|Year : 2020 | Volume
| Issue : 3 | Page : 151-152
Keep an eye on acute optic neuropathy
Department of Ophthalmology, Far Eastern Memorial Hospital, Banciao District, New Taipei City; Department of Electrical Engineering, Yuan-Ze University, Chung-Li, Taoyuan, Taiwan
|Date of Submission||08-Jul-2020|
|Date of Acceptance||08-Jul-2020|
|Date of Web Publication||16-Sep-2020|
Dr. Tzu-Lun Huang
Department of Ophthalmology, Far Eastern Memorial Hospital, No. 21, Section 2, Nanya South Road, Banciao District, New Taipei City 220
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Huang TL. Keep an eye on acute optic neuropathy. Taiwan J Ophthalmol 2020;10:151-2
Getting blind after recovery from general anesthesia in patients who undergo spinal fusion is a catastrophic event. Perioperative visual loss (POVL) is most commonly due to ischemic optic neuropathy (ION), followed by retinal arterial occlusion. The first description of POVL in Medline, named “Postoperative amaurosis,” was published in 1950. Along with the rapid growth in spine procedures, the yearly number of POVL publications accelerated dramatically. However, the number of cases reported POVL registry yearly has been decreasing from a peak in 2000 and has been dropping since. Peri-operative ION (PO-ION) in spine fusion decreased statistically significantly (P = 0.002) from 1.63/10,000 in 1998 to 0.60/10,000 in 2010. This seems a great news to us, but why is the incidence of PO-ION falling? It is probably due to a reduction in operative times along with intraoperative blood transfusion.
One invited article in this issue of TJO highlights the need for all eye doctors to be aware of blind intraoperatively (article by MY Wang and AA Sadun et al.). Two articles highlight the optical coherence tomography (OCT) in neuro-ophthalmology: one shares their findings of no significantly thinner macular and peripapillary choroidal thickness (CT) in typical unilateral retrobulbar optic neuritis (ON) eye (clinical diagnosis without magnetic resonance imaging proven) and non-ON eye compared with the healthy control group (article by A Dehghani and MH Alemzadeh-Ansari et al.). The other one reveals that non-ON eye of neuromyelitis optica (NMO) patients had a significant reduction in retinal nerve fiber layer thickness along with changes of contrast sensitivity as compared to the control group (article by WOC Feng and WHW Hitam). A case report raises the question in differentiating between acute zonal occult outer retinopathy and ON (article by PF Peng and WC Chan). In one cross-sectional study of 122 patients referred for ON, ON was overdiagnosed in 59.8% of referral cases. The most common errors result from overreliance on a simple clinical history or not considering alternative diagnoses.
The article by Wang and Sadun et al. in this issue describes the risks of PO-ION and summarizes PO-ION succinctly: We need to control modifiable vascular risk factors to prevent irreversible neurologic sequelae in PO-ION. The causation in PO-ION remains elusive, however, it is most frequent in spine fusion or cardiac surgery. In ION, only the following six factors were identified as independent risk factors in a multivariate model: male sex, obesity, operation duration, the use of a Wilson frame for positioning intraoperatively, estimated blood loss, and nonblood fluid management., Besides, they found that the average blood loss was 2.3 L (ranging from 0.8 to 7.6 L) in PO-ION cases. On an average, the lowest hematocrit was 26.1% (ranging from 20% to 36.6%), with the hematocrit percentage decreasing from baseline of about 65%. The addition of colloids will reduce the cell's third space and the resultant increase in tissue pressure. The overall visual outcome appears to be inversely related to the length of the surgery, therefore, staged surgery needed to be considered for high-risk patients. Focusing on minimally invasive surgery, staging of complex procedures, and improved anesthesia practices will probably reduce the length of surgery and blood loss. Furthermore, even though anemia and hypotension are common after major surgery, very few patients develop perioperative PO-ION. This suggests the multifactorial etiology and individual susceptibility in PO-ION.
There were some animal models of PO-ION (pig and rat) which represented that optic nerve injury partly resembling human ION can be produced by combining hemodilution and head-down tilt., In those studies, the optic nerve blood flow did not have a compensatory increase in the condition of anemia with or without hypotension comorbidity, thereby resulting in significant reductions on optic nerve oxygen delivery in the model of procaine. The nerves in the experimental group, after an ischemia insult, all demonstrated typical optic atrophy with gliosis. These ischemia changes of axonal degeneration were observed mainly in the intracanalicular portion of the optic nerve.
NMO is an autoimmune demyelinating disease with pathogenic aquaporin-4 autoantibodies that act against the astrocyte water channel protein. NMO is associated with recurrent episodes of ON, transverse myelitis, and other brain stem symptoms, often resulting in severe disability. Inflammatory diseases usually alter the vascular structure, and there is no exception in the retina. In the eye, the choroid is the vascular layer and thus can be possibly changed along with inflammatory optic neuropathy. A previous article described patients with multiple sclerosis who after affected by ON had decreased subfoveal CT. Multiple sclerosis produces retinal structural loss, decreased optic nerve head perfusion, and macular vessel density in ON and non-ON eyes in OCT angiography., However, A Dehghani et al. demonstrated the utilization of OCT in the evaluation of macular and peripapillary CT in patients with acute typical unilateral retrobulbar ON, which showed no significant decrease compared with that of control groups.
In conclusion, different ethnicity and comorbidity will decide the prognosis of visual function and structural loss in ION and ON. Publications of PO-ION in the neuro-ophthalmological literature are still sparse. OCT is an essential imaging technique able to assess structural changes associated with nonglaucomatous optic neuropathy. This issue has the most important theme in acute optic neuropathy which will be an active research area of neuro-ophthalmology in future, in both the basic mechanism and potential medication as well as clinical pathophysiological insight of optic nerve disorders.
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