We know that the cornea is kept moist by the lacrimal fluid. The lacrimal apparatus of eyes consist of the organs concerned with the secretion and drainage of the fluid. By the lacrimal gland lacrimal fluid is secreted and is poured into the conjunctival sac. The fluid passes downwards and medially to reach the lacus lacrimalis.
The lacrimal gland lies in relation to the upper lateral part of the wall of the orbit. Here has an extension of this gland which passes to the upper eyelid and called the palpebral part of the eyelid. From the lacus lacrimalis the fluid passes through the lacrimal puncta into narrow tubes named the lacrimal canaliculi and it opens into the lacrimal sac. The lacrimal sac drains into the inferior meatus through the duct of the nasal cavity called the naso-lacrimal duct.There are two lacrimal canaliculi that are upper and lower in relation to the each eye.
The Lacrimal Sac:
The lacrimal sac is one of the most important lacrimal apparatus of eyes. It lies in the lacrimal groove on the medial wall of the orbit. The lacrimal bone and the frontal process of the maxilla formed the floor of the groove. The groove is bounded anteriorly by the anterior lacrimal crest.
At its upper end the lacrimal sac is blind. The sac is continuous inferiorly with the naso-lacrimal duct. Laterally, it receives the lacrimal canaliculi near its upper end.
The bones are forming the floor of the lacrimal groove. Medially the sac is separated by a thin partition of bone from the anterior ethmoidal sinus and is lowered down from the medial meatus of the nasal cavity. The lacrimal sac is covered laterally by lacrimal fascia and it is attached to the anterior and posterior margins of the lacrimal groove.
The Nasolacrimal Duct:
Another part of the lacrimal apparatus of eyes is the naso-lacrimal duct. It is a tube about 18 mm long and it may regard as the downward continuation of the lacrimal sac. With the lateral wall of the nasal cavity the naso-lacrimal duct is closely related, and it opens below into the inferior meatus of the nose. The wall of this duct is made up of bone lined by the mucous membrane. The lower end of the naso-lacrimal duct is separated from the inferior meatus of the nose , which is made by a fold of mucus membrane named the lacrimal fold.
Laterally the bones helping to form the wall of the duct are the maxilla and medially the lacrimal bone and the inferior nasal concha are helping to form the wall.
The Lacrimal Gland:
The lacrimal gland of the lacrimal apparatus of eyes lies in relation to the upper lateral part of the wall of the orbit. The lacrimal gland is related inferiorly to the levator palpebrae superioris and to the lateral rectus muscle. The lacrimal gland drains into the superior conjunctival fornix through about twelve numbers of ducts.
Next we shall discuss about the eyeball.