AQUEOUS HUMOUR :- Definition , Outflow system, Function

*The aqueous humour is a transparent , watery fluid similar to plasma.

*it containing low protein concentration.

*it is secreted from the ciliary epithelium.

*It is involved with all portion of the eye.

*the principal ocular structures concerned with it are:

1. ciliary body
2. posterior chamber
3. anterior chamber
4. angle of the anterior chamber, and
5. aqueous outflow system.

CILIARY BODY:-

*it is the site of the aqueous production.

POSTERIOR CHAMBER:-

*it contain about 0.06 ml of aqueous humour .

*the fresh formed aqueous humour from the ciliary process collected in this space.

Compartments of posterior chamber.

*it divided in to three compartments-

1- Prezonular space. it lies between the posterior surface of the iris and anterior surface of the zonular fibres.

2- Zonular space. it is bounded centrally by equator of the lens, peripherally by the ciliary processes, anteriorly by the posterior surface of anterior zonular fibres and posteriorly by anterior surface of posterior zonular fibres.

3 - Retrozonular space. it lies between the posterior surface of zonules and the peripheral part of anterior vitreous face.

ANTERIOR CHAMBER :-

*it is about 3 mm deep in the center of adults.

*it is comparatively shallow in very young children and old people.

*it contains about 0.25 ml of the aqueous humour.

*through pupil it communicates with posterior chamber.

ANGLE OF THE ANTERIOR CHAMBER:-

*it is the angle recess formed in between posterior surface of cornea and anterior surface of iris bounded from anterior to posteriorly by-

1. Schwalbe's line
2. Trabecular meshwork
3. Sclera spur
4. ciliary band

1- Schwalbe's line -

• it is formed by the prominent end of the descemet's membrane of the cornea
• it is a fine ridge seen just in front of the trabecular meshwork.
• width 50-150 µm.

2- Trabecular meshwork-

• it is seen as a band just anterior to the sclera spur.
• it has no pigment at birth .
• pigmentation acquired with age.

3- Scleral spur-

• it is the posterior portion of the scleral sulcus.
• it is wedge shaped circular ridge.
• it lies posterior to trabecular meshwork

4- Ciliary  band-

• it is the most posterior part in the angel recess.
• width depend on the level of iris insertion
• wide in myopes and narrow in hypermetropes
• it appears as a grey/dark brown band.

AQUEOUS OUTFLOW SYSTEM:-

it includes the -

1. Trabecular meshwork
2. Schlemm's canal
3. Collector channels
4. Aqueous veins
5. Episcleral veins

1- Trabecular meshwork-

• it is a sieve like structure.
• aqueous leave the eye from here.
• it bridges the scleral sulcus and converts in into tube.

2- Schlemm's canal-

• it is an endothelial lined oval channel present.
• it is single channel but occasionally branches into a plexus-like system.

3- Collector channels-

• it is lined by vascular endothelium .
• they are relatively wide at their origin 60-90mm.
• no valves are present in the collector channels.
• also known as intrascleral aqueous vessels
• these intascleral aqueous vessels can be divided into two system-
• 1- Direct system
• 2- Indirect system

4- Episcleral veins -

• most of the aqueous vessels drain in to episcleral vein.

FUNCTIONS:-

1. Maintenance of intraocular pressure.
2. Metabolic rate
3. Optical function
4. Clearing function

CILIARY BODY :- Definition, microscopic structure

*The Ciliary body is the part of the Uvea, The layer of tissue that delivers oxygen and nutrients to the eye tissues.
*Ciliary body is the forward continuation of the choroid at ora serrata.
*The inner side of the triangle is divided into two parts -

*Pars plicata - the Anterior part having finger like process .
*Pars plana - the Posterior smooth part (about 5 mm wide temporally and 3 mm wide at nasally).

MICROSCOPIC STRUCTURE :-

It consists of following five layers -

*Supraciliary lamina.
*Stroma of the ciliary body.
*Layer of pigmented epithelium.
*Layer of non-pigmented epithelium.
*Internal limiting membrane.

1- Supraciliary Lamina -

*Outermost condensed part of the stroma .
*It consists of collagen fibres.
*It is a continuation of the suprachoroidal lamina ,posteriorly.
*Anteriorly it continues with anterior limiting membrane of the Iris.

2- Stroma of the ciliary body -

*It consists of connective tissue of collagen and fibroblasts.

3- Layer of pigmented epithelium -

*It is forward continuation of the RPE (Retina pigmented epithelium).
*Anteriorly it is become continuation with the Anterior pigmented epithelium of the Iris .

4- Layer if non-pigmented epithelium -

*It consists of cuboidal cells and low columnar cells.
*Forward continuation of the sensory retina which stop at the ora serrata .

5- Internal limiting membrane -

*It is the forward continuation of the internal limiting membrane of the Retina.


CILIARY PROCESSES :-

*Folds on the inner Ciliary epithelium are called ciliary processes.
*Ciliary processes are arranged in a circle, and form a sort of frill behind the Iris .
*It is composed of three basic components :
           *The network of capillaries.
           *Stroma of ciliary processes.
           *Two layers of epithelium.

 FUNCTION:-

1. It helps in production of aqueous humour.

LIMBUS:- Definition

The corneal Limbus is the border of the cornea and sclera.
It refers to a circumcorneal transitional zone of the conjunctivocorneal and corneoscleral junction.
It associated with two junction -

1- Conjunctivocorneal junction.
2- Corneoscleral junction.

*CONJUNCTIVOCORNEAL JUNCTION :-

°At this point, the bulbar conjunctiva is a tightly adherent to the underlying structures.
°The Substantia propria of the Conjunctiva stops here but it is epithelium continues with that of the cornea.
°The cells contains melanin and differ from those of the cornea in having no prickles between them.
°Limbal epithelium is similar to corneal epithelium but its basal cell are arranged in peculiar pattern called as pallisade of vogt, containing stem cells (these stem cells are unipotent stem cells).

*CORNEOSCLERAL :-

°It is the transition region between the Cornea and sclera.
°It is highly vascular.
°It is 1.5 mm width.
°It contains -
 * Trabecular meshwork
 *Canal of schlemm

°At this junction, the transparent corneal lamellae become continues with the oblique , circular and opaque fibres of the sclera.

SURGICAL LIMBUS :-

It is a 2 mm wide circumcorneal transitional zone between cleat cornea on one side and the opaque  sclera on the other side.

  
Border of surgical Limbus :-

1- Anterior limbal border -

° it is the antr boundary of the surgical limbal seen form the exterior.
°Marked by Prominent ridge created by Insertion of the Conjunctiva and Tenon's capsule.
°The antr limbal border overlies the termination of the Bowman's membrane.

2- Mid limbal line -

°Junction of the blue zone with white area.
Overlies the termination of the Descemet's membrane.
°Most useful external landmark.

3- Posterior limbal border -

°It lies about 1 mm posterior to the mid Limbal line .
°It overlies the scleral spur and can only be seen with use of sclerotic scatter illumination.
°It forms the posterior border of the surgical Limbus.

Zones of surgical limbus :-

1- Blue Limbal zone -

°It is bluish translucent zone seen posterior to the antr limbal border.
°Adjacent to this bluish zone posterior is the white sclera.
°The extent of blue Limbal zone is about 1mm in superior quad , 0.8 mm in inferior quad and about 0.4 mm in nasal and temporal quad.

2- White Limbal zone -

°It is a 1 mm wide whitish area which lies between the mid-limbal line and the posterior limbal border.
°Overlies the the trabecular meshwork .
°The total width of the surgical limbus is greatest in the superior quad where width of blue zone is Max.