Ophthalmic Instruments and Equipment Handling
What the exam tests
This domain checks safe handling, calibration and correct use of slit lamps, ophthalmoscopes, tonometers, keratometers, autorefractors, perimeters and ultrasound devices. Expect practical sequence questions.
Slit lamp and ophthalmoscope
The slit lamp gives magnified illumination and biomicroscopy. Adjust the chin rest and fixation light, start with low magnification, and never force the joystick or optics. Filters include cobalt blue for fluorescein and red-free for vessels. A direct ophthalmoscope gives an upright virtual image at roughly 15×; an indirect ophthalmoscope with a 20 D condensing lens gives an inverted, reversed view.
Tonometers and other instruments
Goldmann applanation tonometry uses a 3.06 mm prism, topical anaesthetic, fluorescein and cobalt-blue light; the mires should just touch. Normal intraocular pressure is approximately 10–21 mmHg. Non-contact tonometers use an air pulse, while Schiotz uses indentation. A keratometer measures corneal curvature; an A-scan measures axial length; a B-scan images the posterior segment. Clean and disinfect each device exactly as the manufacturer instructs.
Worked example
A Goldmann reading is 18 mmHg. Reasoning: the cornea was anaesthetised, fluorescein stained the tear film, the prism was centred, and the mires were apposed without pressing on the lids. The value is recorded as 18 mmHg for that eye, with time and instrument noted.
Traps
Do not perform applanation without fluorescein or anaesthetic, press on the eyelids, or omit calibration checks. Never confuse A-scan with B-scan, and never touch optical surfaces with bare fingers.