Why Do Our Eyes Get Bigger When We’re Scared?

There’s an old Russian proverb that says, “Fear has big eyes.” It means that when someone is afraid, everything seems scarier than it really is—fear makes us exaggerate danger. But where did this saying come from? Most likely, it’s based on the fact that when we’re scared, our eyes really do look “bigger”—they open wide and our pupils dilate. This happens because fear triggers major changes throughout the body, including our vision.

What Happens to the Body During Fear?

Fear arises when we sense a threat to our life, health, or well-being, or that of our loved ones. It’s an unpleasant and intense emotion, but it’s also extremely useful. Scientists even call fear a “gift of evolution” because it helps us survive dangerous situations.

Physiologically, the fear response starts in a part of the brain called the amygdala. The amygdala sends signals throughout the body to prepare it for defense or escape—this is known as the “fight or flight” response.

Here’s how it works: the brain sends a signal to the adrenal glands, which release stress hormones like adrenaline and cortisol. These hormones enter the bloodstream, making our heart beat faster and sending more blood to areas that need to be active in emergencies.

Stress hormones also affect our breathing—we start to breathe faster so that oxygen-rich blood can circulate quickly. At the same time, blood vessels constrict and blood pressure rises, allowing more oxygen to reach the muscles.

To give us enough energy to act, the liver releases extra glucose. Muscles tense up, including those near hair follicles, which causes goosebumps. This is why animals’ fur stands on end when they’re scared, making them look bigger than they really are.

While the sympathetic nervous system activates all these processes, the parasympathetic nervous system—which is responsible for conserving energy—gets suppressed. For example, digestion slows down, since it’s not helpful during a “fight or flight” situation and would only use up valuable energy.

Why Do Pupils Dilate When We’re Scared?

Pupil dilation is directly linked to the processes described above, especially the release of adrenaline. The muscles around the eyes tense up and blood flow to the eyes increases. That’s why, when someone is scared, their pupils not only dilate but their eye color can even appear to change.

You might wonder—what’s the advantage of dilated pupils, or so-called “tunnel vision”? This is another evolutionary defense mechanism. In moments of danger, it’s important for more light to reach the retina, especially if the threat appears in low-light conditions. This helps us see better in the dark and assess the situation more accurately, increasing our chances of survival.

It’s important to note that this trait developed in our ancestors long before artificial lighting existed. Today, if someone is frightened in a well-lit environment, dilated pupils can actually be a disadvantage—it can cause blurry or unclear vision and reduce peripheral (side) vision.

How Chronic Fear Can Harm Your Vision

Fear can save our lives by giving the body a temporary “boost” for the “fight or flight” response. However, if this happens too often—if someone is regularly afraid—the body can start to break down.

High blood pressure and a rapid heartbeat primarily affect the cardiovascular system, but stress also negatively impacts vision. Rapid breathing increases oxygen levels in the blood and decreases carbon dioxide, leading to a state called hyperventilation. This can cause unpleasant sensations like “floaters” or a gritty feeling in the eyes.

If the body is under stress for a long time, it can lead to dry eyes, eye muscle strain, eye twitching, and increased eye pressure. Over time, these issues can reduce visual acuity and contribute to the development of various eye conditions.