Introduction
During HD, numerous metabolic parameters can change, including blood urea, sodium, potassium, and glucose levels, these fluctuations result in osmotic changes in blood, aqueous and vitreous humor, and other extracellular fluids, many conflicting IOP results have been published some of them suggest that the decrease in plasma osmolarity may lead to an increase in IOP as contemporary hemodialysis is highly efficient in the removal of urea and other small molecules from the blood. Indeed, the removal of urea has been studied extensively for decades as a method to assess the efficiency or adequacy of dialysis treatments. OPP represents the pressure of blood flowing in ocular blood vessels and is defined as the difference between mean arterial pressure and IOP, which is an important factor in regulating blood flow within the eye. Adequate oxygenation of ocular tissues depends on maintenance of ocular perfusion pressure (OPP) through systemic regulation of blood pressure (BP) and local regulation of IOP. It has been proposed that vascular dysregulation leads to abnormal ocular perfusion and thus optic nerve ischemia, serving as an underlying cause of glaucomatous damage. Ocular perfusion pressure autoregulation which is the ability of a vascular bed to change vascular resistance in response to perfusion pressure changes to maintain a relatively constant blood flow, plays a crucial role in maintaining blood flow to the optic nerve, as intradialytic hypotension is a common complication of HD.