glaucoma screening

Glaucoma ScreeningGlaucoma Screening

Nicholas J. Silvestros, ODClinical Instructor

Department of Ophthalmology and Vision SciencesWashington University St. Louis

School of Medicine

Nicholas J. Silvestros, ODClinical Instructor

Department of Ophthalmology and Vision SciencesWashington University St. Louis

School of Medicine

Causes of Visual Impairment in the World

Causes of Visual Impairment in the World

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GlaucomaGlaucoma

• 2nd most common cause of blindness in U.S.

• Single most common cause of blindness in African Americans• African Americans 4x more likely to have glaucoma

and 6x more likely to be blind from it

• If detected early and treated, blindness can be prevented

• In early stages, most patients asymptomatic

• Peripheral vision can be lost before patient notices visual impairment

Anatomy of the Eye - OverviewAnatomy of the Eye - Overview

Aqueous FlowAqueous Flow

• Ciliary body• Produces aqueous

(fluid in the eye)

• Trabecular meshwork• Drains aqueous

fluid out of eye

Aqueous Humor FormationAqueous Humor Formation

• Involves the combination of 2 known processes:• Active transport (secretion)

• 80% of Aqueous

• Passive transport (ultrafiltration and diffusion)• 20% of Aqueous

• Affected by topical glaucoma medications: beta-blockers, sympathomimetics and carbonic anhydrase inhibitors

Trabecular OutflowTrabecular Outflow

• Conventional outflow• 80-90% outflow• Increased:

• Drugs: Cholinergics (pilocarpine), Adrenergic agonists

• Surgical: ALT/SLT, Trabeculotomy/goniotomy

• Unconventional outflow• 10-20% outflow• Increased:

• Drugs: sympathomimetics and prostaglandins

Aqueous Humor Aqueous Humor

Aqueous Humor TriviaAqueous Humor Trivia

• Nourishes lens, cornea, vitreous

• Decreases production with:• Sleep • Age• Some systemic hypotensive agents

• Decrease outflow with:• Age

Intraocular PressureIntraocular Pressure

• IOP: • Range 11 mmHg to 21 mmHG• 21 considered upper limit of normal• IOP varies time of day, heart beat, BP,

respiration• Tendency for higher AM and lower evening

• Lower during laying/sleeping

• Diurnal variation:• 2-6 mm Hg normal

• >10 mm Hg suggestive of glaucoma

Intraocular PressureIntraocular Pressure

• IOP: • IOP varies time of day, heart beat, BP,

respiration• Tendency for higher AM and lower evening

• Lower during laying/sleeping

• Age (increases with age)

• Caffeine (transiently increases in IOP)

• Alcohol (transiently in IOP)

• Cannibis (mild in IOP)

Intraocular Pressure TriviaIntraocular Pressure Trivia

• IOP: • No absolutes

• A “normal” IOP reading may be misleading and additional reading at different times of the day may be required

• IOP is a risk factor and does not eliminate glaucoma if a “normal” reading is recorded

• Must be compared with all other risk factors and clinical data

Measurement of IOPMeasurement of IOP

• Applanation Tonometry:• Measures the force necessary to flatten an area

of cornea 3.06 mm diameter• Central part of cornea flattened while variable

force records pressure

• Central Corneal Thickness:• >540 micrometers produce falsely high IOP

readings by TA

• <540 micrometers produce falsely low IOP reading by TA


• Applanation Tonometry:• Goldmann tonometer

• Most popular tonometer and accurate tonometer

• Tono-Pen tonometer• Hand held portable tonometer• Over estimates low IOP and underestimates high

IOP


• Non-Contact Tonometry:• Air-Puff tonometer

• Goldmann principles with air instead of prism time required to flatten cornea relates directly to level of

IOP

• Does not require topical anesthetic• Useful for screenings• Disadvantage – accurate low to mid IOP range

Falsely elevated IOP readingsFalsely elevated IOP readings

• Elevated:• Squeezing of the eyelids• Breath holding or valsalva maneuvers• External pressure on the globe• Thick or scarred corneas• Marked astigmatism

• Lower:• Thin corneas• Marked astigmatism

Optic Nerve HeadOptic Nerve Head

• 1.2 million axons• Declines with age• Cell bodies are the ganglion cells

• Magnocellular (M) cells 10%• Large diameter (dim illumination)

• Parvocellular (P) cells 90%• Small diameter axons (color, fine detail)


• Scleral Canal

• Lamina Cribrosa

• Optic Cup

• Neuroretinal Rim

• Size of ON:• AA>Asians>Hispanics>Whites


• Cup-Disc Ratio• Fraction of vertical and horizontal meridians

• C/D=0.3/0.3

• Normal is 0.3 or less

• Ratio greater than 0.7 regarded suspicious• Asymmetry between two eyes of 0.2 or more

regarded suspicious• Cup size is needed to evaluate progression not

initial diagnosis

Optic nerve appearance in glaucomaOptic nerve appearance in glaucoma

• Glaucoma nerve damage ranges from localized to diffuse• Localized easier to recognize with notching

• Description of nerve important• Neuralretinal rim tissue

• Thickness• Symmetry• Color• Notching• Hemorrhage disc margin

Optic Nerve Head

Glaucomatous optic nerve

Normal optic nerve


Visual Field Visual Field

• Anatomy of Visual Field• 60 degrees nasally• 90 degrees temporally• 50 degrees superiorly• 70 degrees inferiorly• Blind spot 10-20 degrees temporally

Anatomy of the Nerve FibersAnatomy of the Nerve Fibers

glaucoma screening

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