Clinical and Technical Skills for the Ophthalmic Assistant
Domain 1 tests the chairside and technical skills that turn a physician's order into reliable, documented data: tonometry, lensometry, keratometry, perimetry, specimen handling, and instrument care. The exam favors standardized technique, calibration, infection control, and recognition of invalid results.
Core rules and concepts
- Goldmann applanation tonometry: verify calibration on the manufacturer's schedule, use fresh fluorescein, align the mires, and avoid eyelid pressure. Record the instrument, eye, time, and patient cooperation.
- Noncontact tonometry: average several readings; poor fixation or blepharospasm lowers reliability.
- Lensometry: focus the eyepiece first, center the target, then read sphere, cylinder, axis, and add. Convert between plus and minus cylinder by transposition.
- Keratometry: measure the central 3 mm, record both meridians, and calculate average K as the mean of the two readings.
- Perimetry: give clear instructions, patch the fellow eye, monitor fixation, and note reliability indices.
- Biometry: correct immersion technique and probe alignment affect axial length; inconsistent readings require repeat measurement.
- Instrument hygiene: match reprocessing to the item's contact category. Tonometer prisms are semicritical and need high-level disinfection or single-use tips.
- Surgical assistance: maintain the sterile field, verify patient identity and site, and label specimens at the chairside.
Worked example
A lensometer reads +2.00 -1.00 x 180. To transpose to plus cylinder, add the cylinder power to the sphere: +2.00 plus -1.00 equals +1.00. Change the cylinder sign to +1.00 and rotate the axis 90 degrees to 090. The result is +1.00 +1.00 x 090. The spherical equivalent remains +1.50 D either way, which is a quick arithmetic check.
Traps that cost marks
- Transposing the axis by 180 rather than 90 degrees.
- Adding the full cylinder instead of half when checking spherical equivalent.
- Recording tonometry without noting calibration, instrument, or time.
- Pressing on the lids during applanation, which falsely raises IOP.
- Calling a visual field unreliable only because the patient is slow; use the reliability indices instead.