Glaucoma Screening

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Glaucoma Screening

  1. 1. Glaucoma Screening Nicholas J. Silvestros, OD Clinical InstructorDepartment of Ophthalmology and Vision Sciences Washington University St. Louis School of Medicine
  2. 2. Causes of Visual Impairment in the World http://www.who.int/entity/mediacentre/factsheets/fs282_2.gif
  3. 3. Glaucoma• 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
  4. 4. Anatomy of the Eye - Overview
  5. 5. Aqueous Flow• Ciliary body • Produces aqueous (fluid in the eye)• Trabecular meshwork • Drains aqueous fluid out of eye
  6. 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. 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. 8. Aqueous Humor
  9. 9. Aqueous Humor Trivia• Nourishes lens, cornea, vitreous• Decreases production with: • Sleep • Age • Some systemic hypotensive agents• Decrease outflow with: • Age
  10. 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. 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. 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. 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. 14. Measurement of IOP
  15. 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. 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. 17. Anatomy of the Eye - Overview
  18. 18. Anatomy of the Eye - Overview
  19. 19. Anatomy of the Eye - Overview
  20. 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. 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. 22. Optic Nerve Head• Scleral Canal• Lamina Cribrosa• Optic Cup• Neuroretinal Rim• Size of ON: • AA>Asians>Hispanics>Whites
  23. 23. Optic Nerve Head
  24. 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. 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. 26. Optic Nerve Head
  27. 27. Optic Nerve Head
  28. 28. Optic Nerve Head
  29. 29. Optic Nerve Head
  30. 30. Optic Nerve Head GlaucomatousNormal optic nerve optic nerve
  31. 31. Optic Nerve Head
  32. 32. Anatomy of the Eye - Overview
  33. 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. 34. Anatomy of the Nerve Fibers

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