Red-eye cause is a term used to describe the various medical conditions that can cause redness in the eyes. INSOMNIA, which is an 8 letter word, is a sleep disorder that can cause redness in the eyes due to lack of restful sleep. STYE, a 4 letter word, is an infection of the eyelid caused by bacteria that can lead to redness and swelling. Iritis, a 6 letter word, is an inflammation of the iris that can cause redness and pain in the eyes.