Conjunctival Physiology Magrane Basic Science Course KATE MYRNA, DVM, MS, DACVO UNIVERSITY of GEORGIA Conjunctiva
Conjunctival Physiology Magrane Basic Science Course KATE 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 nonkeratinized squamous 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 firmly 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 Goblet Cell Response to Disease
Proliferation
KCS
Chronic conjunctivitis
Vitamin A deficiency Feline Conjunctiva
Goblet cells in normal cats % GC/200 basal Epithelial cells Sebag et al 2016
Anterior 3EL 48.8%
Fornical 47%
Palpebral 38.5%
Bulbar 19.6%
Posterior 12.6% 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 Conjunctival Diagnostics
Impression cytology (Eordogh et al)
Ideal technique with topical anesthesia and additional drying.
SUPERIOR bulbar conjunctiva
Biopore membrane device
Conjunctival monolayer
Report as index of goblet cell/epithelial
cell
Normal 0.29-0.3 What is wrong? Conjunctivitis
Chemosis
Hyperemia
Blepharospasm
Cellular exudation 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: Cats
Smooth muscle draws membrane to medial canthus
Innervation: postganglionic adrenergic sympathetic nerve fibers with cell bodies in anterior cervical ganglion
No spontaneous activity because smooth muscle lacks tight junctions that visceral smooth muscle has.
Honestly the literature is confused on the subject…. Nictitans: Avian
Translucent
Movement under direct muscular control
15/20 minute these muscles pull the nictitans over the cornea
Contains a superficial tear gland 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 Eyelids Eyelids
Functions
Screening and sensing (cilia and vibrissae)
Mechanical wiping action
Secretions and spreading of glandular tissue
Screening of light to allow sleep
Most carnivores born with fused eyelids that open between 10 and 14 days 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 divisions:
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 dermis
Composed of smooth muscle fibers
Innervated by sympathetic nervous system (carried by infratrochlear nerve, branch of nasociliary nerve which is branch of ophthalmic division of CNV)
Functions to widen/elevate palpebral fissure 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. Eyelids
Length, orbit size, medial and lateral canthal ligaments all determine palpebral fissure
Brachycephalic is shallow orbit and large eyelid opening and tight medial canthal ligament = ?
Spaniel is normal globe and orbit with long lids and a strong lateral canthal ligament = ?
Shar pei = ???? Eyelids: “normal” length?
Average length when stretched by calipers = 33mm
If lower lid doesn’t contact globe length >39mm Eyelid Sensory Nerves : Dog
Sensory: CN V (Trigeminal) Maxillary Division Zygomaticotemporal nerve: lateral dorsal lid Zygomaticofacial nerve: lateral ventral lid Ophthalmic Division Frontal (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 Normal Tarsal Gland of the Eyelid
Histopathologic features of canine distichiasis, Volume: 15, Issue: 2, Pages: 92-97, First published: 29 September 2011, DOI: (10.1111/j.1463-5224.2011.00946.x) Distichia of the Tarsal Gland of the Eyelid
Histopathologic features of canine distichiasis, Volume: 15, Issue: 2, Pages: 92-97, First published: 29 September 2011, DOI: (10.1111/j.1463-5224.2011.00946.x) Eyelid Skin
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 EYELIDS Human Upper and lower Canine Upper Porcine Upper Equine Upper and few on lower; vibrissae Ruminant Upper and lower Feline 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)
Clinical significance? TFBUT? Blinks/min % bilateral blinks
Dog: 3-5/min 85%
Cat: 1-5/min 70%
Horse: 5-25/min 30%
Pig: 10/min 90% Pathology of the Eyelid
Delayed of complete failure of the lids to open
Ususally bilateral
Ophthalmia neonatorum is a differential (swollen with discharge)