In response to the comment on “Sequential nonarteritic anterior ischemic optic neuropathy in patient on chronic hemodialysis”

Dear editor,

We would like to offer our response to Ibarra-Sifuentes’ et al. [1]. Our case emphasized that non-arteritic anterior ischemic optic neuropathy (NAION) is a disease associated with hypoperfusion of the optic nerve head (ONH) as the patient we presented experienced three distinct episodes of visual loss, each one occurring immediately after experiencing profound intra-dialytic hypotension (IDH).

The questions of NAION being associated with other conditions, specifically hypertention, hyperlipidemia, smoking, diabetes mellitus, and sleep apnea, have all being raised in the past, with some papers confirming and some denying these associations [2, 3]. Patients with hypertension likely develop changes in the arterial wall decreasing the ability of the vessels to autoregulate and respond to changes in blood pressure and many patients with chronic renal failure do in fact have a history of long standing hypertension [3]. We concur that these changes from chronic hypertension could cause further hypoperfusion in response to IDH, although the main cause in our case was profound hypotension as each episode of visual loss happened right after the episode of profound IDH, emphasizing the need for minimizing the risk of IDH in patients who already experienced NAION in one eye.

While associations of NAION with other vascular risk factors most likely imply poor autoregulation of the short posterior ciliary (SPC) arteries in the setting of small scleral opening for the ONH resulting in segmental ONH edema which in turn causes a compartment syndrome. IDH provides a perfect-storm scenario in susceptible patients: profound hypoperfusion of SPC arteries causes segmental swelling of the ONH which then spreads to the surrounding segments of the nerve because of the congenital absence of the cup to accommodate the increased volume in the substance of the ONH.

While levocarnitine has been reported by the same authors to prevent episodes of IDH, it has not been approved for this use and is not used in our center. Our patient has already been receiving daily peritoneal dialysis but required hemodialysis to be performed three times a week in addition to that. He was on the list for kidney transplantation and we have repeatedly tried to expedite the transplant but unfortunately it was difficult to find an immunologic match. The patient has undergone all other standard measures to prevent IDH (dry weight assessment and management, evaluation of ultrafiltration rate and dialysate composition) but still continued to experience it attesting to the fact that it can be very difficult to prevent.

In conclusion, we emphasize that NAION is a disease most likely related to the hypoperfusion of the SPC arteries in the setting of small scleral opening for ONH, creating a potential for compartment syndrome. Hemodialysis patients who have underlying risk factors for NAION are at increased risk of repeated episodes of NAION in the fellow and even the same eye. This could be related to poor autoregulation of SPC during episodes of IDH thus all measures should be taking in order to minimize its occurrence.