Download Pool Tip #24: Why Swimmers See Halos Around Lights (PDF format, 20KB)

The majority of swimmers usually see rainbows or halos around lights after fifteen minutes of entering a swimming pool. This is nothing to be concerned about, but is rather the result of water being absorbed into the eyes.

Since pool water is less salty than human tears, pool water moves by osmotic pressure into the eye. The clear part of the front of the eye becomes swollen and fills with water. This accumulation of fluids in the eye is called corneal edema.

Some cells are also lost off the surface of the cornea causing symptoms of blurred vision and photophobia. Eyes may turn red, but changes in visual acuity do not seem to occur. For a period after leaving the pool, a swimmer may also be more sensitive to smoke or smog. This sensitivity to light and irritants usually disappears within thirty minutes of leaving the pool.

Wearing goggles while swimming in pools and fresh water lakes will lessen the temporary effects of corneal edema.