Does the change of anterior chamber depth or/and episcleral venous pressure cause intraocular pressure change in postural variation?

Purpose. Previous studies have found that the intraocular pressure (IOP) variation from postural change is due to the obstruction of aqueous outflow by an increase in episcleral venous pressure. This study investigated if any shift of anterior lens position from postural variation would be another contributing factor. Methods. Thirty-three Chinese subjects were recruited with their IOP and anterior chamber depth (ACD) measured in the sitting, supine, and prone postures. The IOP was measured using a Pulsair 2000 noncontact tonometer and ACD with a Nidek US-2000 EchoScan unit. Results. The highest IOP was obtained in the prone position and this value was significantly different from the lOP obtained in other postures, whereas there was no significant difference in ACD. Conclusions. Because no significant variation in ACD was demonstrated, the prone and supine lOP variation could be due to something other than the change in lens position. However, a higher IOP in the prone position rather than in the supine position also suggests that it is not merely the episcleral venous pressure causing the IOP change. Investigation of the entire iris profile at different postures would be more informative in future studies.