Book
LACRIMAL SYSTEM
- ANATOMY AND PHYSIOLOGY
The lacrimal apparatus consists of a 3 systems:
I- Secretory system.
II- Distributional system.
III- Excretory system.
I. The secretory system ( lacrimal glands ) These glands are:
a- lacrimal glands
1- The gland of the third eyelid
Which lies within the stroma of the third eyelid, is partially visible on the inner surface of the third eyelid.
2- The tubuloalveolar lacrimal gland
is flattened and lies over the superior temporal part of the globe. The position is similar in species with a fully enclosed bony orbit. Lacrimal secretions enter the superior conjunctival fornix from the canine lacrimal gland via three to five microscopic ducts, and from the gland of the third eyelid via multiple ducts opening on the bulbar surface of the third eyelid between the normal lymphoid follicles. The precorneal tear film is distributed over the ocular surface by gravity, blinking, and movement of the third eyelid.
3-Accessory lacrimal glands Which are near the lid margins and contribute to the precorneal tear film, are composed of the following
The meibomian (tarsal) glands. They produce the superficial layer of the precorneal tear film.
The glands of Moll (modified sweat glands).
The glands of Zeis (modified sebaceous glands associated with the cilia)
The functional significance of the glands of Moll and Zeis in animals is unknown, although infections of the glands of Zeis occur clinically and are called external hordeolum (stye).
