LACRIMAL APPARATUS & TEAR FILM

Sanket parajuli

Lacrimal apparatus. 1. Lacrimal glands

• The main lacrimal gland• The 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 GLAND

• It 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 part• It 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 rectus• Anterior 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 part• It 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 gland

• 10 – 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 gland…secretory function

THE ACCESSORY LACRIMAL GLANDS

Glands 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 supply• Lacrimal 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 secretion

• Excessive 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 anatomy• Obstruction 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 secretion

• The 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

• 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) horizontal (8mm) diameter 0.5mm

• The vertical part turns medially at a right angle to become horizontal part

• Upper canaliculi runs medially & downward, the lower runs medially and upward, upper is shorter

• The junction of two portions, there is a slight dilation called the ampulla.

• The horizontal part of each canaliculus converges towards the medial canthus.

• Each canaliculus pierces the lacrimal fascia separately and unite to form common canaliculus, opens in lacrimal sinus of Maier.

• The opening of sac lies at the middle of the lateral surface of the sac about 2.5mm from its apex.

• In 10% individuals, each canaliculus enters the sac separately..

Structure of the lacrimal canaliculus

(inside outwards::)

• Epithelium lining the canaliculi is of stratified squamous type.

• Corium rich in elastic tissue which makes its wall stretchable and can be dilated about 2mm.

• Fibres of orbicularis help to draw the lid inwards allowing the punctum to glide in the groove between plica semilunaris and eyeball.

• The medial third are covered in front by two bands which connect the medial palpebral ligaments to tarsi, while behind is the lacrimal part of orbicularis oculi (horner’s muscle)

• The common canaliculus bends from posterior to an anterior direction behind the medial canthal tendon at an acute angle before entering sac, thus playing a role in blocking reflux

Applied anatomy• Wall is so thin & elastic that it can be dilated to 3 times normal diameter (i.e

normal 0.5 mm) • Lateral traction on the lids easily straightens them to facilitate probing.

• Should remember the direction & length of canaliculi while passing probe.

• Coloured fluid injected into a canaliculi can be seen through the transluscent tissue of lid margins.

Lacrimal sac

• It lies in the lacrimal fossa anterior part of medial orbital wall

• The lacrimal fossa is formed by lacrimal bone and frontal process of maxilla

• It is bounded by the anterior and posterior lacrimal crests

• The sac is 15mm in length, 5-6mm in breadth with a capacity volume 20 cmm

• The lacrimal sac is enclosed by lacrimal fascia, part of periorbita.

• The periorbita splits at posterior lacrimal crest into 2 layers, enclose the sac and meet at the anterior lacrimal crest.

• Between the lacrimal sac and fascia lie areolar tissue and venous plexus, continuous around the nasolacrimal duct.

• It has three parts:

• Fundus (3-5mm)- portion above the opening of the canaliculi.

• Body (10-12mm)- middle part

• Neck- lower small part which is narrow and continuous with the nasolacrimal duct.

Relations of the lacrimal sacAnteriorly: ●MPL ● Angular vein

Posteriorly: ● Lacrimal part of orbicularis oculi ● Orbital septum ● Check ligament of MR

Medially: ● Upper half of sac –Anterior ethmoidal air sinus ● Lower half of sac--Anterior part of middle

meatus

Laterally: ● Skin, Part of Orbicularis oculi ● Lacrimal fascia ● Few fibres of inferior oblique

Structure of the lacrimal sac• Epithelium: the sac in lined by 2 layers of cells. -The superficial layer is non ciliated columnar and contains goblet cells. -the deep layer is of flattened cells.

• Subepithelial tissue: contains lymphocytes which may aggregate in pathological condition to form follicles

• Fibroelastic tissue of the lacrimal sac becomes continous with that of canaliculi.

Applied anatomy

• Dacryocystitis: An Inflammation of the lacrimal sac

• Anterior to medial palpebral ligament & lateral to facial artery, angular vein crosses 7- 8mm from the medial canthus. Incision for removal of sac should not be more than 2-3mm medial to medial canthus.

The nasolacrimal duct (NLD)• Contiuous downward from the neck of the lacrimal sac to

the inferior meatus of the nose

• It is about 18mm (12-24) in length and about 3mm in diameter

• The upper end of NLD is its narrowest part.• The direction of the NLD is downwards, backward and

laterally.

• Externally its location is represented by a line joining inner canthus with the ala of nose.

It consist of two parts:• Intraosseus part (12.5mm)• Intrameatal part (5.5mm)

• The intraosseus part lies in the bony canal formed anterolaterally by the maxilla and posteriomedially by the lacrimal and inferior nasal concha.

• The intrameatal part of NLD lies within the mucous membrane of the lateral wall of the nose.

• The opening of the NLD in the inferior meatus is at the depth of about 30-40mm from the anterior nares.

Structure of the NLD

• Epithelium: the NLD in lined by 2 layers of cells, the superficial is non ciliated columnar and the deep layer is of flattened cells.

• Subepithelial tissue: contains lymphocytes which may aggregate in pathological condition to form follicles.

• Plexus of vessels is well developed around the NLD • Engorgement of vessel cause obstruction of NLD and produce epiphora.

The valvesDefinition: folds of mucous membrane with no valvular

function.

Typesvalve of Bochdalekvalve of Foltz

valve of Huschkevalve of Rosenmullervalve of medial palpebral ligament valve of Beraud or of Krausevalve of taillefervalve of Hasner

• A fold of mucosa at the junction between common canaliculi & lacrimal sac is Valve of Rosenmuller, which prevent reflux of tear from sac back into the canaliculi, acts as one way valve

• The duct opens in inferior meatus of nose, the opening is guarded by a flap of mucus membrane called the valve of Hasner

• The most constant is valve of Hasner (plica lacrimalis) at the lower end, a relic of fetal septum.

• Well developed plica prevent a sudden blast of air entering the lacrimal sac while blowing the nose.

Arterial supply to lacrimal sac and NLD

• Medial palpebral branches of ophthalmic artery

• Angular artery from facial

• Infraorbital artery from maxillary

• Sphenopalatine artery of maxillary

Venous drainage• Above: drains into angular &infraorbital vessels• Below: into nasal veins

Lymphatics: pass to submandibular & deep cervical nodes

Nerve supply: • Infratrochlear branch of ophthalmic division of trigeminal nerve• Anterior superior alveolar nerve, a branch of maxillary div of trigeminal

nerve

Applied anatomy

• Nasolacrimal duct: direction of NLD is downward, backward and laterally. while passing probe ,it is inserted into punctum of upper lid directed vertically and medially into lacrimal sac then downward at right angle in NLD to inferior meatus. End of the probe should be visible within the nose.

• The distal portion of the duct bends medially in an irregular J-shape in many neonates but it tends to straighten out with growth.

• NLD is easily separable from bone in upper part but below it is closely adherent forming mucoperiosteum which facilitates spread of infection.

Tear filmPrecorneal tear film: first described by FischerFunctions:I. Serves to keep cornea and conjunctiva moistII. Lubricates preocular surfaceIII. O2 for corneaIV. Anti bacterial

Structure:Wolff described first the 3 layers:a) Oily layerb) Aqueous layerc) Mucin layer

Lipid layer:

• Outermost layer• Derived from secretions of Meibomian, Zeiss and Moll

• Forms a strip @ lid margin which extends to posterior margin of openings of meibomian glands---limits anterior end of tear fluid---K/a marginal tear strip

• Made up of lipids such as wax and cholesterol esters• 0.1µm in thickness

• Retards evaporation• Prevents overflow of tears

• Absence of MGs increases evaporation by 10 times

Aqueous layer

•Middle layer of tear film• Secreted by lacrimal glands and accessory

lacrimal glands•Makes up 60% of total tearfilm thickness• 10µm thick• Film covering cornea is thinner than that

covering conjunctiva

Contains:Inorganic salts, glucose,ureaProteins(Lysozyme, lactoferrin, secretory Ig-A)

enzymes

Mucus layer:

•Deepest layer•Vital role in stability of tear film• Secreted by goblet cells, crypts of Henle

and glands of Manz

• Corneal epithelium is hydrophobic---mucin gets adsorbed on the cell membrane---anchored by the microvilli of epithelium---forms a hydrophilic layer---above this lies aqueous and lipid layer• 30µm thick

•Volume: 7 µl

• Rate of secretion: 1.2 µl/min (basal secretion)

• Refractive index: 1.357

• pH: 7.4 (PH is lowest on waking up)

• PaO2: 155mm Hg open lids….55mm Hg with closed lids

Composition of tears:

• Water• Proteins:Specific tear protein(STP) or prealbuminAlbumin=major protein component of tear(58.2%)IgA>IgG>IgM>IgDLysozyme and other enzymes

• Lipids• Glucose• Electrolytes

• Tear film Dynamics:

Can be discussed in chronological order in following headings:a) Secretion of tearsb) Formation of tearsc) Retention and redistribution of tearsd) Evaporation of tear filme) Drying and break up of tear filmf) Dynamic events during blinkingg) Elimination of tears

Secretion of tears

Basal secretion and reflex secretion (in response to sensations in cornea conjunctiva)

Hyperlacrimation occurs due to irritative sensations of conjunctiva or cornea

Most newborn secrete tears within 24 hours and most have a normal secretory rate

However no excess tear fluid even when baby cries….d/t low innervation of cornea

Formation of preocular tear film:

• Wettability: tendency of fluid to spread on it• Drop of liquid placed on solid surface : either spread completely or form a certain

boundary beyond which it wont spread• @ the boundary=contact angle=theta• When theta=0----liquid completely spread on the surface• When theta angle present::surface - non wetted

• Ɵ>90°==hydrophobic• Ɵ between 0° and 90° ==relatively hydrophobic• Ɵ = 0° ==hydrophilic

• Conjunctival mucin = responsible for wetting the corneal surface by convering the surface into hydrophilic

• Lids surfaces cornea with thin layer of mucin

• Aqueous layer spreads over

• Superficial lipid layer spreads at the outermost part providing stability and retarding evaporation

Drying and rupture of tear film:

• When blink is prevented for 15-40 secs –break in film

Mechanism::(Holly and Lemp’s mechanism)::• 1st the film thins uniformly by evaporation

• When thinned to critical thickness---lipid molecules attracted by mucin layer and migrated down to this layer

• When mucin layer sufficiently contaminated by lipids—mucin becomes hydropobic…..tear film breaks

• Blinking can repair rupture by removing contaminant lipids from mucin layer and restoring aqueous layer

• Thus dry spot formation is localized non wetting and NOT localized drying caused by discontinuities in lipid layer

• Occurs frequently in temporal>>nasal

Dynamic events during blinking:

• Upper lid moves down---superficial layer is compressed –whole lipid layer together with associated biopolymers is compressed between lid edges---lipid accumulated mucin then --rolled up like thread and dragged into lower fornix

• When eyes open—lipid spreads in form of monolayer against upper lid—spreading lipid drags some aqueous tear with it— thickenes tear film—this again is controlled by tear meniscus

Drainage of tears: Rosengren-Doane Mechanism

• During the act of blinking, closure of eyelids occurs from lateral to medial

• Brings fluid in the conjunctival sac medially

• Tear then enter the canaliculi by capillarity

• Blinking causes contraction of lacrimal part of orbicularis muscles which dilate the sac partly by pulling medial palpebral ligament which is attached anteriorly & partly by contracting orbicularis which is attached posteriorly.

• This creates negative pressure so that fluid is passed into sac from canaliculi.

on opening the eye the muscle relax and the sac collapse & a positive pressure created which forces the tear passes from sac into NLD then into nose as a result of gravity

evaporation of tear in nose occur during inspiration and expiration of air.

Applied anatomy

•Dry eye: Either due to Decreased tear production or Increased tear evaporation

• Lacrimation: Excessive lacrimation occurs reflexly as in photophobia, inflammations of conjunctiva, cornea, ciliary body

• Epiphora: overflow of tears from the eye due to obstruction , stenosis, punctal malposition or functional disorder of lacrimal passages

• Causes of KCS/dry eye:

Aqueous-KCS, sjogrens syndrome, congenital alacrimia, sarcoidosis, drugs

Lipid –Meibomian gland disease, blepharitis

Mucus-Vit A deficiency, chemical burns, Steven-Johnson syndrome

Investigations• Stability of tear film::Tear Break Up Time (TBUT )

• Tear production :: Schirmer’s Test – I & II , Fluorescein clearing

• Ocular surface disease: corneal stains (fluorescein, Rose Bengal Staining, phenol red thread test and Conjunctival Impression Cytology)

Newer methods: Toposcope

Marginal tear meniscus:

Crude method of measuring volume of aqueous

Tear meniscus: between globe and lower lid

Normally: 0.3-1.0 mm—convex– regular upper edge

Dry eye: <0.3 mm – concave – irregular/thin

Rose Bengal: • has affinity for devitalized epithelial cells • corneal filaments and plaques are visualized clearly • 1% is used• Causes stinging sensation that can last up to a day• Thus topical anesthesia drop kept…immediately

followed by a drop of Rose bengal…excess is immediately washed off

Fluorescein clearance test: rarely5 µl of fluorescein on ocular surface---shirmer’s strip –readings @ interval 1,10,20,30 minutes---amount of fluorescein in each strip measure under blue light & compared to a standard scale---normal eyes value will be 0 after 20 mins

Phenol red thread test:

• Thread impregnated with PH sensitive dye(phenol red) is placed at the eyes like shirmer’s strip• Dye changes to red (yellow to red) • Readings taken after 15 secs• <6mm = abnormal

Impression cytology: to determine the number of goblet cells

Toposcope:Invented in LondonPt places lid inside a bowl of device fixing on a central targetA grid is projected on corneaIts reflection is viewed through Toposcope tubeReflected grid can detect whether Tear film break up has occurred

Causes of Lacrimation (hypersecretion)

• Secondary to ocular inflammation or surface disease.

• Emotional distress

• Irritation of the eyes ( smoke, dust, foreign bodies, injury)

Causes of Epiphora (defective drainage)Compromise of the lacrimal drainage system:

• Malposition of the lacrimal puncta (e.g. ectropion)

• Obstruction (anywhere along the lacrimal drainage system, from puncta to the NLD)

• Lacrimal pump failure (lower lid laxity or weakness of the orbicularis muscle)

Evaluation tests

• Syringing and probing (hard stop or soft stop)• Fluorescein dye disappearance test• Jones dye testing (the primary and secondary test)• Contrast dacryocystography• Nuclear lacrimal scintigraphy

Interpretation of syringing of lacrimal system

• Clear fluid opposite punctum-common canalicular block

• Clear fluid from same punctum-same canaliculus block

• Mucoid fluid from opposite punctum-nasolacrimal duct block

If irrigation confirms lacrimal obstruction –attempt to pass the cannula to lacrimal sac

If the cannula hits on bone (hard stop), the canaliculus is open so the obstruction is probably in the sac or the duct.

If it does not hit on the bone, a 'soft stop' occurs, so the obstruction is probably in the common canaliculus, especially if the medial angle of the palpebral aperture shifts medially as the cannula is advanced toward lacrimal bone.

Fluorescein disappearance test

• The fluorescein disappearance test is performed by instilling fluorescein 2% drops into both conjunctival fornices

• Normally, little or no dye remains after 5 minutes

• Prolonged retention is indicative of inadequate lacrimal drainage

  

Jones dye testing: a) primary, b) secondary

In patients suspected of partial obstruction Patients manifest with epiphora but lacrimal system can be fully irrigated1) Primary test: Primary hypersecretion vs partial

obstruction of NLD2% fluorescein instilled in conjunctival sac---after 5 mins cotton dipped in local anesthetic is kept in inferior turbinate---results::Positive: cotton stained with fluorescein……

hyperlacrimationNeagtive::No recovery of stained cotton ….partial

obstruction or failure of lacrimal pump

2) Secondary test: identifies the probable site of partial obstruction, on the basis of whether the topical fluorescein instilled for the primary test entered the lacrimal sac.

Topical anaesthetic is instilled and any residual fluorescein washed out. The drainage system is then irrigated with saline with a cotton bud under the inferior turbinate

a. Positive: fluorescein-stained saline recovered fromthe nose indicates fluorescein entered the lacrimal sac---confirming functional patency of the upper lacrimal passages. Partial obstruction of the nasolacrimal duct is inferred

b. Negative: unstained saline recovered from the nose indicates that fluorescein did not enter the lacrimal sac---implies partial obstruction of the upper lacrimal passages (puncta, canaliculi or common canaliculus) or a defective lacrimal pump.

Dacryocystography Involves the injection of radiopaque contrast medium into the canaliculi followed by capture of magnified images.

The test is usually performed on both sides simultaneously.

A DCG is not necessary if the site of obstruction is obvious such as in the case of a regurgitating mucocele.

References:• Wolff’s Anatomy of eye and orbit• Snell’s anatomy of the eye• Internet sources• Kanski’s clinical ophthalmology• AAO

• Lacrimal pump mechanics:

• On closing eyelids:

a) Contraction of pretarsal fibers of orbicularis—compresses ampulla—shortens canaliculi---propels tear fluid in ampulla and horizontal part of canaliculi into sac

b) Contraction of preseptal fibers of orbicularis pulls lacrimal fascia and lateral wall of the sac laterally---opens the otherwise closed sac—negative pressure—draws fluid from canaliculi to sac

c) Along with increased tension on lacrimal fascia(which opens the sac) imferior portion closes more tightly thereby preventing aspiration of air from nose

When lids open::Tone in orbicularis decreased---relaxation of pretarsal fibers of orbicularis---allows canaliculi to expand and open---draws lacrimal fluid through the punctum from lacrimal lake

Relaxation of preseptal fibers of orbicularis alloes sac to collapse---expels fluid downwards into now open NLD

• Once lacrimal fluid is in upper part of NLD—influence of lid movements on its downward movements end—factors helping then::

a) Gravity

b) Air current movement inside the nose(in/out)—causes negative pressure in NLD

c) Valve of hasner—opens as long as intranasal pressure is less than pressure in NLD

• MUSCLES OF THE PALPEBRAL REGION• ORBICULARIS OCULI• Orbicularis oculi is the palpebral sphincter. lt is an elliptical sheet extending from the lids, where it surrounds the

palpebral fissure, to the brow, temple and cheek. It consists of two main parts: palpebral; orbital (Fig. 2.29). Palpebral part The palpebral part of orbicularis oculi ts central and confined to the lids. It consists of pale fibres and may divide into pretarsal and preseptal strata, which are joined, by the thinnest parts of the muscle, at the supenor and inferior palpebral sulci. It diverges from the medial palpebral ligament and neighbounng bone, and curves across the lids in a series of half ellipses, which interlace beyond the lateral canthus as the lateral palpebral raphe which is strengthened by the septum orbitalc. Orbital part The orbital part has a curved origin from the upper orbital margin medial to the supraorbital notch, the maxillary process of the frontal bone and the frontal process of the maxilla, from the medtal palpebral ligament, and from the lower orbital margin medial to the infraorbital foramen. This attachm{!nt is musculotcndinou'> and dtscontinuous. Penpheral fibres sweep across the orbital margin in concentric loops, the more central ones forming almost complete rings. Recent studies of volume reconstrucltons of the orbiculans muscle and the dtstribuhon of the motor end plates suggest that both its palpebral and orbital parts are made up of short mu<;cle fibres averaging 1.1 mm long (0.4-2.1 mm) connected by myomyous junctions which interrupt the courc;c of the muscle bundles (Fig. 2.29j) (Wirtschafter et a/., 1995). Neuromuscular junctions arc arranged in staggered clusters along the entire length of the mu<;cle. This arrangement has implications for the use of botulinum A toxin in the treatment of blepharospasm, since it implies that the toxin must be diffused through the lids to achieve a maximum result. Information is available as to orbicularis muscle fibre size and type (Wirtschafter et a/., 1995). It contains myofibres with the smallest diameters of any facial muscle (Polgar et a/., 1973). At increasing distance from the eyelid margin, there ts a gradual increase in fibre diameter and in the proportion of type 1 fibres. These are slow twitch, fatigable oxidative fibres and make up 10-15°/c• of the muscle. Fast twitch, glycolytic tvpc 2 fibres represent almoc;t 100% of the pretarsal fibres, and hmc a cross-sectional area of 400 f..Lm 2; only 3 4°1<. arc type 1. In the prescptal region, 8-l5°'o <~re type 1 and the average cross-sectional area is about 550 f..Lm2 (McLoon and Wirtschaftcr, 1991; Porter, Burns and May, 989) These topographic differences may mfluence the orbicularis contraction during the blink and forced eye closure

• Relations• The palpebral part has areolar tissue b~t no fat ?n both aspects. Anteriorly, this separates 1t from skm;

posteriorly, the submuscular areolar l~yer sep~r~tes it from tarsal plates and palpebral fasCia, contammg main vessels and nerves and fibres of levator. This part is adherent to dermis at the medial. and later~! canthi. Fibres of the levator pass through 1t to the skm (Fig. 2.10). The orbital part spreads above on the forehead (contributing to the structure of the eyebrow and covering corrugator supercilii), laterally on the. Temple (covering the anterior part of the temporal fasc1a), and below on the cheek (overlapping the zygomatic bone and elevator muscles of the upper lip and nostril). Anteriorly it is separated from the skin by a layer of fat, to which it is adherent, and thus to skin. Peripheral fibres of orbicularis attached to skin arc musculus superciliaris (Merkel, 1887), a depressor of the medial end of the eyebrow (Arlt, 1863), to the skin of which some superomcdial peripheral fibres are attached; musculus malaris (Henle, 1853) formed by some medial and lateral peripheral fibres attached to the skin of the cheek. Some fibres are attached to skin round the medial canthus, wrinkling the medial part of the lids (Merkel, 1887). A third part of the orbicularis oculi is a recognizable entity, the pars lacrimalis (tensor tarsi), often named Horner's muscle, although it was earlier recorded by Duverney (1749) and Gerlach (1880). It is a thin layer attached behind the lacrimal sac to the upper posterior lacrimal crest (Figs 2.66 and 2.67) and the lacrimal fascia. Passing anterolaterally, it divides into two, slips around the canaliculi and blends with the pretarsal and ciliary parts of orbicularis .oculi in both lids. The pars ciliaris (muscle of Riolan formed of fine striated muscle fibres, is in the dense tissue of the palpebral margins. The ciliary glands (of Moll) are between these fibres and palpebral parts of orbicularis (Fig. 2.10). They also surround the tarsal (meibomian) glands (Figs 2.10 and 2.6?)· Media~ly the ciliary and lacrimal parts are contmuous (F1g. 2.66).

• Actions• The palpebral part closes the lids gently, as in blinking, which is often involuntary

and frequently without obvious stimulus. Reflex blinking is stimulated by visible threats and loud noises. Voluntary blinking, to clarify vision or to break eye contact, also occurs. Reflex blinking is stimulated by drying of the cornea; it spreads tear fluid, and the pars lacrimalis helps to empty the sac (p.84). The orbital part closes the lids firmly, and draws the skin of the forehead, temple and cheek medially, which forms radial furrows around the lateral canthus. These are temporary in youth, but become permanent later ('crow's feet'). The muscle also contracts during short but powerful expiration, as in crying, coughing, blowing the nose, sneezing, and excessive laughter. Contraction of the orbital part depresses the eyebr ow to reduce excessive light from above, the relaxed palpebral part allowing the lids to remain open. When both parts contract the eyelids are 'screwed up'. The two parts of the muscle affect the volume of the conjunctival sac differently: the palpebral part does not diminish its volume, so that no tears spill, but the orbital fibres compress the sac, and tears spill over the check. Contraction of the orbital part, pressing the puckered lids against the globe, is more effective against external violence than mere blinking. The palpebral part is opposed by levator palpebrae superioris, the orbital by occipitofrontalis.

• Nerve supply• Orbicularis oculi is innervated by the facia l nerve, through its temporal

and zygomatic branches which enter the muscle from its lateral side and deep aspect. Several temporal branches ascend across the zygoma and pass above the lateral canthus to supply the upper half of orbicularis, assisted by upper zygomatic branches, the lower of which cross the zygomatic bone to reach its lower part. As these nerves penetrate the muscle they divide further (Fig. 5.35). Because any nerve may be affected by disease or injury, paralysis may be local: for example, paralysis of the lower palpebral part allows the lower lid to evert (ectropion), leading to epiphora.

• CORRUGATOR SUPERCILII (Fig. 5.36)• This muscle is situated at the medial end of the eyebrow deep to frontalis and orbicularis.

Attached at the medial end of the superciliary ridge, it passes superolaterally through the overlying muscles, to the skin of the eyebrow near its mid point Action The two corrugators pull the eyebrows towards the nose, making them project over the medial canthus, producing \·ertJcal furrows above the bridge of the

• nose, and sometimes a depressiOn at thetr dermal attachments. The corrugator supercilius muscle is used primarily to reduce glare. It is well developed in outdoor workers a nd even in children who wear no hats who, acquire vertical furrows at an early age. In facial expression it is the basis of frowning, evident in crying, sorrow, pain, and when attempting mental recall.

• Nerve supply• The corrugators are supplied by the facial nerve, through its wperior zygomatic branch

• OCCIPITOFRONTALIS• Occipitofrontalis consists of paired occipital and frontal muscles, united by the large, thin,

epicranial aponeurosis, covering most of the cranial vault. Each occipitalis, small and quadrilateral, is attached to the lateral two-thirds of the highest nuchal line and to the mastoid process, immediately superior to the sternocleidomastoid. Its parallel fascicles pass into the epicranial aponeurosis. Frontalis, also quadrilateral, is attached to the epicranial aponeurosis mid-way between the coronal suture and the orbital margin and to the skin of the eyebrows, mingling with orbicularis and corrugator. Above, a distinct triangular interval separates the frontal muscles; below, the medial fibres converge to blend with the procerus, which is ascending and is hence the antagonist of frontalis. Action Frontalis elevates the eyebrows and draws the scalp forwards, wrinkling the forehead transversely in variable furrows, often convex upwards laterally and centrally concave or absent. Occipitalis retracts the scalp in opposition to frontalis. Occipitofrontalis opposes the orbital part of orbicularis oculi to elevate the eyebrows in upward gaze; levator palpebrae superioris opposes the palpebral part. Occipitofrontalis increases access of light to the eye - and also reflection, thus animating expression. Frontalis is contracted when vision is difficult due to distance or insufficient light. It expresses surprise, kadmiration, fear and horror, in all of wh1ch the element of 'attention' is present, as Duchenne (1883) noted. Raised eyebrows, with lids half-closed, suggest forced attentiokn, or craftiness !

• Nerve supply • The occtpato-frontalis is supplied by the facial nerve, through its posterior auricular and

temporal branches.

• MUSCULUS PROCERUS• The paired proceri, dose together near the mid line, occupy the bridge of

the nose and an interval between the lower fibres of frontalis. They are attached inferiorly to the nasal bones and lateral nasal cartilages and pass to blend with the dermis near the bridge of the nose (Fig. 5.36). Pulling on this skin t hey create transverse furrows in the lower central part of the f orehead and root of the nose. Hence also the freq uent concave mid point to the transverse furrows of the forehead. The procerus acts with corrugator supercilii to increase prominence of the eyebrows to reduce bright light. Duchenne named it 'the muscle of aggression‘ (Duchenne, 1883), but it may also express anguish. Frontalis, orbicularis oculi, corrugator supercilii and procerus were regarded by Howe (1907) as accessory muscles of accommodation, contracting when vision is difficult (presumably to achieve stenopaeic viewing). The continuity of frontalis and• occipitalis may sometimes explain occipital headache associated with eye

strain