Superonasal Transconjunctival Optic Nerve Sheath Decompression: A Simplified Technique for Safe and Efficient Decompression

Background: Severe, permanent vision loss is a feared sequela of untreated or refractory idiopathic intracranial hypertension (IIH). For patients with progressive vision loss despite maximally tolerated medical treatment, optic nerve sheath decompression (ONSD) remains a viable and effective option to protect vision. Our objective is to introduce a modified transconjunctival technique for ONSD and determine its safety, efficacy, and efficiency in patients with IIH.

Surgeons’ Corner Section Editors: Vivek R. Patel, MD Prem Subramanian, MD, PhD Superonasal Transconjunctival Optic Nerve Sheath Decompression: A Simplified Technique for Safe and Efficient Decompression Andrew T. Melson, MD, Jacob D. Warmath, BS, Annie Moreau, MD, Bradley K. Farris, MD Downloaded from http://journals.lww.com/jneuro-ophthalmology by BhDMf5ePHKav1zEoum1tQfN4a+kJLhEZgbsIHo4XMi0hCywCX1AWnYQp/IlQrHD3i3D0OdRyi7TvSFl4Cf3VC4/OAVpDDa8K2+Ya6H515kE= on 05/04/2022 Background: Severe, permanent vision loss is a feared sequela of untreated or refractory idiopathic intracranial hypertension (IIH). For patients with progressive vision loss despite maximally tolerated medical treatment, optic nerve sheath decompression (ONSD) remains a viable and effective option to protect vision. Our objective is to introduce a modified transconjunctival technique for ONSD and determine its safety, efficacy, and efficiency in patients with IIH. Methods: We performed analyses for a retrospective case series of consecutive patients with IIH by modified dandy criteria who underwent isolated superonasal transconjunctival optic nerve sheath decompression (stOND) at single eye institute in a large academic center from January 2013 to February 2017. Sixty-six patients were identified who met these criteria with at least 6 weeks of follow-up data. Primary outcome measures were visual field mean deviation, grading of papilledema by the modified Frisen scale, and best-corrected visual acuity. Secondary outcome measures were presence of postoperative diplopia and operative time. Results: One hundred thirty-two eyes of 66 patients were identified; 58 were female (88%), and 8 were male (12%). The mean age was 30 years (range 13–55) with an average lumbar puncture opening pressure of 38 cm H2O. Participants mean body mass index was 36 (range 20–59) with Grade 3 papilledema on average by the modified Frisen scale. No patients experienced operative complications, postoperative diplopia, or worse visual acuity at 1 week after surgery. Average operative time was 50 minutes (range: 25–89). The median decrease in papilledema grading was 3 grades on the Frisen scale (95% confidence interval [CI], 2–3, P , 0.0001). Snellen visual acuity changes did not meet statistical significance. The average Humphrey Visual Field Dean McGee Eye Institute, University of Oklahoma, Oklahoma City, Oklahoma. Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc, New York, NY. The authors report no conflicts of interest. Address correspondence to Andrew T. Melson, MD, Dean McGee Eye Institute, University of Oklahoma, 608 Stanton L. Young Boulevard, Oklahoma City, OK 73104; E-mail: [e-mail] e16 mean deviation change was +1.91 (95% CI, 0.58–3.24, P = 0.0052). Despite successful bilateral decompressions, 4 patients (6.1%) progressed in their visual loss. Conclusions: The superonasal transconjunctival approach to ONSD is a safe, efficient and effective surgical treatment for patients with deteriorating visual function due to IIH. Although additional study is required to further clarify the best timing and indications for ONSD among other treatment options for refractory IIH, providers should be aware of the reduced complication rates and efficacy of the stOND technique. Journal of Neuro-Ophthalmology 2021;41:e16–21 doi: 10.1097/WNO.0000000000000898 © 2020 by North American Neuro-Ophthalmology Society F irst defined by Dandy in 1937, idiopathic intracranial hypertension (IIH) is a disease characterized by elevated intracranial pressure in the absence of other intracranial disease. Although the etiology is unknown, IIH tends to affect overweight and obese women of child-bearing age. The signs and symptoms of IIH, which include papilledema, headache, diplopia, transient visual obscurations, and pulsatile tinnitus, are all believed to be a direct result of elevated intracranial pressure. Permanent vision loss is a feared sequela of untreated or refractory IIH. In addition to weight loss, acetazolamide is the mainstay of treatment (1) and decreases cerebrospinal fluid production and intracranial pressure, despite unfavorable side effects. Unfortunately, up to 10% of patients with IIH experience progressive vision loss despite medical treatment (2). For patients with refractory or advanced IIH despite medical treatment, surgical interventions include optic nerve sheath decompression (ONSD), neurosurgical shunting, and venous sinus stenting. Although neurosurgical shunting procedures may have the benefit of addressing both headache and vision loss related to IIH, ventriculoperitoneal shunts and lumboperitoneal shunts have been Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Surgeons’ Corner reported to fail and require revision in up to 36% and 46%, respectively, in a population with IIH (3). The majority of these failures occur within the first 12 months with an average of more than 2 revisions per patient for both types of shunts (3). For the subset of IIH patients with focal dural venous sinus stenosis, venous sinus angioplasty and stenting has been promising in symptomatic improvement and low complication rates (4). Whether dural venous sinus stenosis is present or not, ONSD remains a viable treatment option when medical treatment fails and vision loss is progressive. DeWecker first proposed ONSD in 1872 for patients with neuroretinitis (5). As the mechanisms of papilledema and optic nerve damage became better elucidated, ONSD was reintroduced for the potential treatment of nonarteritic ischemic optic neuropathy (NAION) and papilledema associated with IIH. Early studies of ONSD for NAION showed no additional benefit or even potential harm (6,7) with a relatively high rate of complications. As techniques have evolved and indications have become more limited to patients with progressive or advanced vision loss related to IIH, the safety and efficacy of ONSD has improved. Recent studies have shown improved success with fewer complications (8–12). In this study, we introduce a modified transconjunctival technique and report on our results from a large series of patients with IIH and progressive vision loss despite maximally tolerated medical treatment. To the best of our knowledge, this is the first report of a medial transconjunctival approach that spares rectus muscle disinsertion and represents one of the largest reports of outcome data for ONSD of any approach. METHODS After Institutional Review Board (IRB) approval was obtained, we performed a retrospective chart review of patients with IIH who underwent superonasal transconjunctival optic nerve sheath decompression (stOND) at the Dean McGee Eye Institute, University of Oklahoma, between January 2013 and February 2017 (Fig. 1). One surgeon supervised all surgeries (B.K.F.), although all cases involved residents or fellows, often operating as the primary surgeon. We reviewed clinical records from the preoperative evaluations, 1-week and 6-week postoperative visits, along with surgical charts. Demographic information regarding age, gender, body mass index, lumbar puncture opening pressure, and symptoms was reviewed. Inclusion required an IIH diagnosis based on the modified Dandy criteria (13). Exclusion criteria included history of previous eye surgery or patients who underwent a combination procedure for strabismus. All patients underwent simultaneous bilateral stOND. Our series consisted of 132 eyes of 66 patients whose characteristics are summarized in Table 1. Primary outcome measures were visual field mean deviation, grading of papilledema by the modified Frisen scale (14), and best-corrected visual acuity. Secondary Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 FIG. 1. A total of 82 patients were found to have undergone stOND during the study period. Four patients were excluded due to dural venous sinus thrombosis. Of the remaining patients, 1 patient underwent combination stOND with strabismus surgery for pre-existing exotropia. Of those remaining, 11 patients had insufficient follow-up data due to geographic limitations to follow-up. stOND, superonasal transconjunctival optic nerve sheath decompression. outcome measures were presence of postoperative diplopia and operative time. Outcome measures were recorded from the closest documented examination before surgery along with the 1-week and 6-week follow-up visits. The operative time was recorded as the total minutes elapsed between the surgical start-time to the surgical end-time for each case, as documented in the surgical chart. Intraoperative and perioperative complications were defined as wound dehiscence, infection, diplopia, tonic pupil, corneal dellen formation, or any condition requiring initiation of additional treatment or return to the operating room in the first 6 weeks after surgery. Pre–post measurements of visual acuity were compared using linear mixed models. Pre–post measurements on optic nerve edema grade (ordinal outcome) and mean deviation were compared using linear quantile mixed models. All statistical analyses were performed in R v3.4.3 and SAS v9.4. The stOND procedure was performed in all cases with a superonasal transconjunctival approach. Under general anesthesia with the primary surgery sitting superiorly at a surgical microscope, a 10-mm curvilinear incision is made through the conjunctiva in the superonasal fornix. Through this incision, a small strip of the underlying Tenon capsule e17 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Surgeons’ Corner TABLE 1. Patient demographics and clinical characteristics # of Patients (%), Unless Otherwise Specified Sex Female Male Age Mean (range) Body mass index Mean (range) Hypertension Diabetes mellitus Complaint Headache Transient visual obscurations Decreased quality of vision Diplopia Pulse synchronous tinnitus 58 (88%) 8 (12%) 30 years (13–55) 36 kg/m2 (20–59) 17 (25.8%) 3 (4.6%) 62 (94%) 40 (61%) 28 (42%) 9 (14%) 4 (6%) is excised and hemostasis is achieved with cautery. The superior and medial rectus muscles are then secured with separate 4-0 silk traction sutures. The eye is then rotated temporally with the traction sutures and held in place by an assistant. The Farris-Tang retractor (15) (Bausch & Lomb Part #SP7-53436) is then inserted through the conjunctival incision to retract the orbital fat and surrounding structures nasally, providing visualization of the optic nerve sheath without disinserting the medial rectus muscle. The nerve sheath is then grasped and elevated away from the nerve with cupped ENT forceps (V Mueller AU14122). With the sheath held away from the nerve, a 2-mm · 3-mm fenestration is created in the dura along the superonasal aspect of the optic nerve sheath with intraocular scissors (Boss 803470). Rhoton nerve retractors (V Mueller NL3785-006/7) are used to gently lyse arachnoid trabeculae within the nerve sheath. The retractor is then removed, and the conjunctiva is reapproximated with buried, interrupted 8-0 absorbable sutures. Throughout each case, the pupil is carefully monitored to ensure no excessive tension is applied to the optic nerve. In all cases, stOND was performed bilaterally under the same general anesthetic. A video demonstration of the technique is available online through the NeuroOphthalmology Virtual Education Library (NOVEL) (16). RESULTS A total of 82 patients were identified who underwent stOND. Of these 82 patients, 4 had dural venous sinus thrombosis identified on neuroimaging and 1 underwent a combination of stOND and strabismus surgery. These 5 patients were excluded. Of the remaining 77 patients, 11 had insufficient follow-up to be included in the study. All e18 11 patients lacked a documented 6-week follow-up appointment, with the majority following up with more local providers due to geographic or financial constraints to travel. Therefore, 132 eyes of 66 patients were identified who met inclusion criteria. Six of the patients were referred for stOND after failing acetazolamide treatment with outside providers. Of the 60 patients treated primarily at our institute, 36 patients progressed despite tolerating a minimum of 1 g of acetazolamide daily, 23 patients were unable to take or intolerant to medication, and one presented with advanced disease prompting urgent surgical intervention. The average time from initial diagnosis to surgical intervention for the medication treatment failure group was 16 weeks. Of the 66 patients, 58 were female (88%) and 8 were male (12%). The mean age at time of stOND was 30 years (range 13–55). Before surgery, lumbar puncture opening pressures were all elevated, with an average opening pressure of 38 cm H2O. Patients had a mean body mass index of 36 (range 20–59). Papilledema was present in 127 of 132 eyes (96%) with an average of Grade 3 by the modified Frisen scale (Table 2). Comorbidities varied, with 17 patients (26%) having been previously diagnosed with hypertension and only 3 patients (5%) diagnosed with diabetes mellitus. Headache was the predominant complaint of patients in our series with 94% prevalence. Visual complaints were frequently reported as transient visual obscurations (61%) or decreased quality of vision (42%). Less commonly, patients complained of diplopia (14%) and pulse synchronous tinnitus (6%). The preoperative symptomatology of our patient population was consistent with that of the IIH treatment trial in all areas except for pulse synchronous tinnitus which was less common in our study (17). All 132 eyes underwent successful, bilateral stOND. There were no intraoperative or perioperative complications identified. None of the 66 patients reported diplopia or had manifest strabismus at the 6-week postoperative visit. The average operative time was 50 minutes per bilateral case with a range of 25–89 minutes, including all cases in which residents and fellows were primary surgeon. Papilledema grading improved in all 127 eyes that had preoperative papilledema (Table 3). Those eyes without preoperative papilledema were fellow eyes of patients with severe, asymmetric disease. The median decrease in papilledema grading was 3 grades on the Frisen scale (95% confidence interval [CI], 2–3, P , 0.0001). Snellen visual acuity improvement of greater than one line was noted in 33 of 132 eyes (25%). No eyes had a worse visual acuity at 1 week after surgery. Overall, the visual acuity changes after intervention did not reach statistical significance. The overall average Humphrey Visual Field mean deviation change was +1.91 (95% CI, 0.58–3.24, P = 0.0052). Despite successful bilateral decompressions, 4 patients (6.1%) experienced progressive visual loss. Of the 4 patients who progressed despite decompression, 2 had opening pressures of 50 cm of Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Surgeons’ Corner TABLE 2. Preoperative papilledema grading Papilledema Grade Grade Grade Grade Grade Grade # of Eyes 0 1 2 3 4 5 5 27 28 29 25 18 H2O, and all 4 had presenting visual acuity of count fingers or worse in one or both eyes. CONCLUSIONS The superonasal transconjunctival approach to ONSD is a safe, efficient and effective surgical treatment for patients with deteriorating visual function due to IIH. Building on the well-established medial transconjunctival technique, stOND uses specific instrumentation to aid the surgeon in safety and efficacy (15). The Farris–Tang muscle retractor allows for adequate visualization of the optic nerve sheath without disinsertion of rectus muscles. This reduces surgical time and eliminates postoperative diplopia while preserving the less invasive nature of transconjunctival approaches to ONSD. A lower powered lens (225 diopter Leica or 225/250 diopter Zeiss) on the operative microscope increases focal length and allows for more clearance between the microscope and operative field. This increased space allows for the use of cupped ENT forceps and Rhoton nerve retractors which prevent the surgeon’s hands from obscuring visualization of the operative field through the microscope. Recent systematic reviews of surgical interventions for IIH reported minor complication rates ranging from 15% to 26% for all ONSD surgeries performed with a major complication rate around 1.5% (18). In our case series, no surgical complications were identified with at least 6-week follow-up in all patients. The lack of postoperative diplopia highlights one of the primary benefits of this technique. Although the medial and lateral transconjunctival techniques involve the disinsertion of a rectus muscle, the stOND does not require muscle disinsertion, reducing postoperative diplopia rates. Furthermore, the time required to suture and reinsert the rectus muscles is saved, increasing efficiency and reducing operative time and cost. Although there is a lack of well-published data on the cost or average length of surgery for different techniques in ONSD, the stOND technique requires minimal disposable material cost and, at 25 minutes on average per eye, is highly efficient. To the best of our knowledge, this study is the first to report operative time for any technique of ONSD. Beyond the cost savings, efficiency in ONSD is essential for safety, as prolonged surgical time increases inherent risk of surgical complications due to compromised optic nerve perfusion or stretching damage to the rectus muscles and ciliary nerves. In addition to being safe and efficient, stOND is highly effective at halting the progression of vision loss in IIH. In this case series, 94% of patients achieved stabilization or improvement in their visual acuity and visual fields, a success rate commensurate to published data from other techniques for ONSD (9,10,12) including previous case series by the same surgeon (8,11). Although 4 patients (6%) experienced progressive visual loss despite stOND, all 4 of these patients had visual acuity of count fingers or worse in one or both eyes before surgery. In addition, of the 4 patients who progressed despite decompression, 2 had opening pressures of 50 mm of H2O or higher, and 1 had unsuccessful lumbar puncture attempt due to body habitus. The association between high lumbar puncture opening pressure and an increased risk of ONSD failure has been demonstrated previously (19). The higher prevalence of progression in patients with advanced disease suggests that future research is warranted to determine whether early surgical intervention may be beneficial in patients with fulminant vision loss due to IIH. TABLE 3. Summarization of outcome variables, before and after intervention Characteristic Acuity (logMAR) Mean ± SD Range Optic nerve edema grade Median [25%, 75%] Range Mean deviation Mean ± SD Median [25%, 75%] Range 95% CI on Change P Preop Postop (Week 6) Change 0.19 ± 0.51 20.12, 2.90 0.18 ± 0.59 20.12, 2.90 20.01 ± 0.41 22.70, 2.00 20.09, 0.08 0.9059* 3 [2, 4] 0, 5 0 [0, 0] 0, 2 22.5 [23.5, 21.5] 25, 0 23.0, 22.0 ,0.0001† 28.27 ± 10.05 24.6 [211.1, 21.9] 233.92, 12.57 25.58 ± 7.76 23.3 [26.0, 21.9] 234.08, 3.73 1.91 ± 5.52 0.7 [20.5, 3.0] 213.87, 30.17 0.58, 3.24 20.18, 2.37 0.0052* 0.2066† Significant P-values (at a = 0.05) are bolded. *From linear mixed model. † From linear quantile mixed model. CI, confidence interval. Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 e19 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Surgeons’ Corner A recent survey of practicing oculoplastic and reconstructive surgeons showed that the most commonly preferred method for ONSD was the medial transconjunctival approach with a windowed fenestration (20). Although the superonasal lid crease incision has gained popularity, it remained the preferred technique of less than a third of surgeons surveyed. The stOND technique is less well known and was not included in the survey. Although unilateral vs. bilateral primary decompression was not evaluated in the survey, the 3 largest medial transconjunctival case series published (8,11,12) reported a very high predominance of bilateral ONSD (820 eyes of 426 patients). It is these authors’ experience that bilateral simultaneous decompression is preferable. Although unilateral ONSD may lead to improvement on the contralateral side (21), the risk of continued or recurrent papilledema and subsequent visual decline may persist in the nonoperative eye. Although no direct comparison trials of unilateral vs. bilateral ONSD studies have been published, histopathologic and anatomic studies suggest potential limitations to unilateral decompression. Hayreh’s foundational histopathologic studies reveal pial connective tissue septae within the CSF space (22). These septations were further elucidated by Killer et al (23) in series of postmortem anatomical studies, which revealed a complex system of arachnoid trabeculae and septa that divide the subarachnoid space into multiple compartments. This multicompartmental nature of the optic nerve sheaths may limit the shunting effect of a unilateral fenestration and may warrant careful lysis of all visible arachnoid trabeculae intraoperatively with the Rhoton nerve retractors as outlined above. This case series is a retrospective chart review and as such is subject to bias and has multiple limitations. A primary limitation to our study is the lack of follow-up data for 11 of the initially identified 82 patients who underwent ONSD, a risk for sampling bias. Although potential differences in their postoperative outcomes are unknown, the demographic information and average preoperative visual function did not differ in a statistically significant fashion from those included. In addition, the nature of our tertiary referral center leads to a higher level of complexity and increased likelihood of previous failure of medical treatment at presentation, which may limit generalizability. An additional limitation is our use of the modified Frisen scale. Although heavily used in clinical practice, the subjective nature of this method of papilledema grading as well as the unmasked nature of the observer introduces opportunity for variability and observer bias. Although this case series indicates that stOND appears to be a safe and effective technique in an experienced surgeon’s hands for surgical treatment of IIH, additional research is indicated. The treatment algorithm for IIH is complex and continues to evolve as ONSD techniques improve and venous stenting procedures are added to the armamentarium. Future research is needed to evaluate the e20 role and timing of surgical interventions for patients with IIH at all stages of disease. Expanding the fund of clinical outcome data for approaches to ONSD is particularly needed due to the lack of clinical guidance for the management of vision loss in IIH. Until such evidence-based guidelines are published, this case series supports the safety, efficacy, efficiency, and teachability of the superonasal transconjunctival approach to ONSD for patients with IIH and vision loss refractory to medical treatment. STATEMENT OF AUTHORSHIP Category 1: a. Conception and design: B. K. Farris, A. Moreau, and A. T. Melson; b. Acquisition of data: A. T. Melson, A. Moreau, and J. D. Warmath; c. Analysis and interpretation of data: A. T. Melson, J. D. Warmath, and B. K. Farris. Category 2: a. Drafting the manuscript: A. T. Melson and B. K. Farris; b. Revising it for intellectual content: A. T. Melson, B. K. Farris, and A. Moreau. Category 3: a. Final approval of the completed manuscript: A. T. Melson, B. K. Farris, A. Moreau, and J. D. Warmath. REFERENCES 1. NORDIC Idiopathic Intracranial Hypertension Study Group Writing Committee, Wall M, MJ McDermott MP, Kieburtz KD, Corbett JJ, Feldon SE, Friedman DI, Katz DM, Keltner JL, Schron EB, Kupersmith MJ. Effect of acetazolamide on visual function in patients with idiopathic intracranial hypertension and mild visual loss: the idiopathic intracranial hypertension treatment trial. JAMA. 2014;311:1641–1651. 2. Wall M, George D. Idiopathic intracranial hypertension. A prospective study of 50 patients. Brain. 1991;114:155–180. 3. Lai LT, Danesh-Meyer HV, Kaye AH. Visual outcomes and headache following interventions for idiopathic intracranial hypertension. J Clin Neurosci. 2014;21:1670–1678. 4. Puffer RC, Mustafa W, Lanzino G. Venous sinus stenting for idiopathic intracranial hypertension: a review of the literature. J Neurointerv Surg. 2013;5:483–486. 5. DeWecker L. On incision of the optic nerve in cases of neuroretinitis. In: Power H, ed. Report of the Fourth International Ophthalmological Congress. Vol. 4, London, United Kingdom: Savill, Edwards and Co, 1873:11–14. 6. The Ischemic Optic Neuropathy Decompression Trial Research Group. Optic nerve decompression surgery for nonarteritic ischemic optic neuropathy (NAION) is not effective and may be harmful. JAMA. 1995;237:625–632. 7. Jablons MM, Glaser JS, Schatz NJ, Siatkowski RM, Tse DT, Kronish JW. Optic nerve sheath fenestration for treatment of progressive ischemic optic neuropathy: results in 26 patients. Arch Ophthalmol. 1993;111:84–87. 8. Banta JT, Farris BK. Pseudotumor cerebri and optic nerve sheath decompression. Ophthalmology. 2000;107:1907– 1912. 9. Agarwal MR, Yoo JH. Optic neve sheath fenestration for vision preservation in idiopathic intracranial hypertension. Neurosurg Focus. 2007;23:E7. 10. Nithyanandam S, Manayath GJ, Battu RR. Optic nerve sheath decompression for visual loss in intracranial hypertension: report from a tertiary care center in South India. Indian J Ophthalmol. 2008;56:115–120. 11. Moreau A, Lao KC, Farris BK. Optic nerve sheath decompression: a surgical technique with minimal operative complications. J Neuroophthalmol. 2014;34:34–38. 12. Vaidya NS, Mahmoud AM, Buzzacco D, Katz SE. Visual outcomes following optic nerve sheath fenestration via the medial transconjunctival approach. Orbit. 2016;35:271– 277. Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Surgeons’ Corner 13. Dandy WE. Intracranial pressure without brain tumor. Ann Surg. 1937;106:492–513. 14. Frisen L. Swelling of the optic nerve head: a staging scheme. J Neurol Neurosurg Psych. 1982;45:13–18. 15. Spiegel JA, Sokol JA, Whittaker TJ, Bernard B, Farris BK. FarrisTang retractor in optic nerve sheath decompression surgery. Orbit. 2016;35:39–41. 16. Lai KE, Lao KC, Hildebrand PL, Farris BK. 2014. Superonasal Transconjunctival Optic Nerve Sheath Decompression (stONSD). Salt Lake City, UT: Spencer S. Eccles Health Sciences Library, University of Utah. Available at: https://collections.lib.utah.edu/ ark:/87278/s6f50xsr. Accessed November 2018. 17. Wall M, Kupersmith MJ, Kieburtz KD, Corbett JJ, Feldon SE, Friedman DI, Katz DM, Keltner JL, Schron EB, McDermott MP; NORDIC Idiopathic Intracranial Hypertension Study Group. The idiopathic intracranial hypertension treatment trial: clinical profile at baseline. JAMA Neurol. 2014;71:693–701. 18. Satti SR. Meta-analysis of CSF diversion procedure and dural venous sinus stenting in the setting of medically refractory IIH. Am J Neuroradiol. 2015;36:1899–1904. Melson et al: J Neuro-Ophthalmol 2021; 41: e16-e21 19. Robinson ME, Moreau A, O’Meilia R, Pagteilan J, Ding K, Siatkowski RM, Farris BK. The relationship between optic nerve sheath decompression failure and intracranial pressure in idiopathic intracranial hypertension. J Neuroophthalmol. 2016;36:246–251. 20. Sobel RK, Syed NA, Carter KD, Allen RC. Optic nerve sheath fenestration: current preferences in surgical approach and biopsy. Ophthal Plast Reconstr Surg. 2015;31:310–312. 21. Alsuhaibani AH, Carter KD, Nerad JA, Lee AG. Effect of optic nerve sheath fenestration on papilledema of the operated and the contralateral nonoperated eyes in idiopathic intracranial hypertension. Ophthalmology. 2011;118:412–414. 22. Hayreh SS. The sheath of the optic nerve. Ophthalmologica. 1984;189:54–63. 23. Killer HE, Laeng HR, Flammer J, Groscurth P. Architecture of arachnoid trabeculae, pillars, and septa in the subarachnoid space of the human optic nerve: anatomy and clinical considerations. Br J Ophthalmol. 2003;87:777–781. e21 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited.