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lacrimation and tear film Flashcards

1
Q

what is the lacrimal apparatus

A
  • a group of structures that secreate tear fluid onto the eye
  • lacrimal gland

distributes it over the surface of the eye

  • lacrimal lake

drains excess fluid out of the eye

lacrimal canuliculi , lacrimal sac , nasolacrimal duct - these are sometimes known as the lactimal apparatus

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2
Q

what structure secreates tear fluid onto the eye

A
  • lacrimal gland
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3
Q

what structures include the lacrimal apparatus

A

lacrimal gland , lacrimal lake, lacrimal canucliculi , nasolacrimal duct

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4
Q
  • describe in summary how tears are secreated and drained
A
  • lacrimal gland secreates tear fluid onto the eye , it is washed across the eye to the lacrimal lake which is on the medial aspect and then the canuliculi drain into the lacrimal sac which drains into the nasolacrimal duct which drains into the inferior meatus of the nasal cavity
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5
Q

describe the structure of the lacrimal gland

A
  • exocrine gland - secreates substances through a duct- produces aqueous secreations and secreates it through ducts on to the eye

it is divided ino two parts by aponeurosis- where the muscle becomes a tendon - of the LPS (elevates the eye)

  • large orbital part in lacrimal fossa in the frontal bone
  • smaller palpebral (associated with the eyelid ) part
  • additional acessory lacrimal glands scattered around conjuctival fornicies
    (responsible for keeping the eye mosit- with background secreation of tear fluid)
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6
Q

describe the histology of the lacrimal gland

A
  • lobulates tubulo acinar structure - it is essentially divided into lobules which form acini

acini = berries are round or tubular - and lined with secretory cells which produce lacrimal fluid - there are acini and tubules which converge on to intralobular and interlobular which then converge to form 12 excretory ducts - which empty into the superior conjuctival fornix

the lacrimal fluid is secreated into excretory ducts which empty into the superior conjictival fornix

most of the excretory ducts come from the orbital portion - and pass through the palpebral part of the gland to get to the eye - main 12 are from the orbital part and pas through the palpebral part to reach the conjuctiva

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7
Q

how does the lacrimal gland recieve its blood supply

A

supplied by the lacrimal artery - which is a branch of the opthalmic artery and enters the orbit via the optic canal

  • venous drainage into superior opthalmic vein which leaves via the superior orbital fissure
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8
Q

how is the lacrimal gland innervated

A

recieves both autonomic and sensory fibres ( they stimulate / inhibit the secretomotor function of lacrimation and are therefore sometimes known as scretomotor nerves)

  • sensory innervation is via the lacrimal nerve
  • a branch of the opthalmic divison of the trigeminal nerve

autonomic innervation

  • parasympathetic innervation - also has sympathetic fibres

both parasympathetic and sympathetic fibres ultimately reach the lacrimal gland via the lacrimal nerve

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9
Q

how is the lacrimal gland autonomically innervated

A
  • lacrimation is under autonomic control

- it also has sympathetic fibres which inhibit lacrimation

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10
Q

how is sensation from the lacrimal gland innervated

A
  • the lacrimal gland is innervated by the lacrimal nerve which is a branch of v1 (opthalmic division of the trigeminal nerve)
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11
Q

how is the lacrimal gland parasympathetically innervated

A
  • the parasympathetic supply is from the facial nerve - which is one of the 4 parasympathetic cranial nerve
  • starts in a nucleus in the pons known as the lacrimal nucleus which is a part of the superior salivatory nucleus
  • preganglionic fibres are carried from the lacrimal nucleus and they travel along the greater petrosal nerve and then the nerve of the pterygoid canal to reach the pterygopaletine gagnlion
  • post gangllionic fibres leave the pterygopaletine ganglion and they travel along with the maxillary nerve along the zygomatico and then zygomaticotemporal branch to eventually reach the lacrimal nerve and then the lacrimal nerve
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12
Q

where do the preganglionic fibres synpase with the post ganglionic fibres

A

— pterygopaletine ganglion

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13
Q

state the components used in the parasympathetic innervation of the lacrimal gland

A
  • lacrimal nucleus which is part of the superior salivatory nucleus in the pons
  • comes along greater petrosal nerve
  • it then reaches the nerve of the pterygoid canal
  • where it synapses is the ptergopaletine ganglion
  • then the postganglionic fibres join with the maxillary nerve or the zygomaticotemporal division and then eventually converge on to the lacrimal gland alongside the lacrimal nerve
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14
Q

what cranial nerve are the parasympathetic fibres that innervate lacrimation apart of ?

A
  • the facial nerve
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15
Q

how is the lacrimal gland sympathetically innervated

A
  • sympathetic fibres have short preganglionic chains and long post ganglionic
  • post ganglionic nerves travel in the deep petrosal nerve and then follow the same course

-

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16
Q

where do the preganglionic fibres of the sympathetic nerves that innervate the lacrimal gland synapse

A
  • in the cervical chain

- they dont synapse in the ptergoplaetine ganglion because they are already postganglionic fibres at that point

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17
Q

how are the deep petrosal nerve and greater petrosal nerve involved in parasympathetic and sympathetic innervation to the lacrimal gland respectivley

A
  • the deep petrosal nerve is the nerve involved in the sympathetic innervation to the lacrimal gland
  • the greater petrosal nerve is involved in the parasympathetic innervation to the lacrimal gland
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18
Q

describe the afferent and efferent limb of the lacrimatory reflex

A

afferent limb = sensory fibre taking sensation from the lacrimal gland

secretomotor limb - efferent limb - parasympathetic fibre- stimulates the lacrimal gland to produce tears

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19
Q

describe the sensory afferent limb that is involved in the lacrimatory reflex

A
  • physical or chemical stimuli to cornea (or conjuctiva / nasal musosa )
  • long cillary nerve (takes sensory imformation from the cornea) - eventually reaches the lacrimal nucleus
  • opthalmic divison trigeminal nerve

lacrimal nucleus ( carries imformation about damage or pain from the cornea)

responses are coordinated via the facial nerve (parasymppathetic cranial nerve 7)

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20
Q

describe the efferent secretomotor limb of the lacrimatory reflex

A
  • lacrimation via parasympathetic fibres via the facial nerve ‘’secretomotor’ - causes lacrimation
  • rapid secreation of fluid by the lacrimal gland to wash away and chemically neutralise potential threat to tear film
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21
Q

what are all the parts of the parasympathetic pathway to the lacrimal gland

A

L N

FN - facial nerve

GPN - greater petrosal nerve

PG- ptergopaletine ganglion

MN - maxillary nerve

ZN - zygomatic nerve

LN - lacrimal nerve

lacrimal gland

LG

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22
Q

describe the role of the acessory lacrimal gland

A
  • the main lacrimal gland is good for washing away damaging stimuli in the lacrimal reflex
  • normal/ baseline tear formation is necessary to keep the eye moist and is provided by the acessory lacrimal glands
  • crying/ excess tears is via main lacrimal gland in lacrimal reflex
  • located throughout conjuctiva and strcturally similar to main gland
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23
Q

what is the lacrimal gland divided by

A
  • lacrimal gland is divided by the aponeurosis of lps into orbital and palpebral parts
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24
Q

what is the lacrimal gland supplied by

A
  • the lacrimal gland is supplied by the lacrimal artery and drained via the superior opthalmic vein
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25
Q

describe the sensory innervation to the lacrimal gland

A

-sensory innervation is via the lacrimal nerve which is from v1 (opthalmic divison of the trigeminal nerve)

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26
Q

where do the parasymapthetic nerves originate from

A
  • parasympathetic innervation is via the facial nerve fibres originating in the lacrimal nucleus
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27
Q

describe the route of preganglionic parasympathetic fibres

A

preganglionic fibres are carries by the greater petrosal nerve and then the nerve of the ptergoid canal to reach the ptergopaletine gagnlion

28
Q

describe the route of the postganglionic parasympathetic fibres

A
  • postganglionic fibres leave and join with v2 (maxillary nerve) and then reach the gland with the lacrimal nerve
29
Q

what is the difference in function between acessory lacrimal glands and main lacrimal glands

A
  • acessory lacrimal glands- provide background tear production and keep the eye moist + are scattered around the conjuctiva
  • main lacrimal glands- involved in crying and the lacrimal reflex
30
Q

what are the different types of tears and what are they responsible for

A

basal tears are responsible for the hydration and nourishment of the eye- (produced predominantly by the acessory lacrimal gland)

reflex tears are produced in response to an irratant or stimulus to cleanse the eye ( produced in response to stimulus - to get rid of damaging stimuli)

psychic tears are produced in response to strong emotional stimuli (crying)

composition may differ depending on the type of tear being produced

31
Q

describe the composition of tear film

A
  • has 3 layers - a mucin layer , aqueous layer , lipid layer

( l, a , m )

32
Q

describe the function of the tear film

A
  • moisture and nourishment is essential for corneal transparency
  • tear film is essential for the cornea to function as a refractive surface
  • lubricates during eyelid movement over globe
  • antiseptic (preventing infection)
  • anti- debris
33
Q

what are the three layers of tear film?

A

mucus layer - which is produced by conjuctival goblet cells

aqueous layer- is produced by lacrimal and acessory glands

lipid layer - produced by glands of moll and glands of ziess

34
Q

what is the most superifical layer of tear film and what is the layer that is deepest

A
  • superficial layer = lipid
  • middle layer - aqueous
  • deepest layer - mucin - sits on top of the cornea
35
Q

what does the mucus layer of the tear film do

A
  • mucus layer - lubricates and aids distribution of tears
36
Q

what does the aqueous layer of tear film do

A
  • nourishes , hydrates and provides immune defense

- what oxgen disolves into in order to provide oxygen to the cornea

37
Q

what does the lipid layer of the tear film do

A
  • limits evaporation of the aqueous component
38
Q

how are tears collected

A
  • tears come from the 12 excretory ducts, sweep across by blinking to the lacrimal lake , and the drains via the canuliculi
  • drains tears that have not evaporated/ excess tears from lacrimal reflex
  • caniculi drain into the nasolacrimal sac and into the nasolacrimal duct
  • the nasolacrimal duct drains into the inferior nasal meautus of the nasal cavity
  • for baseline tear production ,,—— tear production only just. exceeds evaporation from the eye , when your not crying very little drains via the collecting system
39
Q

what are the symptons of dry eye

A
  • dry eye - common
  • lipid / aqeuous dysfunction
  • symptons - gritty , sore red , reflex watering ( you get the irratant response to the cornea) - and then you have the lacrimal reflex

affects quality of life

40
Q

what happens when their is lipid layer dysfucntion

A
  • when their is no lipid layer - because of the fucntion of the lipid layer is to prevent evaporation of the aqueous layer - if you have a insufficent lipid layer production in the tear film then it evaporates

aqueous evaporates

  • very common ,can be secondary to blepharitis = where oil secreating glands on the lid margin get blocked , aging or idiopathic
41
Q

what happens if you have aqueous layer dysfucntion

A
  • reduced aqeuous production and eyelid pathology
  • can be secondary to disease , medication , allergies , trauma (chemical injuries)
    disease to lacrimal gland , sjogrens disease , rheumatoid disease of lacrimal and acessory glands

mucin deficency is rare

42
Q

how do you manage a dry eye

A
  • lubricants - the more viscous the lubricant is the longer it stays in the eye and keeps it moist
  • hot compresses (lipid layer dysfunction)
  • punctual plugs - reduces the drainage of tears - so you increase the amount of fluid on the eye
  • treat the causes e.g. rheumatoid disease

lifestyle factors e.g. quit smoking

43
Q

how does exposure to the cornea cause damage

A

exposure keratopathy - damage to the cornea secodary to exposure

  • you can have exposure to the cornea due to evaporation of the tear film
  • often due to incomplete lid closure - which is often caused by a facial nerve palsy
  • interrupted tear flow

extremley dry eyes with corneal damage

facial nerve palsy - LMN

44
Q

what is the difference between upper and lower motor lesions

A
  • lower motor lesions do not spare the forehead
  • upper motor lesions spare the forehead

therefore if you have incomplete lid closure you have a lower motor neurone lesion because the forehead is not spared

45
Q

what symptons might you see with nasolacrimal duct obstruction

A

congential

acquired, post innefective , cicatrical, mechanical m, iatrogenic secondary to ectropian

what symptons might you see

epiphora (watery eyes) , discharge , irratation and blurred vision (nothing is draining via nasolacrimal duct

46
Q

what is blockage of nasolacrimal duct called

A

dacricytsis (blockage of nasolacrimal duct leads to infection)

47
Q

what is the deep mucin layer produced by

A
  • deep mucin layer is produced by conjuctival goblet cells- aids in even distribution of tears over the surface of the eye
48
Q

what is the middle aqueous layer produced by

A
  • main and acessory lacrimal glands- nourishes the tissues and carries 02 to the cornea
49
Q

what is the superficial lipid layer produced by

A
  • superficial lipid layer is produced by meiobomian glands , glands of ziesss and moll- floats like a layer of oil over the surface
50
Q

how are tears drained

A

after tears are secreated onto the the eye they drain via the puncta, canaliculi, nasolacrimal sac , nasolacrimal duct and the inferior meatus of the nasal cavity

51
Q

what can dysfucntion of the layers of the tear film lead to

A
  • dysfucntion of the layers of the tear film can lead to dry eye via insufficent lipid layer causing aqueous to evaporate or insufficent aqueous layer
52
Q

what can blockage of the nasolacrimal duct lead to

A
  • irratation , blurred vision and watering or infection - dacrocytstisis
53
Q

what divides the lacrimal gland into an orbital and a palpebral part

A
  • aponeurosis of the levator palpebrae superioris
54
Q

describe the structure of the lacrimal gland

A

exocrine lobulated tubular acinar gland

55
Q

what gland is the lacrimal gland supplied by and which vein is drained by

A

supplied by the lacrimal artery and is drained via the superior opthalmic vein

56
Q

what formamen does the opthalmic artery enter the orbit via

A
  • the optic canal - within the ctr
57
Q

what foramen does the superior opthalmic vein exit the orbit via

A
  • the superior orbital fissure

- travels outside the common tendinous ring

58
Q

what nerve does the lacrimal gland recieve its sensory innervation from

A
  • the lacrimal nerve
59
Q

which nerve is the origin of the lacrimal nerve

A

opthalmic branch of the trigeminal nerve

  • rememeber trigeminal nerve supplies sensation to the face , facial nerve does motor
60
Q

parasympathetic fibres reach the pterygopaletine ganglion via

A

the lacrimal nucleus , facial nerve, deep petrosal nerve

61
Q

which autonomic pathway has the greater and deeper petrosal nerve within it respectivley

A

parasympathetic supply is of ‘’greater’’ importance ad then sympathetic= greater petrosal nerve

62
Q

which gland is responsible for baseline tear formation

A

acessory lacrimal gland

63
Q

which is the outermost layer of the tear film

A
  • lipid layer- prevents aqueous from evaporation

produced by the meibomian glands - glands of moll and ziess - if they get infected they produce chalazions and styes

64
Q

which is the innermost layer of the tear film and what is its role

A
  • mucus , lubricates , and aids even distribution of tears and is produced by conjuctival goblet cells
65
Q

what is the function of the aqueous layer and what glands produce it

A
  • aqueous layer
  • nourishes and hydrates , immune defense

lacrimal and acessory lacrimal glands

66
Q

which layers are most commonly implicated by dry eye

A
  • lipid and aqueous

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