Nictitating membrane
The nictitating membrane (third eyelid) has a T-shaped cartilage with a large gland at its base and is covered in nonkeratinized stratified squamous epithelium (Samuelson, 2007; Raskin, 2010).
Lymphoid tissue is also present on the bulbar conjunctiva of the third eyelid. The presence of this normal tissue should be considered when diagnosing inflammatory disease within the third eyelid.Inflammatory disorders of the third eyelid are characterized cytologically by the cells that are identified. These can be an extension of conjunctivitis or follicular hyperplasia accompanying lymphoplasmacytic inflammation.
Neoplasms of the nictitating membrane are similar to those described in the conjunctiva but should also include adenocarcinoma. Adenocarcinoma is one of the most common tumors at this location (Raskin, 2010). These cells will exhibit prominent criteria of malignancy such as anisocytosis and anisokaryosis. The cells are glandular in origin so they will often contain multiple discrete vacuoles within the cytoplasm.
More on the topic Nictitating membrane:
- Nictitating membrane
- Barger A.M., MacNeill A.L. (Eds.). Small Animal Cytologic Diagnosis: Canine and Feline Disease. CRC Press,2024. — 536 p., 2024