anatomy of the angle structure (glaucoma)

Recommended Books for Ophthalmology

1. Vaughan & Asbury’s

General Ophthalmology

16th Edition 2004 a LANGE medical book

2. Parsons’ Diseases of the Eye

19th Edition 2003 Butterworth publication

3. Clinical Ophthalmology by Jack J. Kanski

5th Edition 2003 Butterworth publication

GLAUCOMA

Patho-physiology & Detection

Dr. Nasir Saeed

Epidemiology of Glaucoma

Glaucoma is not a single disease entity,but the result of a

group of different mechanisms which cause a loss of retinal

ganglion cells. This loss may be acute or episodic, or slowly

and relentlessly progressive. Some authors therefore refer to

‘the glaucomas’. The common, connecting feature used to be

regarded as the height of the intraocular pressure (IOP), which

dominated the understanding of the clinical manifestations to a

greater or lesser extent. Although intraocular pressure is

frequently raised, it is now regarded as a risk factor, and no

longer considered a defining characteristic.

Location Age PACG (%) POAG (%) Secondary glaucoma

Congenital/

Developmental

European

Origin

Baltimore, Md. 40+ 0.31 1.29 0.68 No available

Beaver Dam, Wisc. 43-84 0.04 2.1 Not stated Not stated

Blue Mountains, Australia

49+ 0.27 3.0 0.15 Nil

African

Origin

Jamaica 35-74 Nil 1.4 0.35 Nil

Baltimore, Md. 40+ 0.67 4.74 1.42 Not available

Asian

Origin

Umanaq area, Greenland

>40 4.8 1.26 1.00 Nil

NW Alaska 40+ 2.65 0.24 Nil Nil

Beijing, China 40+ 1.4 0.03 Not stated Not stated

Hövsgöl, Mongolia 40+ 1.4 0.5 0.3 Nil

Glaucoma prevalence surveys, by racial groups

Affected Blind

Congenital 300 000 200 000

POAG 13.5 million 3 million

PACG 6 million 2 million

Secondary 2.7 million ?

Glaucoma suspects

(IOP>21 mmHg)

105 million

World estimates of glaucoma prevalence

RISK FACTORS

Age:

The prevalence and incidence of PACG

increase with age. Although a peak has been

claimed, the best evidence suggests that

incidence rises continually with age. Attacks

of ACG are rare before age 45.

GENDER

• POAG Equal• PACG Females > Males

Race• Chinese ACG• European POAG• Africans POAG<ACG• Japanese NTG• Asians ACG<=POAG

Refraction• ACG Hypermetopes • POAG Myopes

Genetics

• Intra-ocular Pressure

• Diabetes

• Family History

• Hypertension

• Vascular Spasm

ANATOMY OF THE ANGLE STRUCTURES

Aqueous Humour

Produced by the ciliary processes into the posterior chamber

• Through the pupil it circulates into the anterior chamber

• 90% of it is drained through the trabecular meshwork into the Schlemm’s canal and the epi-scleral venous system (conventional pathway)

• 10% of it leave the eye through the uveo-scleral route (un-conventional pathway) into the suprachoroidal space and chained by venous circulation of the ciliary body and sclera

Functions of Aqueous humour

It maintains the shape and internal structure of the eye by

sustaining an intraocular pressure higher then atmospheric pressure

and helps in maintaining the optical structure.

It carries oxygen and nutrients to the lens and cornea

It carries waste products away from the lens and cornea

Aqueous humour production

• Produced by the ciliary processes of the ciliary body.

Two Mechanisms

I- Active secretion

• 80% of aqueous is produced by the non pigmented ciliary epithelium as a result of active metabolic process

• Involves several enzymatic systems i.e. Na+ - K + ATPase / Carbonic

Anhydrase

• Na+, K+, Ascrobate, HCO3

• Transported into the posterior chamber

• Secretion diminishes by factors which will inhibit active metabolism

like drugs, hypoxia, hypothermia

• Independent of IOP

Aqueous humour production

II- Passive Secretions

• 20%

• Diffusion to maintain equilibrium between the osmotic pressure and electrical balance on the two sides of the ciliary processes

• Ultra-filtration

• When the diffusion of water and salt is accelerated by blood pressure (hydrostatic pressure) in the ciliary body

The passive secretion is dependent on level of blood pressure in the ciliary body, plasma oncotic pressure and intraocular pressure

• Blood Aqueous Barrier

• Large molecules such as plasma proteins and cells do not get into the aqueous chambers even when the plasma concentration is very high

•Sites of the barrier is tight junctions between the non-pigment ciliary epithelium and their basement membrane

Intra-ocular pressure (IOP)

• The circulation of aqueous humour in the eye maintains the IOP

• The equilibrium of aqueous formation and outflow rate is of crucial

importance

• Normally aqueous humour is secreted at a rate of 0.02µl / minute and

same amount is drained

•The distribution of IOP in general population : 11-21 mm of Hg

•Average = 15 mm of Hg

• Diurnal variation – High in morning

Low in evening by 5 mm of Hg

• No sex difference

Determinants of Intraocular Pressure

• Rate of aqueous humour formation

• Resistance encountered in out flow channels

• Level of epi-scleral venous pressure

Factors influencing Intra-Ocular Pressure

I- Rate of Aqueous Humour formation

Increased by

a. Inflammation

b. Blood Pressure

c. Hypo-osmolarity of plasma

Decreased by

a. Retinal / Choroidal / Ciliary body detachments

b. Drugs

c. Anaesthesia

B-Blocker

Carbonic Anhydrase hulibitors

II- Out flow Resistance

Increased by

Age

Membrane

• Pupillary Block Synechia

Lens

Vitreous

• Trabecular Meshwork block

Inflammation

Cellular debris

Steroids

Inflammatory exudates

Peripheral Iris bowing

Peripheral Anterior Synechia

Idiopathic

• Outflow Resistance Decreased by

• Accommodation

• Drugs

• Miotics

• Prostaglandins

• Adrenaline

III- Episcleral Venous Pressure

Increased by

• Increased CVP

• Valsalva

• Carotid Cavernous fistula

• Hypercarbia

•Dysthyroid eye disease

•Succinyl – choline

• Co-contraction of extra-ocular muscles

Decreased by

• Hypotension

• Decreased carotid blood flow

• Decrease CVP

Applied Anatomy of the optic n. head

Retinal Nerve fibre layers

Relative positions of nerve fibre layer

Cross Section of the Optic N. Head

Optic Cup & Neuro-retinal rim

Physiological Cup & Neuro-retinal rim

Glaucomatous Damage Retinal Nerve fibre layers Normal

Glaucomatous Damage Abnormal Nerve fibre layers

Abnormal nerve fibre layers

Glaucomatous Damage

Optic disc cupping

Bilateral glaucomatous cupping with inferior notching and ‘bayonetting’

Bilateral advanced glaucomatous cupping with nasal displacement of the blood vessels

End – Stage glaucomatous cupping

Clinical Methods for detection and evaluation of glaucoma

• IOP Measurements

• Gonioscopy

• Perimetry Techniques

• Advanced Techniques

Measurement of Intraocular Pressure Tonometry

Principal

• The pressure inside a sphere may be measured directly by canulating

it and connecting it to a measuring device. This is called manometry. It

is the most accurate method but not practical for routine clinical

measurement.

• It can also be measured by the

• Imbert – Fick Law – Pressure = Force /Area.

• The pressure can be measured by measuring the force necessary to

flatten a fixed area or by measuring the area flattened by a fixed force.

• Also a known force will indent a sphere. In low pressure the

indentation will be more and in high pressure the indentation will be

less.

Goldmann Applanation Tonometer

• Applanation tonometry measures the force applied per unit area. The

Goldmann tonometry is a variable force tonometer consisting of a

double prism with a diameter of 3.06 mm. It is the most popular and

accurate tonometer.

Goldmann applanation tonometer

Fluorescein-stained semicircles seen during tonometry

A- Schiotz tonometer

B- Principles of indentation tonometry

• Checking for diurnal changes= phasing

• Demonstrating elevation of IOP after pupillary

dilation, water drinking

• IOP checking in different direction of gaze

• Checking for steroid responsiveness

• IOP-measurement digitally

Gonioscopy

• Visualization of the anterior chamber angle is called Gonioscopy

Purposes

1. Diagnostic: to identify abnormal angle structures and to

estimate the width of the anterior chamber angle. This is

particularly important to classify the open angle and angle

closer glaucoma

2. Surgical: to visualize the angle during the procedures

such as laser trabeculopasty and goniotomy

Optical Principal

• In normal circumstances the angle of anterior chamber can not be visualized because of the total internal reflection

Critical Angle

Lighter Medium

Denser Medium

a

c

d

b

a

c

d

b

Optical Principal of Gonioscopy

Single Mirror goniolens & Zeiss four mirror goniolens

Swan-Jacob surgical goniolens & Koeppe goniolenses

Normal Anatomy of Angle structure

Schaffer’s Grading System

Abnormal Anterior Chamber Angle

Perimetry

• Visual fields ;

• An island of vision surrounded

by a sea of darkness

• Isopter. An Isopter is a line in the field of vision exhibiting similar visual acuity

• Scotoma. Is a defect in the visual field

• Absolute

• Relative

• Positive

• Negative

• Visible threshold. Is the luminance of the stimulus measured in dB at

which it is perceived 50% of times when it is

presented statically

Perimetric Principals

• Perimetry is a method of evaluating the visual fields

• Qualitative Perimetry is a method of detecting a visual field defect

and is the first screening phases of glaucoma suspects

• Quantitative Perimetry

Visual Fields defects in glaucoma1. Arcuate scotomas : develop between 100 and 200 of

fixation in areas that constitute downward or more

commonly, upward extensions from the blind spot

(Bjeerrum area)2. Isolated paracentral scotomas: superior or inferior

scotomas may also be found in early glaucoma.

3. A nasal (Roenne) step

4. Ring scotomas

5. Temporal Wedge

6. End Stage fields defects

1. Arcuate scotomas : develop between 100 and 200 of fixation in

areas that constitute downward or more commonly, upward

extensions from the blind spot (Bjeerrum area)

Isolated paracentral scotomas: superior or inferior scotomas may also be found in early glaucoma

A nasal (Roenne) step

Temporal Wedge

End Stage fields defects

Advanced Techniques

Quantitative Measurements

• Digitalized photogrammetry

• Confocal scanning laser ophthalmoscope (HRT)

• Measurements of ocular blood flow

Digitalized photogrammetry

Confocal scanning laser

ophthalmoscope (HRT)

Glaucoma is the second leading cause of

worldwide blindness.

Early detection and early onset of treatment are

the most important factors for preventing

progressive glaucoma damage.

A comprehensive evaluation of a glaucoma

suspect is the key to diagnosis and management.

The aims of assessment are:

• To assess the risk factors to determine whether

glaucoma is present or likely to develop

• To exclude or confirm the alternative diagnosis

• To identify the underlying mechanism of

damage; so as to select best choice for

management

• To plan a strategy for management

ASSESSMENT

HISTORYSocial

Family

Presenting

Past

Gonio

IOP

Fundus

Lens

Pupils AC

Cornea

Ocu surf

Exoph

OM

VA

EXAMINATION

Ocular Examination

• Record visual functions

• Ocular motility

• Exclude any proptosis/exophthalmos

• Ocular surface for episcleral blood vessels

• Conjunctiva for papillae and follicles

• Cornea for size, shape and transparency

• Check for corneal thickness

Ocular Examination

• Anterior chamber for inflammation, blood, pigment

• Check for AC depth, central and peripheral

• Convex iris-lens diaphragm

• Shallow anterior chamber

• Narrow entrance to chamber angle

Ocular Examination

Iris for atrophy , rubeosis, trans-illumination defects and pseudoexfoliation

Stromal iris atrophy with spiral-like configuration

Mid-peripheral iris atrophy

Central disc with peripheral band

Ocular Examination

• Pupil for size, shape and reaction

• Lens for presence, transparency,

thickness, position and shape

Ocular Examination

• Record intraocular pressure, look for diurnal variations

• Evaluate IOP for 24 hours if in doubt• Use a Goldmann-style applanation

tonometer

Trabecular hyperpigmentation - may extend anteriorly

(Sampaolesi line)

Open angle of normal appearance

Synechial angle closure

Irregular widening of ciliary body band

Ocular ExaminationGonioscopy: look for width of the angle, configuration of the iris and chamber, PAS, vessels and iris processes

Schaffer’s grading of angle

Ocular ExaminationFundoscopy: evaluate optic nerve head and retinal nerve fibre layer

use slit lamp indirect lenses and a dilated pupil

Look for optic disc size, colour, neuro-retinal rim, disc haemorrhage, vascular pattern, peri-papillary atrophy and cup disc ratio

Small dimple central cup Larger and deeperpunched-out central cup

Cup with sloping temporal wall

Optic disc evaluation

Retinal nerve fibre layer analysis

InvestigationsOrder for a visual field examination with a standard automated perimeter

Investigations

HRT

OCT

GDx

Systemic investigation includeImaging of CNSEvaluation of CVSHaematological profile