lecture 14 ocular chambers

8/11/2019 Lecture 14 Ocular Chambers

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Ocular Anatomy and Physiology

Optometry 2nd year: Second semester

Mera Haddad BSc MSc PhD

Lecture 14: Ocular chambers

15.04.2014


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Ocular chambers

Two chambers considered as part of the anterior segment: the anteriorchamber (AC) and posterior chambers (PC)

The anterior segment of the eye is best known as the front of the eye

The AC is bounded anteriorly to the cornea and posteriorly to the front

surface of the iris

Peripherally is bounded by the anterior chamber angle which contains the

trabecular meshwork

Deepest at centre (3mm) and shallowest at the insertion point of the iris


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Bounded anterior by the iris and posteriorly by the anterior surface of the

lens and the zonule

Peripherally bounded by the ciliary processes

The posterior chamber

Posterior aqueous humor is secreted by the epithelium of the ciliary

processes into the PC, then flows to the AC through the pupil


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Watery fluid fills the AC and PC of the eye

Itscomposition is similar to that of the blood plasma without the

blood cells

The aqueous humour

Secreted by the epithelium of the ciliary processes at a rate of 2 -2.5microliters/minute


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Part of the optical pathway through which the light passes, and must

remain clear

Formed in the posterior chamber and circulate to the anterior chamber

through the pupil and leaves the eye through the angle

The aqueous humor

This circulation is generated and maintained by hydrostatic and osmotic

gradient

The aqueous creates resistance to maintain the shape of the ocular coat

and also helps to maintain the pressure within the eye


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Contains very important structures involved in the passage anddrainage of the aqueous: Trabecular meshowrk (TM) and canal of

Schlemm

Anatomical angle created by the root of iris and corneal vault

The angle


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A meshwork-like band lying just posterior to the peripheral corneal

endothelium surrounds the circumference of the anterior chamber

Composed of two portions: 1) Uveal meshwork which faces the anterior

chamber 2) Corneoscleral meshwork that is adjacent to the canal of

schlemm

Trabecular meshwork and canal of Schlemm


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The aqueous leaves the AC through the trabecular meshwork, thenitscollected in the canal of Schlemm

The canal of Schlemm communicates peripherally with the angles

episcleral veins which are the last drainage sites of the aqueous

Aqueous flow

The aqueous passes from the PC to the AC through the pupil

The relationship of the iris plane to the cornea (angle opening) is

very important in the accessibility of the aqueous to its outflow


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Aqueous flow


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This is referred to narrowangleand people in this case are at high

risk of angle closure attack

The hyperopic (farsighted) eye have smaller eyes in general and the

anterior segment is smaller. Thus the angle is smaller

Aqueous flow

If the separation between iris and corneal endothelium is too small

or closed, the aqueous will not flow to TM and canal of Schlemm


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These two forces are normally balanced physiologically

When this balance is disrupted the aqueous inflow will exceed the

outflow resulting in increased IOP

Intraocular pressure (IOP)

Created by the dynamic process of the secretion of aqueous by the

ciliarry processes (inflow) and drainage of aqueous through the

trabecular meshwork and canal of schlemm (outflow)

Normal IOP ranges from 10 to 21 millimeters of mercury (mm Hg) in

adults


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If the IOP is too high, the pressure builds up and move to the back

of the eye, leading to optic nerve damage and loss of visual field

Increased IOP, optic nerve damage and visual field loss are indicative of

the disease glaucoma


People with constant high IOP are referred to as glaucomasuspects or

ocular hypertensive

People tolerates levels of pressure differently


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Some people with normal IOP can develop damage to the nerve

(normal or low tension glaucoma)

Other people may not develop damage even though the IOP is too high

(suspects or hypertensive glaucoma)


Contraction of the ciliary muscles can affect the IOP. Pilocarpine, an olddrug, is thought to open the pores of trabecular meshwork by

constricting and creating tension on the ciliary muscle


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Slit lamp biomicroscope and gonioscopy lens:

Grading depends on the visible structures using the lens (e.g. TM will

not be visible when the angle is narrow)

Evaluation of the angle structures

The angle opening is graded on a grading scale from 1 to 4: grade 4 is

the widest angle (open angle) and grade 1 is the smallest angle(narrow angle)

A lens that uses mirrors with different degrees of tilt to allowviewing and analysing the relationship of the iris to the cornea,

trabecular meshwork and canal of sclemm


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Angle estimation technique


pen light is used to assess the iris/cornea relationship

Evaluate the openness and narrowness of the angle

A wide angle and deep chamber can be viewed by holding the

penlight on the limbal area which will cause the entire iris to lighten,allowing the light to be dispersed evenly

A narrow angle with shallow chamber can be viewed by holding the

penlight from the temporal side which will place a shadow on the

nasal side


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Open and closed angles


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Estimation of the angle is very important if the patient needs to be

dilated


The aqueous cannot drain and the pressure builds up and causes

angle closure attack

This is because dilation may cause the iris to bunch up against the

lens, blocking the flow of the aqueous

Closed angle glaucoma is characterized by redness, pain and

corneal oedema

If sustained long enough, can cause irreversible optic nerve damage


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Evaluation of the chambers

Both AC and PC can be evaluated with ultrasound

B-scan gives a two dimensional image of the structures and their

location, used to evaluate growths and foreign bodies

A-scan gives a one dimensional view, useful for measuring the chamber

depth and location of structures

Endoscopy (scope-mounted camera) can be used to visualise the

chambers during surgery


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Ultrasound biomicroscopy (UBM):

The probe moves over the surface of the eye and records the anterior

segment features

Evaluation of the chambers

An instrument which provides high resolution imaging of the chambers

ocular coherence tomography (OCT), Measures cornealthickness, AC depth and AC angle

lecture 14 ocular chambers

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