Glaucoma Screening

1. Glaucoma Screening
Nicholas J. Silvestros, OD
Clinical Instructor
Department of Ophthalmology and Vision Sciences
Washington University St. Louis
School of Medicine

2. Causes of Visual Impairment in
the World
http://www.who.int/entity/mediacentre/factsheets/fs282_2.gif

3. Glaucoma
•2
nd
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

4. Anatomy of the Eye - Overview

5. Aqueous Flow
•Ciliary body
•Produces aqueous
(fluid in the eye)
•Trabecular
meshwork
•Drains aqueous
fluid out of eye

6. Aqueous 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

7. Trabecular 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

8. Aqueous Humor

9. Aqueous Humor Trivia
•Nourishes lens, cornea, vitreous
•Decreases production with:
•Sleep
•Age
•Some systemic hypotensive agents
•Decrease outflow with:
•Age

10. Intraocular 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

11. Intraocular 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)

12. Intraocular 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

13. Measurement 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

14. Measurement of IOP

15. Measurement of IOP
•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

16. Measurement of 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

17. Anatomy of the Eye - Overview

18. Anatomy of the Eye - Overview

19. Anatomy of the Eye - Overview

20. Falsely 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

21. Optic 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)

22. Optic Nerve Head
•Scleral Canal
•Lamina Cribrosa
•Optic Cup
•Neuroretinal Rim
•Size of ON:
•AA>Asians>Hispanics>Whites

23. Optic Nerve Head

24. Optic Nerve Head
•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

25. Optic 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

26. Optic Nerve Head

27. Optic Nerve Head

28. Optic Nerve Head

29. Optic Nerve Head

30. Glaucomatous
optic nerve
Normal optic nerve
Optic Nerve Head

31. Optic Nerve Head

32. Anatomy of the Eye - Overview

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

34. Anatomy of the Nerve Fibers