NAION [Neurosurgery Wiki]

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====== NAION ======

Non-arteritic [[anterior ischemic optic neuropathy]].
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Nonarteritic [[anterior ischemic optic neuropathy]] (NAION) is the most common acute unilateral known type of [[optic neuropathy]] in older patients with vasculopathy risk factors such as [[hypertension]], [[diabetes mellitus]], and [[obstructive sleep apnea]]. Although [[Shock-induced anterior ischemic optic neuropathy]] (SIAION) and NAION is a similar [[optic neuropathy]] due to [[ischemia]] and, in particular, [[hypotension]], they may have different pathogenic mechanisms (e.g., acute shock or intradialytic hypotension vs nocturnal hypotension), laterality (e.g., unilateral vs bilateral), and severity (e.g., light perception or worse vision). 
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Non-arteritic ischemic optic neuropathy (NAION) has been associated with phosphodiesterase (PDE) inhibitors (i.e. Sildenafil) assumedly due to hypotensive effect and vasodilation, though a causal link has not been established
((Hayreh S.S. Erectile dysfunction drugs and non-arteritic anterior ischemic optic neuropathy: is there a cause and effect relationship? J Neuro Ophthalmol. 2005;25:295–298.)).

Many patients afflicted with NAION and taking PDE inhibitors often have confounding factors due to their poor physiologic health. Nitric oxide supplements act through the same pharmacologic pathway as PDE inhibitors through cGMP to mediate vasodilation
((Di Francescomarino S., Sciartilli A., Di Valerio V., Di Baldassarre A., Gallina S. The effect of physical exercise on endothelial function. Sports Med. 2009;39:797–812.)).
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Al Othman et al. presented a case with restricted diffusion on the [[apparent diffusion coefficient]] and the [[diffusion weighted imaging]] confined to the [[optic disc]] head in a patient with pallid edema after intradialytic [[hypotension]]. Although [[DWI]] of the optic nerve is neither 100% specific nor 100% sensitive for [[ischemia]], they believe that restricted diffusion of the optic nerve head in a case is a clinico-radiologic correlate to pallid edema in SIAION
((Al Othman BA, Naser M, Kini AT, Lee AG. Restricted Diffusion in the Optic
Nerve Head After Shock-Induced Anterior Ischemic Optic Neuropathy. J
Neuroophthalmol. 2020 Jan 29. doi: 10.1097/WNO.0000000000000897. [Epub ahead of
print] PubMed PMID: 32028450.
)). 




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To re-evaluate diabetic papillopathy using [[optical coherence tomography]] (OCT) for quantitative analysis of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell layer (mGCL) and inner nuclear layer (mINL) thickness.

Subjects/methods: In this retrospective observational case series between June 2008 and July 2019 at Moorfields Eye hospital, 24 eyes of 22 patients with diabetes and optic disc swelling with a confirmed diagnosis of NAION or diabetic papillopathy by neuro-ophthalmological assessment were included for evaluation of the pRNFL, mGCL and mINL thicknesses after resolution of optic disc swelling.

Results: The mean age of included patients was 56.5 (standard deviation (SD) ± 14.85) years with a mean follow-up duration of 216 days. Thinning of pRNFL (mean: 66.26, SD ± 31.80 µm) and mGCL (mean volume: 0.27 mm3, SD ± 0.09) were observed in either group during follow-up, the mINL volume showed no thinning with 0.39 ± 0.05 mm3. The mean decrease in visual acuity was 4.13 (SD ± 14.27) ETDRS letters with a strong correlation between mGCL thickness and visual acuity (rho 0.74, p < 0.001).

Conclusion: After resolution of acute optic disc swelling, atrophy of pRNFL and mGCL became apparent in all cases of diabetic papillopathy and diabetic NAION, with preservation of mINL volumes. Analysis of OCT did not provide a clear diagnostic distinction between both entities. We suggest a diagnostic overlay with the degree of pRNFL and mGCL atrophy of prognostic relevance for poor visual acuity independent of the semantics of terminology
((Huemer J, Khalid H, Ferraz D, Faes L, Korot E, Jurkute N, Balaskas K, Egan CA, Petzold A, Keane PA. Re-evaluating diabetic papillopathy using optical coherence tomography and inner retinal sublayer analysis. Eye (Lond). 2021 Jul 9. doi: 10.1038/s41433-021-01664-1. Epub ahead of print. PMID: 34244671.)).

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