In the Hertel exophthalmometer, the 'base' value recorded at each measurement session is important because:
- A It ensures the instrument arms are properly calibrated
- B Comparison of proptosis across sessions must use the same base value for accuracy ✓
- C The base value equals the normal inter-canthal distance
- D It measures the distance between the corneal apex and the medial canthus
Correct answer: B. Comparison of proptosis across sessions must use the same base value for accuracy
Explanation
The Hertel exophthalmometer rests on the lateral orbital rims; the distance between the two lateral rims (base value) varies between patients. For serial measurements in the same patient (e.g., monitoring thyroid eye disease), the same base value must be used each time to ensure comparability, because changing the base changes the apparent proptosis reading. The base value does not represent intercanthal distance or a calibration value; it is simply the lateral rim separation.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.