Download - dynamics of tear film
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