DYNAMICS OF TEAR FILM

Presenter : Dr. Shrey MaheshwariModerator : Dr. K. Kanthamani

TEAR FILM DYNAMICS

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

DYNAMICS OF EVENT DURING BLINKING

ELIMINATION OF TEARS

SECRETION OF TEARS

RATE OF PRODUCTION : 1.2 micro lt.

VOLUME : 7 micro lt.

TURNOVER RATE : 5 TO 7 min.

82% OF FULL TERM INFANTS SECETE TEARS IN 24HRS

95% FULL TERM INFANTS HAVE NORMAL RATE IN 1ST WEEK

“but abnormal crying is not before 4th month”

BASAL SECRETIONS

SECRETED BY ACCESSORY LACRIMAL GLAND

REFLEX SECRETIONS

SECRETED BY MAIN LACRIMAL GLANDS

IN RESPONSE TO SENSATION FROM CORNEA AND CONJUNCTIVA

“Hyperlacrimation occurs due to irritation of cornea and conjunctiva”

PRE OCULAR TEAR FILM

FORMATION OF TEAR FILM

DEPENDS ON THE WETABILITY OF THE SURFACE

CORNEA’S WETABILITY

CORNEA IS HYDROPHOBIC CONJUNCTIVAL MUCUS SPREAD ON CORNEA BY AXN OF LIDS

CONVERTS IT’S SURFACE TO HYDROPHILLIC

RETENTION & RIDISTRIBUTION

SMALL MOLECULES AND MEMBRANE BOUND MUCINS k/a GLYCOCALYX

SERVES AS ANCHOR TO TEAR FILM

DISPLACEMENT

CORNEA IS COVERED BY A FILM POSSESING

STABILITY COMPRESSIBILTY ELASTICITY

THIS THIN MONOMOLECULAR LAYER IS RESPONSIBLE FOR DISPLACEMENT

EVAPORATION OF TEAR FILM

10% OF PRODUCTION RATE (i.e. 0.12 micro lt.)

AIR MOTION HAS LEAST EFFECT d/t OILY LAYER

WAX ESTERS AND CHOLESTEROL ESTERS RETARDS EVAPORATION

STABILITY DRYING AND RUPTURE OF TEAR FILM

TEARS HAS TO COVER ENTIRE PRE OCULAR SURFACE TO FUNCTION PROPERLY

RE-ESTABLISHED COMPLETELY AFTER A BLINK

TAKES 15-40 SECS FOR TEAR FILM TO RUPTURE (when blinking is prevented)

TEAR FILM BREAKUP

1ST DESCRIBED BY HOLLY IN 1973

SOME LIPID MOLECULES ARE ATTRACTED BY MUCIN LAYER

MUCIN BECOMES HYDROPHOBIC AND TEAR FILM RUPTURES

TEAR FILM THINS OUT UNIFORMLY BY EVAPORATION

DYNAMIC EVENTS DURING BLINKING

UPPER LID MOVES DOWNWARDSSUPERFICIAL LIPID LAYER IS COMPRESSED BETWEEN LID EDGES

MUCUS LAYER IS CONTAMINATEDROLLED UP IN THREAD LIKE STATE AND DRAGGED INTO LOWER FORNIX

ON EYE OPENING LIPID LAYER 1ST SPREADAS MONOLAYER

THEN EXCESS LIPID FOLLOWS AND MULTI LIPID LAYER IS FORMED

ELIMINATION OF TEARS

LACUS LACRIMALIS TO

NASOLACRIMAL DUCT

LACRIMAL FLUID OVER PREOCULAR SURFCACE

MARGINAL TEAR STRIP

LACUS LACRIMALIS INNER CANTHUS

LACRIMAL PASSAGENASOLACRIMAL DUCT

NASOLACRIMAL DUCT TO

NASAL CAVITY

AIR CURRENTS INDUCE NEGATIVE PRESSURE IN NLD

DRAWS THE FLUID DOWN INTO THE LUMEN OF NOSE

OPENS THE HASNER’S VALVE

TEAR FILM ABNORMALITIES

LIPID ABNORMALITIES – CHRONIC BLEPHARITIS

AQUEOUS DEFICIENCY – KCS , RILEY DAY , IDIOPATHIC

MUCIN DEFICIENCY – HYPOVITAMINOSIS A , CICATRICIAL PHEMPHIGOID , SJS , CHEMICAL BURNS

IMPAIRED LID FUNCTION – EXPOSURE KERATITIS , PTERYGIUM

EPITHELIOPATHY – ANAESTHETIC CORNEA , EPITHELIAL IRREGULARITY

EVALUATION OF TEAR FILM STABILITY

STAIN WITH FLUROSCEIN DYE

ASK TO BLINK FREQUENTLY TILL IT SPREADS

THEN ASK TO STOP BLINKING

NOTE THE TIME OF APPEARANCE OF 1ST DRY SPOT

OCULAR PROTECTION INDEX

SCHIRMER TEST

DIAGNOSTICS EYE STAINING

ROSE BENGAL STAINIG

STAINS BOTH DEVITALIZED AND HEALTHY TISSUE

CAN EVALUATEPROTECTIVE STATUS OF PREOCULAR TEAR FILM

ROSE BENGAL STAINING

ROSE BENGAL STAINING

pH ( HYDROGEN ION CONCENTRATION)

NORMAL pH NECESSARY FOR TEAR BUFFERING ACTION

NORMAL VALUE 7.0

DETERMINED BY

TEAR FILM OSMOLARITY

NORMAL VALUE IS 305mOsm/l

As tear SECRETION DECREASES OSMOLARITY DECREASES

TEAR EVAPORATION RATE

SMALL GOGGLE TYPE HUMIDITY SENSOR USED

NOT VERY RELIABLE

TEAR MENISCOMETRY

TECHNIQUE TO QUANTIFY HEIGHT AND VOLUME OF LOWER LID MENISCUS

NORMAL VALUE : 1mm

FLUOROPHOTOMETRY

ALSO k/a “FLUORESCEIN DILUTION TEST”

USED TO ESTIMATE :

NORMAL VALUE : 1.2 +/- 0.5 MICRO lt. / minuteDRY EYE VALUE : 0.2 +/- 0.2 MICRO lt. / minute