Materials and Methods: This cross-sectional study included one randomly selected eye of 30 patients with primary open-angle glaucoma (POAG) under medical treatment and 27 healthy controls. IOP was measured using a noncontact tonometer (NT), then with a Tono-pen, followed by gonioscopic examination using a four-mirror goniolens (without gel), and finally a second IOP measurement by Tono-pen. We compared NT and Tono-pen measurements obtained before gonioscopic examination, and Tono-pen measurements obtained before and after gonioscopic examination. We evaluated the relationship between the difference in Tono-pen measurements before and after gonioscopy and central corneal thickness (CCT) and palpebral fissure height (PFH).

Results: Mean IOPs in the POAG and control groups were 15.7±3.2 and 16±2.7 mmHg with NT before gonioscopy, 15.3±2.6 and 14.81±2.27 mmHg with Tono-pen before gonioscopy, and 14.9±3.1 and 14.37±2.13 mmHg with Tono-pen after gonioscopy, respectively. In pre-gonioscopic measurements, NT and Tono-pen measurements did not differ significantly in the POAG group (p>0.05), whereas NT measurements were higher than Tono-pen measurements in controls (p<0.05). The mean change in IOP after gonioscopy was ?0.32±1.60 and ?0.44±1.69 mmHg in the POAG and control groups, respectively (p>0.05). There was no difference in CCT between groups (p>0.05), whereas PFH was smaller in controls (9.67±0.73 vs. 10.1±0.55 mm; p<0.05). Change in IOP was not correlated with CCT or PFH in either group (p>0.05).

Conclusions: Our results indicate that gonioscopic examination using a four-mirror goniolens has no significant effect on IOP in open-angle eyes. Keywords : Gonioscopy, Intraocular pressure, Glaucoma