In Goldmann applanation tonometry, which factor in the Imbert-Fick law is PRACTICALLY accounted for by the design of the tonometer prism (using a 3.06 mm applanation diameter)?
- A Corneal curvature
- B Aqueous viscosity correction
- C The forces of corneal rigidity and tear film surface tension are assumed to cancel each other out at the 3.06 mm applanation diameter, leaving IOP as the only relevant force ✓
- D Scleral rigidity
Explanation
The Goldmann tonometer uses a 3.06 mm applanation diameter, which was empirically determined by Goldmann and Huber to be the point at which the corneal surface tension (capillary attraction of the tear meniscus, pulling the prism toward the cornea) equals the corneal resistance force (rigidity, pushing the prism away). These two forces cancel each other out, so the measured force equals exactly the intraocular pressure multiplied by the applanation area (Imbert-Fick law: P = F/A). This elegant design makes GAT the gold standard for IOP measurement, though it is affected by corneal thickness (CCT).
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.