The light pink tissue that lies between the eye lid and the eye itself is known as the conjunctiva. Under normal circumstances, this tissue is not visible unless the eye lid is moved out of the way, upward for the upper lids or downward for the lower lids. If the conjunctiva is swollen and visible while looking at the bird in its cage or flight, the condition is referred to as conjunctivitis. The cause of conjunctivitis in cockatiels has created much debate over the last several years.

The exact cause of this disease has yet to be determined in all cases. Organisms postulated to be the cause of the disease have included Gram Negative bacteria, Mycoplasma, Chlamydia and viruses. Attempts at isolating mycoplasma or viral agents have been very inconsistent. Chlamydial organisms, the Psittacosis disease agent, have been implicated in a back-handed manner. Many veterinarians have successfully treated this disease by using the drugs to treat Psittacosis. Definitive diagnosis through culture or necropsy has been hit or miss, though.