Hi, I'm trying to improve my understanding of flow rates through fluid filled tubes. The backround is that I am an eye doctor specialising in glaucoma. We implant small plastic tubes in to patients' eyes to relieve raised pressure. The rate of fluid production in an eyeball is approx 2.5 microliters per minute which hopefully will provide info as to the head of pressure. The tubes are currently approx 10 millimeters long and empty into a fluid filled surgically constructed second chamber outside the eyeball. From this second chamber the fluid is absorbed into veins and removed from the system. There should be no air/gas in this system. A big problem is overdrainage, causing low post-operative pressure and with it a significant risk to sight. At the moment we try to guard against this overdrainiage by blocking the lumen of the tube with a piece of stitch material and sometimes tying a stich aroung the outside of the tube to block flow through it. This then makes the post-operative pressure high but these stitches can be removed later once the second chamber has had a chance to become established (i.e. scarred up a bit) and itself can offer some resistance at the tail end of the system. I'm trying to work out if the tube parameters could be targeted to improve predictability of fluid drainage from the eye. Options include choosing a smaller internal diameter tube of using a longer length of tube. My google reading suggests that length is not that important a factor which is a shame as it would be relatively easy just to loop the tube around and around in the eye if more length meant more resistance. Hope this is clear - any questions please ask. Thanks in advance for any thoughts.