Cherry eye is typically diagnosed by examination of the conjunctiva and nictitating membrane. The moderately large eyes are horizontally oval and lack nictitating membranes (protective third eyelids). Instead the eye is lubricated by the nictitating membrane, a third eyelid that moves horizontally. The eyes are small and equipped with nictitating membranes (protective third eyelids). The eyes are small and lack protective nictitating membranes; behind the eyes are spiracles. The eyes are large and oval, with a nictitating membrane (a protective third eyelid). The eyes are large and circular, with nictitating membranes (protective third eyelids). There is also a third eyelid on each eye, the nictitating membrane. The eyes are large and black, without nictitating membranes (protective third eyelids). The spiracles are tiny and positioned well behind the eyes, which lack nictitating membranes. In veterinary medicine, signs can include partial closure of the third eyelid, or nictitating membrane. The nictitating membrane acts a sweeping wiper across the eye. A durable nictitating membrane protects the eye globe. As in many mammals and birds, pinnipeds possess nictitating membranes. North American river otters have transparent nictitating membranes to protect their eyes while swimming.