Is Oxygen the Key? Unlocking the Mysteries of Retinal Ischemia
"A deeper look at how oxygen levels affect vision in retinal vein occlusion and other ischemic conditions."
Recent studies using en face optical coherence tomography (OCT) have highlighted the variable nature of macular middle-retinal infarction (MMRI) in eyes experiencing retinal vein or arterial occlusion. This variability reflects differing levels of circulatory failure during the evolution of an infarct, challenging existing models.
Researchers have proposed that MMRI stems from "misery perfusion," where the inner retina suffers from disproportionate oxygen extraction, leading to ischemic hypoxia and anoxia. This challenges the traditional understanding of tissue oxygenation, suggesting that the anatomic structure of macular arterioles and venules plays a critical role.
This article delves into the concept of oxygenation-based hypoperfusion maculopathy (OHM) to provide a broader perspective on ischemic dysfunction in the retina, moving beyond the limitations of terms like "perivenular PAMM" and addressing the role of oxygen levels in different retinal layers.
Measuring Ischemia Beyond Nonperfusion
In diabetic retinopathy, retinal ischemia is a major feature, but traditional measurements of nonperfused areas on OCT angiography (OCTA) show blood supply rather than ischemia itself. A proposed method uses three-dimensional quantitative analysis to derive ischemia measurements from OCTA data. A review of preclinical models reports that standard treatment has limited potential and describes stem-cell transplantation, intended to provide neuroprotection and replenish damaged cells, as an emerging therapeutic approach.
A 1911 Milestone in Retinal Procedures
At the cellular level, retinal ischemic injury is described as a self-reinforcing cascade involving neuronal depolarisation, calcium influx, and oxidative stress, initiated by energy failure and increased glutamatergic stimulation. In a separate history of retinal procedures, Ohm described intravitreal air injection in 1911 after external drainage of subretinal fluid to treat rhegmatogenous retinal detachment. The account notes that he positioned the patient to maximize bubble contact with the detached retina, without recognizing the causative retinal break. In 1979, Prof. Ingrid Kreissig published the first paper on using expansile gas without drainage to repair complex retinal detachments.
Beyond PAMM: Understanding Oxygenation-Based Hypoperfusion Maculopathy (OHM)
The term PAMM (“paracentral acute middle maculopathy”) has been used to describe specific lesions in CRVO and CRAO. However, this term may be limiting because OCT cannot directly identify hypoxic tissue. This means it might underestimate the full impact of inner retinal hypoperfusion. Furthermore, the expression "perivenular PAMM" is inherently contradictory.
- OHM Grade 1 (OHM1): Corresponds to the "fern-like" perivenular opacification seen in CRVO. The SIR is typically normoxic, while MMRI may show asymmetry.
- OHM Grade 2 (OHM2): Similar to "partial" CRAO, the SIR becomes predominantly hypoxic, and the MR is diffusely affected. Cotton-wool spots may appear.
- OHM Grade 3 (OHM3): Represents "complete" CRAO, where both the MR and SIR are anoxic, although some areas around third-order arterioles might be spared due to residual blood flow.
Oxygen Supply Across Retinal Layers
A review of paracentral acute middle maculopathy reports that the deep and intermediate capillary plexuses change in the region where both choroidal and retinal circulations supply oxygen to the inner nuclear layer (INL) and outer plexiform layer (OPL). The review identifies this region as a watershed zone. A separate 2026 report describes an integrative severity-grading system linking macular ischemia with retinal atrophy and says the Guangdong Diabetic Retinopathy Multi-omics Study established a preliminary quantitative assessment of full-course neurovascular unit injury.
Treatment and Measurement Gaps
Clinical treatment of retinal ischemia–reperfusion remains a problem, and pharmacotherapy research is focusing on drugs with neuroprotective effects or the ability to reduce or inhibit inflammatory mediators. Research on the ischemia–reperfusion model also reports limited knowledge of retinal physiological metrics and how they relate to retinal function and morphology. These gaps mean that both therapeutic approaches and the interpretation of physiological measures remain challenging.
The Future of Retinal Ischemia Research
Moving forward, a deeper understanding of oxygen dynamics within the retina is crucial for developing targeted treatments for ischemic conditions. By recognizing the limitations of previous classifications and embracing the OHM framework, researchers and clinicians can better address the complexities of retinal vascular diseases.
Improving Ischemia Detection in Diabetic Retinopathy
A 2026 case series aims to describe the features of ischemic areas detectable with the imaging techniques it discusses and offers clinicians a step-by-step approach to improve detection of possible ischemia in patients with diabetic retinopathy. It notes that updated classification systems are likely to emerge as retinal imaging becomes more widely used. The source frames improved detection and evolving classification as important considerations for clinical interpretation.
Following Ischemia Across the Retinal Plexuses
A review describes the retinal ischemic cascade as a continuum of ischemic events within the retina. It identifies three capillary plexuses—the superficial, intermediate, and deep (SCP, ICP, and DCP)—and notes that each has distinct susceptibility to ischemia because of differences in blood supply and drainage pathways. This layered framework offers a way to consider how ischemic changes may vary across retinal regions.
Ocular Ischemia and Carotid Disease
Ocular ischemic syndrome (OIS) is described as a rare, vision-threatening condition associated with severe carotid artery stenosis or occlusion that leads to ocular hypoperfusion. Its principal symptoms include visual loss, transient visual loss, and ischemic ocular pain. OIS most commonly occurs in the sixth decade of life, is uncommon before age 50, and affects men about twice as often as women, which the source relates to the higher incidence of atherosclerotic disease in men.
Further research is needed to refine the OHM classification and explore potential therapeutic interventions that can improve oxygen delivery and reduce ischemic damage in the retina. This includes investigating strategies to enhance blood flow, reduce inflammation, and protect retinal cells from oxidative stress.
Ultimately, a comprehensive approach that considers the multifaceted nature of retinal ischemia, including oxygenation levels, vascular structure, and cellular responses, will lead to more effective treatments and improved outcomes for patients at risk of vision loss.