Posterior ischemic optic neuropathy

Posterior ischemic optic neuropathy (PION) is a medical condition characterized by damage to the retrobulbar portion of the optic nerve due to inadequate blood flow (ischemia) to the optic nerve. Despite the term posterior, this form of damage to the eye's optic nerve due to poor blood flow also includes cases where the cause of inadequate blood flow to the nerve is anterior, as the condition describes a particular mechanism of visual loss as much as the location of damage in the optic nerve. In contrast, anterior ischemic optic neuropathy (AION) is distinguished from PION by the fact that AION occurs spontaneously and on one side in affected individuals with predisposing anatomic or cardiovascular risk factors.

Posterior ischemic optic neuropath
SpecialtyOphthalmology 

Signs and symptoms

PION is characterized by moderate to severe painless vision loss of abrupt onset. One or both eyes may be affected and color vision is typically impaired.[1][2][3]

Ophthalmoscopic exam

Looking inside the person's eyes at the time of onset, ophthalmoscope exam reveals no visible changes to the optic nerve head. Weeks after ischemic insult, nerve atrophy originating from the damaged posterior optic nerve progresses to involve the anterior optic nerve head. Four to eight weeks after onset, atrophy of the optic nerve head is observable upon ophthalmoscope exam.[4]

Pupils

If both eyes are affected by PION, the pupils may look symmetrical. However, if the eyes are asymmetrically affected, i.e. one eye's optic nerve is more damaged than the other, it will produce an important sign called an afferent pupillary defect.

Defective light perception in one eye causes an asymmetrical pupillary constriction reflex called the afferent pupillary defect (APD).

Arteritic PION

A-PION most commonly affects Caucasian women, with an average age of 73.[2][5] At onset vision loss is unilateral, but without treatment it rapidly progresses to involve both eyes. Vision loss is usually severe, ranging from counting fingers to no light perception. Associated symptoms are jaw pain exacerbated by chewing, scalp tenderness, shoulder and hip pain, headache and fatigue.[3][4]

Perioperative PION

Vision loss is usually apparent upon waking from general anesthesia. Signs observable to a bystander include long surgery duration and facial swelling. Vision loss is usually bilateral and severe, ranging from counting fingers to no light perception.[1][2][3][4][6][7]

Cause

PION is a watershed infarction of the optic nerve that may cause either unilateral or, more often, bilateral blindness. PION typically occurs in two categories of people:

  • People who have undergone non-ocular surgery that is particularly prolonged or is associated with a significant blood loss.
  • People who have experienced significant bleeding from an accident or ruptured blood vessels. In these cases, the person may develop anemia (too few oxygen-delivering red blood cells in the bloodstream) and often have low blood pressure as well. This combination can produce circulatory shock, and PION has sometimes been called shock-induced optic neuropathy.

The combination of anemia and low blood pressure means that the blood is carrying less oxygen to the tissues. The optic nerve can be at very high risk for damage from insufficient blood supply due to swelling (from lack of oxygen) in a confined bony space resulting in a compartment syndrome. Restricted blood flow can lead to permanent damage to the optic nerve and result in blindness (often in both eyes). For technical reasons this occurs more frequently with spinal surgeries.[8]

Cardiovascular risk factors

Perioperative PION patients have a higher prevalence of cardiovascular risk factors than in the general population. Documented cardiovascular risks in people affected by perioperative PION include high blood pressure, diabetes mellitus, high levels of cholesterol in the blood, tobacco use, abnormal heart rhythms, stroke, and obesity. Men are also noted to be at higher risk, which is in accordance with the trend, as men are at higher risk of cardiovascular disease.[9][1][3][6][7][10][11][12][13] These cardiovascular risks all interfere with adequate blood flow, and also may suggest a contributory role of defective vascular autoregulation.[1][4][6][7]

Perioperative PION

As illustrated by the risk factors above, perioperative hypoxia is a multifactorial problem. Amidst these risk factors it may be difficult to pinpoint the optic nerve's threshold for cell death, and the exact contribution of each factor.[14]

Low blood pressure and anemia are cited as perioperative complications in nearly all reports of PION, which suggests a causal relationship. However, while low blood pressure and anemia are relatively common in the perioperative setting, PION is exceedingly rare. Spine and cardiac bypass surgeries have the highest estimated incidences of PION, 0.028% and 0.018% respectively, and this is still extremely low.[8][15][16] This evidence suggests that optic nerve injury in PION patients is caused by more than just anemia and low blood pressure.[14]

Evidence suggests that the multifactorial origin of perioperative PION involves the risks discussed above and perhaps other unknown factors. Current review articles of PION propose that vascular autoregulatory dysfunction and anatomic variation are under-investigated subjects that may contribute to patient-specific susceptibility.[4][6]

Pathogenesis

PION

In both types of PION, decreased blood flow leads to the death of optic nerve cells. Ischemic injury to the optic nerve causes inflammation and swelling. Because the posterior optic nerve passes through the optic canal, a bony tunnel leading to the brain, swelling in this rigid space causes compression of the optic nerve. This compression worsens ischemia and perpetuates the cycle of injury, and swelling, and compression.[1]

A-PION

A-PION is caused by an inflammatory disease called giant cell arteritis (GCA). GCA is an inflammatory disease of blood vessels. It is believed to be an autoimmune disease caused by inappropriate T-cell activity.[4][17] When T-cells damage arteries supplying the optic nerve, a blood clot forms and stops blood flow. When blood flow stops, oxygen delivery stops and optic nerve fibers die.

Perioperative PION

The exact cause of perioperative PION is unknown. Many risk factors have been identified, all of which contribute to inadequate delivery of oxygen to optic nerve cells. Alone, none of these risk factors is enough to cause PION. However, in susceptible individuals, a combination of these risk factors produces devastating blindness. This evidence suggests that PION is a disease of multifactorial origin.

Risks of perioperative PION can be divided into two categories, intraoperative ischemic pressures, and cardiovascular risk factors.

Intraoperative ischemic pressures

Many causes of decreased blood flow during surgery are systemic, i.e. they decrease blood flow throughout the body. Studies have shown that nearly all perioperative PION patients suffered from prolonged periods of low blood pressure during the operation and postoperative anemia. The average perioperative PION patient loses 4 liters of blood during surgery, and the majority receive blood transfusions. Massive blood loss is just one cause of low blood pressure. Medications used for general anesthesia can also lower blood pressure. The average surgery duration in PION cases is 7 to 9 hours, which increases the risk of prolonged low blood pressure.[8][1][4][6]

Other intraoperative ischemic pressures are local, i.e. they decrease blood flow to the affected area, the optic nerve. Facial swelling, periorbital swelling, direct orbital compression, facedown position during surgery, and a tilted operating table in feet-above-head position, have all been reported to be associated with perioperative PION. All of these factors are believed to increase tissue pressure and venous pressure around the optic nerve, thereby decreasing local blood flow and oxygen delivery.[9][1][4][6][10][11][12][14]

Surgeries with the highest estimated incidence of PION are surgeries with a higher risk of the aforementioned conditions. In spine surgery, patients are susceptible to significant blood loss, and they are positioned face down for long periods of time, which increases venous pressure, decreases arterial perfusion pressure, and often causes facial swelling (increased tissue pressure). Spine surgery is estimated to have the highest incidence of PION, 0.028%.[8] Long duration of feet-above-head position in prostate surgery has also been suggested to increase risk of PION.[18]

Diagnosis

The diagnosis of PION is often difficult since the optic nerves initially appear normal. The injury occurs posterior to that portion of the nerve visible during ophthalmoscopic examination. There may be an abnormal relative pupillary response (APD) if the injury is confined to one optic nerve, but often it is bilateral and the symmetry of pupillary responses is maintained. Furthermore, MRI scanning may not be helpful. It is not uncommon for the erroneous diagnoses of malingering or cortical blindness to be made. If possible, an urgent neuro-ophthalmology consult is most likely to lead to the correct diagnosis.[9]

There is no confirmatory test for PION. PION is a diagnosis of exclusion. To prevent impending blindness, it is urgent to rule out giant cell arteritis when a patient over 50 presents with sudden vision loss.

Differential diagnosis

In the postoperative setting, without gross eye injury, visual loss requires an assessment of the whole visual system for ischemic damage. The optic nerve is not the only tissue of the visual pathway susceptible to decreased blood flow. Decreased oxygenation of the retina or brain could also impair vision.[9]

Anterior ischemic optic neuropathy

PION is less common than Anterior Ischemic Optic Neuropathy (AION).[4] Blood supply and surrounding anatomy make the anterior and posterior portions of the optic nerve susceptible to different ischemic pressures.

The posterior optic nerve receives blood primarily from the pial branches of the ophthalmic artery. The optic canal, a boney tunnel leading to the brain, surrounds the most posterior part of this optic nerve segment.

The anterior optic nerve receives blood primarily from the posterior ciliary arteries. The anterior optic nerve, a.k.a. the optic nerve head, is surrounded by the scleral canal, and is vulnerable to crowding of nerve fibers. The portion of the optic nerve head that is visible by looking into the eye with an ophthalmoscope is called the optic disc.

PION versus AION

At the onset of symptoms, ophthalmoscope examination can differentiate AION from PION. If optic nerve head involvement is observed, it is AION. PION does not produce optic atrophy that is observable via ophthalmoscope until four to eight weeks after onset. In addition, AION often shows a characteristic altitudinal defect on a Humphrey Visual Field test.

GCA

The American College of Rheumatology has defined a combination of physical symptoms and inflammatory changes to diagnose giant cell arteritis.[19]

Prevention

Individuals with a history of high blood pressure, diabetes, and smoking are most susceptible to PION as they have a compromised system of blood vessel autoregulation. Hence, extra efforts may need to be taken for them in the form of careful or staged surgery or the controlling the anemia from blood loss (by administration of blood transfusions), and the careful maintenance of their blood pressure.[1]

Treatment

Once visual loss has occurred, it becomes more problematic, but there are reports of recovered vision if blood transfusions and agents that raise blood pressure are administered within hours.[20]

A-PION

If a diagnosis of GCA is suspected, treatment with steroids should begin immediately. A sample (biopsy) of the temporal artery should be obtained to confirm the diagnosis and guide future management, but should not delay initiation of treatment. Treatment does not recover lost vision, but prevents further progression and second eye involvement. High dose corticosteroids may be tapered down to low doses over approximately one year.[2][3][6][12][21][22][23][24]

Perioperative

Rapid blood transfusions, to correct anemia and raise blood pressure, may improve PION outcomes. In one report of a related disease, hypotension-induced AION, 3 out of 3 patients who received rapid transfusions reported partial recovery of vision.[20] While rapid transfusions offer some hope, the prognosis for perioperative PION remains poor. Prevention remains the best way to reduce PION.

One retrospective report proposes that incidence of PION could be reduced in high-risk cases by altering surgical management. For example, for patients undergoing spine surgery, measures could be taken to minimize intraoperative hypotension, to accelerate the process of blood replacement, and to aggressively treat facial swelling.[1]

Epidemiology

PION most commonly affects the elderly.

References
  1. Dunker S, Hsu HY, Sebag J, Sadun AA (June 2002). "Perioperative risk factors for posterior ischemic optic neuropathy". Journal of the American College of Surgeons. 194 (6): 705–10. doi:10.1016/S1072-7515(02)01210-3. PMID 12081060.
  2. Hayreh SS (November 2004). "Posterior ischaemic optic neuropathy: clinical features, pathogenesis, and management". Eye. 18 (11): 1188–206. doi:10.1038/sj.eye.6701562. PMID 15534605.
  3. Sadda SR, Nee M, Miller NR, Biousse V, Newman NJ, Kouzis A (November 2001). "Clinical spectrum of posterior ischemic optic neuropathy". American Journal of Ophthalmology. 132 (5): 743–50. doi:10.1016/S0002-9394(01)01199-0. PMID 11704036.
  4. Hayreh SS (January 2009). "Ischemic optic neuropathy". Progress in Retinal and Eye Research. 28 (1): 34–62. doi:10.1016/j.preteyeres.2008.11.002. PMID 19063989.
  5. Hayreh SS, Podhajsky PA, Zimmerman B (April 1998). "Ocular manifestations of giant cell arteritis". American Journal of Ophthalmology. 125 (4): 509–20. doi:10.1016/s0002-9394(99)80192-5. PMID 9559737.
  6. Buono LM, Foroozan R (2005). "Perioperative posterior ischemic optic neuropathy: review of the literature". Survey of Ophthalmology. 50 (1): 15–26. doi:10.1016/j.survophthal.2004.10.005. PMID 15621075.
  7. Lee LA, Roth S, Posner KL, et al. (October 2006). "The American Society of Anesthesiologists Postoperative Visual Loss Registry: analysis of 93 spine surgery cases with postoperative visual loss". Anesthesiology. 105 (4): 652–9, quiz 867–8. doi:10.1097/00000542-200610000-00007. PMID 17006060.
  8. Chang SH, Miller NR (June 2005). "The incidence of vision loss due to perioperative ischemic optic neuropathy associated with spine surgery: the Johns Hopkins Hospital Experience". Spine. 30 (11): 1299–302. doi:10.1097/01.brs.0000163884.11476.25. PMID 15928556.
  9. Newman NJ (April 2008). "Perioperative visual loss after nonocular surgeries". American Journal of Ophthalmology. 145 (4): 604–610. doi:10.1016/j.ajo.2007.09.016. PMC 2989384. PMID 18358851.
  10. Ho VT, Newman NJ, Song S, Ksiazek S, Roth S (January 2005). "Ischemic optic neuropathy following spine surgery". Journal of Neurosurgical Anesthesiology. 17 (1): 38–44. PMC 2699455. PMID 15632541.
  11. Alexandrakis G, Lam BL (March 1999). "Bilateral posterior ischemic optic neuropathy after spinal surgery". American Journal of Ophthalmology. 127 (3): 354–5. doi:10.1016/S0002-9394(98)00343-2. PMID 10088754.
  12. Gill B, Heavner JE (April 2006). "Postoperative visual loss associated with spine surgery". European Spine Journal. 15 (4): 479–84. doi:10.1007/s00586-005-0914-6. PMC 3489312. PMID 15926057.
  13. Pazos GA, Leonard DW, Blice J, Thompson DH (1999). "Blindness after bilateral neck dissection: case report and review". American Journal of Otolaryngology. 20 (5): 340–5. doi:10.1016/S0196-0709(99)90039-X. PMID 10512147.
  14. Myers MA, Hamilton SR, Bogosian AJ, Smith CH, Wagner TA (June 1997). "Visual loss as a complication of spine surgery. A review of 37 cases". Spine. 22 (12): 1325–9. doi:10.1097/00007632-199706150-00009. PMID 9201835.
  15. Stevens WR, Glazer PA, Kelley SD, Lietman TM, Bradford DS (June 1997). "Ophthalmic complications after spinal surgery". Spine. 22 (12): 1319–24. doi:10.1097/00007632-199706150-00008. PMID 9201834.
  16. Sweeney PJ, Breuer AC, Selhorst JB, et al. (May 1982). "Ischemic optic neuropathy: a complication of cardiopulmonary bypass surgery". Neurology. 32 (5): 560–2. doi:10.1212/wnl.32.5.560. PMID 7200214.
  17. Weyand CM, Goronzy JJ (July 2003). "Medium- and large-vessel vasculitis". The New England Journal of Medicine. 349 (2): 160–9. doi:10.1056/NEJMra022694. PMID 12853590.
  18. Weber ED, Colyer MH, Lesser RL, Subramanian PS (December 2007). "Posterior ischemic optic neuropathy after minimally invasive prostatectomy". Journal of Neuro-Ophthalmology. 27 (4): 285–7. doi:10.1097/WNO.0b013e31815b9f67. PMID 18090562.
  19. Hunder GG, Bloch DA, Michel BA, et al. (August 1990). "The American College of Rheumatology 1990 criteria for the classification of giant cell arteritis". Arthritis and Rheumatism. 33 (8): 1122–8. doi:10.1002/art.1780330810. PMID 2202311.
  20. Connolly SE, Gordon KB, Horton JC (February 1994). "Salvage of vision after hypotension-induced ischemic optic neuropathy". American Journal of Ophthalmology. 117 (2): 235–42. doi:10.1016/s0002-9394(14)73082-x. PMID 8116753.
  21. Salvarani C, Macchioni PL, Tartoni PL, et al. (1987). "Polymyalgia rheumatica and giant cell arteritis: a 5-year epidemiologic and clinical study in Reggio Emilia, Italy". Clinical and Experimental Rheumatology. 5 (3): 205–15. PMID 3501353.
  22. Delecoeuillerie G, Joly P, Cohen de Lara A, Paolaggi JB (September 1988). "Polymyalgia rheumatica and temporal arteritis: a retrospective analysis of prognostic features and different corticosteroid regimens (11 year survey of 210 patients)". Annals of the Rheumatic Diseases. 47 (9): 733–9. doi:10.1136/ard.47.9.733. PMC 1003589. PMID 3178314.
  23. Lundberg I, Hedfors E (October 1990). "Restricted dose and duration of corticosteroid treatment in patients with polymyalgia rheumatica and temporal arteritis". The Journal of Rheumatology. 17 (10): 1340–5. PMID 2254893.
  24. Foroozan R, Deramo VA, Buono LM, et al. (March 2003). "Recovery of visual function in patients with biopsy-proven giant cell arteritis". Ophthalmology. 110 (3): 539–42. doi:10.1016/S0161-6420(02)01775-X. PMID 12623817.

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