Anterior ischemic optic neuropathy and dialysis: Effect of hypotension
A 72-year-old male on peritoneal dialysis for renal failure from chronic glomerulonephritis presented with sudden loss of vision OS. He had a left AION with an altitudinal field defect affecting the inferior part of this visual field. The ION was attributed to systemic hypotension associated with continuous peritoneal dialysis.\nNonarteritic AION presents as a sudden visual loss that many patients report on awakening, with an afferent pupillary defect and optic disc edema. Visual field analysis mostly shows nerve fiber bundle defects, mainly inferior altitudinal. AION is believed to occur due to interference with the posterior ciliary artery blood supply to the prelaminar optic nerve. Hayreh very importantly described nocturnal hypotension as the most important precipitating factor in the pathogenesis of AION in normal patients and it explains why patients with AION complain of visual loss on awakening.[]\nPatients under dialysis are generally prone to hypotensive events, which places them at risk for developing AION.[–] Jackson described ambulatory blood pressure monitoring in a patient undergoing peritoneal dialysis who suffered bilateral AION, showing severe drops in nocturnal blood pressure, with diastolic readings as low as 41 mmHg.[]\nOne would expect that the continuous nature of peritoneal dialysis will place patients at a lower risk of systemic hypotension when compared with patients on hemodialysis. However, reports in literature are distributed equally into peritoneal and hemodialysis groups and clearly hypotension is the precipitating factor in both types of patients.[–] Uremic patients often may also have other coexisting pathological factors such as hypotension (decreased blood delivery), or hypertension, atherosclerosis, and anemia (low blood oxygen carrying capacity), that predispose them to AION.\nSystemic steroids has often been the mode of therapy in AION. But there is no strong evidence that favors their use. The rationale for use of steroids in NAION comes from the late 1960s that steroids would decrease capillary permeability, thereby inducing faster resolution of disc edema and this would reduce compression of capillaries in the optic nerve head and improve blood flow, restoring the function of surviving, but nonfunctioning, ischemic axons. NAION remains frustrating for clinicians and often devastating for patients. The pathophysiology remains unclear, and it is uncertain whether any treatment will be effective for NAION. The role of steroids remains controversial, and although steroids might accelerate resolution of disc edema, there is currently no evidence that a shorter duration of disc edema is associated with improved visual outcome. The controversy should be seen as stimulus to expand the research on the pathophysiology and treatment of NAION rather than proof that steroids are an effective treatment for acute NAION.”\nTherapy of AION related to dialysis is unsatisfactory. Conolly reported visual recovery in hypotensive AION following vigorous pressure rise. Hyperbaric oxygen therapy elevates the dissolved oxygen content of blood, thereby providing increased tissue oxygen and potentially reducing damage in injured axons.[] The effect of hyperbaric oxygen in 20 nonarteritic AION patients between 3 and 20 days of onset of visual loss was evaluated. There was no improvement in visual acuity or visual field even in the subgroup treated within 9 days of onset of symptoms.[]\nSpecial attention should be given to patients undergoing chronic dialysis. Prevention of severe hypotensive events is very crucial in preventing potentially blinding condition. Once AION is established, treatment will probably be ineffective in restoring vision.