The characteristic visual scotoma of ophthalmic migraine
Ophthalmic migraine and migraine with typical aura . That is, with only visual symptoms . Among these visual symptoms, we essentially find the visual scotome. These are spots in the field of vision and sometimes these spots can be bright, this is called a scintillating scotoma . The patient may describe hatched lines , or spots in a regular or irregular pattern. They can be localized in the center of the visual field and sometimes the periphery. Generally, this symptom is unilateral, that is, it does not affect both eyes at the same time. In all cases in ophthalmic migraine, the visual scotoma is transient and disappears with the end of the attack.
The appearance of this visual aura in ophthalmic migraine would be the consequence of an invasive cortical depression . This is a phenomenon where neurons are suddenly excited, this is called depolarization , then enter a phase of rest or silence. It is an electrophysiological phenomenon which will propagate within the cortex at the speed of a few millimeters per minute. For reasons still unknown, it is the neurons in the visual area of the brain that are most easily affected by this phenomenon. Thus in ophthalmic migraine, when this invasive cortical depression occurs at the level of the visual area, the patient begins to feel the visual scotoma with the appearance of tasks and feelings.
A spread of 2 to 5 mm/minute
The first studies on this invasive cortical depression were carried out in the 1940s by Professor Leao . He was able to record in animals this particular electrical activity in the cortex and record its propagation in the cortex. When a neuron is subjected to this electrical activity, it releases many chemical compounds that will stimulate neighboring neurons . This contributes to the spread of the phenomenon within the visual area in the case of ophthalmic migraine, but also in other areas of the cortex. The motor area, the sensory areas, or even the language area can be affected. The symptoms experienced by the patient correspond to the affected areas.
A recent scientific theory explains that this pervasive cortical depression could be present in all cases , whether ophthalmic migraine or migraines without aura . It is only that it would be in areas that do not cause symptoms experienced by the patient. It would therefore be very present and would go unnoticed .
You now know a little more about this very particular phenomenon of migraine aura in ophthalmic migraine.