Tear film & dynamics


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Due to increase in number of computer users the problem of dry eye is increasing which is generally due to tear film dysfunction, so its essential to know about the tear film, its dynamics and dysfunction. Hope you will like it..!

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Tear film & dynamics

  1. 1. Tear Film & Dynamics Dr Vijay Joshi GMC Haldwani
  2. 2. The Tear Film The main role of lacrimal system is to establish & maintain a continuous tear film over the ocular surface. The presence of the pre-corneal tear film was 1st demonstrated: by Fischer in 1928. Rollet described it as the most superficial 6th layer of cornea.
  3. 3. Structure Of The Tear Film • Wolff was the 1st to describe in detail the structure of the tear film. • Coined the term ‘PRE-CORNEAL FILM’. • Tear film consists of 3 layers. i) Outer Lipid layer ii) Intermediate Aqueous layer & iii) Inner Mucin layer.
  4. 4. Structure Of The Tear Film 0.2um
  5. 5. Components Of Eye Forming Tear Film
  6. 6. Lipid Layer • Outer most layer. • 0.1um thick • Formed from the secretions of Meibomian, Zeiss & Moll glands. • Wolff describes it as ‘marginal tear strip’ extending to the post margin of opening of meb gld. • Contents:-1)low polarity lipids-wax & cholesterol esters 2)high polarity lipids-TG, FFA ,phospholipids. • Fns:-1)prevents the overflow of tears. 2)prevents evaporation. 3)limits ant end of the tear fluid reservoirs
  7. 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-7-8um.  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 because of the presence of HCO3 ions & proteins in this layer.  Fns:1)provides O2 to corneal epithelium. 2)washes away debris & irritants. 3)contains antibacterial sub- lysozyme & betalysin.
  8. 8. Mucus Layer • Innermost layer. • Secreted mainly by the conjunctival goblet cells & by the stratified squamous cells of the corneal & conjunctival epithelium. • 0.2um thick. • 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.
  9. 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. 10. New model of tear film
  11. 11. New model of tear film
  12. 12. Physical Properties Of Tear Film 1)Thickness 8-10um 2)Volume 4-13ul 3)Rate Of Tear Secretion 1.2ul/min 4)Turn over rate 18% per min 5)Refractive index 1.357 6)pH 7.0-7.3 7)Osmotic pressure 0.90-0.95% Nacl soln 8)Temp. 35*C at the limbus ; 3o*C At the centre 9)O2 tension (Po2) 40-160mm Hg
  13. 13. Chemical Composition Of Human Tears & Plasma TEARS PLASMA 1)water 98.2g% 94g% 2)solids, total 1.8% 6g% 3)Na+ 142meq/l 137-142meq/l 4)K+ 15-29meq/l 5meq/l 5)Cl- 120-135meq/l 102meq/l 6)HCO3- 26meq/l 24.3meq/l 7)Ca2+ 2.29mg/100ml 8)Glucose 3-10mg/100ml 80-90mg/100ml 9)Total proteins 0.6-2gm/100ml 6.78g/100ml 10)Aminoacids 8gm/100ml 11)Urea 0.04mg/100ml 20-40mg/100ml
  14. 14. Functions Of Tear Film • To form an almost perfectly smooth optical surface on the surface of cornea. • To keep the surface of cornea & conjunctiva moist. • Serves as a lubricant for the pre-ocular surface & lids. • Transfers O2 from the ambient air to the cornea. • Prevents infection due to the presence of anti bacterial substance as lysozyme, betalysin, lactoferrin etc. • Washes away debris & noxious irritants. • Provides pathway for white blood cells in case of injury. • To provide a perfect refractive media for light.
  15. 15. Neural Aspects Of Tear Production • 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/ spheno palatine ganglion, as efferent pathway. • Applied: A newborn infant has insufficient development of nervous control, so she/he "cries without weeping”.
  17. 17. Neural Aspects Of Tear Production
  18. 18. Neural Aspects Of Tear Production
  19. 19. • Applied: • "Crocodile tears syndrome/ Bogorad's syndrome" is an 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. • It is presumed that one would also salivate while crying due to the inverse improper connection of the lacrimal nucleus to the salivary glands, but this would be less noticeable.
  20. 20. 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
  21. 21. Secretion Of Tears basal reflex
  22. 22. Tear Secretion • 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 • REFLEX SECRETION:- • Results from irritation of the eye by foreign particles. • Can also occur with bright light & hot & peppery stimuli to the tongue & mouth. • These reflex tears attempt to wash out irritants that may have come into contact with the eye. • Secreted by main lacrimal gland Applied : If lacrimal gland malfunctions or 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. 23. 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. 24. Retention & Redistribution • The outer most layer of corneal epithelium+ mucopolysaccharides l/t- 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. 25. Displacement Phenomenon • Demonstrate that cornea is covered by a film which has stability, compressibility, elasticity & unaffected by gravity • Demonstrated 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. 26. Evaporation from the tear film • All lipid films including wax esters & cholesterol esters retard evaporation of water • Imp 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. 27. 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. 28. Elimination of Tear Film  Holly & Lemp’s Mechanism  1st described by Holly in 1973.  Initially all the tear film thins uniformly by evaporation.  When thinned out to some critical thickness, some lipid molecules begin to be 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.
  29. 29. Mech Of Tear Film Break Up
  30. 30. Dynamic Events During Blinking • Was 1st described by Holly in 1980. • 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.
  31. 31. Blinking Dynamic Events During Blinking
  32. 32. 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:-
  33. 33. Lacrimal Pump Mechanism(Doane’s Model ) • On eyelid closure: • Contraction of pretarsal fibres of orbicularis compresses the ampulla & shortens canaliculi propels tear fluid in ampulla & horiz part of canaliculi towards lacrimal sac & opens it. • The inc tension on lacrimal fascia, the inf portion of lacrimal sac, closes more tightly preventing aspiration of air from nose. • On eyelid opening: • Relaxatation of pretarsal fibres of orbicularis allows canaliculi to expand & reopen draws in the lacrimal fluid through the puncta from lacrimal lake. • Relaxation of preseptal fibres (horner’s muscle) allows the lacrimal sac to collapse expels the fluid therein into NLD
  34. 34. Lacrimal Pump Mechanism Elimination of tears by lacrimal pump mechanism
  35. 35. 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. 36. Doane’s Model Relating Blinking & Tear Drainage
  37. 37. Drainage Of Lacrimal Fluid From NLD Into The Nasal Cavity
  38. 38. Tear Film Abnormalities
  39. 39. Tear Film Abnormalities  Lipid abnormalities - chronic blepharitis.  Aqueous deficiency – KCS , Riley-Day syndrome, idiopathic, associated with systemic diseases etc.  Mucin deficiency - hypovitaminosis, ocular cicatricial pemphigoid , steven johnson syndrome, drug induced, chemical burns etc.  Impaired lid function- exposure keratitis, symblepharon, pterygium etc.  Epitheliopathy- anaesthetic cornea, epithelial irregularity of any cause.
  40. 40. Tests For Tear Film Adequacy • Schirmer tests- 1)schirmer test-1 2)schirmer test 2 • Tear film break up time(BUT). • Vital staining- fluorescein, rose bengal, alcian blue, scarlet red etc • Tear proteins- lysozyme, lactoferrin • Tear film osmolarity • Tear film evaporation time..,etc
  41. 41. Evaluation of Tear Film Stability • It generally includes Tear Break Up time (TBUT) • Mechanism: • Stain the tears with fluorescein dye and measure the interval between a complete blink and the appearance of the first randomly distributed dry spot or hole in the pre-corneal tear film. • The normal value is more than 10 seconds.
  42. 42. Ocular Protection Index • Demonstrates how the TFBUT and inter-blink interval (IBI) interact to protect the corneal surface. • If the amount of time between blinks is longer than TFBUT, an insufficient tear film leaves the corneal epithelial cells unprotected, exacerbatin g the signs and symptoms of dry eye.
  43. 43. Evaluation Of Aqueous Tear Production • Schirmer Test • Involves measurement of wetting of a special (no.41 whatman) filter paper, 5mm wide & 35 mm long. • Filter paper is folded 5mm from one end & inserted at junction of middle & outer third of lower lid. • Take care not to touch cornea & lashes. • Patient is asked to keep the eyes gently closed • After 5 min, the filter paper is removed & amount of wetting from fold is determined. •These tests identify the DES caused by inadequate tear production
  44. 44. • Schirmer’s Test : Reading – I – measures basal & reflex sec. – II – measures only reflex If Wetting <3mm = V. Severe Dry Eye If Wetting 3-5 mm = Severe Dry Eye If Wetting 5-10mm = Moderate Dry Eye If Wetting is 10mm = Mild Dry Eye If Wetting >10mm = Normal Eye
  45. 45. Evaluation Of Aqueous Tear Production • Cotton Thread Test • A special cotton thread impregnated with phenol red dye is used. • Inserted into the temporal side of the lower conjuctival sac for 15 seconds. • Turns from yellow to bright orange in the presence of tears due to alkaline nature of tears. • Length of thread wet by tears can be used as a measure of aqueous tear production
  46. 46. Meibomian Gland Evaluation • Diagnosis of meibomian gland ds is made by microscopic demonstration of: : – ductal orifice metaplasia – reduced expressibility of meibomian gland secretion – increased turbidity and viscosity of expressed secretions – morphologic abnormalities of gland acini and ductules • Meibography/meiboscopy: • It is the visualization of the meibomian gland by transillumination of the eyelid. Meibography implies photographic documentation. • Helps to diagnose meibomian gland morphology, density, & dysfunction. • Meibometry: • In this method lipid on the lower central lid margin is blotted onto a plastic tape, and the amount taken up is read by optical densitometry. • This provides an indirect measure of the steady state level of the meibomian lipid.
  47. 47. • Corneal Flourescein Staining • The dye penetrates the intercellular spaces. • Staining indicates increased epithelial permeability • The grading is based upon a scale of 0 to 3 in five areas of the cornea: central, superior quadrant, inferior quadrant, nasal quadrant, & temporal quadrant. • The max possible score is 15 mm. Diagnostic Dye Staining
  48. 48. Rose Bengal staining • 1 % Rose Bengal stains not only devitalized but also healthy epithelial cells and, hence has the unique property of evaluating the protective status of the preocular tear film. • Van Bijsterveld reported a grading scale that evaluates the intensity of staining based on a scale of 0 to 3 in three areas; nasal conj, temp conj and cornea
  49. 49. • A score of 0 for absent, 1 for just present, 2 for moderate staining, & 3 for gross staining was suggested in each of these areas. • A total score was used for interpretation & a score of 3.5 out of 9 was considered abnormal.  Rose Bengal staining • The maximum possible score is 9.
  50. 50. • The rose bengal staining patterns also classified as A, B, C acc to severity of KCS: • Grade A(severe case): Confluent RB staining on exposed bulbar conj & blochy & confluent on the cornea. • Grade B(mod case): extensive stainging on entire exposed area. • Grade C( mild or early cases): fine punctae stains in interpalpebral area. • RB staining system has been quantified by point system. • No of stained dots on cornea, medial & lateral bulbar conj were estimated on slit lamp & were given points from 1 to 5 for < 30, <100, < 1000, <10,000 & > 10,000 stained dots. • Points more than 6 (out of total 15) were considered pathological. Rose Bengal staining
  51. 51. Lissamine Green B Staining • Lissamine green B has been reported to detect dead or degenerated cells, and it produces less irritation after topical administration than rose bengal. • Staining by this dye may indicate existence of membrane abnormalities of the ocular surface epithelial cells. Close-up example of a patient with evaporative dry eye showing a thickened and inflamed eyelid margin—lissamine green staining shows the anterior migration of the mucocutaneous junction and pooling within the contour irregularities
  52. 52. pH (hydrogen ion conc) • Normal ph is necessary for buffering action of tears. • In early literature was reported 7.4 while in modern is about 7. • Results depend upon the method of its determination viz. vital staining, glass electrode, indicator paper or micro combination glass ph probe tech & sources of error, most common due to Co2 evaporation. • Tear ph known to change in many ocular condition • Applied: KCS patients were found to exhibit slight alkaline shift.
  53. 53. Evaluation Of Lysozyme Content Of Tears • Tear Lysozyme makes about 3 % of tear proteins • It is reduced in the tears of patients with dry eye • It is measured by the method of agar diffusion – a slab of agarose gel containing a uniform suspension of micrococcus lysodiekticus, a bacteria sensitive to Lysozyme is prepared. – tear sample is collected and placed in the center of the gel – The gel is then incubated and the enzyme diffuse radially and lyse the bacteria forming a clear zone around the well – more the content of Lysozyme, more will be the zone of clearance.
  54. 54. Evaluation Of Lactoferrin Content Of Tears • Lactoferrin is a tear protein with significant antibacterial activity that is normally produced by the lacrimal gland and has been used as a relative indicator of lacrimal gland function • It is measured by the Lactocard, commercially available colorimetric solid phase ELISA technique
  55. 55. • Tear Film Osmolarity • The normal osmolarity of the tear is 305 mOsm/l • Hypertonic 330 to 340mosm/l in KCS • As the tear secretion decreases, the tear film osmolarity increases technically difficult to assess. • Tear Evaporation Rate • Small humidity sensor with goggle type chamber which fits around eyelids • Evaporation found to be higher in patients with dry eye • Reliability suspect, Clinical test not available
  56. 56. • Tear meniscometry • Is a technique to quantify the height & thus the vol of the lower lid meniscus. • In normal eye the meniscus is about 1mm in height, while in dry eye it becomes thin or absent. Tear meniscus appearance before strip meniscometry
  57. 57. • Ocular Ferning Test • Principle- conjunctival mucus from normal eye crystallises in the form of ‘ferns’ when placed on dry glass slide • Higher sensitivity in diagnosis of dry eye than Schirmer test • Conjuctival Biopsy & Scrapings • Detect the histological changes in dry eye • After staining the material, goblet cell densities & their morphology, & keratinisation of epithelial cells, which is very sp in dry eye, can be seen microscopically Conjuctival biopsy of mucus cells
  58. 58. Impression Cytology • In cases of advanced dry eye, the epithelium undergoes pathologic changes, termed squamous metaplasia, and the density of goblet cell decreases. • It is a quick method to obtain sup cells from the bulbar conjunctiva by applying a small piece of nitrocellulose membrane against the conjunctival surface • The extent & severity of the squamous metaplasia is based on five cytologic features : (1) loss of goblet cells, (2) enlargement and increase in cytoplasmic/nuclear ratio of superficial epithelial cells, and (3) Early & mild keratinization (4) Moderate keratinization (5) Advanced keratinization
  59. 59. Impression Cytology
  60. 60. Fluorophotometry • To quantitate tear secretion, tear volume and tear turnover. • Fluorophotometry developed by Gobbels– Dry Eye patients – tear secretion 0.2 +-0.2 microl/minute. • Normal (Age matched controls) – Tear Secretion 1.2 +- 0.5 microl/minute • Lack of standardisation; Complexity; Cost
  61. 61. Summary Of Tear Film Evaluation Tests Test Basis Use Units Abnormal Values Schirmer's I Decreased reflex tearing in lacrimal gland disease Diagnosis of aqueous deficient dry eye mm/5' < 5 mm wetting/5' Fluorescein tear breakup time A measure of tear stability Diagnosis of tear stability seconds <10 seconds Fluorescein staining Indicator of corneal epithelial integrity Diagnosis of corneal surface disease Grade 0-3 for 5 areas >3 out of 15 Rose bengal staining Indicator of integrity of conjunctiv al surface Diagnosis of conjunctiv al surface disease Grade 0-3 for 6 areas >3 out of 18
  62. 62. Summary Of Tear Film Evaluation Tests Lissamine green Indicator of integrity of conjunctiv al surface Diagnosis of conjunctiv al surface disease Grade 0-3 for 6 areas >3 out of 18 Tear film osmolarity Increased osmolarity in dry eye disease Diagnosis of dry eye mOsm/L >312 mOsm/L Impression cytology Squamous metaplasia in dry eye disease Diagnosis of ocular surface disease Grade 0-3 >1 Tear lactoferrin Decreased levels in aqueous deficient dry eye To confirm the diagnosis of aqueous deficient dry eye mg/ml <0.9 mg/mL
  63. 63. DEWS STUDY • The dry eye work shop study for the definition and classification of Dry Eye Disease held in 1994. • Goal: To develop a contemporary definition of dry eye disease and to develop a three-part classification of dry eye, based on etiology, mechanisms, and disease stage. • DEWS STUDY define Dry Eye as: • Dry eye is a multi factorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface. • It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface
  64. 64. Dry Eye Classification Acc To DEWS
  65. 65. Aqueous Layer Deficiency • Sjogren’s Syndrome tear deficiency (SSTD) • Clinical condition of aqueous tear deficiency combined with dry mouth • Primary- patients without a defined connective tissue disease (CTD) • Secondary – patients who have a confirmed CTD, such as SLE, polyarteritis, Wegener’s granulomatosis, scleroderma, polymyositis, RA • Infiltration of the lacrimal gland by B and CD4 lymphocytes & plasma cells, leading to fibrosis
  66. 66. Aqueous Layer Deficiency Cont. • Non-Sjogren’s tear deficiency (NSTD) • NSTD can occur from impaired glandular production, impaired afferent or efferent stimulation, or local ocular surface disease • Primary lacrimal deficiency – congenital alacrimia – acquired lacrimal gland deficiency – idiopathic Keratoconjunctivitis syndrome (KCS)
  67. 67. Aqueous Layer Deficiency Cont. • Non-Sjogren’s tear deficiency (NSTD) • Secondary lacrimal deficiency can result from infiltration of the lacrimal gland – Lymphoma – sarcoidosis, hemochromatosis – HIV infection – graft-versus-host disease – surgical or radiation-induced destruction of lacrimal tissue – Penetrating keratoplasty – damage to the first division of trigeminal ganglion from – trauma, tumour, herpes simplex, or zoster
  68. 68. Evaporative Dry Eyes • Evaporative dry eye is caused by deficiency and/or alterations in lipid secretions by the meibomian glands resulting in increased evaporation of aqueous tears from the ocular surface • Evaporation leads to both loss of tear volume and a disproportionate loss of water, resulting in hyperosmolarity • Due to meibomian gland dysfunction, exposure & mucin deficiency
  69. 69. DEWS Dry Eye Grading Scheme
  70. 70. Treatment Scheme Under DEWS Study
  71. 71. THANK YOU