Prospective Comparative Analysis of 4 IOP Measurement Techniques and Their Effects on Pressure Readings
Purpose
To compare intraocular pressure (IOP) measurement values using four different methods: Goldmann applanation tonometry without fluorescein, with fluorescein strips (Fluorets), with fluorescein droplets, and IOP measurement with Tonopen alone.
Methods
IOP was measured with four different methods per eye (n = 40 eyes). First with topical anesthetic alone, then after applying a Fluoret strip to the lower palpebral conjunctiva. The fluorescein was allowed to wash out of the eye, indicated by a clear tear film on slit lamp examination, and IOP was then re-measured using a fluorescein droplet. Finally, IOP was measured using the Tonopen device. All measurements were performed with the same Goldmann applanation tonometer and Tonopen, by the same technician, who was blinded to the values. The Goldmann applanation tonometer was reset to 8 mmHg before each measurement.
Results
The mean IOP measurements for the anesthetic only, Flouret strip, fluorescein droplet, and Tonopen groups were 12.65 +/- 3.01, 14.70 +/- 2.82, 15.78 +/- 2.64, and 16.33 +/- 3.08 mmHg respectively. After correcting for asphericity using the Greenhouse-Geisser estimate (ɛ = 0.732), repeated-measures ANOVA showed that the measuring technique used had a significant effect on IOP measurements, F(2.20, 85.59) = 34.66, p < 0.001. Post-hoc pairwise LSD testing (Fisher's least significant difference) showed statistically significant mean differences (p ≤ 0.001) between all techniques except when the fluorescein droplet technique was compared to Tonopen measurement (p = 0.222).
Conclusion
IOP measurement technique significantly impacted the value obtained. Anesthetic alone and Tonopen displayed the greatest measurement variability. Flourescein droplet and Tonopen yielded similar measurement accuracies. The ophthalmologist should ensure a consistent IOP measurement technique is used to minimize variability when following patients.