glaucoma pathophysiology and detection
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Recommended Books for Recommended Books for OphthalmologyOphthalmology
1.1. Vaughan & Asbury’sVaughan & Asbury’sGeneral Ophthalmology General Ophthalmology 1616thth Edition 2004 a LANGE medical book Edition 2004 a LANGE medical book
• Parsons’ Diseases of the Eye Parsons’ Diseases of the Eye 1919thth Edition 2003 Butterworth publication Edition 2003 Butterworth publication
3.3. Clinical Ophthalmology by Jack J. KanskiClinical Ophthalmology by Jack J. Kanski55thth Edition 2003 Butterworth publication 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 Location AgeAge PACG (%)PACG (%) POAG POAG (%)(%)
Secondary Secondary glaucomaglaucoma
Congenital/Congenital/DevelopmenDevelopmentaltal
EuropeanEuropeanOriginOrigin
Baltimore, Md. Baltimore, Md. 40+40+ 0.310.31 1.291.29 0.680.68 No available No available Beaver Dam, Wisc.Beaver Dam, Wisc. 43-8443-84 0.040.04 2.12.1 Not statedNot stated Not statedNot statedBlue Mountains, Blue Mountains, AustraliaAustralia
49+49+ 0.270.27 3.03.0 0.150.15 NilNil
AfricanAfricanOriginOrigin
JamaicaJamaica 35-7435-74 NilNil 1.41.4 0.350.35 NilNilBaltimore, Md. Baltimore, Md. 40+40+ 0.670.67 4.744.74 1.421.42 Not availableNot available
AsianAsianOriginOrigin
Umanaq area, Umanaq area, GreenlandGreenland
>40>40 4.84.8 1.261.26 1.001.00 NilNil
NW AlaskaNW Alaska 40+40+ 2.652.65 0.240.24 NilNil NilNilBeijing, ChinaBeijing, China 40+40+ 1.41.4 0.030.03 Not statedNot stated Not statedNot statedHHövsgöl, Mongoliaövsgöl, Mongolia 40+40+ 1.41.4 0.50.5 0.30.3 NilNil
Glaucoma prevalence surveys, by racial groups
Affected Affected BlindBlindCongenitalCongenital 300 000300 000 200 000200 000POAGPOAG 13.5 13.5
millionmillion3 million3 million
PACGPACG 6 6 millionmillion
2 million2 million
SecondarySecondary 2.7 2.7 millionmillion
??
Glaucoma Glaucoma suspectssuspects(IOP>21 mmHg)(IOP>21 mmHg)
105 105 million 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 Pressurec. 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 Glaucoma is the second leading cause of worldwide blindness. worldwide blindness.
Early detection and early onset of treatment Early detection and early onset of treatment are the most important factors for are the most important factors for preventing progressive glaucoma damage.preventing progressive glaucoma damage.
A comprehensive evaluation of a glaucoma A comprehensive evaluation of a glaucoma suspect is the key to diagnosis and suspect is the key to diagnosis and management. management.
The aims of assessment areThe aims of assessment are:: To assess the risk factors to determine To assess the risk factors to determine
whether glaucoma is present or likely to whether glaucoma is present or likely to developdevelop
To exclude or confirm the alternative diagnosisTo exclude or confirm the alternative diagnosis To identify the underlying mechanism of To identify the underlying mechanism of
damage; so as to select best choice for damage; so as to select best choice for managementmanagement
To plan a strategy for management To plan a strategy for management
ASSESSMENT
HISTORYSocial
Family
Presenting
Past
Gonio
IOP
Fundus
Lens
Pupils AC
Cornea
Ocu surf
Exoph
OMVA
EXAMINATION
Ocular ExaminationOcular Examination
Record visual functionsRecord visual functions Ocular motility Ocular motility Exclude any proptosis/exophthalmos Exclude any proptosis/exophthalmos Ocular surface for episcleral blood vessels Ocular surface for episcleral blood vessels Conjunctiva for papillae and folliclesConjunctiva for papillae and follicles Cornea for size, shape and transparency Cornea for size, shape and transparency Check for corneal thickness Check for corneal thickness
Ocular ExaminationOcular Examination Anterior chamber for inflammation, blood, Anterior chamber for inflammation, blood,
pigmentpigment Check for AC depth, central and peripheralCheck for AC depth, central and peripheral
• Convex iris-lens diaphragm
• Shallow anterior chamber
• Narrow entrance to chamber angle
Ocular ExaminationOcular ExaminationIris for atrophy , rubeosis, trans-illumination defects and pseudoexfoliation 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 Ocular Examination
Pupil for size, shape and reactionPupil for size, shape and reactionLens for presence, transparency, Lens for presence, transparency,
thickness, position and shapethickness, position and shape
Ocular ExaminationOcular Examination
Record intraocular pressure, look for Record intraocular pressure, look for diurnal variationsdiurnal variations
Evaluate IOP for 24 hours if in doubtEvaluate IOP for 24 hours if in doubt Use a Goldmann-style applanation Use a Goldmann-style applanation
tonometertonometer
Trabecular hyperpigmentation - may extend anteriorly
(Sampaolesi line)
Open angle of normal appearance
Synechial angle closure
Irregular widening of ciliary body band
Ocular ExaminationOcular ExaminationGonioscopy: Gonioscopy: look for width of the angle, configuration of the look for width of the angle, configuration of the iris and chamber, PAS, vessels and iris processes iris and chamber, PAS, vessels and iris processes
Schaffer’s grading of angle
Ocular ExaminationOcular ExaminationFundoscopy: Fundoscopy: evaluate optic nerve head and retinal nerve fibre layerevaluate optic nerve head and retinal nerve fibre layer
use slit lamp indirect lenses and a dilated pupiluse slit lamp indirect lenses and a dilated pupilLook for optic disc size, colour, neuro-retinal rim, disc haemorrhage, vascular pattern, peri-Look for optic disc size, colour, neuro-retinal rim, disc haemorrhage, vascular pattern, peri-
papillary atrophy and cup disc ratiopapillary 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
InvestigationsInvestigationsOrder for a visual Order for a visual field examination field examination with a standard with a standard automated perimeter automated perimeter
Investigations
HRT
OCT
GDx
Systemic investigation includeSystemic investigation includeImaging of CNSImaging of CNSEvaluation of CVSEvaluation of CVSHaematological profileHaematological profile
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