Ocular Infections I Flashcards
Extraocular tissues
Eyelids - blepharitis
Conjunctiva - conjunctivitis
Cornea - keratitis
Nasolacrimal system - dacryocytitis
Intra ocular tissues
Uvea = uveitis
Iris & ciliary body = anterior uveitis
Choroid = posterior uveitis
Retina = retinitis
Optic nerve = optic neuritis
Microorganisms inside/around eye
• Conjunctiva few bacteria has low numbers of bacteria
Cornea has very few bactiera
Intraocular tissues are sterile
• Normal flora & transient
• Mostly Intraocular tissues are Gram +
• Fungi are transitory
Organisms in eye
Conjunctival Sac
Predominantly Gram +
• Staphylococci
• Streptococci
• Corynebacterium
Occasional Gram –
• Neisseria
• Moraxella
Fungi
• Rare & transitory
Defense of the eye
Normal flora of conjunctiva
Tears / blinking
Normal flora of conjunctiva
Present in low numbers
Primarily gram positive bacteria e.g., Staphylococci, Streptococci, Cornynebacterium
Fungi only there transitorily
important role in colonization resistance
use of antibiotics may disrupt this defense mechanism.
Tears and blinking
Rinse” the ocular surface
Contain antibacterial substances
e.g., IgA, lysozyme, and lactoferrin
Predisposing factors for extra ocular infections
Most extraocular infections are secondary
They need some breach in ocular defenses to allow
disease to occur:
Trauma - Breaks in epithelial barrier of cornea, conjunctiva, ultraviolet radiation
Infections in adjacent structures - Ears, lip folds, mouth
Drying of the cornea - Keratoconjunctivitis sicca
Immunosuppression - Local or systemic
Co-infection with other agents - Viruses and bacteria; local or systemic infections
Predisposing factors for Intraocular infections
Most intra infections are secondary
Often manifest as systemic infections/disease
Immunosupporession most common factor
Routes of entry for extra ocular infection
direct inoculation
Overgrowth of normal flora in nearby sites - pseudo intermedius*
Inoculation of exogenous bacteria - P. Aeruginosa
Inoculation of viruses or recrudescence of existing infection - herpes
Routes of entry for Intraocular infections
Most common route is systemic infections**
Eyes are target organs for systemic infections
Access via uveal or vascular tracts
Typically infectious agents or immune complexes become established in uvea - chorioretinitis and anterior uveitis
Direct inoculation for Intraocular infections
Local injury - trauma
Less common, usually unilateral
Mechanism of pathogen damage
Adhere
Invade tissues
Evade host defense mechanisms
Cause host cell damage
Bacteria organisms that cause infection in all species eyes
Staphylococcus & Streptococcus spp*
Trueperella & Corynebacterium spp
Pseudomonas aeruginosa**
Coliforms (E. coli, Klebsiella, Proteus)
Chlamydia spp*
Bacteria organisms causing eye infections in dogs
Brucella canis
Ehrlichia canis*
Rickettsia rickettsia*
Bactiera for eye infections in cats
Chlamydia felis*
Mycoplasma felis*
Bacteria for eye infections for dogs & horses
Borrelia burgdoferi*
Leptospira*
Bacteria for eye infections for cattle (sheep/goat)
Moraxella bovis** ü
Listeria monocytogenes ü
Histophilus somni* ü
Moraxella ovis ü
Mycoplasma conjunctivae* ü
Mycoplasma bovoculi
Bacteria for rabbit eye infections
Pasturella multiocida
Bacteria for bird eye infections
Mycoplasma gallisepticum
Viruses for cat eye infections
Feline herpes 1**
Feline corona virus/FIP *
FLeV
FIV
FPLeV
Viruses for dog eye infections
Canine distemper virus**
Canine adenovirus*
Canine herpes virus
Viruses for equine eye infections
Equine herpes virus 1&2
Equine viral arteritis virus
Viruses for cattle eye infections
Bovine herpes virus
BVDV
MCF
Fungi for dog eye infection s
Blastomyces
Histoplasma
Prototheca
Fungi for cat eye infection s
Cryptococcus
Diagnosing eye infections
Often a presumptive diagnosis based on history/signs
Definitive diagnosis is made in <50% of cases
Infections can by polymicrobial
Steps for diagnosing ocular infections
Thorough ocular exams
Sample collection
Cytology/culture/susceptibility testing
Other - PCR, serology, virus isolation, mycoplasma culture
Types of sample collections
Swab /cytobrush- conjunctiva/cornea
Kimura spatula - conjunctiva /cornea
Aqueous centesis
Blepharitis
inflammation of eyelids
Bacteria, fungi, parasites can all cause this. Can occur alone or with other ocular diseases
clinical signs of blepharitis
Eyelid swelling
Erythema
Skin ulceration
Pruritus
Ocular discharge
Bacteria that is most common for causing blepharitis
Gram positive cocci - S. Pseudintermedius, B haemolytic, strep, - canis/zooepidemicus
Fungi (dermatophytes)
Parasites (Demodex, sarcoptes, Cuterebra larvae)
Chlamydia felis
Causes conjunctivitis and keratoconjunctivitis in young cats - infected by carrier animals
DX is commonly presumptive or doing a conjunctival smear
Snuffles
Upper respiratory tract in rabbits caused by pasturellosis can also cause conjunctivitis / eye leaking
Pasturella multocida
Keratitis - causing bacteria
Gram positive cocci - S. pseudintermedius, ß-hemolytic
Streptococci e.g., S. canis, S . zooepidemicus)
Diagnosing equine keratitis - eye exam
Examining eye - nerve blocking is common
Looking for foreign body, perform fluoroscein test to determine presence of ulcer
Diagnosing equine keratitis work up
Corneal scraping for cytology / culture
Culture the scraping - expect low numbers of bacteria in normal flora on cornea
4 pt rule for normal flora
It is part of normal flora at this site.
It is present in increased numbers.
It CAN cause the disease observed?
2 rule with normal flora
Is it NOT part of normal flora at site
It CAN cause disease observed
Pseudomonas keratitis
Direct inoculation from a saphrophyte
Bacterial pili attach/grow on damaged cornea
Multiply & invade into corneal stroma = produce exotoxins
Exotoxins kill corneal epithelial cells = keratin w exudate
P. Aeruginosa keratitis
Causes “melting” ulcers
Due to other exotoxins and enzymes released from lyses inflammatory cells
Can cause rapid iris prolapse and globe collapse
DX pseudomonas keratitis
Cytology / culture
Susceptibility testing - not predictably susceptible w lots of intrinsic Antimicrobials resistance
Treating pseudomonas keratitis
Treat empirically immediately waiting for culture
“Melting” is an emergency
Sub palpebral lavage system - easy treatment
Antibiotics 4-6x a day
Atropine to dilate the pupil, pain relief
NSAID - flunixin
Acetyl cysteine - anti collagenase, activate against exotoxic effects
