Lacrimal aparatus and tear film
Embed Size (px)
Transcript of Lacrimal aparatus and tear film
LACRIMAL APPARATUS & TEAR FILMSanket parajuli
Lacrimal apparatus. 1. Lacrimal glandsThe main lacrimal glandThe accessory lacrimal glands
2. Lacrimal passages Puncta Lacrimal canaliculi Lacrimal sac Nasolacrimal duct
DEVELOPMENT:Lacrimal gland Form as series of 8 epithelial buds, which grow superolaterally from superior fornix @ about 2 months of fetal life
With the development of LPS, gland divides into orbital and palpebral parts.
Lacrimal gland do not function fully until 6 wks. after birth which explains why new born infants do not produce tears when crying
Lacrimal sac and nasolacrimal ductBy the end of 5th wk., the nasolacrimal groove forms as a furrow between the nasal & maxillary prominence
In the floor of the groove, NLD develops from the linear thickening of ectoderm
Solid cord separates from adjacent ectoderm into mesenchyme forming NLD whose superior end becomes dilated to form the lacrimal sac
Canaliculi are formed from invaginated ectoderm
Canalization is usually complete around the time of birth but failure of caudal end to completely canalize results in congenital NLD obstruction
MAIN LACRIMAL GLANDIt is situated in the fossa, formed by the orbital plate of the frontal bone.
It lies in the anterolateral part of the roof of orbit
Divided in anterior aspect by lateral horn of LPS into 2 parts
superior orbital part inferior palpebral part
The orbital partIt lies in the fossa at anterolateral area of orbital roof.
It has 2 surfaces- superior, inferior 2 borders -anterior , posterior 2 extremities- medial, lateral
superior surface: convex and lies in the fossa on the frontal bone Inferior surface: concave & lies successively on the levator, its expansion and the lateral rectusAnterior border: well-defined and in contact with the septum orbitale skin & orbicularis and septum orbitale must be divided to reach the gland. Posterior border: rounded, in contact with the orbital fat and level with the posterior pole of the eye Medial extremity: rests on levator lateral extremity: rests on the LR
The palpebral partIt is about 1/3rd the size of orbital part, consists of only 1or 2 lobules.
It lies below the aponeurosis of LPS and extends to the upperlid.
Superior surface- related to aponeurosis of LPS.
Inferior surface- lateral part of superior fornix of conjunctiva.
visible through the conjunctiva when the upper lid is everted and up to 12 ductular openings may be seen with biomicroscopy
Ducts of Lacrimal gland10 12 ducts in number.
The ducts pass downwards from the main gland to open in the lateral part of the superior fornix.
1 or 2 ducts also open in the lateral part of the inferior fornix.
All the ducts pass through the palpebral part of the gland.
The excision of the palpebral part results in loss of the entire glandsecretory function
THE ACCESSORY LACRIMAL GLANDSGlands of krause - Microscopic glands in the sub conjuctival tissue of the fornices. - 40- 42 in the upper fornix and 6-8 in lower fornix. - their ducts unite to form long duct which open in the fornix. Glands of wolfring- Microscopic glands along the upper border (2-5 ) of superior tarsus and lower border(2-3) of inferior tarsus. Rudimentary accessory lacrimal glands in the caruncle, plica semilunaris and infraorbital region
STRUCTURE OF THE LACRIMAL GLAND
tubuloacinar with short, branched tubules, resembling the parotid gland in structure
glandular tissue consist of acini and ducts arranged in lobes and lobules separated of fibrovascular septa.
The acini are made up of pyramidal secretory cells with their apices directed towards a central lumen
Basal portion of the acinus is separated from a basement membrane by myoepithelial cells
Apical microvilli extend into the lumen.
Myoepithelial cells are elongated, with flattened nuclei and numerous fibrils resembling those of smooth muscle cells.
They are regarded as contractile and may aid the expulsion of secretion
The ducts show two or three cell layers and numerous microvilli at the luminal surface.
Plasma cells of the interstitial space are an important source of Igs in tears
human lacrimal glands contain over three million plasma cells
IgA-secreting (and fewer lgG-, lgM-, IgE-, and IgD-secreting)
In tears, as in other exocrine secretions, lgA is the chief Ig
Secretory IgA is dimeric in form, two molecules of IgA being linked by a polypeptide J chain, also of plasma cell origin
Lacrimal acinar cells synthesize a secretory component (SC) which becomes membrane associated and may provide a binding site for the J chain of dimeric IgA
IgA-SC complex is then transported to the acinar lumen.
Th lymphocytes stimulates B cell to diff into IgA-secreting plasma cells
Arterial supplyLacrimal artery ,a branch of Ophthalmic artery which enters its posterior border
Infraorbital artery ,a branch of maxillary artery
Sometimes a branch of transverse facial artery
VENOUS DRAINAGE: Superior ophthalmic vein via the lacrimal vein.
LYMPHATIC DRAINAGE: Joins that of conjunctiva & into preauricular nodes
Nerve supply:The sensory fibres reach the lacrimal gland in the lacrimal nerve, a branch of ophthalmic division of trigeminal nerve
The sympathetic postganglionic fibers arise from superior cervical sympathetic ganglion then travel in plexus of nerves around the internal carotid artery
They join deep petrosal nerve, nerve of pterygoid canal ,maxillary nerve, zygomatic nerve, zygomaticotemporal nerve and finally lacrimal nerve
The parasympathetic secretomotor nerve supply is derived from superior salivary nucleus of facial nerve
The pre-ganglionic fibres reach pterygopalatine ganglion through facial nerve & its greater petrosal branch & through nerve of pterygoid canal
The post-ganglionic fibres then join the maxillary nerve, then into its zygomatic branch & zygomaticotemporal nerve. They reach the lacrimal gland within lacrimal nerve
Reflex control of lacrimal secretionExcessive production of tears in emotional conditions Parasymapthetic lacrimatory nucleus of facial nerve receive afferent fibres from hypothalamus
Excessive tear production in response to Olfactory stimuli Similar pathway connect olfactory system with lacrimatory nucleus
Reflex Lacrimation secondary to cornea or conjunctival irritation sensory nuclei of trigeminal nerve are connected to lacrimatory nucleus by internuncial neurons
Applied anatomyObstruction to secretion: openings of ducts into conjunctival sac may be obstructed by scarring of conjunctiva like trachoma, chemical burns, ocular cicatricial pemphigoid
Tumors of lacrimal gland: Benign (common)--mixed cell tumor (pleomorphic adenoma),benign lymphoid hyperplasia . Malignant (less common)-malignant lymphoma, adenocarcinoma
Drying of the conjunctiva and cornea results from the deficiency of the aqueous component of tears in the disease of the main lacrimal gland or accessory glands.
Dacryoadenitis: Inflammation of lacrimal gland
Dacryops : cystic swelling in upper fornix due to retention of secretion following blockade of one of the lacrimal ducts
Mikulicz Syndrome: symmetrical enlargement of lacrimal & salivary glands
The smaller palpebral part of the lacrimal gland lies within the upper lid, damage to it may occur during surgery to the upper lid.
Lacrimal secretionThe secretion are produced by acinar cells passes into the duct system where the lining cells of duct modify its composition.
Final lacrimal secretion: Lysozyme IgA Beta-lysin
Functions of the lacrimal secretion Keep corneal epithelium moist so that the surface epithelial cells have a medium to live
First and major refractive surface of eye
Lubricate apposed surface of lids and eyeball so that it moves freely beneath the lids
Lysozyme (antibacterial enzyme)IgA (Immunoglobin) Beta-lysin (bactericidal protein)
Secretes substance which affects ocular surface by regulating epithelial cell turnover
oval opening 1 each on the Upper and lower lid
at the junction of ciliary and lacrimal portion of lid margin
The puncta is situated upon a slight elevation called lacrimal papilla
0.3 mm in diameter
The upper and lower puncta lie about 6mm and 6.5mm lateral to inner canthus
However, in lid closure the puncta often make contact
(upper punctum is slightly medial to the lower)
The puncta are relatively avascular and thus paler than surrounding areas, a pallor accentuated by lateral tension on the lower lid - an aid in finding a stenosed punctum
The upper punctum opens inferoposteriorly, the lower superoposteriorly.
Hence normal puncta are visible only when lids are everted
Each punctum, with lids open or shut, faces into the groove between the plica semilunaris and globe
patency maintained by surrounding dense fibrous tissue continuous with the adjacent tarsal plate.
Fibres of the orbicularis also press the punctum towards the lacus lacrimalis
Muscle atrophy makes the papilla more prominent, commonly so in the aged
The lacrimal canaliculi
The superior and inferior canaliculi join the puncta to the lacrimal sac.
Two parts- vertical (2mm)