Glaucoma

Aka: Glaucoma, Increased Intraocular Pressure, Ocular Hypertension

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II. Definitions

  1. Glaucoma
    1. Increased Intraocular Pressure AND Optic Nerve injury
    2. High risk of blindness if untreated (acuity <20/200)

III. Epidemiology

  1. Within top 3 worldwide causes of blindness
    1. Cataracts are the most common worldwide cause of blindness
    2. Leading cause of blindness in black patients in U.S.
  2. U.S. Prevalence: 3 Million
    1. Affects 3.5% of those over age 40 years (and increases with age)
    2. Only 50% are estimated to now be under treatment
    3. 120,000 are blind due to Glaucoma
    4. Highest risk groups for Glaucoma-related blindness in Blacks and Hispanics
  3. World Prevalence: 60 Million
    1. Bilateral blindness due to Glaucoma estimated at 11 million worldwide by 2020

IV. Physiology

  1. Aqueous Humor
    1. Ciliary body produces Aqueous Humor
    2. Aqueous Humor flows through pupil and into anterior chamber
    3. Trabecular meshwork drains Aqueous Humor into the venous system
  2. Intraocular Pressure
    1. Intraocular Pressure is a balance between Aqueous Humor production (ciliary body) and drainage (trabecular mesh)
    2. Intraocular Pressure may normally vary with Blood Pressure and respiration
    3. Introcular pressure typically decreases at night
  3. Lamina Cribrosa of Sclera
    1. Sleeve-like space at the opening of the Sclera through which Retinal axons pass on their way to the Optic Nerve
    2. Represents hundreds of openings through which 1-2 Million nerves pass (bundled into groups)
    3. Retinal axons are particularly sensitive to injury at the lamina cribosa, where the axons bend and exit the eye
      1. Lamina Cribrosa is an important landmark for Glaucoma related-injury to Retinal axons
  4. Neuroretinal Rim
    1. Outer, pink portion of the optic disc that surrounds the Optic Cup
    2. Neuroretinal Rim contains nerve fibers and glial cells
    3. Injury to the Retinal axons of the results in cell loss and thinning of the rim
    4. Glaucoma-related pressure induces Retinal axon injury and Neuroretinal Rim thinning

V. Pathophysiology

  1. Elevated Intraocular Pressure (IOP)
    1. Increased production of Aqueous Humor by ciliary body
      1. Aqueous Humor is typically produced at 2 ul/min
    2. Increased outflow resistance at Aqueous Outflow Angle
      1. Trabecular meshwork
      2. Canal of Schlemm
  2. Progressive changes in optic disc
    1. Nerve damage related to increased IOP is variable
      1. Glaucoma suspects (66% of those with high IOP)
        1. No damage despite high Intraocular Pressure (>21)
        2. Optic Nerve injury rate in suspects: 1% per year
      2. Normal-pressure Glaucoma (15% of Glaucoma patients)
        1. Normal Intraocular Pressure (21 mmHg or less)
        2. Glaucoma-related Optic Nerve damage
    2. Progressive Glaucomatous cupping at the optic disc
      1. IOP collapses Optic Nerve Head structural support
      2. Retinal axons are destroyed by mechanical compression
  3. Peripheral Visual Field loss
    1. Open Angle Glaucoma: Slowly progressive
    2. Narrow Angle Glaucoma: Rapid Vision Loss

VI. Types

  1. Primary Glaucoma
    1. Open Angle Glaucoma (75 to 89% of cases in U.S.)
      1. Outflow blocked by microscopic outflow changes
      2. Results in progressive peripheral Vision Loss
      3. Usually asymptomatic until 40% of nerve loss
    2. Narrow Angle Glaucoma (11% of cases)
      1. Outflow tract blocked by base of iris
      2. Permanent Vision Loss may occur in hours
      3. Presents as acute painful Red Eye with Vomiting
  2. Secondary Glaucoma
    1. Medications that increase IOP in those predisposed
      1. Corticosteroids (Systemic and Topical)
        1. Reversible
      2. Mild Adrenergic or Anticholinergic Medications
        1. Examples
          1. Cold Medications
          2. Antidepressants
          3. Antidiarrheals
        2. Effect: Dilate Pupil
          1. Theoretically worsen angle closure Glaucoma
          2. Not contraindicated in Glaucoma

VII. Exam: Basic

  1. Tonometry
    1. Intraocular Pressure >21 mmHg is consistent with Ocular Hypertension
  2. Visual Field Testing
    1. Visual Fields by Confrontation
  3. Optic disc exam by Fundoscopy
    1. Enlarged cup-to-disc ratio >0.3 to 0.5 (or >0.2 difference between eyes) is consistent with Glaucoma

VIII. Exam: Ophthalmology

  1. Perimetry
    1. Automated testing of Visual Fields
  2. Gonioscopy (Van Herrick Test)
    1. Evaluates Anterior Chamber Depth and angle
  3. Pachymetry
    1. Corneal thickness measurement
  4. Optical Coherance Tomography (OCT)
    1. Evaluates Optic Nerve Head anatomy by analyzing reflected light off the optic disc
    2. Neuroretinal Rim thinning identified on serial OCT evaluations often precedes Visual Field Deficits

IX. Differential Diagnosis

  1. Open Angle Glaucoma
  2. Narrow Angle Glaucoma
  3. Optic Neuropathy
    1. Ischemic Optic Neuritis
    2. Retrobulbar Optic Neuropathy (Multiple Sclerosis)

X. Resources

  1. Aging Eye Glaucomatrac (Glaucoma Management Tracking)
    1. http://www.agingeye.net/glaucomacharting.index
  2. Aging Eye Glaucoma Video
    1. http://www.agingeye.net/mainnews/video.php

XI. References

  1. Alward (1998) N Engl J Med 339:1298-307 [PubMed]
  2. Distelhorst (2003) Am Fam Physician 67(9):1937-50 [PubMed]
  3. Gupta (2016) Am Fam Physician 93(8):668-74 [PubMed]
  4. Infeld (1998) Postgrad Med 74:709-15 [PubMed]
  5. Michels (2023) Am Fam Physician 107(3): 253-62 [PubMed]

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