Comparison of intraocular pressure measurement using goldmann, tonopen, and non-contact tonometers in patients with penetrating keratoplasty

PURPOSE: The purpose of the study was to compare intraocular pressure (IOP) values measured by Goldmann applanation tonometer (GAT) with IOP values measured by Tonopen and non-contact tonometer (NCT) in patients with penetrating keratoplasty (PKP).
METHODS: Eighty-eight eyes of 72 patients who underwent PKP surgery were included in the study. Detailed ophthalmological examination was performed. Central corneal thickness (CCT) was measured with an ultrasonic pachymeter and recorded. IOPs were measured with GAT, Tonopen, and NCT. Data were analyzed statistically.
RESULTS: The mean age of the patients was 56.2±14.7 years; the mean duration of PKP was 62.5±51.6 months. The mean CCT was 561±65µm. Mean IOP values were 15.4±3.0 with GAT, 12.8±4.5 with Tonopen, and 11.7±4.6 mmHg with NCT (p<0.001). There was a difference between IOP values between GAT and Tonopen (p<0.001) and between GAT and NCT (p<0.001), while there was no difference between Tonopen and NCT IOP values (p=0.06). There was no correlation between IOP values measured in all three methods and CCT (p>0.05). Both Tonopen and NCT IOP values were correlated with GAT IOP values (r=0.424, p<0.001; r=0.374, p<0.001).
CONCLUSION: In patients with PKP, IOP values measured with GAT are higher than IOP values measured by Tonopen and NCT. GAT remains the most established method of IOP measurement in clinical practice, yet it has significant limitations in corneas that deviate significantly from normal values, as is the case in PKP. During follow-up, measurements can be taken with the same device suitable for the structure of the eye. Due to structural differences, if the IOP value measured with a device is too high or too low in patients with PKP, the IOP value should be measured with other devices, and the results should be compared.