The Lacrimal Apparatus
The lacrimal complex, when viewed under a microscope, consists of the lacrimal gland, the accessory lacrimal glands, the canaliculi, the lacrimal sac, and the nasolacrimal duct.
The lacrimal gland consists of the following struc¬tures:
(1) The almond-shaped orbital portion, located in the lacrimal fossa in the anterior upper temporal seg¬ment of the orbit, is separated from the palpebral por¬tion by the lateral horn of the levator palpebrae muscle. To reach this portion of the gland surgically, one must incise the skin, the orbicularis oculi muscle, and the or¬bital septum. Forensic comparison microscopes can be used to examine this structure.
(2) The smaller palpebral portion is located just above the temporal segment of the superior conjuncti¬val fornix. Lacrimal secretory ducts, which open by ap¬proximately ten fine orifices, connect the orbital and palpebral portions of the lacrimal gland to the superior conjunctiva) fornix. Removal of the palpebral portion of the gland cuts off all of the connecting ducts and thus prevents secretion by the entire gland.
The accessory lacrimal glands (glands of Krause and Wolfring) are located in the substantia propria of the palpebral conjunctiva.
Tears drain from the lacrimal lake via the upper and lower puncta and canaliculi to the lacrimal sac, which lies in the lacrimal fossa. The nasolacrimal duct contin¬ues downward from the sac and opens into the inferior meatus of the nasal cavity, lateral to the inferior turbinate. Tears are directed into the puncta by capil¬lary attraction and gravity and by the blinking action of the eyelids. The combined forces of capillary attraction in the canaliculi, gravity, and the pumping action of Horner’s muscle, which is an extension of the orbicu¬laris oculi muscle to a point behind the lacrimal sac, all tend to continue the flow of tears down the naso¬lacrimal duct into the nose.
The proper position, diameter, and number of ducts in the parts of the lacrimal apparatus are useful data for forensic scientists when these are viewed using forensic comparison microscopes.
Blood Supply & Lymphatics
The blood supply of the lacrimal gland is derived from the lacrimal artery. The vein that drains the gland joins the ophthalmic vein. The lymphatic drainage joins with the conjunctiva) lymphatics to drain into the preauricular lymph nodes.
Nerve Supply
The nerve supply to the lacrimal gland, when examined under a microscope, is by (1) the lacrimal nerve (sensory), a branch of the trigeminal first division; (2) the great superficial petrosal nerve (secre¬tory), which comes from the superior salivary nucleus; and (3) sympathetic nerves accompanying the lacrimal artery and the lacrimal nerve. Related Structures
The medial palpebral ligament connects the upper and lower tarsal plates to the frontal process at the inner canthus anterior to the lacrimal sac. The portion of the lacrimal sac below the ligament is covered by a few fibers of the orbicularis oculi muscle. These fibers offer little resistance to swelling and distention of the lacrimal sac. The area below the medial palpebral liga¬ment becomes swollen in acute dacryocystitis, and fis¬tulas commonly open in the area.
The angular vein and artery lie just deep to the skin, 8 mm to the nasal side of the inner canthus. Skin inci¬sions made in surgical procedures on the lacrimal sac should always be placed 2-3 mm to the nasal side of the inner canthus to avoid these vessels.
Forensic comparison microscopes make it possible to detect minute differences in the different parts of the optic system.
