Conjunctival PhysiologyMagrane Basic Science CourseKATE MYRNA, DVM, MS, DACVO

UNIVERSITY OF GEORGIA

Conjunctiva

Vascularized mucous membrane Anterior surface of globe (bulbar conjunctiva),

posterior surface of eyelids (palpebral conjunctiva), anterior and posterior surface of third eyelid

Secretes mucus

Site of Mucosal defense – immunocompetent cells Initiate and mediate inflammatory reactions

Synthesize immunoglobulin

Microvilli and enzyme activity allow phagocytosis of foreign particles

Conjunctiva Anatomy

Palpebral conjunctiva Mucocutaneous junction: zone behind the Meibomian gland openings where stratified

keratinized squamous epithelium of the lid margin transitions to the stratified nonkeratinizedsquamous epithelium of the conjunctiva

Tarsal conjunctiva

Orbital/Bulbar conjunctiva – from the tarsal plate into the fornix

Conjunctival Cul-de-sac or fornix

Bulbar conjunctiva Scleral division: extends from fornix to limbus

Conjunctiva, sclera and tenon’s capsule are fimly attached 3mm from the limbus

Limbal division: 3mm wide ring at junction of conjunctiva and corneal epithelium

Conjunctival Glands

Serous Krause’s glands

Deep in conjunctival fornix (40 superior, 6-8 inferior in humans)

Wolfring’s glands 2-5 in upper lid (along edge of tarsus)

Fewer along lower edge of inferior tarsus

Mucous Henle’s glands or crypts

Epithelial invaginations within chorion, composed of goblet cells

Along upper edge of superior tarsus

Manz’s glands At limbus (reported in pigs, cattle and dogs; absent in human)

Conjunctiva: Goblet Cells

Mucus production per eye per day: 2-3mL in humans

Mucins High molecular eight glycoproteins (2000-4000kDa)

which form a gel

Peroxidase Contribute to anti-infectious defense of ocular surface

of tear film

Hyaluronic acid? Some goblet cells synthesize it to stabilize the tear film

Conjunctival Mucin Function

Anchor aqueous layer of the tear film Tear film is organized into increasingly dense

filaments as one approaches the cell layers

Trap desquamated epithelial cells and acellular surface debris (organisms) Transported to medial canthus during blinking

Immunological barrier Immobilize more than 30% of the secretory IgA

contained in tear films

Conjunctival Glycocalyx

Glycoproteins and glycolipids that cover the microvilli and microplicae of the corneal/conjunctival epithelium

Extends 300 nm from microvilli and microplicae

Angular and branching and extends laterally between microvilli

Filaments branch distally and associated with cell membrane

Mucus layer attaches to glycocalyx Protects epithelium by causing shear forces of blinking

to break up mucus layer away from cell surface

Mucus attachment to glycocalyx allows aqueous

layer to spread evenly

Conjunctival Immunity

Conjunctiva-associated lymphoid tissue (CALT) Uptakes and processes antigens

Produces immunoglobulins and effector cells

Has lymphoepithelium overlying B and T cell lymphoid population (FAE)

Follicular associated epithelium (FAE) Contains membranous (M) cells

M cells deliver antigen particles to lymphoid tissue below

Feline Conjunctivitis

Impression cytology (Eordogh et al) Ideal technique with topical anesthesia and additional drying.

SUPERIOR bulbar conjunctiva

Biopore membrane device

Conjunctival monolayer

Eyelids

Functions Screening and sensing (cilia and vibrissae)

Mechanical wiping action

Secretions and spreading of glandular tissue

Screening of light to allow sleep

Eyelid

Muscles:-Orbicularis oculi-Retractor anguli oculi-Levator anguli oculi-Muller’s muscle

Eyelid

Most movement-upper eyelid Open-

levator palpebrae superioris (CNIII) Müller’s (sympathetic)

Closure-orbicularis oculi Closure mediated by CN VII

Frontalis, retractor anguli medialis Malaris mm (lower eyelid depressor)

Orbicularis oculi

Major eyelid muscle Concentric rings around palpebral opening Fibers originate and terminate on medial palpebral ligament Innervation CN VII Function is eyelid closure Specialized devisions:

Horner’s muscle Branch that runs under lacrimal sac and inserts on medial orbital wall

Negative pressure within lacrimal sac so as to pull tears into sac

Muscles of Riolan Travel along eyelid margin, surrounding the eyelash bulbs

May rotate eyelashes toward eye and propel glandular contents during blink

Levator palpebrae superioris and Muller’s muscle

Levator palpebrae superioris Originates deep within orbit, dorsal to optic canal between origins of dorsal rectus and

dorsal oblique

Functions to elevate upper eyelid

Innervated by CN III

Muller’s muscle Portion of the levator palpebrae superioris that extends deeper into dermix

Composed of smooth muscle fibers

Innervated by sympathetic nervous system (carried by infratrochlear nerve, branch of nasociliary nerve which is branch of ophthalmic devision of CNV)

Functions to widen/elevate palpebral fissue

Levator anguli oculi medialis and Frontalis

Both are eyelid elevators

Innervated by CN VII (palpebral branch)

LAOM also known as corrugator supercilia Small muscle that arises caudodorsal to medial commissure

Contraction raises the medial upper eyelid In horse gives rise to prominent lid notch

Retractor anguli oculi lateralis

Parallel and superficial to lateral palpebral ligament

Innervated by zygomatic branch of CN VII

Functions to draw lateral canthus posteriorly and laterally upon eyelid closure

Pars palpebralis of the m. sphincter colli frofundus (Malaris muscle)

Several straps of muscle originating near the ventral midline, coursing dorsally to insert on lower eyelid Ventral portion lies deep to the platysma

Dorsal portion is subcutaneous and close to eyelid skin

Innervated by buccal branches of CN VII Functions to depress lower eyelid

Eyelid Movement

Most species have Superior lid most mobile Innervation to levator palpebrae superioris m follows Hering’s law

Synergistic muscles receive simultaneous and equal innervation

Motor neurons for levator m. arise from single unpaired central caudal nucleus of the oculomotor complex, and a single motor neuron may innervate bilaterally

Hence, any supranuclear input into motor neuron influences BOTH levator muscles

Clinical significance: when the levator on one side is weak, the lid on opposite side may be retracted in an unconscious attempt to elevate the ptotic lid.

Eyelid Sensory Nerves : Dog

Sensory: CN V (Trigeminal) Maxillary Division

Zygomaticotemporal nerve: lateral dorsal lid

Zygomaticofacial nerve: lateral ventral lid

Ophthalmic DivisionFrontal (Supraorbital) nerve:

middle portion of upper lid.Infratrochlear nerve: medial

dorsal and ventral lid.

Eyelid Sensory Horse

Red: zygomaticofacial nerve (branch of maxillary division of trigeminal)

Yellow: zygomaticotemporal nerve (branch of maxillary division of trigeminal)

Blue: Frontal or supraorbital nerve (branch of ophthalmic division of trigeminal)

Green: Infratrochlear nerve (branch of ophthalmic division of trigeminal)

Eyelid

Composed of skin, palpebral conjunctiva, muscle, glandular tissue (Meibomian glands)

Ducts of meibomian glands on lid margin

Eyelid Glands

Glands of Zeis and Moll Anterior lamella of eyelid

Associated with eyelash cilia

Secrete contents around lash follicle shaft

Zeis Modified sebaceous glands

Surround base of hair follicles

Moll Eccrine, or modified sweat glands

Located just deep to the hair follicles

Meibomian/Tarsal glands Holocrine, sebaceous glands not associated with cilia

Produce lipid layer of tear film

Secretion under hormonal and neural control

Eyelid Skin

Epidermis Strata corneum & granular, spinous and basal layers

Dermis Dense, irregular connective tissue

Most species devoid of far (exception Shar Pei)

Hair follicles extend deep into dermis

Palpebral margin Transition from keratinized/stratified epithelium to non-keratinized/stratified squamous

epithelium

Eyelashes/Cilia located on eyelid leading edge Normal turnover times 3-5 months, regrow in 1 months

Cilia

SPECIES LOCATION ON EYELIDSHuman Upper and lowerCanine UpperPorcine UpperEquine Upper and few on lower; vibrissaeRuminant Upper and lowerFeline None per se (normal hair appears as

cilia)Avian Some species have filoplumes:

rudimentary feathers without barbs

Blinking

Spontaneous blinking Most common (15/min humans)

Lateral to medial (part of lacrimal pump mechanism)

Blinks/min % bilateral blinks

Dog: 3-5/min 85%

Cat: 1-5/min 70%

Horse: 5-25/min 30%

Pig: 10/min 90%

Third eyelid: Nictitating Membrane

Topographical distribution Originates in the anterior ventromedial orbit

Triangular in shape; covered with conjunctiva

“T-shaped” hyaline cartilage

Function Protects the globe

Secretion/distribution of tears

Aid in removal of particulate matter

Nictitans

Movement – passive Orbital tone

Orbital fat

Hydration status

Exception CATS Believed to have some smooth muscle and sympathetic innervation to third eyelid

movement

Nictitans

Gland of the 3rd Eyelid Encompasses base of cartilage

Seromucous secretions in dog (serous in horses), exit through ducts open in posterior aspect of the third eyelid between lymphoid follicles

Important contributor to basal tear production