Chapter 3 Third Eyelid
The third eyelid (membrana nictitans) is composed of a T-shaped cartilage with the third eyelid lacrimal gland at its base, entirely covered with conjunctiva. The third eyelid is often affected when conjunctivitis is present. Hereditary nictitans diseases in dogs, including scrolled cartilage and prolapsed gland of the third eyelid (cherry eye), are illustrated in this chapter. Other miscellaneous conditions affecting the nictitans also are shown.
Figure 3-1 Scrolled nictitans. Abnormalities of cartilage growth cause the nictitans to scroll outward rather than lying flat on the globe. Correction involves removal of the abnormal cartilage while preserving the conjunctiva of the nictitans. A breed predisposition to this condition exists.
(Courtesy Dr. Robert Playter.)
Figure 3-2 Scrolled nictitans. The middle of the T-piece of this cartilage is bent and can be seen in the medial canthus. The leading edge of the nictitans is hidden by the lower eyelid.
Figure 3-3 Scrolled nictitans. In dogs with a scrolled nictitans the third eyelid cannot be repositioned manually, in contrast to those with a cherry eye (prolapsed gland of the third eyelid; see Figure 3-4), which can be repositioned, at least temporarily.