Opening your eyes underwater is a common experience, triggering immediate sensations and changes in vision. Understanding these effects clarifies what happens when eyes meet water.
What You Immediately Feel
Upon opening your eyes underwater, you typically experience an immediate stinging or burning sensation. This discomfort can range from mild irritation to a more pronounced pain, depending on the water’s composition. Simultaneously, your vision becomes noticeably blurry, making it difficult to discern clear shapes or details.
The Science of Underwater Vision
The stinging sensation in your eyes underwater primarily stems from osmosis. Your eyes have a natural tear film, a thin layer of fluid with a specific solute concentration. When exposed to water with a different solute concentration, water molecules move across the eye’s semi-permeable membranes to balance these concentrations. If the water has a lower solute concentration than your tears, water moves into the eye, causing cells to swell and leading to irritation. Conversely, if the water has a higher solute concentration, water is drawn out, resulting in dehydration and a burning feeling.
The blurriness of underwater vision results from how light behaves in different mediums and the human eye’s adaptation to air. Light rays bend, or refract, when they pass from one medium to another. The cornea performs the majority of light focusing when in air due to the significant difference in refractive index between air and the cornea. However, water has a refractive index very similar to the cornea. This similarity effectively negates much of the cornea’s focusing power, causing light to focus behind the retina and resulting in a highly blurred image.
How Different Waters Affect Your Eyes
The specific type of water significantly influences the degree of irritation experienced by your eyes. In freshwater environments, the water typically has a lower solute concentration than your tear film. This hypotonic condition causes water to osmose into your eye cells, leading to a sensation of fullness or mild irritation. In chlorinated pools, chemicals called chloramines, formed when chlorine reacts with organic matter like sweat and urine, can also irritate the eyes, causing redness and a stinging sensation.
Conversely, in saltwater, the water has a higher salt concentration compared to your tears, making it a hypertonic solution. This draws water out of your eye cells through osmosis, leading to a drying sensation and more pronounced stinging. While refractive blurriness remains consistent across all water types, the level of discomfort from irritation varies considerably based on the water’s solute concentration and chemical content.
Keeping Your Eyes Safe Underwater
Prolonged exposure or opening eyes in water, especially if it is contaminated, can potentially lead to eye irritation or minor infections. Waterborne pathogens, including bacteria and viruses, can cause conditions like conjunctivitis (pink eye). Even well-maintained pools might harbor some germs that can infect the eyes.
Using swim goggles avoids discomfort and potential issues. Goggles create an air-filled space in front of your eyes, restoring the air-cornea interface and allowing for clear vision underwater. They also provide a barrier that protects your eyes from irritating chemicals and potential pathogens present in the water. Occasional, brief opening of eyes in clean water is generally not harmful, but protection is advisable for extended periods or in uncertain water conditions.