Anterior ischemic optic neuropathy

Anterior ischemic optic neuropathy (AION) is a medical condition involving loss of vision caused by damage to the optic nerve as a result of insufficient blood supply (ischemia). This form of ischemic optic neuropathy is generally categorized as two types: arteritic AION (or AAION), in which the loss of vision is the result of an inflammatory disease of arteries in the head called temporal arteritis, and non-arteritic AION (abbreviated as NAION, or sometimes simply as AION), which is due to non-inflammatory disease of small blood vessels.[1]

"AION" redirects here. For other uses, see Aion (disambiguation).
Anterior ischemic optic neuropathy
SpecialtyOphthalmology, optometry 

Symptoms

NAION typically presents suddenly upon awakening. The afflicted person notes seeing poorly in one eye. Vision in that eye is obscured by a dark shadow, often involving just the upper or lower half of vision, usually the area closer to the nose. There is no pain. Within approximately six months following the infarct, visual acuity improves by three or more lines of vision on the Snellen Chart (the chart with smaller letters on each lower line) in 42.7% of patients, while in 12.4% of patients, vision worsens by three lines. Opposite eye involvement occurs in approximately 15% to 20% of patients with NAION within 5 years.[2] It is not always devastating as visual acuity may remain only moderately impaired. Furthermore, most cases of NAION involve the loss of a hemifield (either the upper or lower half of the visual field, but not both). A few cases of NAION involve near-total loss of vision.

Risk factors

The mechanism of injury for NAION used to be quite controversial. However, experts in the field have come to a consensus that most cases involve two main risk factors. The first is a predisposition in the form of a type of optic disc shape. The optic disc is where the axons from the retinal ganglion cells collect into the optic nerve. The optic nerve is the bundle of axons that carry the visual signals from the eye to the brain. This optic nerve must penetrate through the wall of the eye, and the hole to accommodate this is usually 20-30% larger than the nerve diameter. In some patients the optic nerve is nearly as large as the opening in the back of the eye, and the optic disc appears "crowded" when seen by ophthalmoscopy. A crowded disc is also referred to as a "disc at risk". While a risk factor, the vast majority of individuals with crowded discs do not experience NAION.

The second major risk factor involves more general cardiovascular risk factors. The most common are diabetes, hypertension and high cholesterol levels. While these factors predispose a patient to develop NAION, the most common precipitating factor is marked fall of blood pressure during sleep (nocturnal arterial hypotension)- that is why at least 75% of the patients first discover visual loss first on waking from sleep. These vascular risk factors lead to ischemia (poor blood supply) to a portion of the optic disc. The disc then swells, and in a crowded optic disc, this leads to compression and more ischemia.

Since both eyes tend to have a similar shape, the optometrist or ophthalmologist will look at the good eye to assess the anatomical predisposition. The unaffected eye has a 14.7% risk of NAION within five years.[3]

A number of uncontrolled single case or small number of patient reports have associated NAION with use of oral erectile dysfunction drugs.[4][5][6][7][8][9]

Diagnosis

Since arteritic AION is similar in presentation to non-arteritic AION, patients over the age of 50 diagnosed with NAION must be evaluated to exclude AAION (symptoms: painful jaw muscle spasms, scalp tenderness, unintentional weight loss, fatigue, myalgias and loss of appetite); NAION patients over the age of 75 should always be tested.

The distinction between AAION and non-arteritic AION was made to highlight the different etiologies of anterior ischemic optic neuropathy. AAION is due to temporal arteritis (also called giant-cell arteritis), an inflammatory disease of medium-sized blood vessels (Chapel-Hill-Conference) that occurs especially with advancing age. In contrast, NAION results from the coincidence of cardiovascular risk factors in a patient with "crowded" optic discs. Non-arteritic AION is more common than AAION and usually occurs in slightly younger persons. While only a few cases of NAION result in near total loss of vision, most cases of AAION result in nearly complete vision loss.

Nonarteritic anterior ischemic optic neuropathy is an isolated white-matter stroke of the optic nerve (ON). NAION is the most common cause of sudden optic nerve-related vision loss, affecting more than 10,000 Americans every year, often bilaterally. No clinically effective treatments exist, largely because little is known about its pathophysiology, and there are few histopathological studies of the acute condition.[10]

An exhaustive review article published in March 2009 described the latest information on arteritic and non-arteritic ischemic optic neuropathy, both anterior (A-AION and NA-AION) and posterior (A-PION, NA-PION, and surgical).[11]

Treatment

Once NAION happens, it was thought that there was no accepted treatment to reverse the damage. However, a recent uncontrolled retrospective large study has shown that if patients are treated with large doses of corticosteroid therapy during the early stages of NAION, in eyes with initial visual acuity of 20/70 or worse, seen within 2 weeks of onset, there was visual acuity improvement in 70% in the treated group compared to 41% in the untreated group (odds ratio of improvement: 3.39; 95% CI:1.62, 7.11; p ¼ 0.001).[12] That study and a natural history study on NAION (Ophthalmology 2008;115: 298–305.) showed that visual acuity can improve up to 6 months and not after that. To minimize the risk of further visual loss in the fellow eye or the same eye, it is essential to reduce the risk factors. Common sense dictates trying to control the cardiovascular risk factors for many reasons, including protection from this happening to the second eye. Sudden vision loss should lead to an ophthalmological consultation. If NAION is suspected, then ideally a neuro-ophthalmologist's consultation should be obtained.

A recent Cochrane Review sought to determine the extent of safety and efficacy of optic nerve decompression surgery for NAION, compared to other treatments, or no treatment.[13] The one study included in the review found no improvements in visual acuity among patients who underwent surgery for NAION, and adverse events (pain, double vision) experienced by participants who underwent surgery.[13]

There is much research currently underway looking at ways to protect the nerve (neuroprotection) or even regenerate new fibers within the optic nerve.[14][15][16][17][18] So far there is no evidence in human studies that the so-called neuroprotectors have any beneficial effect in NAION. However, there is a new current clinical trial for the treatment of NAION in the United States with plans to include sites in India, Israel, Germany and Australia (see NORDICclinicaltrials.com and https://clinicaltrials.gov/). This trial will test the use of a synthetic siRNA that blocks caspase 2, an important enzyme in the apoptosis cycle.[19] In addition to such research, patents have been applied for by Pfizer, The University of Southern California, Otsuka Pharmaceutical and other individual inventors for innovations related to the treatment of anterior ischemic optic neuropathy.[20]

Incidence

It is estimated that the incidence of AION in the US is about 8,000 persons per year.[21]

References
  1. Atkins, EJ; Bruce, BB; Newman, NJ; Biousse, V (2010). "Treatment of nonarteritic anterior ischemic optic neuropathy". Survey of Ophthalmology. 55 (1): 47–63. doi:10.1016/j.survophthal.2009.06.008. PMC 3721361. PMID 20006051.
  2. IONDT(The Ischemic Optic Neuropathy Decompression Trial) Study
  3. Newman NJ, Scherer R, Langenberg P, et al. (September 2002). "The fellow eye in NAION: report from the ischemic optic neuropathy decompression trial follow-up study". American Journal of Ophthalmology. 134 (3): 317–28. doi:10.1016/S0002-9394(02)01639-2. PMID 12208242.
  4. Pomeranz HD, Bhavsar AR (March 2005). "Nonarteritic ischemic optic neuropathy developing soon after use of sildenafil (viagra): a report of seven new cases". Journal of Neuro-Ophthalmology. 25 (1): 9–13. doi:10.1097/00041327-200503000-00003. PMID 15756125.
  5. Egan R, Pomeranz H (February 2000). "Sildenafil (Viagra) associated anterior ischemic optic neuropathy". Archives of Ophthalmology. 118 (2): 291–2. PMID 10676804.
  6. Pomeranz HD, Smith KH, Hart WM, Egan RA (March 2002). "Sildenafil-associated nonarteritic anterior ischemic optic neuropathy". Ophthalmology. 109 (3): 584–7. CiteSeerX 10.1.1.616.3702. doi:10.1016/S0161-6420(01)00976-9. PMID 11874765.
  7. Cunningham AV, Smith KH (March 2001). "Anterior ischemic optic neuropathy associated with viagra". Journal of Neuro-Ophthalmology. 21 (1): 22–5. doi:10.1097/00041327-200103000-00006. PMID 11315976.
  8. Boshier A, Pambakian N, Shakir SA (September 2002). "A case of nonarteritic ischemic optic neuropathy (NAION) in a male patient taking sildenafil". International Journal of Clinical Pharmacology and Therapeutics. 40 (9): 422–3. doi:10.5414/cpp40422. PMID 12358159.
  9. Akash R, Hrishikesh D, Amith P, Sabah S (August 2005). "Case report: association of combined nonarteritic anterior ischemic optic neuropathy (NAION) and obstruction of cilioretinal artery with overdose of Viagra". Journal of Ocular Pharmacology and Therapeutics. 21 (4): 315–7. doi:10.1089/jop.2005.21.315. PMID 16117695.
  10. Tesser RA, Niendorf ER, Levin LA (October 2003). "The morphology of an infarct in nonarteritic anterior ischemic optic neuropathy". Ophthalmology. 110 (10): 2031–5. doi:10.1016/S0161-6420(03)00804-2. PMID 14522783.
  11. Hayreh SS (March 1999). "Retinal and optic nerve head ischemic disorders and atherosclerosis: role of serotonin". Progress in Retinal and Eye Research. 18 (2): 191–221. doi:10.1016/S1350-9462(98)00016-0. PMID 9932283.
  12. Hayreh SS, Zimmerman MB (July 2008). "Non-arteritic anterior ischemic optic neuropathy: role of systemic corticosteroid therapy". Graefe's Archive for Clinical and Experimental Ophthalmology. 246 (7): 1029–46. doi:10.1007/s00417-008-0805-8. PMC 2712323. PMID 18404273.
  13. Dickersin K, Li T (2015). "Surgery for nonarteritic anterior ischemic optic neuropathy". Cochrane Database Syst Rev. 3 (3): CD001538. doi:10.1002/14651858.CD001538.pub4. PMC 4439207. PMID 25763979.
  14. Bernstein SL, Guo Y, Kelman SE, Flower RW, Johnson MA (October 2003). "Functional and cellular responses in a novel rodent model of anterior ischemic optic neuropathy". Investigative Ophthalmology & Visual Science. 44 (10): 4153–62. doi:10.1167/iovs.03-0274. PMID 14507856. Archived from the original on 2014-06-05.
  15. Bernstein SL, Guo Y, Slater BJ, Puche A, Kelman SE (May 2007). "Neuron stress and loss following rodent anterior ischemic optic neuropathy in double-reporter transgenic mice". Investigative Ophthalmology & Visual Science. 48 (5): 2304–10. doi:10.1167/iovs.06-0486. PMID 17460295.
  16. Bernstein SL, Koo JH, Slater BJ, Guo Y, Margolis FL (2006). "Analysis of optic nerve stroke by retinal Bex expression". Molecular Vision. 12: 147–55. PMID 16541015.
  17. Goldenberg-Cohen N, Guo Y, Margolis F, Cohen Y, Miller NR, Bernstein SL (August 2005). "Oligodendrocyte dysfunction after induction of experimental anterior optic nerve ischemia". Investigative Ophthalmology & Visual Science. 46 (8): 2716–25. doi:10.1167/iovs.04-0547. PMID 16043843.
  18. Bernstein SL, Mehrabyan Z, Guo Y, Moianie N (2007). "Estrogen is not neuroprotective in a rodent model of optic nerve stroke". Molecular Vision. 13: 1920–5. PMC 2185481. PMID 17982415.
  19. Ahmed, Z.; Kalinski, H.; Berry, M.; Almasieh, M.; Ashush, H.; Slager, N.; Brafman, A.; Spivak, I.; Prasad, N. (2011-06-16). "Ocular neuroprotection by siRNA targeting caspase-2". Cell Death & Disease. 2 (6): e173. doi:10.1038/cddis.2011.54. PMC 3168996. PMID 21677688.
  20. Patents related to treatment of anterior ischemic optic neuropathy Archived 2015-09-24 at the Wayback Machine
  21. Hattenhauer MG, Leavitt JA, Hodge DO, Grill R, Gray DT (January 1997). "Incidence of nonarteritic anterior ischemic optic neuropathy". American Journal of Ophthalmology. 123 (1): 103–7. doi:10.1016/s0002-9394(14)70999-7. PMID 9186104.

Further reading
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External resources
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