Intraocular pressure (IOP) changes induced by regular dialysis treatment (RDT)

It has been long known that uremia and RDT could alter the optical fibers of the Central Nervous System: we also previously demonstrated the persistence of a delayed P100 wave evoked by Visual Potentials (VEPs) in RDT patients. Our present study evaluates changes in IOP during RDT and possible correlations between electrophysiological and tonometrical modifications. In twenty patients undergoing RDT (12 hrs/weekly, mean age 42.05 +/- 10.80 yrs) we performed, just before and immediately after the dialytic session the tonographic recordings and serum osmolality. The pre-dialysis IOP of all 20 patients ranged from 9.00 to 27.19 mmHg with a mean of 16.40 +/- 7.20. Serum osmolality predialysis was 326.10 +/- 5.72 mOsm/l and post-dialysis 290.33 +/- 2.95 mOsm/l. Our studies suggest a correlation between decrease in plasma osmolality and increase in IOP during dialysis. The effect of RDT on IOP depends on the balance between the rise in IOP with the reduction of the concentrations of "waste products" and the extracellular volume reduction associated with ultrafiltration. The elevation of IOP may be due to a decrease in post-dialysis outflow facility inducing an osmotic influx of water into the eye because of hyperosmolality of intraocular fluids. These continuous modifications may be partially responsible for the defective propagation and the delayed transmission documented by VEPs.