Effects of puff times on intraocular pressure agreement between non-contact and Goldmann applanation tonometers

AIM: To compare intraocular pressure(IOP)values obtained from two different puff modes of Canon TX-F non-contact tonometer(NCT)and Goldmann applanation tonometer(GAT)in patients with primary open angle glaucoma(POAG). METHODS: The study group comprised 55 right eyes of 55 patients with a confirmed diagnosis of POAG, which were under treatment. All patients underwent detailed ophthalmological examinations, optical coherence tomography imaging and automated perimetry. Intraocular pressure measurements were performed using 1-puff mode of NCT(NCT1), 3-puffs mode of NCT(NCT3)and GAT with 5 minutes intervals in order. RESULTS: Fifty-five eyes of 55 patients with POAG(mean age of 64.1±8.1 years)were enrolled into the study. NCT1 and NCT3 gave similar IOP values when compared with GAT measurements(14.22±3.42, 14.28±3.29, 14.66±3.49mmHg respectively, P=0.291). Intertonometer agreement was assessed using the Bland-Altman method. The 95% limits of agreement(LoA)for NCT1-GAT, NCT3-GAT and NCT1-NCT3 comparisons were -4.9 to +4.4mmHg, -4.1 to +3.4mmHg, and -3.4 to +3.3mmHg respectively.CONCLUSION: Although IOP measurements obtained from two puff modes of NCT and GAT showed similar values, wide range of LoA might restrict use of NCT1, NCT3 and GAT interchangeably in POAG patients.