A 34-year-old woman who underwent LASIK five years ago is screened for glaucoma. Goldmann applanation tonometry reads 14 mmHg bilaterally, but her central corneal thickness is 480 micrometres. The measured pressure compared with her true intraocular pressure is:
- A Accurate, since applanation is independent of corneal thickness
- B Falsely high because the cornea is thinner than average
- C Falsely low because the cornea is thinner than average ✓
- D Accurate only if the corneal curvature is normal
Correct answer: C. Falsely low because the cornea is thinner than average
Explanation
Goldmann tonometry assumes a central corneal thickness near 520 micrometres. C thinner cornea offers less resistance to applanation, so less force is needed and the device underestimates the true pressure. After LASIK the stromal bed is thinned, so readings are falsely low and glaucoma can be missed. The opposite occurs in thick corneas, as seen in ocular hypertension, where readings are falsely high.
Reference: American Academy of Ophthalmology, BCSC Section 10: Glaucoma, 2022-2023 ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.