1. Tear Film And Blinking
Presenter
Junu Shrestha
B. Optom 3rd year
MMC, IOM
Moderator
Sanjeev Bhattarai
2. Contents
• Tear film introduction
– Composition
– Properties
– Dimensions
• Tear film dynamics
– Secretion
– Distribution
– Stability
– Tear flow
– Drainage
• Tear film functions
• Blinking
• Clinical correlations
3. Tear Film
• Layer of fluid on the surface of cornea
• First demonstrated by Fischer in 1928 by
using reflectography
• Also called precorneal film-Wolff(1946)
• Is a trilaminar structure
4. Development of tear film
• Within 24 hours of birth with normal tear production rate within 1
week
• Abnormal or reflex tearing starts only when the infant is 4 months
old
5. Composition
• Tear film….
composed of three layers:
• (a) the outer or superficial lipid layer
• (b) the middle aqueous layer
• (c) the inner mucoid layer
6. 1. Lipid layer
• Derived from secretions of
Meibomian glands, Glands of Zeis &
Glands of Molls.
• Primary Constituents: hydrocarbons,
fatty acids, sterol esters, wax esters,
triacylglycerol.
7. Functions of lipid layer
• Retards evaporation.
• Contribute to the optical properties of the film.
• Maintain a hydrophobic barrier that prevents tear overflow by
increasing surface tension.
• Prevent damage to lid margin skin by tears.(skin lipid contamination)
9. Functions of aqueous layer
• Supply oxygen to the avascular corneal epithelium.
• Antibacterial (lysozymes & lactoferrin), immunoglobulins (IgA, IgM,
IgD, IgE, S- IgA) and antiviral (interferons) defense.
• Wash away debris (cleansing)
• Maintain a constant electrolyte composition over the ocular surface
epithelium.
• Smoothing minute irregularities of anterior corneal surface (optical
surface enhancement)
• Bicarbonates regulates pH
10. 3. Mucus layer
• Deepest structure of the film
• Covers the microplicae of the superficial
corneal epithelial cells & forms fine
network over the conjunctival surface.
• Contains mucins, proteins, electrolytes &
water.
• Tear mucins are secreted principally by
conjunctival goblet cells ,the stratified
squamous cells of the conjunctival &
corneal epithelia ,& minimally by lacrimal
glands of Henle & Manz.
11. Functions of mucus layer
• Converts the corneal epithelium from a hydrophobic to hydrophilic layer .
• The mucin also interacts with tear lipids layer to lower surface tension
thereby stabilizing the tear film.
• Provides lubrication for eyelid movements.
• Loose mucin network covering the bulbar conjunctiva traps exploited
surface cells, foreign particles & bacteria.
17. Secretion
• Are continuously secreted throughout the day by
– Accessory lacrimal glands (basal secretion)
– Main lacrimal glands (reflex secretion)
• Reflex secretion occurs in response to sensations from the cornea
and conjunctiva.
• Afferent pathway of this secretion is formed by 5th nerve and
efferent by parasympathetic (secretomotor) supply of lacrimal
gland.
• Tear turnover rate: 5 to 7 minutes
18.
19. Distribution
Distribution of tear is possible due to
• Conjunctival mucus that makes cornea hydrophilic(wetting)
Holly and Lemp
• Interaction of eyelids and tears in corneal wetting (blinking)
Doane 1980
20. Sequence of events in the formation of
the precorneal continum:
1. Lids surfacing cornea with a thin layer
of mucus
2. On this, the aqueous then spreads
spontaneously
3. Then the superficial lipid layer
spreads over it retarding its
evaporation and enhancing stability.
21. • As the upper lid moves downwards, the superficial layer is
compressed. As it thickens it begins to exhibit interference colors.
The whole lipid layer together with the associated biopolymers is
compressed between the edges.
• This lipid contaminated mucus is rolled up in a thread like shape
and dragged into lower fornix.
• On opening the eye, at first the lipid spreads in the form of a
monolayer against the upper eyelid. The spreading lipid drags
some aqueous tears with it, thereby thickening the tear film.
24. • The compositional factors are
responsible for producing 3 major tear
components: aqueous fluid, lipids, and
mucins.
• Hydrodynamic factors generate
effective tear clearance (turnover) and
spread to cover the ocular surface and
intermittent closure to avoid unwanted
exposure and desiccation.
26. The tear film is transient.
After a finite period of time the integrity of the tear’s structure is
lost, leading to tear film rupture (and, thus, loss of confluent
coverage of the ocular surface).
• 2 theories:
30. Tear Flow: Lid Closure
• Contraction of the orbicularis oculi muscle
causes lid closure with a scissor-like action
towards the nose.
• Lid closure propels the tears towards the
medial canthus.
31. Drainage
• Tear is drained from lacus lacrimalis to the nasolacrimal duct via
active lacrimal pump mechanism.
• Operates during blinking
• On closure of eyelids contraction of pretarsal fibres of the
orbicularis compresses the ampulla and shortens the canaliculi.
This propels the tear present in the ampulla and horizontal part of
the canaliculi toward the lacrimal sac.
32. • Contraction of preseptal fibres of orbicularis pulls the lacrimal
fascia and lateral wall of a the lacrimal sac laterally, thereby
opening the normally closed lacrimal sac.
• Produces a relative negative pressure and draws the tears from
the canaliculi into the lacrimal sac.
• Along with the increased tension on the lacrimal fascia, the
inferior portion closes more tightly, preventing aspiration of air
from the nose.
33. • When the eyelids are open
Relaxation of pretarsal fibres of orbicularis allows the canaliculi to
expand and reopen. It draws in the lacrimal fluid through the
puncti from the lacrimal lake.
• Relaxation of portions of preseptal fibres allows the lacrimal sac
to collapse. It then expels the fluid therein into the now open
nasolacrimal duct
34.
35. Optical functions
The tear film is spread by the eyelids over the rough ocular surface
to form a uniform surface for refraction of light that is to focus on the
retina.
Protective functions
Mechanical
Debris and metabolic wastes are flushed from the ocular surface by
the tears. Foreign bodies result in increased tear secretion
The ocular surface is a complex
biological continuum responsible for:
36. Antimicrobial
The tears contain antibacterial substances (lysozyme, lactoferrin, beta-lysin)
antiviral immunoglobulins (secretory IgA), and complement.
Environmental
The tears protect the surface of the eye from the external environment by
responding to constant, varying challenges, such as desiccation, bright light,
cold, mechanical stimulation, and noxious chemicals.
There is exquisite control of tear volume, composition, and structure in
response to these challenges.
37. Lubricative function
• The conjunctival and corneal surfaces are lubricated by the tears so that they
slide over each other during blinking.
Osmotic function
• Appropriate corneal hydration levels are maintained partly through the osmotic
activity of the tears.
Nutritional function
• Oxygen passes through the tears and across the anterior surface of the eye.
Fat soluble nutrient (e.g., vitamin A) could be provided through the tears,
although it is absent in tears.
38. LAMBS
The five major elements that causes tearfilm dysfunction
are
• L = lipid abnormality
• A = aqueous abnormality
• M = mucin abnormality
• B = base abnormality (or epitheliopathy)
• S = surfacing abnormality (spreading of the tears by the
lids) or causes of dry eye produced by exposure
40. ‘Dry eye’ is a generic term for a group of conditions characterized
• symptomatically by irritated, gritty, burning eyes, and
• clinically by alterations in the tear film and anterior surface of the
eye.
In a classic review, this syndrome was defined as
• ‘a disorder of the tear film due to tear deficiency or excess
tear evaporation which causes damage to the interpalpebral
ocular surface and is associated with symptoms of ocular
discomfort’ (Lemp, 1995).
44. Blinking
• Coordinated opening and closing movements of the eyelids.
Blinking
Complete
Movement of both eyelids, which begins in
the normal alert open position, reaches a
halfway point when the upper and lower
eyelids’ciliary margin appose each other
along at least one half of their ciliary
margins and ends when the upper and
lower eyelids return to the starting, alert
open position
Incomplete
Blink which is terminated at any stage
that occurs in complete blink phase
46. Closure of Eyelids
• Brought about by the contraction of the orbicularis oculi muscle
(OO), innervated by the facial nerve (N7).
• The lid action is ‘zipper-like’ or ‘scissor-like’ from the temporal to
the nasal canthus. The lower lid moves relatively little during a
normal blink.
• Blink rate: approx. 15 blinks/min.
• Duration: 0.3 - 0.4 seconds.
47. Closure of eyelids
• The globe moves up and in towards the nose as well as
backwards, and then returns on eye opening.
• Forced closure involves the whole of the orbicularis oculi
(especially the orbital portion) and Müller's muscle.
• Eye closure in sleep involves tonic stimulation of the orbicularis
oculi and concurrent inhibition of the levator palpebrae superioris
muscles.
48. Opening of Eyelids
• Brought about by contractions of the levator palpebrae superioris
(LPS) muscle.
• Some assistance comes from Müller's muscle which is smooth
and sympathetically innervated.
• Main innervation comes from the oculomotor nerve (N3). As it
has no reciprocal innervation, the orbicularis oculi does not relax
even when the levator palpebrae superioris elevates the upper lid.
49. Voluntary blinking
• Blinking carried out as a willed act in both eyes
• When in one eye – winking
• Produced by simultaneous contraction of palpebral and orbital
portions of orbicularis muscle
50. Involuntary blinking
• Spontaneous blinking occurs without any obvious external
stimulus or voluntary willed efforts
• Since it does not require retinal stimulation, it is also present in
visually challenged (blind) people
• Does not produce discontinuity in vision, despite vision is
interrupted during the blink for about 130 msec
51. • Reflex blinking occurs reflexly in response to direct stimulus
• Depending on stimulus it can be
• Tactile reflex afferent via 5th nerve and efferent via 7th nerve
excited by tactile stimulation of conjunctiva, cornea, eyelashes,
eyelid and eyebrow
• Optic reflex afferent 2nd nerve and efferent via 7th nerve -bright
light or menace reflex
• Auditory reflex afferent 8th nerve an efferent 7th nerve – loud
noise
• Stretch reflex in orbicularis
52. • Blink Reflexes
• Facial nerve (N7) nucleus connects with
– superior colliculus (optic impulses)
– trigeminal nucleus (sensory impulses)
– superior olive (acoustic impulses).
• Optic reflex
– eye closure when threatened
– eye closure when exposed to bright light/dazzle.
53. • Sensory reflex
– eye closure when lid or cornea is touched.
• Auro-palpebral and cochleo-palpebral reflexes
– eye closure caused by a loud sound stimulus.
• Stretching or striking reflex eye closure
– resulting from stretching or striking anatomical features close to the
lids (protective).
• Psychogenic reaction (non-reflex)
– eye closure caused by emotional stimulus (this reflex is involuntary).
54.
55. TEAR QUANTITY ASSESSMENT
• Tear film fluorophotometry/fluorescein clearance
• Schirmer test
• Phenol red thread test
OTHER TESTS
• Marginal tear strip
• Fluorescein staining
• Rose Bengal staining
• Conjunctival impression cytology
• TBUT test
56. Tearfilm fluorophotometry/ fluorescein
clearance
• Fluorescein sodium is applied topically whish is homogenously
on the corneal surface and conjunctival sac after several blinks.
• Tears containing fluorescein are removed by flow and are
replaced by fresh tears not containing fluorescein.
57. • Measurement of disappearance via fluorophotometry or other
fluorescein clearance tests is used to determine tear turnover
• which is percentage decrease of fluorescein concentration in tears
per unit of time (% minute-1).
• Basal tear turnover, defined as the tear turnover at the lowest
level of reflex tear production possible under physiologic
conditions, is taken as an indirect quantitative assessment of tear
production.
58. Schirmer’s Tear test
• Test for tear quantity
• Based on wetting length of the
strip 5x35mm Whatman 41
filter paper
• Placed in the lower fornix at
medial 1/3rd and lateral 1/3rd
• 2 variations
59. Schirmer’s test I
• Measures total tear secretion (basic and reflex)
• Open eye technique
• Normal
– 10-30 mm at the end of 5min
• If wetting >30mm before 5 min
– Reflex tearing overactive/ insufficient tear drainage
• Value < 5mmHyposecretion
60. Basic Secretion Test
• Variant of Schirmer test I measures basal tear secretion
• Topical anesthetic is applied
• Cul-de-sac is dried out before the strip is inserted
• Difference between Schirmer I and BST reading gives reflex
secretion
• Normal value > 10mm
• Basic Secretion of 3mm or less Abnormal
61. Schirmer Tear test II
• Measures reflex tear secretion
• Irritate nasal mucosa by rubbing it with cotton
swab or smelling ammonia
• Measure wetting after 2min
• Wetting < 15mm Failure of reflex secretion
• Parasympathetic supply
62. Phenol Red Thread Test
• Measures basal secretion
• Sensitive to change in pH
• 75mm long cotton thread impregnated with phenol red-temporal
cul-de-sac for 15 secs
• Color changes from Yellow to red (pH range 6.6-8.2)
• Wetting of ≥16.7 mm in 15 secs (Normal)
• ≤6mm (Dry Eye)
• Phenolsulphophthalein
63. • Fluorophotometry offers the greatest potential for providing an
accurate assessment of tear production. Although
unconventional, the PRT appears to offer the next best accuracy
and reproducibility followed by the Schirmer test.
• Quantitative assessment of tear production: A review of methods and utility in
dry eye drug discovery Michelle Senchyna and Martin B Wax
• J Ocul Biol Dis Infor. 2008 March;
64. 1.Tear Meniscus Height
• Tear lake (or prism) accumulates at the junction of the bulbar conjunctiva
in the inferior lid margin
• is approx 0.3 to 0.4 mm in ht.
• Decrease in tear meniscus & with accumulation of debris, is suggestive of
lacrimal deficiency, an unstable tear film.
• A measurement scale in the reticule or an adjustable slit beam height can
be used to measure tear meniscus height.
65. 2. Fluorescein Staining
• Fluorescein dye is used to detect epithelial
defects on the anterior surface of the eye.
• Penetrates only the corneal epithelium at sites
of interrupted continuity of the epithelial
surface.
• Is enhanced with the use of cobalt blue filter
that blocks extraneous light and highlights
staining patterns.
66. 3. Rose Bengal Staining
• Devitalized cells on the cornea and conjunctiva and mucus in the
tear film
• detected using 1% rose bengal
• highlighted by red punctate staining
67. • Rose bengal staining patterns are classically graded on a 0 to 3
graded scale proposed by van Bijesterveld,
• Three regions of the interpalpebral ocular surface are assessed
– the triangular wedge of the nasal interpalpebral conjunctiva,
– the corneal surface
– the wedge of the temporal conjunctiva
• The grade of each region is summed, and a score greater than 3.5
is considered indicative of dry eye
68. 4. TBUT
• Tear film Break Up Time in cobalt blue filter
• Interval between the last blink & the first appearance of black spot in the
fluorescein-stained tear film (Norn & Hamil 1973)
• A black island in the sea of green fluorescein
• Assessment of tear film stability
• >10 sec Normal
69. 5. Conjunctival Impression Cytology
• Millipore filter paper of cellulose acetate (with 0.02-µm pores) can be employed
to assess conjunctival goblet cell density.
• The filter paper is cut into strips approximately 5 x 5 x10 mm in size. After
instillation into the inferior cul-de-sac of one drop of proparacaine or a similar
anesthetic, with the aid of a forceps, the pieces of filter paper are pressed
against the nasal, temporal, inferior, and superior bulbar conjunctiva.
• Pressure is applied to the paper for 2 to 3 seconds.
70. • The filter paper is then fixed for 10 minutes in a mixture of 70% ethyl
alcohol, 37% formaldehyde, and glacial acetic acid in a proportion of
20:1:1.
• Each paper is stained, using periodic acid–Schiff (PAS), hematoxylin
and eosin, and Papanicolaou.
• Under the light microscope, the epithelial cells are evaluated for
morphology and density.
71. Nelson (1988) classified impression cytology of the conjunctiva in
grades:
• Stage 0: normal cellular structure
• Stage 1: early loss of goblet cells without keratinisation
• Stage 2: total loss of goblet cells with slight enlargement of
epithelial cells
• Stage 3: early and mild keratinisation
• Stage 4: moderate keratinisation
• Stage 5: advanced keratinisation
• Grades 1 and 2 are considered normal.
73. Tear film
1. Deturgensence of cornea
2. Tear film in contact lens
3. Dry eye related contraindication of contact lens wear
4. Effect of blinking during contact lens wear
74. 1. Deturgesence of cornea
• Is maintained due to osmotic pressure of the precorneal tear film
and the aqueous humour
• The osmotic pressure of the precorneal tear film is greater than
that of corneal epithelium due to constant evaporation of tears
that causes water to be removed from the cornea.
• But blinking is necessary for the replenishment of oxygen to the
cornea
75. 2. Optics of the RGP lens
• Depends largely on the tear layer between cornea and the lens.
• Refraction that we think as taking place at the cornea as
measured by keratometer actually takes place at the air tear
interface.
• Contact lens alters the curvature of air tear interface if the back
surface of the lens is not parallel with the interface.
• When the curvature of the tear lens is steepened, the eye is made
more myopic(back surface of the contact lens is steeper than the
tear layer).
• When the curvature is flattened, the eye is made more hyperopic
(back surface flatter than tear layer)
76.
77. 3. Benefits of blinking on contact lens wear
• Better oxygen and carbon dioxide exchange, providing increased
comfort, better tolerance of the lenses on eyes
• Removal of keratinized epithelial cells and other debris from
underneath the lenses
• Cleaner lens surfaces, reducing the possibility of the occurrence
of coating
• Reduced possibility of lens dehydration and the deleterious effect
that may follow
• Extends lens life
78. 4. Dry eye related contraindications of contact
lens wear
Dryness
• Volume or quality of tears.
• Poor blinking.
• Dry environment.
• Drug-induced (e.g. antihistamine).
• Work-induced (e.g. VDUs).
79. From which component of the tear film do contact
lens deposits originate ?
• originate in any of the layers of the tear film.
• The aqueous layer of the tear film is composed of 98% water;
2% is mineral content, including K, Cl, and Ca, ascorbate ions
• Among proteins, lysozyme has a special attraction to the
materials from which hydrophilic contact lenses are made.
• Lipids produced by the meibomian glands also deposit on
contact lenses, as do products of the mucin layer.
80. Short -term changes in the tear film induced by
contact lens
• decrease in osmolarity due to the contact lens storage solutions
and reflex tearing due to lens insertion.
• mild short-term fluctuations in the tear film pH.
• The pre–contact lens tear film differs from the post-lens tear film
once the tear film has stabilized.
• The prelens tear film - postulated to be lipid and slightly aqueous,
while the post-lens layer - mucin and aqueous.
81. 3 & 9-O'Clock Staining/Peripheral Corneal
Desiccation
• Epithelial punctate staining of
the peripheral cornea in
regions adjacent to the edge
of a rigid contact lens.
• Its location is limited to the 2
to 4-o'clock and 8 to 10-
o'clock regions of the
peripheral cornea.
82. • The presence of a lens may exaggerate the effect by shifting the lid
margin further from the cornea thereby increasing the size of the
bridged zone. It is in this bridged zone that 3 & 9 o’clock staining
occurs.
The corneo-scleral sulcus represents
a zone of no contact between the
globe and the upper eyelid margin,
i.e. it bridges the midperipheral
cornea and the perilimbal
conjunctiva.
83. • The fundamental cause of 3 & 9 o'clock staining is the irritation
produced by the lens which inhibits the normal blinking process
leading to a disturbanceof the tear layer, and a failure of wetting
of the corneal epithelium adjacent to the edge of the lens
• consists of isolated punctate stains. It can coalesce, with
engorgement of the adjacent conjunctival blood vessels.
84. Blinking
• Reflex blepharospasm
• Occurs due to reflex sensory stimulation via branches of 5th nerve
in conditions such as phlyctenular keratitis, Interstitial Keratitis,
corneal foreign body, corneal ulcers, iridocyclitis
85. • Benign essential blepharospasm (BEB)
• is a bilateral, involuntary, spasmodic forced eyelid closure with
accompanying brow depression in the absence of any other ocular or
adnexal cause.
• May also be secondary to ocular surface disease or neurodegenerative
diseases such as Parkinson’s.
• BEB affects women more often than men, and typically presents during
5th to 7th decades of life.
86. Effect of incomplete blinking on tear film stability.
M1, Uozato H, Kawamorita T, Shibata Y, Yamamoto S.
Optom Vis Sci 2013
Purpose : assess changes in tear film stability caused by incomplete
blinking.
Methods : 11subjects (mean age, 21.3 years) participated in study. All
subjects had a visual acuity of 20/20 or better and normal ocular
health. The subjects were asked to play a game for 60 min on a
personal computer as part of a visual display terminal (VDT)
experiment. Each subject's blinking was observed by a Web camera that
was attached to the top of the display. Every 15 min, the VDT
experiment was interrupted for measurement.
• .
87. Results :
Although the total blink rate changed very little, the complete and
incomplete blink rates fluctuated during the VDT experiment.
Noninvasive breakup time at 30 min (4.33 ± 2.57 s) was significantly
shorter (p < 0.01) than that at baseline before the VDT experiment
(8.62 ± 1.54 s). After 30 min, the incomplete blink rate began
decreasing (fewer incomplete blinks), whereas the complete blink rate
began increasing. Ring breakup time increased (improved) after 45 min;
however, the incomplete blink rate began to increase again after
approximately 50 min.
Conclusions :
Even if the total blink rate decreases, the tear film remains stable so
long as almost all blinks are complete. The incomplete blinking
contributes to tear film instability and is variable with prolonged VDT
exposure. The tear film stability was determined by blinking quality,
and the predominance of blinking type relates to tear film stability
88. References
1. IACLE Module 1, 2 and 7
2. Anatomy and physiology of eye 2nd edition A.K. Khurana
3. Adler’s Physiology of the eye 11th edition
4. Dry eye a practical approach Butterworth
5. Quantitative assessment of tear production: A review of
methods and utility in dry eye drug discovery
6. Impression cytology of the ocular surface Br J Ophthalmol. 2005
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