A 52-year-old woman is found on routine examination to have an intraocular pressure of 26 mmHg bilaterally, a cup-to-disc ratio of 0.7, and gonioscopy showing open angles. Automated visual fields reveal an arcuate scotoma in the superior field of the left eye. Central corneal thickness (CCT) is 490 µm. Regarding interpretation of this IOP in the context of CCT, which statement is most accurate?
- A CCT of 490 µm is thicker than average, so true IOP is likely lower than measured
- B CCT of 490 µm is thinner than average; the true IOP is likely higher than the Goldmann-measured value, increasing glaucoma risk ✓
- C CCT has no independent influence on IOP measurement with Goldmann tonometry
- D Thin CCT is a risk factor only for angle-closure glaucoma, not POAG
Correct answer: B. CCT of 490 µm is thinner than average; the true IOP is likely higher than the Goldmann-measured value, increasing glaucoma risk
Explanation
The average central corneal thickness is approximately 540–545 µm. Goldmann applanation tonometry assumes a standard CCT; a thinner cornea (< 520 µm) results in underestimation of true IOP because less force is required to applanate a thinner cornea. This patient's CCT of 490 µm means the measured IOP of 26 mmHg likely underestimates true IOP. The OHTS confirmed thin CCT as an independent risk factor for conversion from ocular hypertension to POAG, beyond its effect on IOP measurement alone.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.