Costas, NBC's prime time host for the Winter Olympics, told the New York Times the infection appeared in his left eye Thursday and spread to his right eye Sunday. Tuesday, Costas said his eyes were swollen and crusted shut.
Costas, who wears contact lenses, was wearing glasses, since NBC's Winter Olympic coverage began Thursday.
"It was increasingly uncomfortable with each passing night, but I could cope with it," Costas said. "But last night until today, it got to where I couldn't look in the bathroom light without squinting and blinking and my eye watering. You hear it called pinkeye or conjunctivitis, but, as a practical matter, I haven't had it before. You have swelling and stinging and burning and eventually tearing. And last night was the most difficult night of the five."
Conjunctivitis is an inflammation or infection of the transparent membrane -- conjunctiva -- that lines the eyelid and covers the white part of the eyeball. When small blood vessels in the conjunctiva become inflamed, they're more visible causing the whites of the eyes to appear reddish or pink, the Mayo Clinic said.
Pinkeye is commonly caused by a bacterial or viral infection, an allergic reaction, or in babies an incompletely opened tear duct.
Pinkeye can be irritating and highly contagious, but it rarely affects vision. The infection spreads via direct or indirect contact with the eye secretions of someone who's infected, the Mayo Clinic said.
The most common pinkeye symptoms include:
-- Redness in one or both eyes.
-- Itchiness in one or both eyes.
-- A gritty feeling in one or both eyes.
-- A discharge in one or both eyes that forms a crust during the night that may prevent the eye or eyes from opening in the morning.
Pinkeye can be highly contagious for as long as two weeks after symptoms begin.
Viral conjunctivitis and bacterial conjunctivitis might affect one or both eyes. Viral conjunctivitis usually produces a watery discharge. Bacterial conjunctivitis often produces a thicker, yellow-green discharge. Both viral and bacterial conjunctivitis can be associated with colds or with symptoms of a respiratory infection, such as a sore throat, the Mayo Clinic said.
The Centers for Disease Control and Prevention said those with infectious -- viral or bacterial -- conjunctivitis, can help limit its spread to others by:
-- Washing hands often with soap and warm water. If soap and water are not available, use an alcohol-based hand sanitizer that contains at least 60 percent alcohol.
-- Avoiding touching or rubbing the eyes.
-- Washing any discharge from around the eyes several times a day. Hands should be washed first and then a clean washcloth or fresh cotton ball or tissue can be used to cleanse the eye area. Throw away cotton balls or tissues after use; if a washcloth is used, it should be washed with hot water and detergent. Wash your hands with soap and warm water when done.
-- Washing hands after applying eye drops or ointment.
-- Not using the same eye drop dispenser/bottle for infected and non-infected eyes -- even for the same person.
-- Washing pillowcases, sheets, washcloths and towels in hot water and detergent; hands should be washed after handling such items.
-- Avoiding sharing articles like towels, blankets and pillowcases.
-- Cleaning eyeglasses, being careful not to contaminate items such as towels that might be shared by other people.
-- Not sharing eye makeup, face makeup, makeup brushes, contact lenses, containers, or eyeglasses.
-- Not using swimming pools.