TEAR FILM PHYSIOLOGY Presentation ophthal

TEAR FILM PHYSIOLOGY

1. TEAR FILM PHYSIOLOGY DR.SANDEEP KRISHNAN PG1 OPHTHALMOLOGY RESIDENT

2. TEAR FILM The main role of lacrimal system is to establish & maintain a continuous tear film over the ocular surface. The blinking action of lids is essential for spreading the tears and maintaining the moist surface on anterior portion of globe .

3. FUNCTIONS Form a perfectly smooth optical surface on the cornea by filling in and smoothening out small surface irregularities in the corneal epithelium. Serves to keep the cornea and conjunctiva moist . It serves as a lubricant for the preocular surface and lids. It transfers oxygen from the ambient air to the cornea . It prevents infection due to the presence of antibacterial substance such as lysozyme , betalysin , lactoferrin ,immunoglobulins and other proteins. It wash away debris and noxious irritants . It provide a pathway for WBC in case of injury.

4. STRUCTURE OF TEAR FILM Precorneal film - term coined by Wolff . It consist of three layers outer lipid layer intermediate aqueous layer inner mucoid layer 6 layers proposed by Tiffany include the 3 layer coined by Wolff along with air-lipid, lipid aqueous and aqueous mucin interfaces The current concept is that the tear film is bilayer structure consist of an aqueous mucinous phase , with a overlying superficial lipid phase.

5. LIPID LAYER Outermost superficial oily layer of tear film derived from the secretions of Meibomian,Zeiss and Moll glands covers the entire free surface of tear fluid. Marginal tear strip- on the lid margins forms a strip which extends to the posterior margin of the opening of meibomian glands and limit the anterior ends of the tear fluid reservoirs. Physical integrity of lipid layer –Thickness 0.1-0.2mm and depends on palpebral fissure width ,it increases when the lids are partially closed.

6. Chemically, this layer consist of lipids – low polarity,made of wax and cholesterol esters . These lipids are fluid at body temperature Lipid layer formed by polar and neutral lipids . polar lipids face the aqueous component , bound to lipocalins within the aqueous layer Non polar lipid face the air Control of lipid secretion- Neuroendocrinal Androgen sex hormone – to regulate lipid synthesis and secretion Neurotransmitters from the nerves surrounding the acini can alter lipid synthesis or alveolar cell rupture

7. FUNCTION OF LIPID LAYER Oily layer- prevents the overflow of tears and retards their evaporation. It prevents the migration of skin lipids onto ocular surface. It provide a clear ocular medium for smooth surface for refraction of light. Act as a barrier for preventing contamination of tear film. It act as a surfactant layer which makes an effective bridge between non polar lipid phase and aqueous- mucinous phase. It acts as a lubricant to facilitate smooth movement of eyelids during blinking. lid movement during blinking is important in releasing lipid from gland.

8. AQUEOUS LAYER Middle layer of tear film It secreted by the lacrimal gland and the accessory glands of Krause and Wolf rings Main bulk of thickness of tear film is constituted by this layer- 60% of tear film Thickness –aqueous layer of precorneal tear film is uniform over the cornea - 7 micrometer composition -Aqueous layer of low viscosity, inorganic salts , glucose,urea,enzymes,proteins and glycoproteins,secretory Ig A, tear specific prealbumin. Buffering capacity of tear film is due to HCO3 ions and protein Surface tension- 40 – 42 dyn /cm

9. FUNCTIONS provide oxygen to corneal epithelium. washes away debris and irritants. contain antibacterial substance lysozyme and betalysin .

10. MUCUS LAYER Inner most layer Deepest stratum of the precorneal tear film Secreted by conjunctival goblet cells, crypts of Henle and the gland of Manz 0.02um thick Clear corneal epithelium is relatively hydrophobic surface.It contain glycocalyx helps to hold mucin to the corneal surface. Glycocalyx migrate out from the surface of microvilli to form a hydrophilic network that holds mucin on the ocular surface.

11. FUNCTIONS Mucin lubricates the ocular and palpebral surface ,minimal energy is lost as the friction during blinking and eye movements. It also provides a slippery coating over the foreign bodies, protecting the cornea and conjunctiva against abrasive effect of such particle on blinking.

12. CHEMICAL COMPOSITION Water Major component, 98.2% With salts dissolved Na+, K+, Cl-, HCO3-, Ca2+ Proteins Albumin Tear specific protein (prealbumin) Lysozyme Glycolytic enzymes, lactate dehydrogenase,Betalysin : antibacterial agent Mucopolysaccharides Glycoproteins Amino acids Lipids Metabolites: glucose, lactate, pyruvate, urea.

13. 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.

14. TEAR FILM DYNAMICS The primary role of tear film is to establish, refractive surface of high quality for the cornea and to ensure the wellbeing of cornea and the conjunctival epithelium. secretion of tears formation of tear film retention and redistribution of tear film displacement phenomenon evaporation from tear film drying and break up of tear film dynamic events during blinking elimination of tears

15. SECRETION OF TEARS Tears are continuously secreted through out the day by accessory and lacrimal gland basal tear secretion by accessory gland reflex secretion by main lacrimal gland Basal tear secretion - cornea is continuously kept moist & nourished by basal tears. Reflex secretion – occurs in response to sensations from the cornea and conjunctiva, produced by break up of tear film Hyper lacrimation -irritative sensation of cornea and conjunctiva. Neural pathways from the sphenopalatine ganglion (SPG) and superior cervical ganglion (SCG) control meibomian glands, lacrimal gland, and goblet cells The trigeminal nerve bears the sensory pathway (afferent) of the tear reflexes The motor pathway is autonomic (involuntary), &, in general, uses the pathway of the facial nerve in the parasympathetic division via pterygopalatine/ spheno palatine ganglion , as efferent pathway

16. normal rate of tear production 1.2ul/min Tear volume- 7ul , turn over rate- 5 to 7min Most(85%) of full term newborn secrete tear within 24 hrs. 95% secrete within first week of life Abnormal tearing occurs only after 4month of age. An absence of excess tearing in very young infants may be connected with the low innervation of cornea. Main lacrimal gland secrete water and electrolytes only during reflex tearing.

17. FORMATION OF PREOCULAR TEAR FILM Corneal epithelium is a relatively hydrophobic surface . conjunctival mucus which spreads on to the cornea by the action of lids and converts its surface to a hydrophilic one Sequence of events in the formation of a continuous precorneal tear film Lid surfacing cornea with a thin layer of mucus On this new surface ,the aqueous component spreads .The superficial lipid layer spread over the aqueous film contributing to its stability and regarding evaporation between blinks

18. RETENTION AND DISTRIBUTION OF TEAR FILM The tear film is retained at a uniform thickness over the corneal surface against a gravitational force. The fluid in the precorneal tear film is stagnant, unless it is mixed by blinking and eye movement with the tear fluid in the marginal strips. Redistribution occurs in the form of bringing of new tear fluid by way of marginal strips where there is constant flow of tears.

19. DISPLACEMENT PHENOMENON The surface of the cornea is covered by a film possessing a certain stability, compressibility and elasticity and that it is more or less unaffected by gravity The displacement phenomenon is possible due to thin monomolecular layer on the surface of cornea that is displaced upward over the eyeball ,the particles are seen move up the cornea .

20. EVAPORATION FROM THE TEAR FILM Wax and cholesterol esters retard the evaporation of water . Evaporation from the tear film is estimated to be about 10% of the production rate Production rate - 1.2ul/min Evaporation rate- 0.12ul/min There is little effect of air motion on the evaporation rate, bcz most of the resistance to evaporation rate is the oily layer on the tear film.

21. STABILITY , DRYING AND 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.

22. MECHANISM OF TEAR FILM BREAK UP HOLLY AND 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

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

24. ELIMINATION OF TEARS Lacrimal fluid flows over the preocular surface and reaches marginal tear strip running along the ciliary margin of each eyelid and collets as lacus lacrimalis in the inner canthus.Then drained by lacrimal passage in to nasal cavity.(lacrimal pump mechanism) 25 % of tears lost by evaporation. 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:-

25. On eyelid closing movement Contraction of pretarsal fibres of orbicularis- compress ampulla and shorten canaliculi-tear moves to lacrimal sac. Contraction of preseptal fibres of orbicularis –pulls the lacrimal fascia and lateral wall of lacrimal sac laterally-opening of lacrimal sac-negative pressure –draws tears from canaliculi into sac Along with increased tension of lacrimal fascia – inferior portion closes more tightly-there by prevent aspiration of air from the nose. When eyelids open Relaxation of pretarsal fibres -canaliculi expand and reopen-draws tears from lacrimal lake to pucta . Relaxation of portion of preseptal fibres- lacrimal sac to collapse –expels fluid to open NLD-inferior meatus

26. 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

27. CHIEF COMPLAINTS 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

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

29. DRY EYE State of abnormal tear film Classification Aqueous deficiency –keratoconjunctivitis sicca ,Riley-Day syndrome, congenital alacrimia, paralytic hyposecretion, idiopathic arid in association with systemic disease Soluble surfactant (mucin) deficiency – hypo- vitaminosis A,Stevens -Johnson syndrome, drug induced disease, chemical burns Lipid abnormality – chronic blepharitis Impaired lid function – exposure keratitis, symblepharon, pterygium and other major epithelial elevations Epitheliopathy- anesthetic cornea, epithelial irregularity of any cause

30. SCHIRMER TEST Test for tear quantity 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 1/3 rd and medial 2/3 rd of the lower conjunctival sac. Performed in dim light with fans and ACs switched off Normal secretion- 0.50 to 0.67ml of tear per day More than 15 ml of wetting in 5 minutes is normal

31. Without Anesthesia Measures Reflex Tear Secretion (dry eye = < 6mm wetting) With Anesthesia Measures Basal Tear Secretion (dry eye = < 3mm wetting)

32. TEAR FILM BREAKUP TIME Difference Between the last blink and the first randomly appearing dry spots Assessed with fluorescein and cobalt blue filter in broad beam
Average of three reading is taken
Suspect Dry Eye when TBUT<10secs

33. VITAL STAINING Fluorescein staining- break in the epithelium barrier permits rapid fluorescein penetration and staining of areas denuded of epithelium Due to slight acidic reaction of normal tear film, staining appears yellow or orange More alkaline aqueous humour colours fluorescein brilliant green in denuded areas Fluorescent staining of eye is transient and disappear within 30 min Fluorescein staining is considered a sensitive test for detection of KCS and positive staining in 96% case of Sjogren s syndrome .

34. Rose Bengal staining Dark red powder soluble in water. 1% aqueous solution irritating in tear deficient eye. Selectively Stain the mucus, debris and devitalized cells of cornea and conjunctival epithelium visible as red color Useful in diagnosing KCS The palpebral aperture divided into three area- nasal, temporal, cornea scoring 0 – absent 1- just present 2 – moderate staining 3- gross staining Score of 3,5 out of 9 considered abnormal

35. Lissamine green staining –has been reported to detect dead or degenerated cells, and it produce less irritation after topical administration than rose Bengal Staining by this dye may indicate existence of membrane abnormalities of the ocular surface epithelial cells

36. Marginal tear strip/ tear meniscus characteristics Continuous, full and slightly concave meniscus formed by tears between the eyelid margin and the inferior bulbar conjunctiva where the lid touches the globe. Height of tear strip - 0.5 mm on slit lamp examination is normal Discontinuous or absent tear film meniscus is important sign of dry eyes and tear deficiency

37. DISEASES RELATED TO DYSFUNCTION IN TEAR FILM Watering of eye- Overflow of tear from conjunctival sac due to Hyper secretion of tear film may result from obstruction to the outflow of normally secreted tears(epiphora) Hyperlacrimation primary hyperlarimation – rare condition, direct stimulation of lacrimal gland occurs in early stage of lacrimal gland tumours and cysts and due to the effect of strong parasympathomimetic drugs. Reflex hyperlacrimation - stimulation of sensory branch of 5 th nerve due to irritation of cornea or conjunctiva.

38. Occur in conditions like Affection of lids- stye,Hordeolum internum , acute meibomitis , trichiasis, concretions and entropion Affection of the conjunctiva- conjunctivitis Affection of cornea- corneal abrasion ,corneal ulcer, non ulcerative keratitis Affection of sclera-episcleritis and scleritis Affection of uveal tissue- iritis, cyclitis, iridocyclitis Acute glaucomas Endophthalmitis and pan ophthalmitis Orbital cellulitis

39. EPIPHORA Inadequate drainage of tear due to physiological or anatomical cause. Physiological cause – lacrimal pump failure – due to lower lid laxity or weakness of orbicularis muscle Mechanical obstruction -obstruction in passage lie in the level of punctum, canaliculi, lacrimal sac or nasolacrimal duct. punctal cause- Eversion of lower punctum (in old age) also occurs following chronic conjunctivitis, chronic blepharitis ,ectropion Punctal obstruction- congenital absent of puncta or cicatricial closure following injuries , burns or infection. Small foreign body ,concretions and cilia may also block the punctum Prolonged use of idoxuridine and pilocarpine cause punctal stenosis

40. Cause in canaliculi- obstruction may be congenital/acquired due to foreign body ,trauma, stricture and canaliculitis . cause in the lacrimal sac – congenital mucous membrane fold, traumatic stricture, dacryocystitis, TB, syphilis, dacryolithiasis . tumours and atony of sac. Cause in NLD – congenital lesion include non canaliculisation , partial canalization or imperforated membranous valve. acquired cause of obstruction- traumatic/inflammatory strictures,tumour and disease of surrounding bones.

41. CLINICAL EVALUATION OF CAUSING WATERING EYE Examination with diffuse illumination using magnification `rule out any cause of reflex hypersecretion and punctal cause of epiphora, swelling in the sac area. Regurgitation test steady pressure with index finger is applied over the lacrimal sac area above the medial palpebral ligament. Reflex of mucopurulent discharge indicates- chronic dacryocystitis with obstruction at lower end of the sac or NLD.

42. FLUORESCEIN DYE DISAPPEARANCE TEST 1 drop of fluorescein dye is instilled in to the conjunctival sac Observation is made after 5 min The color intensity is graded on a scale of 0 to +4 after 5 min 0 to + 1 - seen in conjunctival sac Retention of +2 to +4 dye in conjunctival sac – inadequate drainage may due to atonia of sac or mechanical obstruction.

43. LACRIMAL SYRINGING TEST Topical anesthesia with 2% or 4% xylocaine is applied. Normal saline is pushed into lacrimal sac of lower punctum with the help of syringe and lacrimal cannula. A free passage of saline through lacrimal passage into the nose rules out the mechanical obstruction . In partial obstruction saline passes with considerable pressure on the syringe. In obstruction- no fluid passes into nose and may reflux through same punctum(indicating obstruction in same canaliculi) reflux through upper punctum( obstruction in lacrimal sac or NLD or common canaliculus)

44. When the saline reflux through same punctum ,procedure repeated through upper punctum Free passage of saline into the nose confirms the block in the lower canaliculus Regurgitation back through the same punctum indicated block in both canaliculi PROBING Using Bowmans lacrimal probe Hard stop – NLD blockage Soft stop – lacrimal sac /canaliculi block

45. JONES DYE TEST Performed when partial obstruction is suspected johns primary test – differentiate between partial obstruction of sac from primary hypersecretion. johns secondary test- differentiates between partial NLD obstruction from functional block.

46. Test 1 1% fluorescein dye is instilled in the conjunctival sac and a cotton bud dipped in 2% xylocaine with epinephrine is placed in the inferior meatus at the opening of nasolacrimal duct After 5 min the cotton bud is removed and inspected Dye stained cotton bud indicate adequate drainage through the lacrimal passage Cause of watering is hypersecretion. Unstained cotton buds –partial obstruction or failure of lacrimal pump mechanism

47. Test 2 4% xylocaine instilled in the conjunctival sac residual fluorescein washed out by irrigation(NS) BUD STAIN positive –fluorescein stained saline recovered from the nose showing functional patency of upper lac passage, ie , partial obstruction of NLD BUD STAIN negati ve - unstained saline recovered from the nose shows partial obstruction in the upper lac passage or defective lacrimal pump mechanism

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