Factors Affecting Change in Intraocular Pressure after Pharmacological Mydriasis: The Shihpai Eye Study

Abstract

Purpose: : To determine ocular factors associated with change in intraocular pressure (IOP) after pharmacological mydriasis in phakic eyes.

Methods: : 460 participants, aged 72 years or older, in the Shihpai Eye Study underwent a follow-up visit for a complete ocular examination in 2006, including A-scan biometry, Goldmann tonometry, and gonioscopy. Measurements of IOP were performed before and 1-hour after pupil dilation with 1% tropicamide. The change in IOP was defined as IOP after pupil dilation minus IOP before pupil dilation. We excluded pseudophakic and aphakic eyes. Eyes with a narrower anterior chamber angle between the fellow eyes were selected for analysis.

Results: : A total of 356 phakic eyes were included. The mean change in IOP was 0.36 ± 2.61 mmHg (range: -6 to 13.7 mmHg) after pupil dilation. Only 7 (2%) subjects had an IOP elevation more than 6 mmHg, and none had acute angle closure. Deeper anterior chamber and longer axial length were significantly associated with a greater reduction in IOP after pupil dilation (P = 0.003 and 0.032, respectively), while thicker lens were associated with a greater elevation in IOP after pupil dilation (P = 0.001). Furthermore, for each Shaffer grade wider in anterior chamber angle, IOP decreased by 0.36 mmHg (95% confidence interval [CI]: 0.16, 0.56) on average after pupil dilation. After adjustment for anterior chamber angle width, only lens thickness remained significantly associated with the change in IOP; for each mm increase in lens thickness, IOP after pupil dilation increased by 0.67 mmHg (95% CI: 0.09, 1.24).

Conclusions: : The risk of acute angle closure is insignificant after pupil dilation in this elderly Chinese cohort. Eyes with a thick lens and a narrow anterior chamber angle are more likely to experience IOP elevation after pupil dilation.

Keywords: intraocular pressure • anterior chamber • pupil