aqueous humor dynamics
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Aqueous humor dynamicsTRANSCRIPT
AQUEOUS HUMOR DYNAMICS
BY DR. RAHULMODERATOR:DR.
DHAMANKAR
ANATOMYUVEAL TRACT CONSIST OF IRISCILIARY BODYCHOROID
IRISCILIARY ZONEPUPILLARY ZONE
MICROSCOPICANTERIOR LIMITING LAYER
STROMAANTERIOR PIGMENTED EPITHELIAL LAYERPOSTERIOR PIGMENTED EPITHELIAL LAYER
CILIARY BODY
FORWARD CONTINUATION OF CHOROID
ANTERIOR PART HAVING FINGER LIKE CILIARY PROCESSES CALLED PARS PLICATA
POSTERIOR SMOOTH PART PARS PLANA
CILIARY PROCESSESTHESE ARE FINGER LIKE PROJECTIONS70-80 IN NUMBER2 MM LONG AND 0.5 MM IN DWHITE IN COLOUREACH PROCESS LINED BY 2 LAYERS OF EPITHELIAL
CELLS IT CONTAINS BLOOD VESSELS AND LOOSE
CONNECTIVE TISSUSESITE OF AQUEOUS PRODUCTION
ANATOMY
Ciliary epitheliumNonpigmented - inner layer, adjacent to aqueous in
the posterior chamber,consisting of columnar cells (cuboidal in pars plana). Intercellular tight junctions (zonulae occludens)
form major element of blood-aqueous barrier.
Tips or crests of nonpigmented ciliary epithelia are site of active secretion,
hence numerous mitochondria, roughendoplasmic reticulum, pinocytic
Angle of anterior chamberClinically angle structures can be visualized
by goniosciopic examinationStarting from posterior to anterior
1)Ciliary band
2)Scleral spur3)Trabecular meshwork4)Schwalbes line
. Shaffer’s system of grading the angle widthGrade Angle width Configuration Chances of closure
Structures visible on gonioscopy IV 35-45o Wide open Nil SL, TM, SS, CBB III 20-35o Open angle Nil SL, TM, SS II 20o Moderately narrow Possible SL, TM I 10o Very narrow High SL only0 0o Closed Closed None of the angle structures
visibleSL = Schwalbe’s line, TM = Trabecular meshwork, SS =
Scleral spur, CBB = Ciliary body band
Shaffer’s system of grading the angle width
Shaffer’s system of grading the angle width
AQUEOUS OUTFLOW SYSTEMIT INCLUDES TRABECULAR MESHWORKSCHLEMMS CANALCOLLECTOR CHANNLESAQUEOUS VEINS EPISCLERAL VEINS
TRABECULAR MESHWORK IT IS SIEVE LIKE STRUCTURE THROUGH WHICH
AQUEOUS HUMOUR LEAVES EYECONSIST OF 3 PORTIONS1)UVEAL MESHWORK-Innermost part of TM, extends from iris root and ciliary body
to schwalbes line-the arrangement of uveal trabecular bands create opening of
25 mu to 75 mu-least resistance to flow
2)CORNEOSCLERAL MESHWORK-larger middle portion ,extends from scleral
spur to lateral wall of scleral sulcus-opening 5 mu to 50 muModerate resistance to flow
3)JUXTACANLICULAR , ENDOTHELIAL MESHWORK
It form outer most part Lined on either side by endothelium IT MAINLY OFFERS NORMAL RESISTANCE
TO AQUEOUS OUTFLOW
AQUEOUS DRAINAGE
SCHLEMMS CANALIT IS ENDOTHELIAL LINED OVAL CHANNEL
PRESENT CIRCUMFERENTIALLY IN SCLERAL SULCUS
THE ENDOTHELIAL CELLS OF ITS INNER WALL ARE IRREGULAR, SPINDLE SHAPED AND CONTAIN GAINT VACUOLES
THE OUTER WALL OF THE CANAL IS LINED BY SMOOTH FLAT CELLS
CONTAINS OPENING OF COLLECTOR CHANNELS
COLLECTOR CHANNELS
ALSO CALLED INTRASCLERAL AQUEOUS VESSELS
ABOUT 25-35 IN NUMBERLEAVES SCHLEMMS CANAL AT OBLIQUE
ANGLES TO TERMINATE INTO EPISCLERAL VEINS
NO VALVES ARE PRESENT IN COLLECTOR CHANNELS
THESE INTRASCLERAL AQUEOUS VESSELS CAN BE DIVIDED INTO TWO SYSTEM
DIRECT SYSTEM ON SLIT LAMP , THESE APPEAR AS CLEAR VESSELS
WITH AQUEOUS CALLED AS AQUEOUS VEINS BY ASCHER
AS THESE VESSELS TERMINATE INTO EPISCLERAL AND CONJUNCTIVAL VEINS IN LAMINATED JUNCTIONS ,CALLED AS LAMINATED VEIN OF GOLDMANN
EPISCLERAL VEINS
MOST OF AQUEOUS VESSELS DRAIN INTO EPISCLERAL VEINS
Aqueous humor
is a relatively cell free,protein free fluid formed by non pigmented ciliary
epitheliumSlightly hypertonicAcidic , PH IS 7.2 Marked excess of ascorbateMarked deficit of proteinsSlight excess of chloride and lactic acid
PHYSICOCHEMICAL PROPERTIES
VOLUME0.31 ML (0.25 ml in AC 0.06 ml in PC)REFRACTIVE INDEX 1.336 SLIGHTLY LOWER THAN CORNEA
SLIGHT DIVERGENCE OF LIGHT AS IT PASS CORNEA -AQUEOUS INTERFACE
DENSITYSLIGHTLY GREATER THAN WATER
OSMOTICS PRESSURE AQUEOUS IS SLIGHTLY HYPEROSMOTIC TO PLASMA BY
3 TO 5 MOSM/L
PH ACDIC IN AC 7.2
RATE OF FORMATION2.3 Ul/min
Formation of aqueous humourCiliary processes are site of aqueous
productionThe various constituents of aqueous humour
have to pass 3 tissue layers of cililary processes
1)capillary wall2)stroma3)two layers of epithelium
Formation processes involved1)diffusion 10 %2)Ultarafiltration 20%3)secretion 70%
DIFFUSIONDiffusion - lipid-soluble substances are transported through the lipid portions of the cell membraneproportional to a concentration gradient across the
membrane
ULTRAFILTRATIONUltrafiltration - water and water-soluble
substances,limited by size and charge, flow through
theoretical micropores in the cell membrane in response to
an osmotic gradient or hydrostatic pressure;
influenced byintraocular pressure, blood pressure in the ciliary capillaries, and plasma oncotic pressure
Diffusion and ultrafiltration are both passive mechanisms, with lipid- and water-soluble
substances from the capillary core traversing the stroma
and passing between pigmented epithelial cells and limited by the tight junctions of the non-
pigmented epithelial cellsc. Active transport (secretion) - water-soluble
substances
SECRETIONActive transport (secretion) - water-soluble substances of larger size or greater charge are actively transported across the cell membrane, requiring the expenditure of energy; Na-K ATPase and glycolytic enzymes are present in nonpigmented epithelial cells.Active transport is decreased by hypoxia, hypothermia, and any inhibitor of active metabolism. Active transport accounts for the majority of aqueousproduction.
MEDIATED BY GLOBULAR PROTEINS IN MEMBRANE
STEPS OF AQUEOUS FORMATION
FORMATION OF STROMAL POOL
PASSIVE TRANSPORT ACROSS NON PIGMENTED CILIARY EPITHELIUM
Active transport across non pigmented epithelium result in osmotic and electical gradient
Sodium is primarily responsible for movement of water into posterior chamber and its secretion is major factor in formation of aqueous
ACTIVE TRANSPORT OF STROMAL FILTRATES
The tight junction between non pigmented epithelial cells creat part of blood aqueous barrier
Substances actively transported are1)NA2)chloride3)potassium3)ascorbic acid4)amino acid n bicarbonate
Control of aqueous formationADRENERGIC INNERVATIONCILIARY EPITHELIUM DOES NOT SHOW NERVE
SUPPLY , BUT VESSELS HAVE NERVE SUPPLYMAJORITY OF RECEPTORS IN CILIARY BODY ARE α2 &
β2 RECEPTORSSTIMULATION OF α 2 RECEPTOR LOWER AQUEOUS
HUMOUR PRODUCTION THROUGH INHIBITION OF ADENYLATE CYCLASE
STIMULATION OF β 2 RECEPTOR LEADS TO INCREASE IN PRODUCTION BY STIMULATION OF ADENYLATE CYCLASE
α 2 AGONIST LIKE CLONIDINE AND β2 ANTAGONIST LIKE TIMOLOL DECREASES AQUEOUS PRODUCTION
Functions It serves the circulatory function for the
avascular tissues of the eye.
Brings essential nutrients such as oxygen glucose and amino acids .
Removes harmful substances such as lactic acid and CO2
Maintains the IOP and structural integrity of the eye.
Contains high concentrate of ascorbate which act to scavenge free radicles and protects against effects of radiation.
Facilitates cellular and humoral immunity in case inflamation and infections
Conditions decreasing SECRETION
1.General conditions
Age
Diurnal
Exercise
2. Systemic conditions
Decrease BPReduction in internal carotid arterial blood
flowDiencephalic stimulationAcidosisGeneral anaesthesia
3.Local conditionsIncreased IOPUveitisRetinal detachment Retrobulbar anaesthesia Choroidal detachment
4.Pharmacological agents1)BETA BLOCKERS DECREASE IN AQUEOUS PRODUCTION BY BETA 2
RECEPTOR STIMULATION IN CILIARY PROCESSESTIMOLOL ,BETAXOLOL ,LEVOBUNOLOLCARTEOLOL
2)PILOCARPINEPILOCARPINE CONTRACTS LONGITUDINAL MUSCLE OF
CILIARY BODY AND OPENS SPACE IN T.M , SO MECHANICALLY INCREASEING AQUEOUS OUTFLOW
3)CARBONIC ANHYDRASE INHIBITORBY DECREASING AQUEOUS SECRETIONDORZOLAMIDE
4) PROSTAGLANDINSACT BY INCREASING UVEO SCLERAL OUTFLOW OF
AQUEOUS
ADRENERGIC DRUGS-SELECTIVE ALPHA 2 ADRENERGIC AGONIST BY
DECREASING AQUEOUS PRODUCTION-APRACLONIDINE-BRIMONIDINE
CONDITIONS DECREASING SECRETION
5.Surgical conditionsCyclodialysisCyclocryothermyCyclodiathermyCyclophoto coaguation.
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