Letter to the editor: partial central retinal artery occlusion offers a unique insight into the ischemic penumbra

David McLeod
  • Clinical Ophthalmology, December 2011, Dove Medical Press
  • DOI: 10.2147/opth.s28232

Lindsay Symon's ischemic penumbra in association with retinal hypoperfusion.

What is it about?

The clinical picture of acute subtotal visual loss and reduced retinal blood flow features multiple cotton-wool sentinels and macular middle-retinal infarction with peri-arterial sparing (incorrectly referred to nowadays as perivenular PAMM). This is often attributed to multiple small retinal strokes or is called "Purtscher-like retinopathy". In reality, the cause is partial occlusion of the central retinal artery with obstructed retrograde axoplasmic transport and mitochondrial accumulation along the critical oxygen tension (or pO2) isobar for hypoxia (or the "hypoxia threshold" at pO2 < 10 Torr) and oxygen watershed infarction of the macular interneurons (or "middle retina") within the critical pO2 isobar for anoxia (or the "anoxia threshold" at pO2 = 1-2 Torr). Spontaneous reinstatement of perfusion is the rule, with marked recovery of vision from reversal of the hypoxic state (or Symon's "ischemic penumbra") to the usual normoxic state. Of course, infarcted retina cannot recover, and secondary damage to the retinal nerve-fiber layer often results from hypoxia due to a "compartment syndrome" at the location of the largest cotton-wool sentinels (which are made up of grossly swollen axons full of mitochondria). Thus, cotton-wool spots are not "nerve-fiber layer infarcts" albeit they sometimes act like such infarcts by secondary intention.

Why is it important?

Retinal vascular disorders are frequently misdiagnosed both in clinical practice and in the ophthalmic literature. Furthermore, there is very limited cross-fertilization of pathophysiological concepts and semantics between neurology and ophthalmology despite the well-established subspecialty of neuro-ophthalmology. This article is an extended comment about a small case-series of patients (n= 4) with "misery perfusion" from partial central retinal artery occlusion. Such patients typically experience remarkable visual improvement when retinal perfusion is restored, ostensibly courtesy of re-oxygenation of the ischemic penumbra.

Perspectives

David McLeod

For over half a century, common manifestations of retinal ischemia such as retinal cotton-wool spots have been subject to mass misinterpretation by ophthalmic specialists. Now, history threatens to repeat itself with the advent of high-resolution optical coherence tomography and associated angiography. These techniques cannot identify hypo-oxygenation from misery perfusion, only infarction. The retinal manifestations of hypoperfusion are an exquisite illustration of oxygen physiology and topography that specialists in other disciplines could only dream of demonstrating using sophisticated imaging. Ironically, alternative, overly simplistic explanations are being proffered for what ophthalmologists can readily observe in patients' fundi. Furthermore, the virtues of expensive new investigative technologies may be extolled in circumstances in which their contribution to patient care is likely to be at best marginal.

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http://dx.doi.org/10.2147/opth.s28232

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