Glaucoma, Open-Angle

SOURCE

Source: Fiscella RG, Lesar TS, Owaidhah OA, Edward DP. Glaucoma. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=133893440. Accessed May 12, 2017.

DEFINITION

• Ocular disorder leading to optic neuropathy characterized by changes in optic nerve head (optic disk) associated with loss of visual sensitivity and field.

ETIOLOGY

• Inherited disorder, congenital, or secondary to disease, trauma, or drugs.

• Secondary open-angle glaucoma caused by:

  • Exfoliation syndrome.

  • Pigmentary glaucoma.

  • Systemic diseases.

  • Trauma.

  • Surgery.

  • Ocular inflammatory diseases.

  • Drugs (Table 1)

• Secondary glaucoma classified as:

  • Pretrabecular.

  • Trabecular.

  • Posttrabecular.

PATHOPHYSIOLOGY

• Cause of optic neuropathy unknown.

  • Increased intraocular pressure (IOP)

  • Ischemia.

  • Excitotoxicity.

  • Autoimmune reactions.

  • Other abnormal physiologic processes.

• Risk of visual field loss increases with increasing IOP.

  • IOP is not constant and changes with:

    • Pulse.

    • Blood pressure.

    • Forced expiration or coughing.

    • Neck compression.

    • Posture.

  • IOP demonstrates diurnal variation with minimum pressure around 6 P.M. and maximum pressure upon awakening.

  • IOP determined by balance between inflow and outflow of aqueous humor.

    • Inflow.

      • Increased by β adrenergic agents.

      • Decreased by α ₂- and β adrenergic blockers, dopamine blockers, carbonic anhydrase inhibitors (CAIs), and adenylate cyclase stimulators.

    • Outflow.

    • Increased by cholinergic agents, prostaglandin analogs, and β and α ₂-adrenergic agonists.

EPIDEMIOLOGY

• Affects up to 4 million individuals in the US and 70 million individuals worldwide.

• Second leading cause of blindness.

  • 135,000 people in the US have glaucoma-related bilateral blindness.

• Incidence increases with increasing age as well as family history, thinner central corneal thickness, lower ocular perfusion pressure, type 2 diabetes, myopia, and certain genetic mutations.

SCREENING

• Essential to early diagnosis.

  • Annual eye examinations recommended with family history of glaucoma and in diabetics.

  • IOP measurement and eye examinations recommended every 3–5 years for those older than 50 years.

RISK FACTORS

• Ocular hypertension.

• Increased IOP

• Older age.

• Family history of glaucoma.

• Lower ocular perfusion pressure.

• Lower blood pressure.

• Thinner central cornea.

• Optic disk hemorrhage.

• Larger cup-to-disk ratio.

• Specific visual field findings.

CLINICAL PRESENTATION

• Slowly progressive and usually asymptomatic until onset of substantial visual field loss. Central visual acuity maintained, even in late stages.

SIGNS AND SYMPTOMS