Tear Film & Lacrimation Flashcards
1
Q
What type of gland is the lacrimal gland?
A
A compound tubuloacinar gland it is made up of many lobules separated by connective tissue, each lobule contains many acini
2
Q
What are Acini?
A
The lacrimal gland is composed of numerous acini that are primary secretory units responsible for tear production
3
Q
What make up Acini?
A
Lacrimal acinar cells
4
Q
What are Acinar cells?
A
Specialised epithelial cells that contain abundant secretory granules that store proteins, electrolytes and other substances that contribute to tear composition
5
Q
What do Acini play a crucial role in?
A
Production & secretion of tears
6
Q
What do acinus consist of?
A
Grape-like mass of lacrimal gland cells with their apices pointed to a central lumen that converge to form intralobular ducts. The gland lack striated ducts.
7
Q
What surround acini in the lacrimal gland?
A
Myoepithelial cells
8
Q
What are myoepithelial cells?
A
Contractile cells are situated between the acinar cells and the basal lamina (membrane)
9
Q
What do myoepithelial cells assist in?
A
They have contractile properties and assist in the expulsion of secretory products from the acini into the lacrimal ducts during tear production
10
Q
What are the role of ductal cells in the lacrimal gland?
A
Transport tears from the acini to the ocular surface; intercalated and striated ducts interspersed between the acini and help in transport to tears towards the main excretory ducts.
11
Q
What are the lacrimal ducts also known as?
A
The main excretory ducts
12
Q
What is the role of the lacrimal ducts?
A
The ducts ensure the proper drainage and delivery of tears to maintain the health and lubrication of the eye.
13
Q
What is the lacrimal apparatus?
A
Lacrimal Gland
Lacrimal Lake
Lacrimal Puntum
Lacrimal Canaliculi
Lacrimal Sac
Nasolacrimal Duct
14
Q
What parts are the lacrimal gland made up of?
A
Large orbital part
Small palpebral part (upper eyelid, 1/3rd size of Orbital part)
15
Q
What shape is the lacrimal gland?
A
C-shaped structure
16
Q
What does the lacrimal gland wrap around?
A
LPS aponeurosis (LPS fans out to the whole of the eyelid which is where a muscle has spread out and attached itself to something)
17
Q
How many glands come away from the lacrimal gland?
A
12
18
Q
Where do the 12 glands of the lacrimal glands extend into?
A
The superior conjunctival fornix
19
Q
Where are the small accessory glands?
A
Upper & lower conjunctival fornices
20
Q
What’s in anatomical relation to the lacrimal gland?
A
Superior –
Zygomatic process of frontal bone
Anterior – orbital septum
Posterior – orbital fat
Inferolateral – lateral rectus muscle
21
Q
What’s in anatomical relation to the Orbital portion of the lacrimal gland?
A
Superior of Orbital part =
Zygomatic processes of the frontal bone in orbit
Inferior border of Orbital part = Aponeurosis
Posteriorly =
Orbital fat
Anterior =
Septum
22
Q
What’s in anatomical relation to the Palpebral portion of the lacrimal gland?
A
Superior part of Palpebral part = Aponeurosis
Anterior =
Septum
Posterior =
LR muscle and fat
Medial =
Septum
23
Q
Where does the levator aponeurosis transmit contractions?
A
The levator aponeurosis transmits the contractions of the levator palpebrae superioris muscle to elevate the upper eyelid. It works in opposition to the normal pull of gravity and the palpebral part of the orbicularis oculi muscle, which close the eyelids
24
Q
Where do the ducts from the palpebral part open?
A
Into the superior fornix
25
If the main lacrimal gland is not working to keep the cornea moist, what takes over?
Small accessory glands
26
What artery supplies the lacrimal gland?
A branch of the ophthalmic artery and enters its posterior border
27
What is another artery (that's not the ophthalmic artery) that sometimes supplies the lacrimal gland
A branch of the maxillary artery being the infraorbital artery
28
What is the venous drainage of the lacrimal gland?
Ophthalmic Vein
29
Where is the lymphatic drainage in the lacrimal gland?
Lymphatic drainage joins that of the conjunctiva and passes to the superficial parotid lymph nodes.
Immune products, run parallel to venous network and empties at the top of the lungs
30
LEARN THE INNERVATION OF THE LACRIMAL GLAND DIAGRAM
31
What does parasympathetic and sympathetic stimulation of the lacrimal gland lead to?
The secretion of aqueous
32
Where does parasympathetic innervation of the lacrimal gland originate?
Lacrimatory nucleus of the facial nerve in the pons
33
How do parasympathetic presynaptic parasympathetic fibres travel?
Presynaptic parasympathetic fibres travel with the facial nerve to the geniculate ganglion, where they diverge, forming the greater superficial petrosal nerve. The greater superficial petrosal nerve passes through the foramen lacerum and is joined by the deep petrosal nerve (which contains sympathetic fibres from the superior cervical ganglion), forming the nerve of the pterygoid canal. This nerve then synapses on the pterygopalatine ganglion where it synapses (first synapse along this pathway). It then goes through the post-ganglionic branches and across the zygomatic nerve up to the communicating branches of the zygomatic nerve to the lacrimal gland.
34
What forms the greater superficial petrosal nerve (parasympathetic)?
Where the geniculate ganglion diverges
35
Where does the greater superficial petrosal nerve pass (parasympathetic)?
Through the foramen lacerum
36
What joins the greater superficial petrosal nerve (parasympathetic)?
The deep (or greater) petrosal nerve
37
What does the the Deep Petrosal Nerve contain?
Sympathetic fibres from the superior cervical ganglion
38
What forms the pterygoid canal (parasympathetic)?
The meeting of the superficial petrosal nerve and the deep petrosal nerve
39
Where does the parasympathetic fibres of the lacrimal gland synapse?
On the pterygopalatine ganglion (first synapse)
40
At what point do parasympathetic fibres first synapse?
At the pterygopalatine ganglion
41
Where do post-synaptic parasympathetic fibres first leave?
Pterygopalatine ganglion to form the zygomatic nerve, zygomaticofacial nerve and zygomaticotemporal nerve (as the lacrimal nerve is near these bones)
42
Where do the zygomatic, zygomaticofacial and zygomaticotemporal nerves travel?
Travel with the lacrimal branch of the maxillary nerve to reach the lacrimal gland.
43
Is innervation of the parasympathetic fibres direct or indirect?
Innervation of the gland by these parasympathetic fibres is either direct, indirect via communication with the lacrimal nerve, or both.
44
Which nerve directly enters the lacrimal gland?
Majority of cases the zygomaticotemporal nerve directly enters
45
Where does sympathetic innervation of the lacrimal gland originate?
Superior Cervical Ganglion
46
Where does sympathetic supply enter the spinal cord?
Lower than the superior cervical ganglion so it travels upwards to be able to synapse at the superior cervical ganglion
47
Where is the first synapse of the sympathetic innervation of the lacrimal gland?
Superior Cervical Ganglion
48
Where do postsynaptic fibres travel in the sympathetic innervation of the lacrimal gland?
Postsynaptic fibres travel with the internal carotid artery before joining the greater petrosal nerve (aka deep petrosal nerve) which forms the pterygoid canal.
49
What forms the pterygoid canal in the sympathetic innervation of the lacrimal gland?
Greater petrosal nerve (deep petrosal nerve) and the internal carotid artery meet
50
Where the sympathetic fibres reach in innervation of the lacrimal gland after the pterygoid canal?
Reaches the pterygopalatine ganglion, sympathetic fibres do not synapse but continue to travel with the post-ganglionic fibres via the parasympathetic fibres. These release ACh, don't excessively tear to avoid blur during fight or flight until the threat has passed.
51
What's the afferent sensory system for innervation of the lacrimal gland for?
For when there's a foreign body in the eye
52
How does the sensory innervation of the lacrimal gland occur?
Oculomotor nerve carried sensory stimuli back to the trigeminal ganglion, processed and sent to the brain in ascending pathway and then back through descending pathways to the eye and comes from the lacrimal reflex. Sensory innervation of the lacrimal gland is via the lacrimal nerve, a branch of the ophthalmic nerve.
53
What is the lacrimatory reflex?
The lacrimatory reflex is the tearing reflex, causing tears to secrete under certain conditions. The two stimuli most obviously connected to eye health that can cause tearing include bright lights and exposure to certain physical or chemical stimuli, such as smoke.
54
What happens during the corneal reflex in general?
The cornea has bare nerve endings on it coming from the long and short ciliary nerves which come off of the nasociliary nerve off of the ophthalmic nerve. Which explains how it goes back to the trigeminal ganglion. This ganglion will then send impulses to other parts of the brain through the spinal nucleus and generally 3 things happen; blink, excessive tearing & miosis occurs.
55
How does pupil constriction occur during corneal reflex?
Pupil constricts (E-W nucleus) --> OM nerve --> Ciliary Ganglion --> Short ciliary nerves --> Sphincter,
56
How does blinking occur in the corneal reflex?
Blink is through facial nerve nucleus -- > Facial nerve nucleus --> Zygomatic nerve --> Orbicularis Oculi
57
How does excessive tearing occur during the corneal reflex?
Excessive tearing (Lacrimal nucleus part of facial nerve nucleus --> Great petrosal nerve --> Vidian nerve (pterygoid canal) --> Pterygopalatine ganglion --> Maxillary nerve --> Zygomatic nerve --> Lacrimal nerve --> Lacrimal gland (lacrimation occurs)
58
In the corneal reflex, which nerve is the afferent limb detecting the stimuli?
Ophthalmic Nerve
59
In the corneal reflex, which nerve is the efferent limb that responds to contraction of the Obicularis Oculi?
Facial Nerve
60
How is the blink reflex divided into?
Early & Late Stages
61
What are the early-stage blink reflex?
A-beta fibres that initiate movement of the eyelid on the ipsilateral side
62
What are the late-stage blink reflexes?
Largely modulated by the secondary motor system and stimulate the facial nerves bilaterally so both eyes blink
63
What does absence of the blink reflex indicate?
Damage to the trigeminal/ophthalmic nerve or the facial nerve
64
What does peripheral (PNS) damage cause in relation to the lacrimal blink reflex? What about Central (CNS) damage?
Peripheral damage causes ipsilateral reflex deficits, while central damage tends to be associated with bilateral deficits.
65
What does Glaucoma cause related to the blink reflex?
Glaucoma is a disorder that increases the intraocular pressure within the eye, causing the trigeminal nerves to bend. The bends within the nerve correlate with a decreased corneal blink reflex sensitivity and increased ocular pathology.
66
What does Diabetes contribute to in relation to the blink reflex?
Diabetes also contributes to a reduced late-phase corneal reflex sensitivity from the decreased density of nerve branches and plexuses secondary to diabetic peripheral neuropathy
67
How is the lacrimal reflex stimulated?
Irritation of the cornea and conjunctiva stimulate tear production --> Ciliary fibres of the nasociliary branch of the Ophthalmic nerve of the Trigeminal nerve act as the afferent limb of the reflex arc.
68
What makes up the central nervous system (CNS) component of the reflex arc?
The facial nerve (CN VII) and the superior salivary nucleus make up the central nervous system (CNS) component of the reflex arc. Preganglionic parasympathetic secretomotor fibers travel parallel to the lacrimal branch of V1 and the zygomatic branch of V2
69
What is the primary function of tears?
To keep the corneal epithelium moist
70
What is the secondary function of tears?
To lubricate the anterior globe so it moves freely beneath the lids and keeps conjunctiva moist (lubrication may also be performed by the lipids excreted by the meibomian glands)
71
What are the 3 types of tear?
1) Basal
2) Reflex (& Emotional)
3) Closed Eye
72
Where are basal tears?
Typically present on the ocular surface
73
What do basal tears do?
Provide nutrients to the ocular surface, maintaining ocular comfort and ridding the surface of debris. Parasympathetic system generated.
74
What are reflex tears?
Reflex tears are those released in response to irritants, including chemicals and foreign bodies. Reflex tears are produced in higher quantities than basal tears and are involved in flushing the ocular surface of irritants. Excessive tearing to get rid of debris.
75
What are closed-eye tears do?
Closed eye tears are those lubricating the eyes during sleep. When asleep the eyes still make fluid but it’s to keep the eye hydrated when lids are closed = different composition. This is a theory
76
How are the osmolarities in tears?
Despite differences in composition, the osmolarities in tear types remain relatively constant
77
How are tears secreted?
Produced by the acinar cells passes into the duct system and onto the surface of the eye
78
What does the lacrimal gland also secrete as well as aqueous for tears?
The lacrimal gland also secretes substances that affect the ocular surface by regulating epithelial cell turnover.
79
What hormones support lacrimal secretion?
Furthermore, hormones, particularly androgens, support lacrimal secretion and also suppress immunologic activity within the lacrimal glands.
80
What's in the mucin layer of tears?
immunoglobulins, urea, salts, glucose, and proteins
So nutrients for the eye, sugars, salts etc and immunoglobulins are for immune defense.
81
What's the aqueous layer of tears made up of?
Proteins, metabolites, inorganic salts, glucose, oxygen and electrolytes but is mainly water
82
What's the lipid layer of tears made up of?
Cholesterol, wax esters, fatty acids, and phospholipids – to reduce amount of evaporation of the tear film
83
What's the precorneal tear film composed of?
3 layers;
1) Thin, superficial oily layer
2) Thick, watery layer
3) Thin mucin
84
What are the sizes of the 3 layers of the precorneal tear film?
1) The thin, superficial oily layer, measuring about 0.9 to 0.2 11m, is produced predominantly by the tarsal (meibomian) glands and to a slight extent by the sebaceous glands (Zeis) and sweat glands (Moll);
2) The thick, watery layer, measuring about 6.5 to 7.5 11m, is secreted by the lacrimal glands; and
3) The thin mucin,* measuring about 0.5 11m, is secreted by the conjunctival goblet cells and from the lacrimal gland cells.
85
What's the role of the 3 precorneal layers?
1) Thin, oily layer
Inhibits evaporation of the underlying watery layer
2) Watery later
Contains nutrients and is the defense against invading organisms
3) Deep mucin layer
Wets the microvilli of the corneal epithelium
86
What is the lacrimal punctum (punctum lacrimale) and the lacrimal papilla (papilla lacrimalis)?
Small round or oval orifice situated on the summit of a small projection (punctum) and at the medial end of the lid margin (papilla).
87
How does the lacrimal puncta meet the lacrimal lake?
Tone of the orbicularis oculi muscle presses the puncta backwards towards the lacus lacrimalis (lacrimal lake)
88
How do tears enter the lacrimal canaliculi?
Via the papilla
89
Describe the size and direction of the lacrimal canals
Each canaliculus measures about 10mm long and consists of a vertical and a horizontal portion. The lacrimal canaliculi begin at the puncta and they pass almost vertically from the lid margin. After 2mm they turn sharply medially. The upper canaliculus runs medially and downward; the lower one, medially and upward. At the junction of the vertical and horizontal portions the canaliculi are slightly dilated to form an ampulla (roman flask with two handles). The canaliculi now pierce the periorbita (lacrimal fascia) that encloses the lacrimal sac. The two channels now enter the lateral surface of the sac about 2.5 mm below its apex
.
90
Where do the canaliculi lie?
The canaliculi lie behind the medial palpebral ligament and are surrounded by the fibers of the pars lacrimalis of the orbicularis oculi muscle.
91
What is the Medial Palpebral Ligament?
Where superior and inferior tarsal muscle meets and attaches to the medial aspect of the orbit
92
How do the canaliculi dilate the lacrimal sac?
During blinking of the eye the canaliculi are pulled medially, shortened, and compressed by the lacrimal part of the orbicularis oculi. This pumping action assists in dilatation of the lacrimal sac.
93
How long does the lacrimal sac measure?
The lacrimal sac, measuring about 12mm long, is situated in the lacrimal fossa formed by the lacrimal bone and the frontal process of the maxilla.
94
How long is the nasolacrimal duct?
About 18mm long and connects the lower end of the lacrimal sac with the inferior meatus of the nose. It is narrower in the middle than at either end.
95
What pathway does the nasolacrimal duct follow?
The direction of the duct is downward, backward, and lateral. Plica Lacrimalis (or valve of hasner) is a thin membrane which covers the opening of the duct and stops air entering when someone blows their nose
96
What are the turbinates?
With the inferior meatus below the nasolacrimal duct. Their function is to warm air, to make air more turbulent for you when you breathe in = swallow tears from lacrimal sac, but if excessive tearing it won’t hold in the lacrimal sac due to its size.
97
What does dry eye look like under a slit lamp with flourescein and blue light?
Healthy cornea should only see the fluorescein in few areas but the cornea shouldn’t take it up unless the cornea is dry
98
What are the symptoms, treatment and risk factors of dry eye?
Can be due to a deficiency of any of the 3 components of the tear film but more commonly it is due to reduced aqueous or lipid elements
Itchy eye = lead to Keratoconus, excessive tears, blurred vision
Management is with lubrication, hot compress if there is a lipid dysfunction, sometimes surgery if there is too much fluid being lost from the eye (such as punctal plugs).
If eye drops don’t work = referred to the cornea team. After a week the majority get significant improvement but then will stop taking drops.
Lifestyle factors = Smokers, physically don’t make tears like in sjogrens or rheumatoid disease
99
If dry eyes is left untreated, what does it lead to?
Left untreated. Conjunctiva becomes very red which stop at the limbus. Exposure keratopathy as a result of corneal damage secondary to dry eye. Epithelia of cornea very damaged and harder to fix. Can do corneal transplants or try to regrow or graft epithelium. Or try to give a new endothelium
100
What is a nasolacrimal duct obstruction?
Acquired obstruction can be from viral infections, trauma, infection of the drainage system, topical drugs
Managed with solo or combined treatments: antibiotics, massage, probing, stent insertion, balloon catheter dilation
Symptoms can include epiphoria, mucous dischargem irritation, blurred vision, excess fluid in the tear lake
Valve closes when cries (in the nasolacrimal duct) as we don’t want air into caniculli. Will start to attach if untreated and leads to infection which results in dacrocytitis and can lead to sepsis.
101
What does the lacrimal gland being tubuloacinar mean?
This means it’s like a raspberry with little blobs in a rounded pyramid that’s apex meet at a canal), it is made up of many lobules separated by connective tissue, each lobule contains many acini. It’s an exocrine system (secretes via ducts whereas endocrine systems secrete into the bloodstream)
102
What happens when Myoepithelial cells contract?
When it contracts fluid goes into the canals from the acini into the interlobular ducts which then all feed into the intralobular ducts where they converge into the 12 glands going from orbital portion to palpebral portion.
103
What is the role of myoepithelial cells in the lacrimal gland?
Contractile properties (muscular structure)
Produce the basal membrane that covers all of the lacrimal structures
104
What is the role of the interlobular ducts?
(Intra is between 2 similar systems whereas inter is within a system).
The lining of interlobular ducts are columnar. The smaller ones have 1 layer of columnar cells that are non-secretory whereas the bigger cells have 2 layers. These non-secretory columnar cells change fluid structure so by the time that they get into the intralobular they’re good to be secreted.
