Opening your eyes underwater, whether in a pool, lake, or ocean, immediately changes how you perceive your surroundings, often resulting in blurry vision and a stinging sensation. Understanding these effects and potential risks helps explain how our eyes interact with aquatic environments and how to protect them.
Why Vision Blurs Underwater
Light bends when traveling from one medium to another, a phenomenon known as refraction. The human eye is adapted for vision in air, where the cornea, its clear front surface, performs most of the light bending to focus images sharply onto the retina. When submerged, water directly contacts the cornea. Since water has a refractive index very similar to the cornea, the cornea’s ability to bend light is significantly diminished.
This reduced refractive power means light rays entering the eye underwater are not focused correctly on the retina, instead converging behind it. This results in a condition similar to extreme farsightedness, causing blurry images. Creating an air pocket in front of the eye, as swimming goggles or diving masks do, restores the necessary air-cornea interface for clear vision.
The Sensation of Stinging
The stinging or discomfort experienced when opening eyes underwater is due to differences in osmotic pressure and the presence of chemical irritants. Human tears contain a specific salt concentration. When eyes are exposed to water with a significantly different concentration, osmosis occurs. In freshwater, which has a lower salt concentration than tears, water moves into the eye cells, causing them to swell and leading to discomfort. Ocean water, much saltier than tears, draws water out of eye cells, resulting in dehydration and a burning sensation.
Chlorinated pool water introduces additional factors. Chlorine and other chemicals used for disinfection can disrupt the eye’s natural tear film. This protective tear film keeps the eyes moist and lubricated; when compromised, the eyes become more vulnerable to irritation and dryness. Chloramines, which form when chlorine reacts with organic substances like sweat or urine, are chemical irritants that can cause red, itchy eyes and discomfort.
Risks of Eye Exposure to Water
Opening eyes underwater carries health risks, primarily from microbial contamination. Water sources, including pools, lakes, rivers, and even tap water, can harbor bacteria, viruses, fungi, and protozoa. These microorganisms can lead to various eye infections, from conjunctivitis (pink eye) to more severe conditions like infectious keratitis or corneal ulcers. While chlorine in pools helps kill many germs, it does not eliminate all pathogens.
A particularly concerning risk is Acanthamoeba keratitis, a rare but serious eye infection caused by Acanthamoeba species, free-living amoebae found in water sources. This amoeba can invade the cornea, potentially leading to severe vision loss or blindness if not promptly diagnosed and treated. Contact lens wearers face a significantly higher risk, as contact lenses can trap the amoebae against the eye. Lakes and rivers pose a higher infection risk than treated pools because they are not disinfected and can contain contaminants from agricultural runoff or sewage.
Safeguarding Your Eyes Underwater
Protecting your eyes during water activities is straightforward and effective. The most reliable method is to wear properly fitting swimming goggles or a diving mask. These devices create an air barrier in front of the eyes, allowing for clear underwater vision and preventing direct contact with water and potential irritants or contaminants. Prescription goggles are available for individuals who require vision correction, ensuring both clarity and protection.
Individuals who wear contact lenses should remove them before swimming, as water can trap harmful microorganisms between the lens and the eye, significantly increasing the risk of infection. If contact lenses get wet, remove them immediately and either discard (for daily disposables) or thoroughly disinfect overnight. After swimming, rinsing eyes with clean, fresh water or sterile saline solution can help flush out any lingering chemicals or debris. Lubricating eye drops can alleviate dryness and irritation.