Effect of Intravitreal Injection on Intraocular Pressure – Biomechanical Model and Measured Values

Abstract

Purpose: : Intravitreal injections have been extensively used to treat retinal diseases. When applying an intravitreal injection the intraocular volume is increased by the amount of fluid brought into the eye. To calculate the effect of different volume changes on intraocular pressure (IOP) a biomechanical model is used and evaluated by postinjectional IOP measurements.

Methods: : A model was developed to calculate the short term effect on IOP after intravitreal injection of 0,1 ml fluid for hypermetropic, emmetropic and hyperopic eyes. Our calculations were compared with IOP measurements obtained immediately after intravitreal injection of 4mg/0,1ml Triamcinolone (TA) in 20 patients. Briefly after the measurement the IOP was reduced through a paracentesis to 15 mmHg

Results: : The calculation of the expected IOP elevation and the measurements were comparable. Immediately after intravitreal injection of 4mg/0,1ml TA the intraocular pressure was elevated up to 80mmHg. In hypermetropic eyes the calculated and measured intraocular pressure increase was highest.

Conclusions: : With a biomechanical model the effect of fluid injection on intraocular pressure can be calculated. Since IOP increases are regulated by increasing outflow volume in non glaucomatous eyes (outflow of up to 0,3mm³/min in normal eyes) this increase in IOP especially in myopic eyes might be only present for a short term period. A postoperative pressure measurement half an hour after intervention might miss the effect. Intravitreal injections are mostly applied in diseases which are due to vascular compromise. So even a short term increase in IOP might be able to impair the already dysfunctional perfusion. The results of our calculations and the short term measurements of IOP show that a paracentesis is recommended after injection of 0,1 ml to avoid IOP levels of 80 mmHg and more especially in hyperopic short eyes.

Keywords: injection • clinical (human) or epidemiologic studies: outcomes/complications • corticosteroids