ANATOMY OF ANTERIOR CHAMBER AND ANGLE OF DRAINAGE.

MODERATOR: DR.T.R MANJULA PRESENTER: PRATHIBHA. S

INDEX Anterior chamber Angle of anterior chamber Outflow of apparatus Innervation of outflow apparatus

ANTERIOR CHAMBER: Anterior chamber is an

angular space. Anteriorly by the

posterior (inner) surface of the cornea.

posteriorly by the lens within the pupillary aperture, anterior surface of the iris and a part of cilliary body.

  Anterior chamber is 3 mm deep and it

contains 0.25 ml of the aqueous humour. Anterior chamber depth is shallower in the

hypermetropic eye than the myopic eye. It is also shallower in children and in older

people.

Volume: 220 µL. Chamber Volume decreases by 0.11 µL/year

life Diameter: 11.3-12.4mm Depth: 3.15mm (2.6- 4.4mm) Chamber depth decreases by 0.01mm/year

of life. Chamber deepens by 0.06mm for each

diopter of myopia.

Chamber depth is slightly diminished during accommodation, partly by increased lens curvature & partly by forward translocation of the Lens.

Wide angle of anterior chamber denotes the eye in which the angle between iris and surface of the trabecular meshwork is between 20 to 45 degrees.

Angles less than 20 degrees are termed as narrow angles

ANGLE OF ANTERIOR CHAMBER It is the angle recess formed in between post. Surface of

cornea and ant. Surface of iris bounded from anterior to posteriorly by

Schwalbe’s line Trabecular meshwork Scleral spur Anterior surface of cilliary body along with root of iris

DEVELOPMENT : By 7th week , angle is occupied by

mesenchymal cells from neural crest cells to develop trabecular meshwork.

In posterior aspect, iris is formed from advancing bilayered optic cup.

Coreneal endothelium meets derivative of iris at 15th week to demarcate the angle.

Angle deeping continues even after birth.

SCHWALBE’ S LINE• Just anterior to the apical portion of the

trabecular meshwork is a smooth area called as zone S.

• Width-50 to150 μm

This anterior border of this zone marks transition from1. trabecular to

corneal endothelium

2. termination of the Descemet’s membrane

3. Insertion of trabecular meshwork into corneal stroma.

• The posterior border is demarcated by a discontinuous elevation, called Schwalbe's line, formed by the oblique insertion of uveal trabeculae into limbal stroma.

• Clusters of secretory cells, called Schwalbe’s line cells, produce a phospholipid material that facilitates aqueous humor flow through the canalicular system.

Trabecular meshwork: Anterior to scleral spur and forms inner

aspect of schlemm’s canal. pigmentation acquried with age.

SCLERAL SPUR: wedge shaped circular ridge. pale, translucent narrow strip of scleral

tissue. lies posterior to trabecular meshwork. gives attachment to anteriorly to

corneosceral meshwork and posteriorly to cilliary muscle.

CILIARY BAND: It marks the posterior most part of the angle. Represents the anterior face of ciliary body

between its attachment to the scleral spur and insertion of iris.

Width depends on the level of iris insertion Wide in myopes and narrow in

hypermetropes. It appears as a grey/dark brown band

OUTFLOW OF APPARATUS It consists of :- Internal scleral sulcus trabecular meshwork schlemm’s canal collector channels episcleral veins

INTERNAL SCLERAL SULCUS 1. Sulcus 2. Schwalbe’s ring 3. scleral spur

Limbus is the transition zone between the cornea & sclera.

On the inner surface of the limbus, there is an indentation or groove, which is known as the scleral sulcus.

1. SCLERAL SULCUS This scleral sulcus has a sharp posterior

margin- the scleral spur & a sloping anterior wall which extends to the peripheral cornea.

Bounded anteriorly by schwalbe’ s line and posteriorly by scleral spur.

Accomodates schlemm’s canal and corneoscleral meshwork

The portion of the spur which forms the post. boundary of the sulcus is sometimes called scleral roll.

2. SCHWALBE’ S RING Is the anterior border ring of the trabecular

region contians circularly arranged collagen fibres

intermixed with elastic fibres. With age there are also patches of long

spacing or curly collagen. This ring marks the transition between the

corneal endothelium and the trabecular cells and also the termination of descement’s membrane.

3. SCLERAL SPUR Scleral spur is composed of a group of fibres

known as scleral roll. Scleral roll is composed of 75-80% collagen

+ 5% elastic tissue. This circular structure prevents ciliary

muscle from causing Schlemm’s canal to collapse.

• Attached

anteriorly : trabecular meshwork posteriorly : sclera and longitudinal fibers of

ciliary muscle.

• varicose axons characteristic of mechanoreceptor nerve measure stress in the scleral spur due to ciliary muscle contraction or changes in IOP.

TRABECULAR MESHWORK Trabecular meshwork is a

spongy, sieve like tissue. It is roughly a triangular anteriorly by periphery of

the cornea and posteriorly scleral spur and anterior surface of the ciliary body.

Trabecular meshwork is pale tan to dark-brown in colour, varying with pigmentation of the tissue, which is darker posteriorly.

It is divided into three portions:

(a) uveal meshwork, (b) corneoscleral meshwork, and (c) juxtacanalicular

tissue

UVEAL MESHWORK• This inner most portion is

adjacent to the aqueous humor in the anterior chamber

• It is arranged in cord or rope like trabeculae that extend from the iris root to the Schwalbe's line .

• The arrangement of the trabecular bands creates irregular openings that vary in size from 25 to 75 μm.

CORNEOSCLERAL MESHWORK• This portion extends

from the scleral spur to the anterior wall of the scleral sulcus

• It consists of 8-14 sheets of trabeculae that are interconnected via cytoplasmic processes.

They are perforated by elliptical openings which become progressively smaller as the trabecular sheets approach Schlemm's canal .

• These perforations are not aligned and have a diameter ranging from 5 to 50 μm

ULTRASTRUCTURE OF MESHWORK

• Both the uveal and corneoscleral trabecular bands or sheets are composed of four concentric layers

1. An inner connective tissue core is composed of collagen fibers, with 64nm periodicity. The central core contains collagen types I and III and elastin.

2. Elastic fibers are arranged in a spiraling pattern with periodicity of 100nm.

3. Cortical zone also called as glassy membrane

4. An outer endothelial layer provides a continuous covering over the trabeculae

TRABECULAR ENDOTHELIAL CELLS Larger, more irregular and have less

prominent borders than corneal endothelium. Joined by gap junction and

desmosomes ,which provide stability. Two types of microfilaments: 1. Actin filaments: cell periphery, around nucleus, in ctyoplasmc

processes. cell contraction, phagocytosis, pinocytosis,

and cell adhesions Regulating the shape and cytoskeletal

organization.

2. Intermediate filaments: Numerous, composed of vimentin and

desmin Imparts the contractile n motility functions.

JUXTACANALICULAR TISSUE

The outermost portion of the meshwork (adjacent to Schlemm's canal)

This structure has three layers consisting of a layer of connective tissue lined on either side by endothelium

The inner trabecular endothelial layer is continuous with the endothelium of the corneoscleral meshwork

The central connective tissue layer has variable thickness and is unfenestrated with several layers of parallel, spindle shaped cells loosely arranged in a connective tissue ground substance.

The outermost portion of the trabecular meshwork is the inner wall endothelium of Schlemm's canal.

This endothelial layer has significant morphologic characteristics, which distinguish it from the rest of the endothelium in both the trabecular meshwork and in Schlemm's canal.

SCHLEMM'S CANAL

This 360-degree endothelial-lined channel It is a single channel but occasionally

branches into a plexus-like system .

The endothelium of the outer wall is a single cell layer that is continuous with the inner wall endothelium but has a smoother surface with larger, less numerous cells and no pores .

The outer wall also differs in having numerous, large outlet channels

Lip-like thickenings are present around the openings of the outlet channels and septa are noted to extend from these openings to the inner wall of Schlemm's canal, which help keep the canal open.

Theory of transcellular aqueous transport in which a series of pores and giant vacuoles opens (probably in response to transendothelial hydrostatic pressure) on the connective tissue side of the juxtacanalicular meshwork (2–4). Fusion of basal and apical cell plasmalemma creates a temporary transcellular channel (5) that allows bulk flow of aqueous into Schlemm’s canal.

COLLECTOR CHANNELS• Schlemm's canal is connected

to episcleral and conjunctival veins by a complex system of intrascleral channels.

• Two systems of intrascleral

channels have been identified:

(a) An indirect system of numerous(15-20), finer channels, which form an intrascleral plexus

before eventually draining into the episcleral venous system and

(b) A direct system of large caliber vessels, which run a short intrascleral course and drain directly into the episcleral venous system, they are about 6-8 in number and also called as aqueous vein.

since these aqueous vessels terminate into the episcleral and conjunctival veins in laminated junction- laminated vein of goldmann.

EPISCLERAL AND CONJUNCTIVAL VEINS

The aqueous vessels join the episcleral and conjunctival venous systems by several routes.

Most aqueous vessels are directed posteriorly, with most of these draining into episcleral veins, whereas a few cross the subconjunctival tissue and drain into conjunctival veins.

The episcleral veins drain into the cavernous sinus via the anterior ciliary and superior ophthalmic veins,

while the conjunctival veins drain into superior ophthalmic or facial veins via the palpebral and angular veins .

INNERVATION OF OUTFLOW APPARATUS Derives from the supraciliary nerve plexus and

the ciliary plexus in the region of scleral spur Both sympathetic adrenergic and

parasympathetic and sensory innervation present

Nerve endings contain mechanoreceptors which are located in scleral spur.

1. act as proprioceptive tendon organs for the ciliary muscle,who longitudinal fibres insert into scleral spur.

2. contraction myofibroblast scleral spur cells. 3. baroreceptor function in response t change in

IOP.

REFERENCE: Shields’ textbook of Glaucoma, 8th edition.

Wolff’ s Anatomy of the Eye and Orbit, Anthony J. Bron, 8th edition.

Anatomy and Physilogy of Eye ,2nd edition, A K Khuran and Indu khurana.

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