Eye infection: types, causative agents, clinical symptoms and diagnosis




Eye infection: types, causative agents, clinical symptoms and diagnosis
Eye infection: types, causative agents, clinical symptoms and diagnosis

 Eye Infection

  • Different infectious agents may get entrance to the eye either through the external or endogenous source.
  • Superficial structures like the conjunctiva and the cornea are affected during external infections.
  • Microorganisms present in the blood (e.g., endocarditis )may cause infection endogenously
  • Endogeneous infection may be caused by the reactivation of latent viruses or parasites (e.g., cytomegalovirus or toxoplasmosis).

Different types of eye infections

1. Blepharitis:

  • It is the inflammation of the margins(edges) of the eyelids; (eyelids, eye lashes, or associated pilosebaceous glands or meibomian glands).
  • Symptoms include irritation, redness, burning sensation, and occasional itching. Condition is typically bilateral.
  • Causative agents:
    • Bacteria: Staphylococcus aureus
    • Virus: Herpes simplex virus
    • Fungi; Malassezia furfur
    • Parasites: Phthirus pulis

2. Conjunctivitis:

  • Inflammation (conjunctivitis) produces redness (pink eye), itching, and a discharge, which may be mucous or purulent.
  • In this case, eyelids may stick together because of the exudation in bacterial infections which are thick, sticky, and encrusted.
  • In patients having seasonal allergies, acute noninfectious inflammation may also occur.
  • Conjunctivitis is highly contagious and can be transferred easily to the other eye or other individuals by contact (e.g., rubbing the infected eye and then the normal eye).
  • Causative agents:
  • Bacteria
    • Streptococcus pneumoniae
    • Haemophilus influenzae
    • Staphylococcus aureus
    • Haemophilus spp.
    • Pseudomonas aeruginosa
    • Chlamydia trachomatis
    • Neisseria gonorrhoeae
    • Streptococcus pyogenes
    • Moraxella spp.
    • Corynebacterium spp.
  • Viruses
    • Adenoviruses
    • Herpes simplex (HSV)
    • Varicella-zoster
    • Epstein-Barr virus (EBV)
    • Influenza virus
    • Paramyxovirus
    • Rubella
    • HIV
    • Enterovirus
    • Coxsackie A

3.Keratitis:

  • Keratitis, inflammation of the cornea, is a much more serious infection than conjunctivitis.
  • Although there are no specific clinical signs to confirm infection, most patients complain of pain.
  • Usually decrease in vision may occur, with or without discharge from the eye.
  • Keratitis can result in scarring and blindness.
  • Causative agents:
  • Bacteria
    • S. aureus
    • S. pneumoniae,
    • Pseudomonas, aeruginosa
    • Moraxella lacunata
    • Bacillus spp.
  • Virus
    • Herpes Simplex Virus
    • adenoviruses,
    • varicella-zoster
  • Fungi
    • Fusarium solani,
    • Aspergillus spp.
    • Candida spp.
    • Acremonium,
    • Curvularia
  • Parasites
    • Acanthamoeba spp
  • A different non-infectious injury like trauma and ultraviolet radiation can cause keratitis.

4. Keratoconjunctivitis:

  • It is an infection that involves both the conjunctiva and cornea.
  • Ophthalmia neonatorum is acute conjunctivitis or keratoconjunctivitis of the newborn which is caused by either gonorrhoeae or C. trachomatis.
  • Causative agents:
  • Bacteria
  • It includes the agents for keratitis/ conjunctivitis.
    • Streptococcus pneumoniae,
    • Haemophilus influenzae,
    • Staphylococcus aureus,
    • Haemophilus spp.
    • Pseudomonas aeruginosa
    • Chlamydia trachomatis,
    •  Neisseria gonorrhoeae,
    • Streptococcus pyogenes,
    • Moraxella spp.,
    • Corynebacterium spp.
    • Bacillus spp
  • Virus
    • It includes the agents for keratitis/ conjunctivitis
    • Adenoviruses,
    • Herpes simplex (HSV),
    • Varicella-zoster.
    • Epstein-Barr virus (EBV)
    • Influenza virus,
    • Paramyxovirus,
    • Rubella,
    • HIV
    • Enterovirus,
    • Coxsackie A
  • Fungi
  • It includes the agents for Keratitis
    • Fusarium solani,
    • Aspergillus spp.,
    • Candida spp.,
    • Acremonium,
    • Curvularia
  • Parasites
    • Toxoplasma gondii,
    • Toxocara

5. Chorioretinitis and uveitis:

  • It is the inflammation of the retina and underlying choroid or the uvea.
  • The infection can result in loss of vision.
  • Causatiive agents:
  •  Bacteria:
    • Mycobacterium tuberculosis
    • Treponema pallidum,
    • Borrelia burgdorferi
  • Virus
    • Cytomegalovirus
    • HSV
  • Fungi
    • Candida spp.
  • Parasites
    • Toxoplasma gondii,
    • Toxocara
    • Treponema pallidum

6. Endophthalmitis

  • It is the infection of the aqueous or vitreous humor.
  • This infection is usually caused by bacteria or fungi. It is rare, develops suddenly, and progresses rapidly, often leading to blindness.
  • During the movement of the eye, there is pain. Vision is decreased.
  • Causative agent:
  • Bacteria:
    • S. aureus,
    • S. epidermidis,
    • pneumoniae,
    • Streptococcal spp.
    • P. aeruginosa,
    • Gram-negative organisms,
    • Nocardia spp
  • Virus
    • HSV
    • Varicella zoster
  • Fungi
    • Candida spp.,
    • Aspergillus spp.,
    • Volutella spp.,
    • Acremonium spp
  • Parasite
    • Toxocara
    • Onchocerca volvulus

7. Lacrimal infections, canaliculitis:

  • It is a rare, chronic inflammation of the lacrimal canals in which the eyelid swells and there is a thick, mucopurulent discharge.
  • Causative agent:
  • Bacteria:
    • Actinomyces,
    • Propionibacterium
    • Propionicum

8. Dacryocystis:

  • It is the inflammation of the lacrimal sac that is accompanied by pain, swelling, and tenderness of the soft tissue in the medial canthal region.
  • Causative agents:
  • Bacteria:
    • S. pneumoniae
    • S. aureus,
    • S. pyogenes,
    • Haemophilus influenza
  • Fungi:
    • C. albicans,
    • Aspergillus spp.

9. Dacryoadenitis

  • It is an 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.
  • Causative agents:
  • Bacteria:
  • S. pneumoniae,
  • S. aureus
  • S. pyogenes

Laboratory Diagnosis of eye infection:

Specimen Collection and Transport

  • A sterile swab should be taken for sample collection.
  • From the lower conjunctiva sac and inner canthus (angle) of the eye, purulent material is collected on the sterile swab.
  • Both eyes need to be cultured separately.
  • For the Chlamydial culture, a dry calcium alginate swab should be taken.
  • Then it should be placed in a 2-SP (2-sucrose phosphate) transport medium.
  • If for the detection, Direct Fluorescent antibody (DFA) are to be used, then in such case additional slide also should be prepared.
  • In that slide, the swab should be rolled across its surface which needs to be fixed with methanol.
  • In the case of keratitis, scrapings of the cornea should be taken with a heat-sterilized platinum spatula.
  • Multiple inoculations with the spatula are made to blood agar, chocolate agar, an agar for the isolation of fungi, thioglycollate broth, and an anaerobic blood agar plate.
  • Other special media may be used if indicated.
  • Corneal specimens for the detection of HSV and adenovirus should be cultured. They should be placed in viral transport media.
  • Recently, the collection of two corneal scrapes (one used for Gram stain and the other transported in brain heart infusion medium and used for culture) was determined to provide a simple method for diagnosis of bacterial keratitis.
  • From the anterior and posterior chambers of the eye, wound abscesses, and wound dehiscence (splitting open) specimens are collected for the culture of endophthalmitis.
  • Lid infection material is collected on a swab conventionally.
  • Under anaerobic conditions, transportation of the material should be done from the lacrimal canal in the case of canaliculitis.
  • Aspiration of fluid from the orbit is contraindicated in patients with orbital cellulitis.

Direct Visual Examination:

  • The smear should be prepared and a Gram stain should be performed.
  • If there are other appropriate microscopic techniques, it should be performed.
  • In bacterial conjunctivitis, polymorphonuclear leukocytes predominate; in viral infection, the host cells are primarily lymphocytes and monocytes.
  • For the detection of Chlamydia, elementary body or inclusions should be checked.
  • For this, it should be stained immediately with a monoclonal antibody conjugated to fluorescein.
  • Using histologic stains, basophilic intracytoplasmic inclusion bodies are seen in epithelial cells.
  • To detect herpes group infection in the conjunctivitis specimens, a Tzanck smear can be made. It shows the multinucleated epithelial cells.
  • For the rapid diagnosis of the virus infection, DFA stains available for both HSV and VZV
  • For the keratitis, the examination can be done using:
    • Gram stain
    • Giemsa stain
    • periodic acid-Schiff (PAS)
    • methenamine silver stains.
  • Motile trophozoites should be observed by using the direct wet preparation in case of Acanthamoeba or other amebae and a trichrome stain should be added to the regimen.
  • Culture is the most sensitive detection method for the diagnosis.
  • In the case of endophthalmitis, the specimen needs to be examined by:
    • Gram
    • Giemsa
    • Periodic Acid-schiff (PAS)
    • Methenamine silver stains.
  • Centrifugation should be done if the specimen is fluid and is in large volume.

Culture for eye infection:

  • The number of organisms recovered from culture is low due to the washing action of tears.
  • If the specimen is not purulent, large inoculums in a variety of media should be used to find out the etiological agent.
  • The best result can be obtained when the conjunctival scrapings are placed directly onto the media.
  • At a minimum, blood and chocolate agar plates should be inoculated and incubated under increased carbon dioxide tension (5% to 10% CO2).
  • Sample from Both eyes should be cultured.
  • Potential pathogens also may be present in an eye without causing infection.
  • If the organism is isolated from both the infected and non-infected eye, it may not responsible for causing infection.
  • If an organism only grows in culture from an infected eye, it might be the causative agent.
  • Loeffler’s medium can be used when Moraxella lacunata is suspected.
  • In this case, the growth of the medium causes the proteolysis and pitting of the medium.
  • Loeffler’s or cystine-tellurite medium should be used if diphtheritic conjunctivitis is suspected.
  • For the isolation of the organism from the keratitis, endophthalmitis, and orbital cellulitis, a reduced anaerobic blood agar plate, a medium for the isolation of fungi, and a liquid medium such as thioglycolate broth should be used.
  • A reduced anaerobic blood agar plate should be used for the more serious eye infections.
  • Blood culture also should be done in severe infections.
  • From the transport broth, Chlamydia and virus should be inoculated inappropriate media.
  • Cycloheximide-treated McCoy cells should be used for the Chlamydia
  • For viral isolation, human embryonic kidney, primary monkey kidney, and Hep-2 cell lines can be used.

Molecular diagnosis for eye infection:

  • Enzyme-linked immunosorbent assay (ELISA) tests and DFA staining are available for the detection of Chlamydia trachomatis.
  • An ELISA test of aqueous humor is available for the diagnosis of Toxocara
  • Single and multiplex polymerase chain reaction (PCR) assays