The word “flashes” in a health context refers to two distinct phenomena: a systemic, temperature-related event known as a hot flash, or a sensory, visual disturbance called a visual flash (photopsia). These two types of flashes differ significantly in origin and physical experience. Hot flashes are physiological responses involving the body’s temperature regulation system, often linked to hormonal changes. Visual flashes are sensory events originating in the eye or the brain’s visual pathways, typically caused by mechanical or neurological stimulation. This article defines these experiences, explains their causes, and details when they signal a need for medical evaluation.
The Experience of Hot Flashes
A hot flash is a sudden, intense sensation of heat considered a vasomotor symptom, involving the widening and narrowing of blood vessels. This event most frequently affects the upper body, spreading across the chest, neck, and face. The skin often appears flushed or blotchy as blood flow increases near the surface.
The rush of heat is frequently followed by profuse sweating, the body’s attempt to cool down. As the heat dissipates, the person often feels a sudden chill or coldness. A single hot flash can last anywhere from 30 seconds to five minutes. When these episodes occur at night, they are called night sweats and can significantly disrupt sleep and quality of life.
Understanding Visual Flashes
Visual flashes, medically termed photopsia, are the perception of light when no external source is present. People describe these sensory events as seeing shooting stars, lightning streaks, or flickering lights. The flashes are typically brief, lasting less than a second, and often appear in the periphery of the visual field.
Photopsia can occur in one or both eyes and may be accompanied by floaters, which are small dark dots or lines that drift across the vision. Visual flashes are purely a visual disturbance. They represent a signal sent to the brain’s visual center, even without external light stimulation.
Why Hot Flashes Occur
The mechanism behind a hot flash involves a temporary malfunction in the hypothalamus, the brain’s thermoregulation center. The hypothalamus acts as the body’s internal thermostat, maintaining a narrow range of acceptable core body temperature, known as the thermoneutral zone. The decline of estrogen associated with perimenopause and menopause is the most common trigger.
This hormonal decline causes the thermoneutral zone to narrow, making the hypothalamus highly sensitive to minor elevations in core body temperature. When the temperature crosses this lowered threshold, the hypothalamus mistakenly perceives the body is overheating. It then initiates an aggressive cooling response through the sympathetic nervous system. This response includes peripheral vasodilation (widening blood vessels near the skin) and sweating, causing the sensation of intense heat and flushing.
While the menopausal transition is the most frequent cause, hot flashes can also result from other systemic conditions. Certain medications, thyroid issues, or medical conditions affecting the central nervous system can disrupt hypothalamic function.
What Causes Visual Flashes
The majority of visual flashes originate from mechanical stimulation of the retina, the light-sensitive tissue lining the back of the eye. The eyeball is filled with a clear, jelly-like substance called the vitreous humor. As a person ages, the vitreous naturally begins to shrink and pull away from the retina in a process called Posterior Vitreous Detachment (PVD).
When the shrinking vitreous tugs on the retina, the photoreceptor cells are physically stimulated. This mechanical force causes the cells to fire an electrical signal, which the brain interprets as a flash of light. These flashes are often described as lightning streaks in the far side of the vision. If the vitreous pulls hard enough, it can create a retinal tear, potentially leading to a retinal detachment.
Visual flashes can also have a neurological origin, most commonly associated with a migraine with aura. This type of flash is caused by a wave of electrical activity, called cortical spreading depression, that moves across the visual cortex. Migraine-related flashes are often described as shimmering, jagged lines and tend to last longer, up to 30 minutes. The distinction is the source of stimulation: mechanical force on the retina or electrical activity in the brain.
Recognizing Urgent Symptoms
While many flashes are harmless, recognizing when they signal a serious condition is important for both types. For hot flashes, a sudden, severe onset of symptoms suggests a non-hormonal, underlying medical issue. These red flags include high fever, unexplained weight loss, or a rapid heart rate. If hot flashes significantly interfere with daily life or sleep, a medical consultation is warranted to discuss management options.
For visual flashes, certain symptoms require immediate attention from an eye care professional. A sudden, dramatic increase in the number of flashes or floaters may indicate an acute PVD or a developing retinal tear. The most concerning symptom is the appearance of a dark shadow, curtain, or veil moving across the vision, which suggests a retinal detachment. Because prompt treatment is necessary to prevent permanent vision loss, any new or worsening visual flashes must be evaluated quickly.