COT Ophthalmic Instrumentation and Equipment Maintenance — Questions and Answers
Question 1: A Goldmann applanation tonometer is being calibrated using the calibration bar. At the 20 mmHg position, a reading of 22 mmHg is obtained. What action should be taken?
- Continue using the instrument; a 2 mmHg deviation is within acceptable limits
- Remove the instrument from service and schedule repair (Correct answer)
- Re-zero the tonometer and repeat the measurement only at 0 mmHg
- Switch to a non-contact tonometer for all patients that day
Correct answer: Remove the instrument from service and schedule repair
The acceptable calibration tolerance for the Goldmann applanation tonometer is ±0.5 mmHg. A deviation of 2 mmHg at the 20 mmHg check point exceeds this tolerance, meaning the instrument must be taken out of service and sent for calibration or repair before further clinical use.
Question 2: Which disinfection method is recommended between patients for a Goldmann applanation tonometer prism to prevent transmission of adenovirus and other pathogens?
- Autoclave sterilization at 121°C for 15 minutes
- Soak in 1:10 diluted bleach for 30 seconds
- Wipe with 70% isopropyl alcohol and allow to air dry for at least 5 minutes (Correct answer)
- Rinse with sterile saline and dry with gauze
Correct answer: Wipe with 70% isopropyl alcohol and allow to air dry for at least 5 minutes
The CDC and JCAHPO recommend disinfecting tonometer tips between patients by wiping with 70% isopropyl alcohol and allowing a contact time of at least 5 minutes before reuse. Autoclaving damages the prism coating, and saline alone does not adequately disinfect.
Question 3: A keratometer is producing mire images that appear distorted and asymmetric even after lens cleaning. The MOST appropriate next step is to:
- Perform the measurement anyway and document the irregularity in the chart
- Verify accuracy by measuring a steel calibration sphere of known radius (Correct answer)
- Replace the eyepiece lens immediately
- Use the autorefractor reading as a substitute
Correct answer: Verify accuracy by measuring a steel calibration sphere of known radius
When a keratometer produces suspect or distorted readings, the standard troubleshooting step is to measure a steel calibration sphere of known radius to verify whether the instrument is producing accurate values. This confirms whether the issue is instrument calibration or corneal irregularity.
Question 4: When cleaning the objective lens of a slit lamp biomicroscope, the correct technique is to:
- Use a dry cotton swab in a vigorous circular motion to remove debris
- Apply 70% isopropyl alcohol directly to the glass surface with a paper towel
- Use a lens-cleaning solution with a lint-free cloth, wiping gently from center outward (Correct answer)
- Rinse with tap water and pat dry with a soft cloth
Correct answer: Use a lens-cleaning solution with a lint-free cloth, wiping gently from center outward
Optical surfaces should be cleaned using an appropriate lens-cleaning solution and a lint-free cloth, wiping from center outward to avoid dragging debris across the optical surface. Isopropyl alcohol can damage coatings, and dry or abrasive materials can scratch the lens.
Question 5: Which sterilization method is MOST appropriate for ophthalmic surgical instruments with heat-sensitive components?
- Steam autoclave at 134°C
- Dry heat oven at 160°C for 2 hours
- Ethylene oxide (EtO) gas sterilization (Correct answer)
- Boiling in distilled water for 10 minutes
Correct answer: Ethylene oxide (EtO) gas sterilization
Ethylene oxide (EtO) gas sterilization achieves full sterilization at low temperatures (37–63°C), making it safe for heat-sensitive materials such as plastics, rubber, and certain instrument components that would be damaged by autoclaving or dry heat. Boiling does not achieve sterilization.
Question 6: During routine maintenance checks, which action should be performed DAILY on a non-contact tonometer (NCT)?
- Replace the internal air puff mechanism filter
- Perform a calibration check using the instrument's built-in verification procedure (Correct answer)
- Disassemble and clean the nozzle tip in an autoclave
- Lubricate the joystick mechanism with medical-grade oil
Correct answer: Perform a calibration check using the instrument's built-in verification procedure
Non-contact tonometers should undergo a daily calibration verification check using the instrument's built-in self-calibration or a reference target to ensure accurate IOP readings. Nozzle tips are wiped with alcohol between patients, not autoclaved, and internal components are serviced by biomedical technicians.
COT Ophthalmic Instrumentation and Equipment Maintenance
A Goldmann applanation tonometer is being calibrated using the calibration bar.
At the 20 mmHg position, a reading of 22 mmHg is obtained.
What action should be taken?