Glaucoma :An introduction

Professor K N Jha,MS.

Learning AimsTo learn :

Definition of Glaucoma

Secretion and drainage of aqueous humor , and control of intraocular pressure (IOP)

Classification of glaucomas

Optic nerve head changes in glaucoma

Investigations of a case of glaucoma

DefinitionGlaucoma represents a group of diseases defined by a characteristic optic neuropathy that is consistent with excavation and undermining of the neural and connective tissue elements of the optic disc and by eventual development of distinctive patterns of visual dysfunction. Although elevated intraocular pressure (IOP) is one of the primary risk factors, its presence or absence does not have a role in the definition of the disease.

Intraocular pressure(IOP)Normal IOP : 10-22 mm Hg (mean 16 mm

Hg , SD 3)

> 22mm Hg is considered abnormal.

No clear line exists between safe and unsafe IOP.

Intraocular Pressure

Aqueous humor production

Aqueous humor out flow

Aqueous humor productionActive secretion by

double-layered ciliary epithelium

Ultrafiltration

Simple diffusion

Aqueous humorSecretion depends on:

Integrity of blood aqueous barrier

Blood flow to ciliary body

Neurohormonal regulation of blood and ciliary

body

Composition of aqueous humorEssentially protein freeExcess of H+, Cl- ion, ascorbate , and deficit in

HCo3Others: growth factor, enzymes, prostaglandins,

steroid hormones.Rate:2.0 µl/minCarries metabolic substrate to , and waste from,

cornea and lens.

Aqueous humor outflowTrabecular out flow

Uveoscleral out flow

Aqueous outflowAnatomy Physiology

Trabecular outflow channelPosterior chamber

Anterior chamber

Angle of anterior chamber ( Trabecular meshwork)

Schlemm’s canal

Aqueous vein

Trabecular outflowThrough trabecular

meshwork- Schlemm’s canal-venous system

It is the site of pressure-dependent outflow

Uveoscleral outflowPressure independent

outflowResponsible for 5-15 %

of outflowIncreased by

cycloplegia, adrenergic agents, prostaglandin analogues and cyclodialysis.

Decreased by miotics

Factors affecting IOPRate of aqueous production

Resistance to aqueous outflow

Pretrabecular , trabecular and post trabecular

Level of episcleral venous pressure

Factors influencing IOPTime of the day

Heartbeat

Respiration

Exercise

Fluid intake

Systemic medication

Topical drugs

Diurnal variationIn normal individuals 2-6mm Hg

Diurnal fluctuation > 10Hg suggestive of glaucoma

TonometryIndentation: Schiötz tonometer

Applanation tonometry

Non-contact tonometer

Pneumatotonometer

Tonometers

GoldmannContact applanation

PerkinsPortable contact applanation

Pulsair 2000 (Keeler)Air-puff

Schiotz

Portable non-contact applanationNon-contact indentation

Contact indentation

Tono-Penportable contact applanation

Optic Disc ( ONH)

Optic Nerve Head: Schematic

Normal Glaucomatous

Visual field analysis

Visual field analysis gives a record of the individual’s visual field.

Types: static/ kinetic, manual/automated,etc.

It records impairment/loss of visual function and helps in identifying any deterioration.

It is an essential part of follow-up of the glaucoma patients.

GonioscopyGonioscopy is the clinical method to visualise

the corneoscleral angle and descibe it as opne, closed, occludable,etc.

Methods: Direct/ indirect

Gonioscopy is done at slit lamp with a gonioscopic mirror.

Gonioscopy

Angle structures

Schwalbe line

Schlemm canal

Trabeculum

Scleral spur

Iris processes

Shaffer grading of angle width

• Ciliary body easily visibleGrade 4 (35-45 )

• At least scleral spur visibleGrade 2 (20 )

Grade 3 (25-35 )

Grade 1 (10 )

• Only trabeculum visible

• Only Schwalbe line and perhaps top of trabeculum visible• High risk of angle closure

• Iridocorneal contact present• Apex of corneal wedge not visible

• Angle closure possible but unlikely

• Use indentation gonioscopy

3 2 1

0 4

Grade 0 (0 )

Classification of Glaucomas• Open-angle glaucoma : POAG, NTG,JOAG, glaucoma

suspect, SOAG

• Angle-closure glaucoma: PACG,ACG,Sub acute ACG, Chronic AC, SAC with/ without pupillary block, Plateau iris

Childhood glaucoma : Primary congenital/ infantile glaucoma, glaucoma associated with congenital anomalies, Secondary glaucoma in infant and children.

Points to rememberDefinition of glaucoma

Aqueous humor production and its drainage

Diagnosis, and investigation of glaucoma