Chapter 19. Glaucoma

A 50-year-old black man was noted to have a large cup-to-disc ratio during a funduscopic examination by his primary care provider (Figure 19-1). The patient reported no visual complaints. Further evaluation revealed elevated intraocular pressure and early visual field defects. He was started on medication to lower his intraocular pressure. He remained asymptomatic, and his visual field defects did not progress for the next several years.

Glaucoma is a leading cause of blindness in the United States and globally. Open-angle glaucoma is an acquired loss of retinal ganglion cells characterized by either normal or increased intraocular pressure, a large cup-to-disc ratio, and visual field defects. Open-angle glaucoma is treated by reducing intraocular pressure, most commonly with eye drops. Angle-closure glaucoma, which is much less common, is an acute increase in intraocular pressure from a mechanical obstruction that must be treated emergently to preserve vision.

• Approximately 2.5 million persons in the United States have glaucoma.
• Glaucoma is the second leading cause of blindness in the United States and the leading cause of blindness among African Americans.1
• Population studies predict there will be 60.5 million people worldwide with glaucoma by 2010, and of these, 74% will have open-angle glaucoma.2
• Women comprise approximately 60% of all glaucoma cases, but 70% of patients with acute angle-closure glaucoma.2
• Asians comprise approximately 47% of all glaucoma cases, but 87% of acute angle-closure glaucoma.2
• The incidence of primary open-angle glaucoma was 8.3 per 100,000 population in people older than 40 years in a Minnesota population study.3
• According to a population-based study, a family history of glaucoma increased the risk of having glaucoma (odds ratio [OR] = 3.08).4

• Glaucoma pathophysiology is incompletely understood, but the end point is the acquired loss of retinal ganglion cells and axons with resulting irreversible vision loss.
• Increased intraocular pressure (IOP) is a well known risk factor; however, recent attention has turned to ocular perfusion pressure (OPP), the difference between blood pressure (BP) and IOP. OPP is essentially BP minus IOP. As such, OPP is decreased by either high IOP or low BP.5 If a patient with apparently well-controlled IOP continues to have progressive visual field loss, it may be because of lack of perfusion of the optic nerve from aggressively lowered diastolic BPs. Therefore the management of glaucoma requires attention to diastolic BP.
• Glaucoma is categorized as either:
  • Open-angle—Dysfunction of the aqueous humor drainage system with no visible pathology to the anterior chamber angle.
  • Angle-closure—Occlusion of the anterior chamber angle.
• Impaired outflow of aqueous humor elevates IOP in some patients, but many patients with open-angle glaucoma have normal IOPs.
• Optic nerve atrophy is seen as optic disc cupping and irreversible visual field loss. Compare Figures 19-1 and 19-2 to see the difference between abnormal (Figure 19-1) and normal (Figure 19-2) optic disc cupping.

Open-angle risk factors include:

• Nonmodifiable: age older than 50 years, first-degree family history, and African ancestry.6
• Modifiable: high IOP, high or low BP, and maybe diabetes mellitus.6

Acute closed-angle glaucoma is more common in persons of Asian descent.

Clinical Features

• Open-angle glaucoma:
  • History—Usually asymptomatic, occasionally “tunnel vision.”
  • Physical examination—Optic cupping and/or elevated IOP (glaucomatous changes can occur with IOPs in the normal range), loss of peripheral vision by automated perimetry (typically bilateral, but may be asymmetric).
• Acute closed-angle glaucoma:
  • History—Painful red eye (unilateral), vision loss, headache, nausea, halos around lights, and vomiting (Figure 19-3).
  • Physical examination—Shallow anterior chamber, optic cupping and elevated IOP, injection of the conjunctiva, and cloudy cornea (Figure 19-3).
• Typical distribution
  • Open-angle glaucoma is typically bilateral.
  • Closed-angle glaucoma is typically unilateral. However, there is risk for the other eye to undergo the same process, as the abnormal anatomically narrow angle is usually present in the other eye too.

Glaucoma is the most common cause of optic disc cupping and is sometimes accompanied by elevated IOP.

• Optic disc cupping without elevated IOP can be caused by:7
  • Physiologic cupping (Figure 19-2).
  • Congenital optic-disc anomalies (i.e., coloboma or tilted discs).
  • Ischemic (i.e., compression by tumors), traumatic (closed-head injury), or hereditary optic neuropathies.
• Glaucomatous optic disc cupping compared to other causes has:7
  • Larger cup-to-disc ratios (compare Figure 19-1 to Figure 19-2).
  • Vertical (as opposed to horizontal) elongation of the cup.
  • Disc hemorrhages.

• Treat with topical agents to decrease IOP by 20% to 40%, which has been demonstrated to decrease glaucoma progression.8 SOR A Many medications are available including:
  • Nonspecific β-blockers (e.g., timolol 0.5%, once or twice a day).
  • Prostaglandin analogs (e.g., latanoprost 0.005%, once a day).
  • Carbonic anhydrase inhibitors (e.g., dorzolamide 2%, 2 to 3 times a day).
  • α-Agonists (e.g., brimonidine 1.0%, 2 to 3 times a day).

Referral

• Emergently refer patients with suspected angle-closure glaucoma to an ophthalmologist (see Figure 19-3).
• Evaluate (or refer for evaluation) patients with abnormal optic nerve cupping (cup-to-disc ratio of greater than 0.5; difference in cup-to-disc ratio of 0.2 or greater between eyes; asymmetric cup), or increased IOP measured by tonometry, or visual field deficits.
• Document the location and extent of visual field deficits with automated perimetry.
• Refer patients with shallow anterior chambers, severe far-sightedness (hyperopia) or previous history of acute angle closure glaucoma to an ophthalmologist.
• Refer for surgical evaluation if you are unable to medically reduce the IOP.

• Screening—According to the U.S. Preventive Services Task Force update in 2005 (http://www.ahrq.gov/clinic/uspstf/uspsglau.htm), there is insufficient evidence to recommend for or against population screening for open-angle glaucoma. However, African Americans have been underrepresented in trials. Previously screening has been recommended for African Americans older than age 40 years, whites older than age 65 years, and patients with a family history of glaucoma.1 SOR C

Most patients with open-angle glaucoma, provided they are treated, will not lose vision.

Angle-closure glaucoma must be treated emergently to prevent vision loss.

Patients with glaucoma should have regular measurements of their IOP and visual fields to follow treatment efficacy.

Advise patients that glaucoma is a progressive disease requiring continued therapy to prevent vision loss.

Patient Resources

• Glaucoma research foundation Web site has information on treatment, research progress, personal stories, and practical tips at www.glaucoma.org.
• http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002587/.

Provider Resources

• Acute angle-closure glaucoma—http://emedicine.medscape.com/article/798811.
• Primary open-angle glaucoma—http://emedicine.medscape.com/article/1206147.