To determine the correlation between intraocular pressure (IOP) and the bottle heights during vitrectomy using TONO-PEN®XL applanation tonometer and Icare® PRO rebound tonometer.

Twenty-four eyes of 24 patients who underwent 23-gauge sutureless vitrectomy were evaluated. After complete vitrectomy, the IOP was gradually increased by lifting the irrigation bottle height from the trocar insertion site by 40 cm, 45 cm, 50 cm, and 55 cm. The distance between the floor and patient's eye was consistent in all cases (105.5 cm). Before the removal of 23-gauge microcannulas, IOP was measured five times using each of the two methods, Tono-Pen®XL and Icare® PRO.

The mean IOPs were 8.25 ± 0.35 mm Hg for TONO-PEN®XL and 8.96 ± 0.32 mm Hg for Icare® PRO at 40 cm bottle height. As the bottle height increased, the differences in IOP was also increased, 10.71 ± 0.37 mm Hg at 45 cm, 14.18 ± 0.39 mm Hg at 50 cm and 17.93 ± 0.40 mm Hg at 55 cm for TONO-PEN®XL and 11.48 ± 0.31 mm Hg at 45 cm, 14.64 ± 0.31 mm Hg at 50 cm and 18.13 ± 0.38 mm Hg at 55 cm for Icare® PRO. In TONO-PEN®XL, the linear equation was Y = 0.65 X - 18.108 (R² = 0.794, p = 0.000) and the quadratic equation was Y = 0.013 X² - 0.569 X + 10.446 (R² = 0.801, p = 0.000). In Icare® PRO, the linear equation was Y = 0.614 X - 15.842 (R² = 0.820, p = 0.000) and the quadratic equation was Y = 0.010 X² - 0.306 X + 5.688 (R² = 0.825, p = 0.000). The results show correlation of the quadratic equation was stronger than the linear equation in both tonometers.

The differences of IOP were positively correlated with bottle heights in the form of a curve during vitrectomy. Therefore, the patients who are susceptible to retina or optic nerve damage during vitrectomy should be closely monitored.