THE NICTITATING MEMBRANE
by Sally Blanchard
The Nictitating (from the Latin nictare "to blink") Membrane can be found on birds, reptiles and some other animals. Parrots actually have 3 eyelids – the upper, the lower, and the nictating membrane. Often called the “third eyelid”, this thin, almost transparent membraine spreads moisture horizontally over the eye but also acts as "safety goggles" when a bird is in flight. Because it is almost transparent or translucent, the bird still has some vision in its eyes as the membrane "washes" the eye. Birds can actually control the use of the nictitating membrane if there is dust or dirt on their eye or if they need to protect it. When this membrane is not being used, it is folded up in the nasal corner of the eye. It moves so quickly that we rearely see it in our parrots, but if we do, the eye looks momentarily filmed over as this membrane blinks across the eye. In some birds with eye injuries, the nictitating membrane may either slow or get stuck over part of the eye.