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    Add as FriendThe tear film

    by: Vimal Krishna

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    2 : It is that fluid produced by the lacrimal gland that normally moistens the surface of the cornea.
    3 : Structure Functions Physical properties Chemical composition Dynamics
    5 : Lipid layer Outermost Secretions of meibomian, Zeiss moll glands 0.1 microns Chemically, low polar lipids
    6 : Aqueous layer Middle layer Lacrimal gland – main accessory 10 microns Contents-glucose,salts,enzyme,proteins,glycoproteins
    7 : Mucus layer Deepest Secreted by goblet cells, crypts of henle and glands of Manz 30 microns Contains mucin
    8 :
    9 : FUNCTIONS Lipid layer Prevents overflow of tears Avoids skin excoriation Aqueous layer Provides atmospheric oxygen Washes away debris Contains antibacterial enzymes
    10 : Mucus layer Lubricates ocular palpebral surfaces Protect cornea conjunctiva against abrasion Keeps surface of cornea conjunctiva moist Perfect smooth optical surface on cornea
    11 : PHYSICAL PROPERTIES Thickness – 40 microns Volume- 7 microliter Rate of secretion- 1.2per min (10 cu. ml) Turn over rate- 18% per min Refractive index-1.357 ph- 7.4 Osmotic pressure-0.90 to 0.95% NS
    12 : CHEMICAL COMPOSITION Water 98.2% Dissolved solids 1.8% Proteins-Gp.A(albumin, Ig G) Gp.B (Ig A, lysozyme, lactoferrin) Lipids Metabolites (Glu,lactate) Electrolytes (Na, K,Cl,HCO3)
    13 : Bio-chemical components Solutes Protiens -Na120-160 -Cl 118-135 -HCO3 20-25 -K 20-42 -Mg 0.7-0.9 -Ca 0.5-1.1 -Glucose 0.5-1.1 -Lysozyme -Lactoferrin -lipocalin -IgA, IgG -Albumin Enzymes Glycolytic enz Amylase Plasminogen activator Latent proteanases Latent Collegenase
    14 : DYNAMICS Secretion Formation Distribution Displacement Evaporation Drying Break-up Drainage
    15 : Secretion Basal Reflex-neural pathway Rate Turn over rate Infants- 80% in 1 day, 95% in 1 week
    16 : Formation Wettability Contact angle Corneal epithelium hydrophobic mucus layer hydropihilic Sequence
    17 : Retention against gravitational force layers resposible Redistribution
    18 : Displacement What is it ?? Stable, Compressible elastic Why ??? Evaporation Lipid film Under environmental conditions Rate
    19 : Drying Break-up Short- lived stability Tear film break up
    20 :
    21 : Drainage
    22 : TEAR FILM ABNORMALITIES Holly and Lemp classification Aqueous deficiency Mucin deficiency Lipid deficiency Impaired lid function Epitheliopathy
    24 : Early Signs of Tear Dysfunction Precorneal Tear Film Increased amount of mucin strands and debris Lipid contaminated mucin accumulates Marginal Tear Strip MTS is reduced in height (0.3mm) Attains concave shape In CDE it can be absent
    25 : Tear Film Break-up Time(TBUT) It is the 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
    26 : 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
    27 : Schirmer test Without Anesthesia Measures Reflex Tear Secretion (dry eye = < 6mm wetting) With Anesthesia Measures Basal Tear Secretion (dry eye =< 3mm wetting)
    28 : Rose Bengal staining Rose Bengal solution 1% placed into the conjunctival sac. After a wait of 2 mins, degree of rose bengal staining on bulbar conjunctiva and cornea is quantitated by microscopic exam. Stains devitalized cells. J Am Optom Assoc 1991, 62:187-199
    29 : Rose Bengal staining inEarly, Moderate and Late KCS EARLY MODERATE LATE
    30 : Phenol Red Thread test A sterile cotton thread is draped over the non-anesthetized lid margin It changes color upon aqueous contact and the length of colored thread is measured This test is used to evaluate the tear secretion quantity without inducing significant reflex tearing The normative value is 13±4 mm of wetting over a fifteen second period
    31 : Impression cytology Removal of superficial layers of conjunctival epithelium Application of circular discs of cellulose acetate filter paper for a certain period of time. Obtained specimen observed under microscope for signs and symptoms of squamous metaplasia or presence of inflammatory cells. In CDE conditions the cells appear fewer, irregular in size shape and takes up stain less uniformly
    32 : Impression Cytology Mapping Healthy Mild Moderate Severe
    33 : Lysozyme Assay Hyposecretion of tears may be due to the reduction in the concentration of lysozyme Wetted filter strip is placed into an agar plate containing specific bacteria The plate is incubated for 24 hrs and the zone of lysis is measured The zone will be reduced if the concn of lysozyme in tears is decreased
    34 : Tear Globulin Assay Decreased tear formation may be due to dec IgA Performed on spl tripartigan immunodiffusion plates containing specific agar gel in wells Twenty microliters of tear samples is put into these wells and the plates are incubated for 48 hrs The diffusion of rings around wells are measured to nearest 0.1mm with partigen ruler The ring will be reduced if the concn of IgA in tears is decreased
    35 : Tearscope Assess patient's tear film quantity, quality and stability Non invasive method Tear quantity is assessed with one full-length view along the tear meniscus Tear quality is assessed by matching the patient's tear film with the equivalent pattern in the Guillon-Keeler Tear Film Grading System, and by viewing the tear film flow dynamics. Tear stability is assessed by directly viewing the tear film on the contact lens or corneal surface and measuring the non invasive break up time
    36 : Cold cathode illumination Timer Star/stop button On/off High/low Lap time reset button Tearscope -the instrument itself…

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