20.5 Microbiology, Infection Control, and Readiness Drills
Key Takeaways
- Standard Precautions treat every patient as potentially infectious; hand hygiene is the single most effective infection-control measure.
- Tonometer tips and contact instruments must be disinfected between patients to prevent transmission of adenovirus and other pathogens.
- Know the difference between cleaning, disinfection, and sterilization, and which applies to ophthalmic instruments.
- Readiness means decoding terminology, naming a disease's ocular sign, choosing the emergency action, and disinfecting correctly under a one-day-later recall test.
20.5 Microbiology, Infection Control, and Readiness Drills
The eye clinic is a high-touch environment where instruments contact the ocular surface, so microbiology and infection control are core General Medical Knowledge content.
Pathogen basics
- Bacteria (Staphylococcus, Pseudomonas) cause most bacterial conjunctivitis and corneal ulcers; Pseudomonas keratitis is aggressive in contact-lens wearers.
- Viruses: adenovirus causes highly contagious epidemic keratoconjunctivitis (EKC, or "pink eye"); herpes simplex causes dendritic keratitis; herpes zoster causes shingles around the eye.
- Fungi (Fusarium, Candida) cause keratitis after vegetable-matter trauma.
- Acanthamoeba, a protozoan, causes painful keratitis linked to contaminated contact-lens water.
Standard Precautions
Standard Precautions require treating every patient as potentially infectious. Hand hygiene — soap-and-water or alcohol-based rub before and after every patient contact — is the single most effective measure to break transmission. Gloves are worn when contacting body fluids, and a new pair is used per patient.
Cleaning vs disinfection vs sterilization
| Level | What it does | Ophthalmic example |
|---|---|---|
| Cleaning | Removes visible debris/organic matter | Wiping the slit-lamp chin rest |
| Disinfection | Kills most pathogens, not all spores | Soaking a tonometer tip in dilute sodium hypochlorite or hydrogen peroxide |
| Sterilization | Destroys all microbial life including spores | Autoclaving surgical instruments |
Goldmann tonometer tips and any instrument that touches the cornea must be disinfected between every patient because adenovirus and herpes survive on surfaces; disposable tip covers are an alternative. Multidose drop bottles must never touch the eye or lashes to avoid contaminating the tip.
Chain of infection and how to break it
The exam frames transmission as a chain of infection: a pathogen, a reservoir (a sick patient or a contaminated surface), a portal of exit, a mode of transmission, a portal of entry, and a susceptible host. Infection control works by breaking any link. In the eye clinic the dominant mode is direct contact and contaminated instruments, so hand hygiene and instrument disinfection break the chain most effectively. Epidemic keratoconjunctivitis from adenovirus has caused real clinic outbreaks traced to shared instruments and unwashed hands, which is why these are heavily tested.
Bloodborne pathogens and PPE
Under OSHA's Bloodborne Pathogen Standard, blood and body fluids may carry hepatitis B (HBV), hepatitis C (HCV), and HIV. Hepatitis B is the most transmissible of the three on contaminated surfaces, and a vaccine exists, which is why HBV vaccination is offered to clinical staff. Personal protective equipment (PPE) — gloves, and when splash is possible eye protection and a gown — plus safe sharps handling and never recapping needles, protects the worker. A needlestick is reported immediately and managed per protocol.
Readiness drills
Use short, mixed drills to confirm mastery rather than rereading:
- Decode drill: write five unfamiliar terms and break each into prefix-root-suffix in under two minutes.
- Vitals drill: state the normal range and the red-flag value for temperature, pulse, respiration, blood pressure, and SpO2 from memory.
- Disease-to-sign drill: name the ocular finding for diabetes, hypertension, Graves disease, rheumatoid arthritis, and HIV.
- Emergency drill: given a stem (faint, anaphylaxis, BP 190/130, FAST-positive), state the first action in one sentence.
- Infection-control drill: classify a task as cleaning, disinfection, or sterilization.
Readiness markers
| Marker | What good performance looks like |
|---|---|
| Recall | Reproduce the vital-sign and BP-stage tables without notes |
| Recognition | Spot the systemic disease when the stem only lists ocular signs |
| Application | Choose the emergency action and name why distractors are unsafe |
| Retention | Repeat a mixed set after a one-day break with stable accuracy |
A domain is ready when you can return after a day away, answer scenario items that never name the topic, and still justify the reasoning aloud. If accuracy drops sharply after the break, the knowledge is recognition-based and needs more active recall before test day.
Spaulding classification of instruments
Infection-control questions often map to the Spaulding classification, which sets the required reprocessing level by how an instrument contacts the body:
| Category | Contact | Reprocessing | Ophthalmic example |
|---|---|---|---|
| Critical | Enters sterile tissue | Sterilization | Surgical blades, cannulas |
| Semi-critical | Touches mucous membrane / non-intact surface | High-level disinfection | Tonometer tip, contact lens trial set |
| Non-critical | Touches intact skin | Low-level disinfection / cleaning | Slit-lamp chin rest, BP cuff |
A tonometer tip is semi-critical, which is why disinfection (or a disposable cover) — not mere cleaning — is the standard between patients.
A weekend-test for readiness
The true measure of readiness is recall after a gap. Study a mixed set on day one, then on day three answer 20 scenario items that never name the topic. If you can still decode terminology, recite vital-sign and blood-pressure thresholds, link diseases to ocular signs, and name the first emergency action without hesitation, the domain is consolidated. If accuracy collapses, the knowledge was recognition-based — rereading felt productive but built no durable memory — and you should switch to active retrieval and spaced repetition.
Final integration
General Medical Knowledge is the connective tissue of the whole COA exam: terminology lets you read the chart, vital signs and systemic disease let you triage the patient, pharmacology lets you flag risk, and infection control plus emergency response keep everyone safe. Practice these as job tasks, escalate within scope, document accurately, and you will recognize the right answer even when the stem hides the topic inside a patient story.
Between patients, an ophthalmic assistant must reprocess a Goldmann applanation tonometer tip that touched the cornea. Which level of reprocessing is appropriate and why?