brief discussion on tear film

1. TEAR FILM
Dr Md Ferdous Islam
Department of Ophthalmology
CMH, Dhaka

2. THE TEAR FILM
 The main role of lacrimal system is to establish &
maintain a continuous tear film over the ocular
surface
 Pre-corneal tear film was 1st demonstrated by
Fischer in 1928.
 Rollet described it as the most superficial 6th layer
of cornea.

3. STRUCTURE OF THE TEAR FILM
 Wolff
 Coined the term ‘PRE-CORNEAL FILM’.
 Tear film consists of 3 layers.
1)Outer Lipid layer
2)Intermediate Aqueous layer &
3)Inner mucin layer

6. LIPID LAYER
 Outer most layer.
 0.1um thick
 Formed from the secretions of Meibomian, Zeiss &
Moll glands.
 Contents 1)low polarity lipids-wax & cholesterol
esters 2)high polarity lipids-TG, FFA ,phospholipids.
 Functions 1)prevents the overflow of tears.
2)prevents evaporation.

7. AQUEOUS LAYER
 Middle layer.
 Formed by secretions from the main & accessory lacrimal
glands of Krause & Wolfring.
 Constitutes the main bulk of tear film.
 thickness over the cornea 10um.
 Film covering the cornea is thinner than over the
conjunctiva.
 Contents inorganic salts, glucose, urea, enzymes, proteins
& glycoproteins.
 Buffering capacity of the tear film is d/t HCO3 ions & protein
 Functions 1)provides O2 to corneal epithelium.
2)washes away debris & irritants.
3)contains antibacterial sub- lysozyme &
betalysin.

8. MUCOUS LAYER
 Innermost layer.
 Secreted mainly by the conjunctival goblet cells
 30um thick.can be demo in living eye by alician blue drops
 Functions 1)plays a vital role in the stability of the tear film.
2)converts the hydrophobic corneal epithelium to a hydrophilic
one.
3)lubricates the ocular & palpebral surfaces.
4)provides a slippery coating over the foreign bodies; thereby
protecting the cornea & conjunctiva against the abrasive effects of
such particles as they move about with blinking.
5)absorps various organic compounds in tears

9. NEW TEAR FILM MODEL
 Recent observation--
mucins exist as a network
distributed in the aqueous
body of the tear film.
 Glycocalyx emanate as
transmembrane molecules
into the aqueous & are
anchored at the cell
membrane.
 Membrane associated
proteins-MUC1,4&16 as
well as secretory mucins-
MUC5AC &MUC7 have
been identified at the
ocular surface.

10. PHYSICAL PROPERTIES OF TEAR FILM
Property
Thickness 4-8um
Volume 4-13ul
Rate of secretion 1.2ul per min
Turn over rate* 18% per min
Refractive index 1.357
Ph of tears* 7.3-7.7
Osmotic pressure* 0.90-0.95%
Temperature 30’c at cornea and 35’ at limbus
Oxygen tension 40-160 mm hg

11. TEAR FULID COMPOSITION
 Mainly composed of 3 protein factors-albumin,globulin
and lysozyme
 IgA is the most prominent Ig.
 IgE levels increase in patients with allergic
conjunctivities.
 IgM increases in patients with acute infections.
 Lysozyme constitutes 20% all tear protiens,highest in
conc among all body fluids
 Electrolytes Na,K and Cl higher concetrations in tears
than in blood

13. FUNCTIONS OF TEAR FILM
 Makes corea a smooth optical surface
 Wets cornea and conjunctiva and prevent from drying
 Flushes out debris and organisms
 Bactericidal properties (presence of lusozyme,lactoferrin
and betalysin)
 Ig’s and specific Ab in tears defend the eye against
infections
 Lubricating action
 Enables anti inflammatory cells to reach injured cornea
and conjunctiva
 Provides epithelial cells with O2 ,Glucose and Growth
Factors

14. NEURAL ASPECTS
 The trigeminal v1 (fifth cranial) nerve bears the sensory
pathway(afferent) of the tear reflexes.
 The motor pathway is autonomic (involuntary), &, in
general, uses the pathway of the facial (seventh) nerve
in the parasympathetic division via pterygopalatine
palatine ganglion, as efferent pathway.
 Applied A newborn infant has insufficient development of
nervous control, so she/he "cries without weeping”.

17. APPLIED ASPECTS
 Crocodile tears syndrome/ Bogorad's syndrome"
uncommon consequence of nerve regeneration
subsequent to Bell's palsy or other damage to the facial
nerve in which efferent fibers from the superior salivary
nucleus become improperly connected to nerve axons
projecting to the lacrimal glands (tear ducts), causing one
to shed tears (lacrimate) during salivation while smelling
foods or eating.
 Presumed that one would also salivate while crying due to
the inverse improper connection of the lacrimal nucleus to
the salivary glands, but less noticeable.

18. TEAR FILM DYNAMICS
Secretion of tears
Formation of tear film
Retention & redistribution of tear film
Displacement phenomenon
Evaporation from the tear film
Drying & break up of tear film
Dynamic events during blinking
Elimination of tears

19. 1.SECRETION OF TEARS

20. BASAL SECRETION
In the human eyes the cornea is
continually kept moist & nourished by
basal tears.
• They lubricate the eye & help to keep it
clear of dust.
• Secreted by accessory lacrimal glands

21. •
REFLEX SECRETION
•Results from irritation of the
eye by foreign particles,
bright light,hot & peppery
stimuli to the tongue.
•These reflex tears attempt
wash out irritants that may
have come into contact with
the eye.
•Secreted by main lacrimal
gland

22. Applied If lacrimal gland is damaged in
surgery or other failure of lacrimal
function occur, it is not a serious matter,
for the accessory glands are enough for
general secretion

23. 2.FORMATION OF PRE OCULAR TEAR FILM
Conjunctival mucus spreads on to the
cornea by the action of the lids.
On this new surface- aqueous layer is
spread spontaneously.
Over this the superficial lipid layer
spreads; probably contributing to its
stability & retarding evaporation b/w
blinks.

24. 3.RETENTION & REDISTRIBUTION
The outer most layer of corneal
epithelium+mucopolysaccharides leads to
retention.
Precorneal film is stagnant. Redistribution
occurs in the form of bringing of new tear
fluid by way of marginal strip where there
is constant flow of tears

25. 4.DISPLACEMENT PHENOMENON
 Demo that cornea is covered by a film which
has stability, compressibility, elasticity &
unaffected by gravity
 Demo by upward movement of particles in the
film on displacing lower eyelid upwards over
eyeball
 This phenomenon is possible due to presence
of thin monomolecular layer on the surface of
cornea

26. 5.EVAPORATION
 All lipid films including wax esters & cholesterol
esters retard evaporation of water
 Important in low humidity & turbulent air flow
near cornea, such as exists in a windy & arid
climate
 Evaporation from tear film = 10% of production
rate, so, evaporation = 0.12ul/min (as tear
production = 1.2ul/min)

27. 6.STABILITY, DRYING & RUPTURE OF TEAR FILM
 Tears has to cover entire preocular surface to function
properly
 It is re-established completely after a blink , but has short
lived stability
 It takes 15-40 secs for tear film to rupture & dry spots to
appear, when blinking is prevented
 Drying of corneal surface cannot be a result of evaporation
of water alone, as it takes at least 10 mins to eliminate
whole tear film by drying alone.

28. 7.ELIMINATION OF TEAR FILM
HOLLY & LEMP’S MECHANISM
 Initially all the tear film thins uniformly by evaporation.
 When thinned out to critical thickness, some lipid
molecules attracted by the mucin layer & migrate
down to this layer.
 When the mucin layer is sufficiently contaminated by
lipid from the top, the mucin becomes hydrophobic &
the tear film ruptures
 Blinking repair this and restore aqueous layer

30. 8.DYNAMIC EVENTS DURING BLINKING
 As the upper lid moves downwards, the superficial
lipid layer is compressed b/w the lid edges
 This will contaminate the mucus & this lipid
contaminated mucus is rolled up in a thread like
shape & dragged into lower fornix
 When the eye opens, at 1st the lipid spreads in the
form of a monolayer against the upper eye lid
 Then spreading of the excess lipid follows & in
about 1 sec multimolecular lipid layer is formed
 The spreading lipid drags some aqueous tears with
it thereby thickening the tear film.

32. 9.ELIMINATION OF TEARS
 Lacrimal fluid over the preocular surfacemarginal tear
stripLacus lacrimalisinner canthus lacrimal
passages  nasal cavity
 Lacrimal pump mechanism:- fibres of the pretarsal &
preseptal portion of the Orbicularis which arise from the
lacrimal fascia & posterior lacrimal crest.
 This LPM operates with the blinking movements of the
eyelids as follows:-

34. DRAINAGE OF LACRIMAL FLUID FROM NLD INTO
NASAL CAVITY
 Gravity helps downward flow.
 Air currents in nose induce negative pressure within
NLD draw the fluid down the potential lumen of the
duct into the nose.
 Hasner’s valve present at lower end of NLD,
remains open as long as the pressure within nose
is less than the NLD, allows the tears to flow from
NLD to nose

36. CHIEF C/O THE PATIENTS WITH TEAR FILM
DYSFUNCTION
 Burning or Itching
 Fluctuating Vision
 Foreign Body Sensation
 Grittiness or irritation
 Watering or excessive tearing
 Sore or tired eyes
 History of Styes
 Ocular Discharge
 Light sensitivity
 Contact Lens Discomfort

37. HISTORY FOR A DRY EYE(DE) PATIENT
 Duration of reading or computer use
 Using contact lens
 Living in air conditioned environment
 Frequent air traveling
 Cigarettes smoking
 Exposure to allergans or systemic allergies
 Hormonal change
 Autoimmune diseases

38. DISEASES RELATED TO DYSFUNCTION IN
TEAR FILM
 Evaporative Dry Eye
 Oil deficiency- secondary
to obstructive meibomian
gland dysfunction
 Defective resurfacing of the
eye by the tear film (result of
poor blinking or abnormal lid-
globe congruity)

39. DRY EYE: MULTIFACTORIAL NATURE
Elderly woman
Contact lens
user
Post
menopausal
Taking
glaucoma
medications
Working for long
hours in front of
computer
Air-conditioned
environment

40. DISEASES RELATED TO DYSFUNCTION IN
TEAR FILM
•Hyper secretion of tear film
 C/O Wet eyes
Lacrimation from
excess tearing
Obstructive
epiphoria as a result
of failure of tear
drainage
( Schirmer’s value)

42. TEAR FILM BREAK-UP TIME(BUT)
 Difference b/w the last blink and
the first randomly appearing dry
spots
 Assessed with fluorescein and
cobalt blue filter in broad beam
 Avg of three reading is taken
 Suspect Dry Eye when
BUT<10secs

43. CAUSES OF TEAR FILM DESTABILITY
Tear Film rupture occurs when
hydrophobic lipid diffuses from the
superficial layer and contaminates the
underlying hydrophilic mucin layer
Epithelial change

44. SCHIRMER’S TEST
 Rate of tear formation is
estimated
 Whatman filter paper no 41 is
used
 Dimension 5mm X 35mm
 5mm tab is folded at one end
 The bent end is placed at the
junction of the lateral 1/3rd and
medial 2/3rd of the lower
conjunctival sac
 Performed in dim light with fans
and ACs switched off

45. SCHIRMER TEST
 Without Anesthesia
 Measures Reflex Tear
Secretion (dry eye = < 6mm
wetting)
 With Anesthesia
 Measures Basal Tear
Secretion (dry eye =< 3mm
wetting)

46. JONES-I (PRIMARY) TEST
 Differentiates excessive watering due to blockage in
lacrimal passage with primary hypersecretion of tears
 1 drop of 2% fluorescein in instilled in the conjunctival
sac
 After 5mins a cotton tipped bud (moistened with
4%proparacaine) is inserted under the inferior turbanate
 Fluorescein if recovered from the nose then the
excretory system is patent
 Otherwise should go for Jones-II test

47. JONES-II (SECONDARY) TEST
 Helps to identify the probable site of partial obstruction
 4% xylocaine instilled in the conjunctival sac
 residual fuorescein washed out
 NLD irrigated with NS
 Patient is positioned his/her down by 45deg
 +ve –fluorescein stained saline recovered from the nose showing
functional patency of upper lac passage
 -ve- unstained saline recovered from the nose shows block in the upper
lac passage or defective lacrimal pump mechanism

48. Jones Dye-I
Jones Dye-II

49. THANK YOU