Infections of the eye                                              Reading: pg. 343 – 346

• Introduction
• Conjunctivitis (fig. 25.1, pg. 343)
  • Clamydia trachomatis
  • Other infections
  • Contact lenses
  • Systemic sources
• Deep layers of the eye (fig. 25.6, pg. 345)
  • Toxoplasmosis
  • Parasitic worms
    • Toxocara canis
    • Onchocerca volvulus

Infection of the eye

Introduction

• Eye

  n   protected by the eyelids and tears

  n   infections of the conjunctiva (S. aureus)

• Other routes of infection:

n   blood or nervous system

n   deep tissues of the eye by protozoans and worms.

Conjunctivitis

n    Pinkeye

n    Fig. 25.1 Caused by a variety of viruses and bacteria

Chlamydial infections

n    Chlamydia trachomatis

n   Have specific mechanisms of attachment to conjunctival cells

n   Diseases:

n   Inclusion conjunctivitis

§    Transmitted to a newborn's eyes during passage through birth canal

§    Spread through swimming pool water

n   Trachoma

§    Leading cause of blindness worldwide

§     scarring of cornea leading to blindness

§    Transmitted by contact – contaminated flies, fingers, and towels

n   Can infect urogenital tract

Trachoma

n    Chronic infection of the eyelids

n    Diagnosis:

n   Looking at conjunctival fluids or scrapings

n    Treatment:

n   Topical or oral antibiotics

n   No vaccine – immunopathology is a major contribution to disease

n    Prevention:

n   Improvement in hygiene standards (face-washing) – since most cases are due to overcrowding, shortage of water, and abundant fly populations

Other conjunctival infections

n   Other bacteria that can cause conjunctivitis

n   S. pneumoniae

n   H. influenzae

n   S. aureus – from newborn’s body or from infected adult

n   N. gonorrhoeae – in newborn due to birth through infected birth canal (requires immediate antibiotic treatment)

Contact lenses

n   May contribute to eye infections by

n   Reducing effectiveness of eye’s defensive mechanisms

n   Contaminated eye drops, cleaning solutions, or contact lenses

n   Acanthamoeba – grow in lens cleaning solution à infected lens into eye à causing damage to cornea

Systemic sources

n   Organisms may invade eye by way of blood or nervous system

n   HSV moves to eye along trigeminal nerve

n   development of keratitis with formation of dendritic ulcers à corneal damage

Infection of deeper layers of the eye

n   Involves a wider spectrum of organisms

n   Enter by many routes

n   P. aeruginosa – opportunitic pathogen introduced by trauma to eye or eye drops

n   Rubella and CMV – invade fetal eye in utero causing cataracts and microphthalmia, and chorioretinitis (also in AIDS patients)

n   Syphilis

n   Reinopathy and keratinitis

n   Secondary syphilis – causes ocular inflammation

Toxoplasmosis

n   Causes chorioretinitis leading to blindness

n   Transmitted by ingestion or inhaling of oocytes of T. gondii from infected cat feces

n   Serious when acquired by pregnant women – invades all tissues especially CNS

n   May be reactivated when immunosuppressed.

Parasitic worms

n    Toxocara canis

n    Natural inhabitant of intestines of dogs

n    Eggs released in dog droppings

n    When swallowed by humans will migrate to eyes and CNS triggering an inflammatory response à detachment of retina

n   Retinoblastoma

n    Onchocerca volvulus

n    Causes river blindness

n    Transmitted by biting Similium flies infected with larvae from skin of infected hosts

• Larvae migrates to eye causing an inflammatory response leading to the disease