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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