Tonometry in corneal edema after cataract surgery: rebound versus goldmann applanation tonometry

Goldmann applanation tonometry (GAT) is known to be influenced by corneal properties, whereas the effect of corneal edema on intraocular pressure (IOP) measurement using Rebound tonometry (RT) is not clear. In this study, IOP was measured before and after cataract surgery using GAT and RT to investigate differences between methods and the effect of postsurgical corneal edema.

Thirty patients with cataract were included in a prospective study. IOP was measured using GAT and RT (Icare PRO, Tiolat Oy, Finland) before and after one day of phacoemulsification. Central corneal thickness (CCT) was determined before and after surgery (Pentacam, Oculus, Germany).

CCT increased significantly after surgery by 52.2 ± 35.1 µm (p < 0.0001). IOP values of GAT and RT were significantly correlated before surgery (r = 0.65, p < 0.0001) and after surgery (r = 0.94, p < 0.0001). No significant correlation of GAT and RT to CCT before surgery (GAT: r = 0.18, p = 0.36; RT: r = 0.03, p = 0.87) or after surgery (GAT: r = -0.08, p = 0.69; RT: r = 0.17, p = 0.37) was found. The mean difference between GAT and RT (GAT-RT) was -1.0 ± 2.9 mmHg (range -6.2 to 6.4 mmHg, p = 0.08) before surgery and -1.1 ± 2.2 mmHg (range -5.1 to 4.8 mmHg, p = 0.01) after surgery. Before surgery, a positive correlation of GAT-RT with mean IOP of both methods is apparent (r = 0.45, p = 0.01). After surgery, no such correlation was found (r = -0.08, p = 0.69).

RT underestimates IOP in higher values and overestimates IOP in lower values compared to GAT before surgery. This is not apparent in eyes with corneal edema. Large differences between methods may be present in individual patients with and without corneal edema.