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Glaucoma, Primary Open-Angle

Glaucoma, Primary Open-Angle is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Primary open-angle glaucoma (POAG) is an optic neuropathy resulting in visual field loss frequently associated with increased intraocular pressure (IOP).
  • Normal IOP is 10 to 22 mm Hg. However, glaucomatous optic nerve damage also can occur with normal IOP and as a secondary manifestation of other disorders such as corticosteroid-induced glaucoma.
  • System(s) affected: nervous
  • Synonym(s): chronic open-angle glaucoma

Pregnancy Considerations
Prostaglandins should be avoided during pregnancy in the treatment of POAG.

Epidemiology

Incidence
  • Predominant age: usually >40 years
  • Increases with age
  • Predominant gender: male = female

Prevalence
Prevalence in persons >40 years of age is ∼1.8%.

Geriatric Considerations
Increasing prevalence with increasing age

Etiology and Pathophysiology

  • Abnormal aqueous outflow resulting in increased IOP
  • Normally, aqueous is produced by the ciliary epithelium of the ciliary body and is secreted into the posterior chamber of the eye.
    • Aqueous then flows through the pupil and enters the anterior chamber to be drained by the trabecular meshwork (TM) in the iridocorneal angle of the eye. It then drains into the Schlemm canal and then into the episcleral venous system.
  • 5–10% of the total aqueous outflow leaves via the uveoscleral pathway.
  • Impaired aqueous outflow through the TM
    • Increased resistance within the aqueous drainage system

Genetics
  • A family history of glaucoma increases the risk for developing glaucoma.
  • TMCO1 genotype has been found to increase the risk of developing glaucoma among non-Hispanic whites (1)[A].
  • The myocilin (MYOC) gene was the first gene associated with POAG.
    • MYOC cascade genetic testing for POAG allows identification of at-risk individuals (2)[C].

Risk Factors

  • Increased IOP
  • Myopia
  • Diabetes mellitus (DM)
  • African American
  • Elderly
  • Hypothyroidism
  • Positive family history
  • Central corneal thickness <550 μm
  • Larger vertical cup-to-disc ratio (CDR)
  • Larger horizontal CDR
  • CDR asymmetry
  • Disc hemorrhage
  • Prolonged use of topical, periocular, inhaled, or systemic corticosteroids
  • Obstructive sleep apnea
  • Hypertension
  • Corneal hysteresis (CH)
    • A measure of the viscoelastic damping of the cornea
    • Lower CH associated with faster rates of visual field loss

General Prevention

  • Possible reduced risk of open-angle glaucoma with long-term use of oral statins among persons with hyperlipidemia
  • Higher dietary nitrate and green leafy vegetable intake has been associated with a lower POAG risk (3)[A].
    • Evidence suggests that nitrate, a precursor of nitric oxide, is beneficial for blood circulation.
      • The vascular endothelium regulates the microcirculation via vasoactive factors with nitric oxide being one of them.
      • Nitric oxide reduces IOP by causing relaxation of the TM and Schlemm canal, resulting in increased aqueous humor outflow.

Commonly Associated Conditions

DM

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Citation

Stephens, Mark B., et al., editors. "Glaucoma, Primary Open-Angle." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117486/all/Glaucoma__Primary_Open_Angle.
Glaucoma, Primary Open-Angle. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117486/all/Glaucoma__Primary_Open_Angle. Accessed March 19, 2019.
Glaucoma, Primary Open-Angle. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117486/all/Glaucoma__Primary_Open_Angle
Glaucoma, Primary Open-Angle [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 March 19]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117486/all/Glaucoma__Primary_Open_Angle.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Glaucoma, Primary Open-Angle ID - 117486 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/117486/all/Glaucoma__Primary_Open_Angle PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -