Why Do Onions Make Us Cry (and Other Vision Facts)

The only organ in the human body more complex than the eye is the brain. There are two million working parts in your eyes, and over one million nerves that connect to our brains. This is partly why annual vision checkups with an eye doctor are so important. There are many aspects of our eye health that we don’t see or understand. In fact, most of us aren’t aware of what’s really going on with everyday experiences, such as tearing up from cutting onions. The professionals at Complete Eye Care of Medina can help maintain or improve your eye health and bring some understanding to all things eye related. Here are some interesting vision facts.

1. Why do onions make us cry?

When you slice, crush, or bite an onion, it’s very uncomfortable. Your eyes don’t just water, they burn. It stings, as if there’s sulphuric acid in your eyes. Does that sound dramatic? Well, that’s exactly what’s happening! An enzyme is released that triggers the production of a gaseous sulfur chemical, propanethial S-oxide. When you cut an onion, this gas moves through the air and into your eyes. When it hits your tear ducts, it reacts with water and creates sulfuric acid. No wonder our eyes react so violently! Your tear ducts begin to work overtime, producing excess tears in an attempt to flush out the irritant.

2. Why do our eyes take time to adjust to darkness?

A chemical found in rod cells called rhodopsin is the key to night vision. When this chemical is exposed to the photons in light, it splits into two different molecules: retinal and opsin. These are molecules that help you see in bright light. When the lights suddenly go out, retinal and opsin molecules are still present, but they don’t help you see in darkness. That key night vision chemical is missing. In the absence of photons, retinal and opsin recombine back into rhodopsin. However, this happens slowly at a fixed rate. Over time as rhodopsin returns, you can begin to see in the dark. It takes hours for our eyes to fully adjust to darkness.

3. Why does red-eye happen in photos?

When you see red-eye in photos, it’s not an illusion or a camera malfunction. When you see this effect, you have actually taken a photograph of the rich blood vessels in the back of your eyes. That may sound creepy, but here’s how it happens. You probably know that your pupils get bigger in the dark and smaller in bright light. In darker rooms, your pupils help you see better by dilating and allowing more light in. When your pupils are larger in a dim setting and a quick camera flash goes off, their reflex to constrict can’t work fast enough. As a result, the burst of light is able to reach your retina, lighting up the connective tissue in the back of your eye. This blood rich tissue that is captured in the image is what we call red-eye.

Trust Complete Eye Care of Medina

Your eyes are as complex as they are important. Let the experts at Complete Eye Care of Medina help you improve and maintain your eye health and vision. Schedule a visit with a professional eye doctor today. Complete Eye Care of Medina takes a one-on-one approach to your eye health. During a visit to our clinic, an eye doctor will evaluate the health of your eyes and your current vision through a comprehensive eye exam. For our patients, we offer comfortable, easy testing that allows us to evaluate your risk for eye conditions such as glaucoma, macular degeneration, and dry eye disease. Contact us today and schedule your visit.