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Download MBBS Ophthalmology PPT 42 Primary Open Angle Glaucoma Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Ophthalmology PPT 42 Primary Open Angle Glaucoma Lecture Notes

This post was last modified on 07 April 2022

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Acknowledgement

? Figures and photographs - Courtesy

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Kanski's Clinical Ophthalmology

2
Learning Objectives

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? At the end of this class the students shall be able to :
? Define primary open angle glaucoma(POAG).
? Understand the pathophysiology and the
risk factors of POAG.
? Understand the clinical features of POAG.

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? Understand the fundamentals of managing
primary open angle glaucoma

3

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What is glaucoma ?

? The term glaucoma is derived from the

Greek word "glaukos" meaning "gray blue"

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? Is the second leading cause of blindness

worldwide

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? The third most common cause of blindness

in India

? Not reversible

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? More than 50% of patients unaware of

disease.

4

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Definition of POAG

? Chronic, progressive optic neuropathy

characterised by morphological changes at

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the optic nerve head and retinal nerve fibre

layer leading to characteristic visual field

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changes, in the absence of other ocular

diseases or congenital anomalies (with or

without a raised IOP)

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5

Etiopathogenesis

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? Multifactorial aetiology
? Risk factors include:
?Elevated Intra Ocular Pressure(IOP)
(More than 21 mm Hg)
?Optic disc cupping

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?Increasing Age : More common in 5th to 7th

decades of life

?Race: More common and severe in Black

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population

6
Etiopathogenesis

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?Heredity/ Family History: Risk of about

10% in siblings; 4% in off springs

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?Diabetes
?Systemic Hypertension
? Myopia
?Thin central corneas
?Steroid usage

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? ?Migraine, Cigarette smoking,Graves

disease

7

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Pathogenesis of POAG

? Decrease in aqueous outflow facility due to

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increased resistance to outflow leads to rise

in IOP

? Two theories of axonal loss in optic disc

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? 1. Mechanical: Distortion of lamina cribrosa

leading to impaired axoplasmic flow

2. Vascular: Optic disc ischaemia with

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defective autoregulation of blood vessels

8


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FORMATION OF AQUEOUS HUMOR

CILIARY PROCESSES

-approx. 70-80 radial folds in the pars plicata which form

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the site of aqueous production.

-Zonular fibers attach primarily in the valleys of the ciliary

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processes and also along the pars plana

DIFFUSION

SECRETION

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(80-90%)

ULTRA-
FILTRATION

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FORMATION PROCESSES 10
Formation of aqueous humor

? Diffusion and ultrafiltration are both

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passive mechanisms so no active cellular

partcipation occurs.

? Active secretion is an active process.

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? Rate of formation of aqueous humor in a

healthy human eye is-

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2 - 3 microlitres/minute

11

Table 1. Constituents of Human Aqueous Humor*

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Constituent (?mol/mL) Anterior Chamber

Aqueous

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Plasma

Ascorbate

1.06

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0.04

Bicarbonate

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22.0

26.0

Calcium

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2.5

4.9

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Chloride

131.0

107.0

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Glucose

2.8

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5.9

Lactate

4.5

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1.9

Magnesium

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1.2

1.2

Phosphate

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0.6

1.1

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Potassium

22.0

26.0

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Sodium

152.0

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148.0

Urea

6.1

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7.3

Protein (gm/dL)

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0.024

7.0

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pH

7.21

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7.4
Differences between

aqueous humor & plasma

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AQUEOUS PLASMA

-Marked deficit of

0.024 7.0

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proteins

gm/dl gm/dl

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-Marked excess of

1.06 0.04

Ascorbate

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micromol/ml micromol/ml



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-Excess of Lactate

4.5 1.9

micromol/ml micromol/ml

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-Excess of Chloride &

certain amino acids

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13

Functions of aqueous humor

*Maintaining IOP :

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-important for early ocular development &

maintaining global integrity throughout life.

*Serves as a vascular system for the avascular

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structures of the eye: cornea, lens & TM.

- by providing substrates & nutrients & removing

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metabolites.

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Functions of aqueous humor

*Delivering high concentration of Ascorbate:

- scavenges free radicals & protects against UV

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rays & other radiations.

*Local paracrine signaling & immune responses.

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*Colourless & transparent medium as part of eye's

optical system.

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Aqueous humor outflow

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Major amount of aqueous humor leaves the

eye by

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BULK FLUID FLOW

i.e. fluid flows along normal pressure

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gradient through non-energy dependent

process

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Ciliary processes

Aqueous Humor in PC

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through pupil

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Anterior Chamber

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Trabeculo-canalicular outflow

*It is the main outlet for aqueous from the AC

*70-90% of total aqueous is drained by this route

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TRABECULAR MESHWORK

-A sponge work of
connective tissue

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beams arranged as
super-imposed
perforated sheets.
-It's extracellular spaces
contain hydrophilic

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glycosaminoglycans &

collagen.

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-Inner portion
Uveal meshwork

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-Outer portion
Corneoscleral meshwork

-In between

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Juxta-canalicular
(endothelial)meshwork

21

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Uveal meshwork

Corneo-scleral meshwork

Juxta-canalicular tissue

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Endothelial lining of SC

Schlemm's Canal

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UVEAL MESHWORK

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-Extends from the iris

root & ciliary body to

schwalbe's line.

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-Trabeculae are cord

like, 2-3 layer thick.

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-Openings of 25-75

microns size.

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CORNEOSCLERAL MESHWORK

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-Extends from SS to the

lateral wall of scleral

sulcus

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-Flattened perforated

sheets, 8-15 layers

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-Openings of 5-50

microns size

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JUXTACANALICULAR

(ENDOTHELIAL) MESHWORK

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-The outermost portion

of TM which mainly

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offers the normal

resistance to

aqueous outflow .

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-Connects the

corneoscleral

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meshwork with

schlemm's canal

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? Veins from the anterior part of ciliary body form the

Ciliary venous plexus

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Anterior ciliary veins & Episcleral veins

communicate with Schlemm's canal

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Schlemm's Canal

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20-30 Collector channels Aqueous Vein

Intra-scleral venous plexus

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Episcleral venous plexus
& Anterior Ciliary vein

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UNCONVENTIONAL

OUTFLOW

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*responsible for 10-25% of total aqueous outflow


UVEO-SCLERAL OUTFLOW

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Trans-corneal outflow

- Aqueous humor from anterior chamber

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goes into tear film through cornea.

- Very little aqueous passes through this

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pathway.

- Total volume of fluid transferred is limited

by high hydraulic resistance of the cornea.

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ANGLE OF ANTERIOR

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CHAMBER

- The peripheral recess of anterior chamber is known as

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the angle of anterior chamber.

- It is clinically visualized by gonioscopy.
- Starting at the root of iris & progressing anteriorly

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towards the cornea, the following structures can be

identified in a normal angle in an adult :

1) Ciliary body band (CBB) & root of iris

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2) Scleral spur (SS)
3) Trabecular meshwork (TM)
4) Schwalbe's line (SL)

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---------

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Grade
IV

III

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II

I
0

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33

34
Clinical features of POAG

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Symptoms
? Usually asymptomatic in early cases
? Mild headache and eye ache
? Frequent changes in presbyopic glasses
? Delayed dark adaptation

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? Loss of peripheral vision
? Loss of central vision(late cases)

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Signs of POAG

? Normal anterior segment
? Pupil reaction to light may be sluggish(in

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advanced cases only)

? Elevated IOP(More than 21 mm Hg) with

diurnal variation more than 5-8 mmHg

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? Optic disc changes (Progressive,

asymmetric)

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? Visual field defects

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Optic disc changes in glaucoma

? Early changes

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o Retinal nerve fibre layer atrophy

o Vertically oval cup

o Asymmetry of the cups(More than 0.2

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difference)

o Large cup(CD more than 0.6)

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o Splinter haemorrhages

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Advanced glaucomatous disc changes

? Marked cupping (More than 0.7)
? Thinning of NRR (Neuroretinal rim)
? Lamellar dot sign

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? Vascular alterations
o Nasal shifting of retinal vessels

o Bayonetting sign(convoluted path due to NRR

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loss)

o Baring of circumlinear vessels and overpass

vessels

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o Multiple haemmorrhages at disc

? Glaucomatous optic atrophy

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Recording and documenting disc changes

? Serial drawings (10 square grid) after

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seeing fundus by ophthalmoscopy/slit

lamp with +90D/+78D lens

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? Disc photography
? HRT(Heidelberg retinal tomography)
? OCT (Optical coherence tomography)
? NFA(Nerve fibre analyser)

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Visual field defects in glaucoma

? Arcuate nerve fibres in the superior and

inferior temporal portions of the optic disc:

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Most sensitive to damage
? Macular fibres : Most resistant to damage

CENTRAL VISION IS PRESERVED TILL

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THE LAST IN GLAUCOMA

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Progression of field defects

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? Isopter contraction: Generalised field

constriction

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? Baring of blind spot : Non specific
(Exclusion of blind spot from central field)
? Paracentral scotoma: Wing shaped and

occurs above or below the blind spot in the

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Bjerrum's area(10-25 degrees from

fixation)

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Is the earliest clinically significant defect

45

Progression of field defects

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? Seidel's scotoma: sickle shaped
Due to joining of blind spot and
paracentral scotoma
? Bjerrum's/Arcuate scotoma:

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Extension of Seidel's scotoma to reach the
horizontal line.
? Double arcuate/ring scotoma


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46
Progression of field defects

? Roenne's central nasal step:
Sharp right angled defect at the horizontal

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meridian when arcuate scotomas run in
different arcs
? Peripheral field defects
? Advanced defects
Residual Tubular vision

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Temporal island of vision

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Quantification of visual field defects

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? Visual field analyzer
Kinetic perimeter
Static perimeter (automated)

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Testing more than once is required before
final interpretation

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Enlarged blind spot

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Superior arcuate scotoma

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Bjerrum's scotoma

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Roenne's nasal step

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Double arcuate

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10-2- Advanced VFD , macular split

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Advanced glaucoma

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Diagnostic work up/Investigations

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? Tonometry
? Goniscopy: Open angles
? Perimetry: To detect visual field defects
? Slit lamp examination: To rule out causes

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of secondary open angle glaucoma

? Fundus examination to document optic

disc changes

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? Diurnal variation testing
? Provocative testing: Water drinking test 55

Diagnosis

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? POAG: Raised IOP(More than 21 mm Hg),
glaucomatous optic disc cupping, visual
field changes.
? Ocular hypertension/glaucoma suspect:

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Raised IOP
? NTG(Normal tension glaucoma):
glaucomatous optic disc cupping with or
without visual field changes with normal
IOP

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56
Management of POAG

? Therapeutic choices

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q Medical therapy

q Argon/Diode Laser Trabeculoplasty

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q Filtration surgery

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Basic principles of therapy

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? Make a correct diagnosis
? Set a target IOP
? Start with a single drug to lower IOP
? Switch to another group of drugs if needed

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? Add drugs from different groups
(Combination therapy)
? Control IOP on minimal medication
? Monitor therapy and reset target IOP

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whenever needed

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Topical drugs used for POAG therapy

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? Prostaglandin/Prostamides
Latanoprost, Bimatoprost, Travoprost
? Beta blockers
Timolol maleate, Betaxolol
? Carbonic anhydrase inhibitors

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Dorzolamide, Brinzolamide
? Sympathomimetics
Brimonidine, Apraclonidine
? Parasmpathomimetics

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59

Pilocarpine

Systemic drugs used for POAG therapy

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? Used rarely, for short term control of IOP
? Oral carbonic anhydrase inhibitors
Acetazolamide, Methazolamide

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60
Laser treatment

? Indications
Target IOP not achieved with medical

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therapy
Non compliance of medical therapy

Argon/ Diode Laser Trabeculoplasty (ALT)
Selective Laser Trabeculoplasty (SLT)

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Surgical therapy

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? Indications
v Target IOP not achieved with maximal
tolerated medical therapy and laser
trabeculoplasty
v Non compliance of medical therapy

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v Non availability of laser therapy
v Advanced glaucoma

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Surgical therapy

? Filtration surgery : Trabeculectomy
? Modified trabeculectomy :

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Use of antifibrotic agents
Mitomycin/5FU
? Aqueous drainage devices:
Ahmed glaucoma valve

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In cases with no/poor visual potential:
Cycloablative therapy with laser/cryo- Last 63

resort

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