Lacrimal aparatus and tear film

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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.

Almond shape

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

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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

PUNCTA

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)

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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)