5.1 Infections of Eyes, Ears & Sinuses

Flashcards covering key concepts, definitions, and important facts from the lecture on infections of the eyes, ears, and sinuses.

Describe the three layers of the eyeball and their functions.

• Sclera: Tough, white, fibrous tissue providing structural support. The anterior portion forms the cornea, which is transparent and allows light entry.

• Choroid: Vascular layer supplying blood and nutrients to the eye.

• Retina: Contains photoreceptors (rods and cones) that detect light and transmit signals to the brain.

What are the internal and external structures of the eye?

• External structures: Eyelids, conjunctiva (mucous membrane lining the eyelids), and lacrimal apparatus.

• Internal structures:

  • Anterior chamber: Contains aqueous humor.

  • Posterior chamber: Contains vitreous humor.

Which bacteria are commonly associated with bacterial conjunctivitis (think shakir)?

S. pneumoniae, Haemophilus spp., S. aureus, S. pyogenes, N. gonorrhoeae, C. trachomatis. (Some happy students study nursing constantly).

What is a common cause of keratitis?

Infection of the cornea, often after trauma.

What is endophthalmitis?

Infection of the internal tissues of the eye.

What organisms can cause endophthalmitis? Silly elephants never hide candy

S. aureus, S. epidermidis, N. meningitidis, H. influenzae, C. albicans.

What is the purpose of the lacrimal glands?

To wash the eye and provide natural defenses against infection.

What is the common cause of orbital cellulitis?

Exogenous infections from trauma or surgery, or endogenous from paranasal sinuses.

How is a specimen for bacterial culture collected in case of blepharitis?

Using a sterile swab of purulent material or drainage fluid.

What are the acute and chronic forms of otitis externa?

Acute is localized or diffuse; Chronic can lead to malignant otitis externa.

Which bacteria are frequently involved in acute otitis media?

S. pneumoniae, H. influenzae, S. pyogenes.

What is the primary difference between acute and chronic sinusitis?

Acute develops during a cold; chronic occurs when acute persists.

What procedure is performed for suspected cases of mastoiditis?

Swabs or bone biopsy taken during surgery.

What are common fungal causes of keratitis?

Fusarium spp., Aspergillus spp., Candida spp.

What role does the ciliary action play in sinus health?

It helps clear secretions and contaminants from the sinuses.

What type of swab is used for collecting specimens for otitis media?

Middle ear needle aspirate (tympanocentesis).

Which organism is associated with dacryocystitis?

S. aureus, S. pneumoniae, S. pyogenes.

What is the incubation condition for bacterial cultures in eye infection cases?

5-10% CO2 at 37℃ for 48 hours.

How do the cornea and lens contribute to the process of vision?

The cornea refracts light to focus it, while the lens adjusts its shape to further focus light onto the retina.

Which structures are involved in tear production and drainage?

The lacrimal glands produce tears, which drain through the nasolacrimal duct into the nasal cavity.

Describe the function of the paranasal sinuses.

The paranasal sinuses reduce skull weight, provide resonance for voice, and produce mucus to moisten nasal passages.

What is the function of the lacrimal apparatud?

Produces and drains tears to lubricate the eye and protect it from infections via lysozyme and IgA present in tears.

Describe the anatomy of the ear, dividing it into its three main sections.

• External Ear: Auricle, external auditory canal, tympanic membrane.

• Middle Ear: Tympanic cavity, auditory ossicles (malleus, incus, stapes), connected to the nasopharynx via the Eustachian tube.

• Inner Ear: Cochlea (hearing), vestibule, and semicircular canals (balance).

What are the paranasal sinuses, and what is their function?

• Air-filled cavities in skull bones: Maxillary, Frontal, Ethmoid, and Sphenoid sinuses.

  • Function: Reduce skull weight, humidify and filter air, contribute to voice resonance.

Describe the specimen collection and transport for ocular infections.

• Blepharitis & Conjunctivitis: Sterile swab from purulent material, transported in Amies gel (bacterial), viral transport medium, or Chlamydia transport medium.

• Keratitis: Corneal scrapings collected by an ophthalmologist, directly inoculated onto media.

• Endophthalmitis: Aqueous and vitreous humor aspirates collected via needle aspiration.

• Orbital Cellulitis: Needle aspirates from abscess or infected tissue, transported anaerobically.

What laboratory techniques are used for diagnosing eye infections?

• Direct Microscopy: Gram stain for bacterial infections, wet prep for Acanthamoeba, fungal stains (PAS, Calcofluor).

• Culture Media:

  • Bacteria: Chocolate Agar (Choc), Blood Agar (BA), MacConkey Agar (MAC).

  • Fungi: Sabouraud’s Agar (SAB).

  • Anaerobes: Anaerobic Blood Agar (ABA), Thioglycollate broth.

  • PCR and ELISA for viral and chlamydial detection.

List the types of specimen collected for otitis externa, otitis media, and mastoiditis.

• Otitis externa: Swab of fluid or scrapings from external canal.

• Otitis media: Middle ear aspirate (tympanocentesis), swab from ruptured tympanic membrane.

• Mastoiditis: Swabs or bone biopsy collected during surgery.

Describe the common bacterial causes of otitis media.

• Acute otitis media: Streptococcus pneumoniae, Haemophilus influenzae, Streptococcus pyogenes, Moraxella catarrhalis.

• Chronic otitis media: Peptostreptococcus spp., Prevotella spp., Fusobacterium nucleatum.

• Otitis media with effusion: Alloiococcus otitidis.

Explain how specimens for otitis media are processed in the lab.

• Direct Microscopy: Gram stain for bacterial morphology.

• Culture Media:

  • Standard plates (HBA, Choc, MAC, CNA).

  • Anaerobic plates for chronic OM.

  • Thioglycollate broth for A. otitidis (incubated for 5 days).

What specimens are collected for sinusitis, and how are they processed?

• Specimens: Maxillary sinus puncture aspirate, saline lavage sample.

• Direct Microscopy: Gram stain.

• Culture Media:

  • HBA, BCA/Choc, MAC (bacterial detection).

  • SAB (fungal detection, incubated at 25°C and 37°C for up to 6 weeks).

  • Anaerobic plates for suspected anaerobic pathogens.

Define the following conditions and list two common bacterial agents for each (Blepharitis, conjunctivitis, keratitis, endophthalmitis, canaliculitis, dacryocystitis, dacryoadenitis, and orbital cellulitis).

• Blepharitis: Inflammation of eyelid glands (S. aureus, S. epidermidis).

• Conjunctivitis: Inflammation of conjunctiva (S. pneumoniae, Haemophilus spp.).

• Keratitis: Corneal infection (Pseudomonas aeruginosa, Staphylococcus aureus).

• Endophthalmitis: Infection of internal eye tissues (S. epidermidis, Candida albicans).

• Canaliculitis: Inflammation of lacrimal canal (Actinomyces israelii, Propionibacterium propionicum).

• Dacryocystitis: Infection of lacrimal sac (S. aureus, S. pneumoniae).

• Dacryoadenitis: Infection of lacrimal gland (S. aureus, S. pneumoniae).

• Orbital Cellulitis: Infection of tissue surrounding the eye (S. aureus, H. influenzae).

What are the most common viral causes of conjunctivitis and keratitis?

• Conjunctivitis: Adenoviruses, HSV, Varicella-Zoster Virus (VZV).

• Keratitis: HSV, Adenoviruses, VZV.

Describe the laboratory diagnosis of Moraxella catarrhalis infections.

• Gram Stain: Gram-negative diplococci in PMN leukocytes.

• Culture: White/grey colonies on BA and Choc agar.

• Key Tests:

  • Oxidase-positive.

  • Hockey puck test (colony slides on agar without breaking).

  • Tributyrin test positive for beta-lactamase production.

Describe the incubation conditions required for bacterial and fungal cultures in ocular, ear, and sinus infections.

• Bacteria: 37°C, 5-10% CO2, 48 hours.

• Fungi: 25°C and 37°C, up to 6 weeks.

• Anaerobic organisms: 48 hours in anaerobic conditions.

Describe the common bacterial causes of otitis media.

• Acute otitis media: Streptococcus pneumoniae, Haemophilus influenzae, Streptococcus pyogenes, Moraxella catarrhalis.

• Chronic otitis media: Peptostreptococcus spp., Prevotella spp., Fusobacterium nucleatum.

• Otitis media with effusion: Alloiococcus otitidis.