![]() For visual scotomas, the primary pathogenesis may occur at the level of the receptors, retinal arterial tree, short posterior ciliary arteries, ophthalmic artery, optic nerve, carotid artery, vertebrobasilar artery or cerebral hemisphere. The differentials for scotoma likewise include migraine and seizure, but the term is more appropriately linked to ischemia, retinal degenerations and inflammations, paraneoplastic syndromes and other neurologic disorders. The definition of visual scotoma is similar to that of visual aura. Visual auras may be transient (e.g., a few seconds) or longstanding (perhaps for months) and, importantly, they may be accompanied by headaches or other types of aura such as vertigo, numbness, tingling or aphasia. Furthermore, an actual image may be adulterated (appears larger, perseverates, etc.). Aura can be defined as either positive (seeing something that is not there) or negative (not seeing something that is there). Visual changes described by patients are often referred to as blur, a word abused by patients as frequently as the word “dizzy.” Blur has different connotative meanings to patients. A visual aura is a transient or longstanding visual perceptual disturbance experienced with migraine or seizure that may originate from the retina or the occipital cortex. With scintillating, or fortification, scotomas, the central scotoma is bordered by a crescent of shimmering zigzags. An understanding of the different types of aura and scotomas and how they present allows eye care practitioners to differentiate causes and order testing appropriately for potentially very different pathologies. Because of this, the complaint of visual aura or scotoma requires a comprehensive evaluation and should not simply be assumed to be migrainous (a diagnosis of exclusion). Nonetheless, each term, when used in the right circumstance, may define remarkably similar visual deficits in one or both eyes.Ī substantial list of differentials must be considered when a patient describes such visual disturbances, some associated with significant morbidity. Likewise, terms such as visual scotomas, amaurosis fugax or transient visual obscurations also represent a disturbance of vision however, they do not classically precede migrainous headache or cortical seizure activity and are associated with other types of pathology. Although classically preceding migraine or seizure, an aura, simply defined, is a symptom, not a medical condition unto itself. Guan is now an assistant professor at the University of Illinois at Urbana- Champaign but has a continuing association with the Center on Food Security and the Environment (a joint effort of the Stanford Woods Institute for the Environment and the Freeman Spogli Institute for International Studies).Visual aura represent a type of neurologic deficit familiar to any eye care practitioner. Changes in greenness, they pointed out, show up in satellite imagery more gradually than fluctuations in fluorescence.Īs Lobell, PhD ’05, details in the video, changes in flux-such as dimming that occurs on some days-provide immediate insight into environmental impacts on plants: “What do we need to worry about in terms of stresses that crops are really responding to? What should we really be focusing on in terms of the next generation of crops? What should they be able to withstand that the current crops can’t withstand?” Among other advances, ongoing research will lead to greater accuracy for crop-productivity forecasts, says Guan, although even the early work has drawn attention from the agriculture and commodity industries. NASA scientists, who already use satellites to map vegetation “greenness,” noted in 2011 that their additional success in measuring fluorescence would lead to a variety of applications for monitoring crop activity and health. This kind of work, as Guan emphasizes, “is very new” it’s made possible by the ability to calculate flux, which became globally detectable by satellites only in recent years. So the more they’re growing, the more photosynthesis they’re doing, and the brighter they’re fluorescing.” Led by former Stanford postdoctoral fellow Kaiyu Guan, a team of researchers used the data to measure the rate of photosynthesis, which fuels plant growth, and thereby project the ultimate size of a harvest.ĭavid Lobell, an associate professor of earth system science and co-author of the study, explains the connection this way in a video for the School of Earth, Energy & Environmental Sciences: “This glow that plants have seems to be very proportional to how fast they’re growing. That fluorescence-reddish light from solar energy absorbed by plants and released back into the atmosphere-can be tracked by satellites. That could be the mantra of the scientists who used “flux,” a very faint flow of fluorescence from growing plants, to estimate crop yields. ![]()
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