You are sitting at home one quiet Sunday afternoon reading the paper, and suddenly the words you are trying to read blur. Nothing you do helps the situation, reading glasses, rubbing your eyes, artificial tears—the words are just blurred out, almost as if they never existed.
Immediately, you begin to panic, thinking you’re having a stroke or losing your vision all together. Then phenomenon then expands to encompass a greater area of your vision before slowly dissipating and your vision returns to normal.
What on earth just happened? Is something serious going on?
Believe it or not, you may have just experienced an ocular migraine! But what exactly is an ocular migraine, and why do they occur?
Before getting into the nitty-gritty details regarding ocular migraines, it may be helpful to have an understanding of what migraines are in general.
What are Migraines?
Migraines are a phenomenon isolated to the brain. Within the brain, we have billions of specialized informational transmitting cells called neurons.
Neurons have branches called axons which can transmit information, when stimulated, to and from other neurons in a matter of microseconds.
Neurons are responsible for our senses (detecting touch, pain, smells, tastes, sight, etc.), motor skills, and overall relay of information for comprehension and processing.
Neurons function through stimulation and generation of electrical impulses called action potentials.
Action potentials are an all-or-nothing response. When a stimulus is strong enough, it causes an action potential which fires the neuron and its consequential function ensues. For example, when a certain set of neurons in the brain fire, the right index finger will twitch.
This being said, there are over 86 billion neurons in the brain. These neurons are responsible for every little thing the body does—small movements, big movements, a thought, the perception of a flash light, a taste, the human perception of life is literally just combinations of different neurons firing to create different actions.
A migraine occurs when a set of neurons becomes hyper-stimulated, firing at a heighten rate. This rapid firing of neurons causes nearby blood vessels to dilate, temporarily enlarging the size of the blood vessels in that area of the brain.
When these blood vessels dilate, they press on surrounding nerves, which is then perceived as pain. Often times, this process occurs quickly, resulting in an intense localized pain within the brain best known as a migraine headache.
Where the pain occurs depends on which neurons are hyper-stimulated. There is no rhyme or reason as to why the neurons become hyper-stimulated in migraine attacks, however there are some well–known triggers associated with migraines including stress, spicy foods, bright lights, hormones, chocolate, and even certain smells!
As mentioned above, migraines can occur and therefore affect any given neuron, which means they can occur in any part of the brain.
This being said, the eyes are actually an extension of the brain, which means neurons are also found in the eyes.
Vision, therefore, is a neurological process that involves both the detection of light, transmission of signals, and processing of this information within a different part of the brain.
More specifically, the eyes contain special light-detecting cells called photoreceptors. Photoreceptors are located in the backmost layer of the eye called the retina.
When there is light, certain photoreceptors become stimulated. They then send electrical signals via axons to neurons within the brain via the visual pathway.
The electrical signals must travel from the eyes all the way to the vision-processing center of the brain called the occipital cortex, which is actually located in the back-most part of the brain.
At this point, the brain compiles the information gathered from the millions of photoreceptors (stimulated and non-stimulated) to create an image.
Thus, “vision” can be broken down into two major components—detection via the eyes and processing via the brain.
This is where things can get a little confusing. Since neurons are located in both the eyes and the occipital cortex, migraines can occur in either place and therefore can affect vision in two different ways.
When neurons within the occipital cortex become hyper-stimulated, it creates visual disturbances called a visual aura.
Auras present as colorful, or black and white, zig-zags of light sometimes described as looking through a kaleidoscope, as “stars” in the vision, or as flashes of light.
These visual disturbances occur because the hyper-stimulation of the neurons in the visual occipital cortex trick the brain into thinking it has received a signal from the eyes to create that image.
Migraines with auras are also referred to as a classic migraine headache. These migraines are often associated with a painful headache, but may also only be a visual disturbance sans headache.
Visual auras can last anywhere from a few seconds to about an hour, although most resolve within 15-30 minutes. Auras also typically start in one part of the vision and move across in a wave-like pattern as the hyperstimulation sweeps across the occipital cortex.
When is a Migraine is an Ocular Migraine?
On the other hand, when neurons within the eyes themselves become hyper-stimulated, the phenomenon is referred to as an ocular migraine.
In an ocular migraine, an individual loses vision as the neurons in the eyes are responsible for detection of light, not image processing.
For this reason, the hyper-stimulation creates a strong signal of photoreceptor stimulation, which is perceived in the occipital cortex as a massive wave of stimulation, or “washing-out” of vision.
To us as humans, this “washing-out” of vision is seen as temporary blur or blindness.
The retina, where photoreceptors are located, does not contain pain-detecting nerves. For this reason, most individuals experiencing an ocular migraine often will not have a painful headache as seen with a classic migraine with aura, although a headache is possible following one of these events.
Similar to a visual aura, the blur seen with an ocular migraine has a wave-like motion as the hyper-stimulation of photoreceptors sweeps across the retina.
Ocular migraines can also occur in a matter of seconds to about an hour, but will resolve completely without treatment intervention. If vision does not return, you are not experiencing an ocular migraine and should seek medical attention immediately.
What to Do When an Ocular Migraine Hits
Generally speaking, ocular migraines are frustrating, but do not cause serious damage to the eyes. When one occurs it is best to stop what you are doing and take a break until the phenomenon has subsided.
Sit down, sip on some water, close your eyes momentarily, and try to relax.
If ocular migraines, or classic migraines, begin to occur frequently it is best to make an appointment with your primary care doctor to ensure there is not an underlying trigger to the event, and perhaps initiate medication to lessen the frequency of the migraine from occurring.
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