae, other streptococcal spp., P. aeruginosa, other gram-negative organisms, Nocardia spp. HSV
Varicella zoster
Candida spp., Aspergillus spp., Volutella spp., Acremonium spp. Toxocara, Onchocerca volvulus
Lacrimal infections, canaliculitis A rare, chronic inflammation of the lacrimal canals in which the eyelid swells and there is a thick, mucopurulent discharge Actinomyces, Propionibacterium propionicum      
Dacryocystis Inflammation of the lacrimal sac that is accompanied by pain, swelling, and tenderness of the soft tissue in the medial canthal region S. pneumoniae, S. aureus, S. pyogenes, Haemophilus influenzae   C. albicans, Aspergillus spp.  
Dacryoadenitis Acute infection of the lacrimal gland; these infections are rare and can be accompanied by pain, redness, and swelling of the upper eyelid, conjunctiva discharge S. pneumoniae, S. aureus, S. pyogenes      

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Pathogenesis

The eye has a number of defense mechanisms. The eyelashes prevent entry of foreign material into the eye. The lids blink 15 to 20 times per minute, during which time secretions of the lacrimal glands and goblet cells wash away bacteria and foreign matter. Lysozyme and immunoglobulin A (IgA) are secreted locally and serve as part of the eye’s natural defense mechanisms. Also, the eyes themselves are enclosed within the bony orbits. The delicate intraocular structures are enveloped in a tough collagenous coat (sclera and cornea). If these barriers are broken by a penetrating injury or ulceration, infection may occur. Infection can also reach the eye via the bloodstream from another site of infection. Finally, because three of the four walls of the orbit are contiguous with the paranasal (facial) sinuses, sinus infections may extend directly to the periocular orbital structures.

Epidemiology and Etiology of Disease

Blepharitis

Blepharitis is a bump that appears on the eyelid that is red, swollen, and resembles a pimple. Most bumps on the eyelid are caused by an inflamed oil gland on the edge of the eyelid commonly referred to as a stye. Bacteria, viruses, and, occasionally, lice can cause blepharitis, an infection of the eyelid surrounding the eye. Although occasionally isolated from surfaces surrounding the healthy eye, Staphylococcus aureus and S. epidermidis are the most common infectious agents associated with blepharitis in developed countries. Symptoms include burning, itching, the sensation of the presence of a foreign body, and crusting of the eyelids.

Viruses can also cause a vesicular (blister-like) eruption of the eyelids. Herpes simplex virus (HSV) produces vesicles on the eyelids that typically crust and heal with scarring within 2 weeks. Unfortunately, once this vesicular stage has resolved, the lesions can be confused with bacterial blepharitis.

Finally, the pubic louse Phthirus pubis has a predilection for eyelash hair. The presence of this organism produces irritation, itch, and swelling of the lid margins (edges).

Conjunctivitis

Bacterial conjunctivitis, commonly referred to as “pink eye,” is the most common type of ocular infection and may be caused by allergies or bacterial or viral infection. The principal causes of acute conjunctivitis in the normal host are listed in Table 72-1. Age-related factors are key in the identification of the etiologic agent. In neonates, neisserial and chlamydial infections are frequent and are acquired during passage through an infected vaginal canal. With the common practice of instilling antibiotic drops into the eyes of newborns in the United States, the incidence of gonococcal and chlamydial conjunctivitis has dropped dramatically. However, Chlamydia trachomatis remains responsible for one of the most important types of conjunctivitis, trachoma, one of the leading causes of blindness in the world, primarily in underdeveloped countries.

In children the most common causes of bacterial conjunctivitis includes Haemophilus influenzae, S. pneumoniae, and perhaps S. aureus. S. pneumoniae and H. aegyptius have been isolated from conjunctivitis epidemics. Inflammation of the conjunctiva is characterized by redness, itching, and discharge, and the condition is highly contagious; it can be transferred from one eye to the other by rubbing the infected eye and can easily be transferred to other individuals.

Numerous other bacteria may also cause conjunctivitis. For example, diphtheritic conjunctivitis may occur in conjunction with diphtheria elsewhere in the body. Moraxella lacunata produces a localized conjunctivitis with little discharge from the eye. Distinctive clinical pictures may also occur with conjunctivitis caused by Mycobacterium tuberculosis, Francisella tularensis, Treponema pallidum, and Yersinia enterocolitica.

Fungi may be responsible for this type of infection as well, often in association with a foreign body that has been introduced into the eye or an underlying host immunologic problem. However, these infections are infrequently encountered.

In adults, the etiology of conjunctivitis is usually viral, with adenovirus being the most common viral cause; 20% of such infections in children resulted from adenoviruses in one large U.S. study and 14% of infections in adult patients in another study. Adenoviruses types 4, 3, and 7A are common. Most viral conjunctivitis is self-limited but is highly contagious, with the potential to cause major outbreaks. Worldwide, enterovirus 70 and Coxsackie virus A24 are responsible for outbreaks and epidemics of acute hemorrhagic conjunctivitis.

Keratitis

Keratitis (corneal infection) may be caused by a variety of infectious agents, usually following some type of trauma to the ocular surface. Keratitis should be regarded as an emergency, because corneal perforation and loss of the eye can occur within 24 hours when organisms such as Pseudomonas aeruginosa, Staphylococcus aureus, or HSV are involved. Bacteria account for 65% to 90% of corneal infections.

In the United States, S. aureus, S. pneumoniae, and P. aeruginosa account for more than 80% of all bacterial corneal ulcers. Many culture-positive cases are now being recognized as polymicrobial. A toxic factor known as exopeptidase has been implicated in the pathogenesis of corneal ulcer produced by S. pneumoniae. With P. aeruginosa, proteolytic enzymes (Neisseria gonorrhoeae) are responsible for the corneal destruction. Gonococcus may cause keratitis in the course of inadequately treated conjunctivitis. Acinetobacter, which may look identical microscopically to gonococcus and is resistant to penicillin and many other antimicrobial agents, can cause corneal perforation. Many other bacteria, several viruses other than HSV, and many fungi may cause keratitis. Fungal keratitis is usually a complication of trauma.

Although still unusual, a previously rare etiologic agent of corneal infections has become more common in users of soft and extended-wear contact lenses. Acanthamoeba spp., free living amebae, can survive in improperly sterilized cleaning fluids and be introduced into the eye with the contact lens. The fungus, Fusarium, is emerging as an infectious disease associated with contact lens use or contact lens solutions. This genus of fungus is ubiquitous and can be found in soil and tap water and on many plants; fungal keratitis is rare but usually associated with trauma to the eye from an object contaminated with plant matter. This infection can be serious and can lead to the loss of vision. Other bacterial and fungal causes of infections have also been traced to inadequate cleaning of lenses.

Endophthalmitis

Surgical trauma, nonsurgical trauma (infrequently), and hematogenous spread from distant sites of infection are the typical routes of transmission for endophthalmitis. The infection may be limited to specific tissues within the eye or may involve all of the intraocular contents. Bacteria are the most common infectious agents responsible for endophthalmitis.

After surgery or trauma, evidence of the disease is usually identified within 24 to 48 hours. Postoperative infection involves primarily normal flora bacteria from the ocular surface. Although Staphylococcus epidermidis and S. aureus are responsible for the majority of cases of endophthalmitis following cataract removal, any bacterium, including those considered to be saprophytic, may cause endophthalmitis. In hematogenous endophthalmitis, a septic focus elsewhere is usually evident before onset of the intraocular infection. Bacillus cereus has caused endophthalmitis in people addicted to narcotics and following transfusion with contaminated blood. Endophthalmitis associated with meningitis may involve various organisms, including Haemophilus influenzae, streptococci, and Neisseria meningitidis. Nocardia endophthalmitis may follow pulmonary infection with this organism.

Mycotic infection of the eye has increased significantly since the 1980s because of the increased use of antibiotics, corticosteroids, antineoplastic chemotherapy, addictive drugs, and hyperalimentation (overeating). Fungi generally considered to be saprophytic are important causes of postoperative endophthalmitis (see Table 72-1

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