Anatomy of the eye includes lacrimal gland, cornea, conjunctiva, uvea (iris, choroid & ciliary body), lens, blood supply, retina, vitreous & optic-nerve. For ophthalmologists, optometrists, medical, dental, and optometry students, eye-anatomy forms the basis for eye-pathology in diseases: dry eye, retinal detachment, macular degeneration, diabetic retinopathy, eye-trauma etc.

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Monday, February 13, 2006

Lacrimal gland-human

How many lacrimal glands are there in each orbit? Main (orbital and palpebral portions) + Glands of Krause (50) + Glands of Wolfring (5) + caruncle (1) = About 57!
Which lacrimal glands can be identified in the photograph below? This is an anterior posterior section of the orbit cut in the vertical plane.

Main Lacrimal gland- orbital and palpebral portions
Where is the main lacrimal gland? The lacrimal gland consists of an orbital or superior portion; and a small palpebral or inferior portion; which are continuous. Shaped like an almond the main lacrimal gland is situated above and lateral to the eye in the orbit in a shallow depression of the frontal bone. (The lacrimal gland does not lie in the lacrimal fossa or lacrimal bone where the nasolacrimal duct is!). The lacrimal gland secretes tears into ducts in the upper fornix. The lobules of the orbital portion of the lacrimal gland (#1 in photo above) are near the orbital septum. The levator muscle (4) initially lies under the lacrimal gland (#4 photo above) but the enfolds the palpebral portion. The bulbar portion continues forward and is contiguous with Muller's muscle. The levator inserts into the eyelid in a more anterior position than Mullers as fibers rejoin anterior to the palpebral lacrimal gland. The levator is posterior to the orbicularis that joins from beneath the skin and enters the eyelid.
Accessory Lacrimal Glands of Krause
Where is the accessory lacrimal gland of Krause? The accessory lacrimal gland of Krause(#3 photo above) lies immediately adjacent to the fornix of the upper eyelid (#2 photo above). The glands of Krause are accessory lacrimal glands having the same structure as the main gland. They are placed deeply in the substantia propria of the upper fornix between the tarsus and the inferior lacrimal gland, of which they are offshoots. The sclera (5), ciliary body(6) and iris (7) are all identifiable in photograph above.

How many accessory lacrimal glands of Krause are in the upper eyelid?
How many accessory lacrimal glands of Krause are in the lower eyelid?
There are some 42 in the upper fornix and 6 to 8 in the lower fornix. The glands of Krause are found largely on the lateral side of the orbit. Their ducts unite into a rather long duct or sinus which opens into the fornix.
Are lacrimal glands a normal part of the caruncle? Similar lacrimal glands are found in the caruncle. (Check back for photo).
Accessory Lacrimal glands of Wolfring.
Identify the glands of Wolfring in the photograph.
What structure corresponds to each letter?
Where are the accessory lacrimal glands of Wolfring? The Glands of Wolfring or Ciaccio are also accessory lacrimal glands, but larger than the glands of Krause. There are 2 to 5 in the upper lid and 1-3 in the lower lid, situated in the upper border of the tarsus midway between the end of the tarsal glands. In the photograph of a cross section of the eyelid, A points to one of the sebaceous glands embedded in the tarsus. B is a gland of Wolfring, C is a nerve and D is the orbicularis muscle. The excretory duct for the gland of Wolfring (not shown in the photograph) is large and short and lined by a basal layer of cubical cells and a superficial layer of cylindrical cells like the conjunctiva onto which it opens.
Lacrimal Gland Histology
Identify each of the numbered histologic features below.

Photomicrograph (above) shows a higher magnfication of a human lacrimal gland complete with acinar structures that contain lumens (1) and protein rich acinar cells that secrete lysozyme, tear lipocalin, lactoferrin and IgA. The reddish granules (2) are secretory vesicles replete with protein. Some lumens are filled with protein that is being secreted. Lymphocytes and plasma cells are scattered in the interstitium(3).
The lacrimal gland consists of a lobules and is a tubulo-racemose gland with short branched gland tubules somewhat similar to the parotid. The acini consist of two layers of cells placed on a thin hyaline basement membrane and surrounding a central lumen. The basal cells are myoepithelial in character while the acinar cells are cylindrical, and secrete fluid into a series of ducts of increasing size until becoming the excretory duct.
What species do not have lacrimal glands? The lacrimal gland and its tears exist in animals which live in air. Fish do not have lacrimal glands.

What is the blood supply to the lacrimal glands? The arterial blood supply originates from the ophthalmic artery via the lacrimal artery. The lacrimal artery arises from the ophthalmic artery lateral to the optic nerve and runs forward along the upper border of the lateral rectus muscle in company with the lacrimal nerve. The drainage is to the lacrimal vein which joins the opthalmic vein.
What is the innervation of the lacrimal gland? The lacrimal nerve provides sensory innervation.
Describe the lacrimal reflex arc. The Vth cranial nerve is the afferent pathway from the sensory fibers in the nose and the corneal surface (arrow 1 in the figure below). Corneal fibers traverse the long posterior ciliary nerve in the sclera and exit posteriorly (arrow 2 in the figure below). The fibers pass join the nasociliary nerve as the long sensory root (passing through the ciliary ganglion (arrow 3). The nasociliary nerve exits the orbit thru the superior orbital fissure and enters the cavernous sinus lateral to the internal carotid artery. The nerve passes thru the trigeminal ganglion (also called semilunar or Gasserian ganglion, #4 in the figure below) which is present in Meckel's cave. From the trigeminal ganglion the fibers enter the pons and descend in the ipsilateral spinal trigeminal tract, synapsing in the most ventral portion (synapse 1, see figure- arrow 5). The output from the sensory nucleus is then to the lacrimal and salivatory nuclei (synapse 2, see figure- arrow 6). From here efferents (arrow 7) pass into the seventh nerve (nervus intermedius of the facial nerve) thru the geniculate ganglion (arrow 8), the greater or superficial petrosal nerve. The superficial petrosal nerve enters the pterygoid canal, continues in the pterygopalantine fossa and synapses in the pterygopalantine ganglion (synapse 3, arrow 9). Unmyelinated postganglionic parasympathetic fibers enter the inferior orbital fissure and form a retrobulbar plexus of nerves that include sympathetic fibers from the carotid plexus. These nerves supply the lacrimal gland (arrow 10) as the rami oculares . Tear secretion is mediated by parasympathetic output and vasoactive intestinal polypeptide (VIP) mediated fibers (synapse 4).
Describe the pathway for emotional tearing. Afferents to the lacrimal nucleus from the hypothalamus with cortical input mediate emotional tearing. The pathway through the seventh nerve is identical as described for the reflex lacrimation.


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