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