Comparison of intraocular pressure measurements with and without fluorescein using Goldmann applanation tonometry

This study aimed to evaluate the effect of fluorescein on intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT). The study compared IOP readings with and without fluorescein to determine its influence on measurement accuracy in clinical practice.

This cross-sectional study included 39 patients (78 eyes). IOP was measured three times under each condition: fluorescein-free with green light and fluorescein-aided with cobalt blue light. The prespecified primary comparison was between the first fluorescein-free reading and the first fluorescein-aided reading, separated by approximately 1 minute (the time needed to apply fluorescein). Statistical analysis (repeated-measures ANOVA for within-series change; Wilcoxon signed-rank tests for paired comparisons) was used to compare measurements, while corneal astigmatism, keratometry, and central corneal thickness were assessed for their potential influence on discrepancies. A sensitivity analysis excluding patients with >3.0 D corneal astigmatism was conducted.

No significant difference was found between the first fluorescein-free and first fluorescein-aided IOP measurements (Wilcoxon P = 0.75; mean difference +0.04 mmHg). Consecutive measurements showed significant IOP reductions within each group, attributed to mechanical effects of the tonometer (repeated-measures ANOVA P < 0.01). Corneal parameters, including central corneal thickness and keratometry, did not significantly affect the differences. Results were unchanged after excluding patients with >3.0 D astigmatism.

Fluorescein does not significantly affect IOP measurements using GAT, supporting fluorescein-free measurement as a viable alternative in routine practice. Further research is needed to evaluate its application in cases of high astigmatism or altered corneal geometry.